NASA Tecbnid Memormdm 86234 

$TARO 3'sn051~5 &him.Q 

Fundmental Remote Sensing 

Science Research Program. 

1985 Summary Report of the 

Scene IQdiation and Atmospheric 

Effects Characterization Project 

Sptembe: 1985 

(E8b- 100 11 NASA-31-86239) FDNbAlENTAL 

N86-13754 

BEHOTE SENSING SClENCE RESEARCH EBOGBAM: 

THRU 

THE SCElE RADIAIICl BBC ATIOSPBEBIC EFFECTS 

N86-13812 

CHARliCTERIZATIOB EBOJECT Summary Report, Unclas 

1985 (IBSB) 195 F HC A09/LIF 101 CSCL 05B 63/43 OOdll 
NASA TF&cMca.l Memorandum 86234 

Fundamental Remote Sensing 

Science Research Program 

1985 Sumary Report of the 

Scene Radiation and Atmospheric 

Effects Characterization Project 

National Aeronautics and 

Space Administration 

Goddard Space Flight Center 

Greenbelt, Malyland 20771 
PREFACE 

Following a decade of research in the application of remote 

sensing technology to earth resources measurement and monitoring 

with earth observing satellites, the National Aeronautics and 

Space Administration found a need developing for the advancement 

of our understanding of the physical processes associated with 

the remote sensing. Therefore, at the beginning of the 1980s 

NASA established a continuing research program in fundamental 

remote sensing science that would enhance our ability to learn 

mo7-e about the physical and biological processes of our planet 

from space acquired data and would contribute to a base of 

~cientific understanding needed to support the planning of new 

and effective sensors and flight programs. The Scene Radiation 

and Atmospheric Effects Characterization (SRAEC) Project was 

established within this program to improve our understanding of 

the fundamental relationships of energy interactions between the 

sensor and the surface target, including the effect of the 

atmosphere. 

This report has been prepared to provide a very brief 

overview of the SRAEC Project history and objectives and to 

report on the scientific findings and project accomplishments. 

An attempt has been made to elucidate the overall project 

progress and accomplishments through principal investigator team 

introspection, and the principal investigators have prepared 

succinct summaries of their individual study results achieved 

since the project's initiation just over three years ago. 

A meeting of the PIS is conducted annually to bring the 

scientists together to present and discuss their results with one 

another. This annual summary report derives from the most recent 

annual meeting held at the Massachusetts Institute of Technology 

in Cambridge, Massachusetts during January 29-31, 1985. The 

overall program management is under the direction of Dr. Robert 

E. Murphy of NASA Headquarters, Code EE, Washington, D.C. 

Donald W. Deering 

GSFC Project Science Manager, 

Fundamental Remote Sensing Science 

Research Program 

Earth Resources Branch (Code 623) 

Goddard Space Flight Center 

Greenbelt, MD 20771 

iii 
FUNDAMENTAL REMOTE SENSING SCIENCE RESEARCH PROGRAM 

1985 SUMMARY REPORT OF THE 

SCENE RADIATION AND ATMOSPHERIC EFFECTS CHARACTERIZATION PROJECT 

TABLE OF CONTENTS 

PREFACE 

Page 

iii 

TABLE OF CONTENTS iv 

I . SRAEC PROJECT BACKGROUND ............... 1 

A . Project History and Objectives .......... 2 

B . Principal Investigator Workshops ......... 5 

I1 . SRAEC PROJECT RESEARCH RESULTS ............ 8 

A . Progress and Accomplishments ........... 9 

B . Principal Investigator Summary Reports ...... 36 

C . List of Publications and Presentations ...... 155 

APPENDIX ....................... 177 

A . Third Annual Principal Investigator Workshop 

..Invitation Letter and Agenda .......... 178 

B . Third Annual Meeting Participants 

..List and Photo ................. 183 

C . Message to PIS from Dr . Murphy .......... 188 
I. SRAEC PROJECT BACKGROUND 
I.A. SRAEC PROJECT ORIGIN AND OBJECTIVES 

During the "Landsat Era" of the 1970's, the development of 

rapid, empirical approaches to satellite data interpretation took 

precedence over the development of a full scientific understanding of the earth-atmosphere scene radiation complex. The 

importance ~f synoptic remote measurements of the earth's 

surface and the atmosphere has been clearly demonstrated, but the 

need to more fully utilize the powerful satellite remote sensing 

measurement potential has led to the realization that purely 

empirical techniques are no longer sufficisnt. 

Significant advancements in both nomote sensi~g components 

and systems and in the remote sensing deri*6f~?d undenctanding of 

physical and biological processes on the ea~lt.~'~ surface require 

increased understanding of the characteristics of earth scene 

radiation and atmospheric effects at visibie, infrared and 

microwave wavelengths. Thus, NASA established the Fundamental 

Remote Sensing Science Research Program within the Land Processes 

Branch of the Earth Science and Applications Division at NASA 

Headquarters. 

The Scene Radiation and Atmospheric Effects Characterization 

Project is conducted ae the primary element of the program with 

the general goal being to improve our understanding of the energy 

emitted or reflected from an earth surface target, through the 

intervening atmosphere as measured by a remote sensing system. 

Emphasis has been placed on theoretical model development with 

some observational studies and empirical characterizations 

relating electromagneZdc energy reflected and emitted from earth 
surfaces to their biophysical characteristics. 

Fundamental research needs for future applications research 

in aerospace remote sensing were identified through a series of 

workshops during fiscal year 1980 that involved Leading scientistn from universities, industry and government. The research 

issues that were identified through these workshops and reported 

as a fine.; report to NASA Johnson Space Center (under NAS 

9-3.6'316) in August 1980 are summarized in last year's annual 

SHhGC report (NASA Technical Memorandum 86078, March 1984) and, 

therefore, ar2 not repeated here. 

Proposals from organizations outside NASA were solicited in 

July 1981, and following a NASA Headquarters conducted peer 

review, sixteen investigations were funded during fiscal year 

1982. Most of these were proposed as three-year studies, such 

that this annual report reflects the end-of-study results for 

many of the principal investigators. Since the initial call for 

proposals, other unsolicited proposals have been received and 

peer reviewed. Therefore, there are a few principal investigators who have only recently begun their studies under this 

project. Even though there is finite funding available, proposals for new research are continually encouraged, especially in 

those topical areas that were identified in the early planning 

phase as being important research issues that have yet to be 

adequately addressed. 

The product of the SRAEC project is an improved understanding of the physical radiant energw interaction (remote sensing) 

processes through measurements and modeling that will ultimately 
enable the proper specification of earth observing space sensor 

systems and the measurement and modeling of the important 

physical, chemical, and biological processes and their interactions. The success of the individual scientists in the program 

is measured by the quality professional papers that are produced 

and contribute4 through refereed scientific journals. 
I.B. PRINCIPAL INVESTIGATOR WORKSHOPS 

Following the selection and announcement of successful SRAEC 

proposals, a "kick-off" meeting was held on June 15, 1982 at NASA 

Goddard Space Flight Center. The objective of this meeting was 

tu enaB?.e the principal investigators in the SRAEC Project to 

Eeh a F BP Bheir new collegues in the project were planning to do 

4n ki~exr various studies and begin the process of sharing 

iri% *~~waf.nan and ideas for synergistic benefit to the remote 

sensing science program. Collaboration among principal investigators was encouraged. 

The next meeting of the SRAEC principal investigators was 

held January 5-7, 1983 at the University of Colorado in Boulder 

in two separate sessions as a part sf the National Radio Science 

Meeting. The objectives for this gathering of the PIS was to 

provide NASA management with a review of early progress, to 

initiate the sharing of results between SRAEC investigators and 

to emphasize the importance of reporting the study results with 

the broader remote sensing scientific community. 

The second meeting to report on the research results was 

conducted at Colorado State University in Fort Collins from 

January 9-11, 1984. This second annual meeting was conducted 

with a workshop format and to serve as a forum for sharing 

terminology and articulate the merging sf visible, IR, and 

microwave theoretical and experimental techniques. Tutorial 

presentations were made by representatives of these remote 

sensing disciplines. Although time constraints did not allow a 

full development of the ideas, good progress was made in bridging 
the communications gap between the groups, which has been 

apparent in the most recent meeting. 

The Third Annual Meeting of the SRAtEC principal investigators was held on the campus of the Massachusetts Institute of 

Technology in Cambridge, Massachusetts during January 29-31, 

1985. Dr. Jin Kong of the Research Laboratory of Electronics at 

MIT hosted thie meeting and arranged for local scientists Ken 

Hardy and Dave Staelin to address the PIS and stimulate their 

thinking. 

The letter of invitation to the principal investigators and 

the meetiag agenda are included in Appendix 8. A list of the 

workshop participants, their affiliations and addresses is 

provided in Appendix B. AE~ e teleco=sunicationa ressage to the 

meeting participants from Dr. Robert Murphy, Fundamental Remote 

Sensing Science Research Program Manager at NASA Headquarters, is 

included in Appendix C. Dr. Murphy was personally unable to 

attend the meeting due to other comittments. 

The current document is the product of the contributions 

made by the SRAEC Principal Investigators, all of whom were 

present, at thie annual workshop (Figure 1). This SRAEC annual 

status report is intended to 1) document responses to some of the 

questions addressed during the workshop concerning the progress, 

accompliehments and future directions of the project (Section 

1I.A) and 2) to provide a concise summary of the justification, 

goals and objectives, and results of the individual SRAEC 

investigations (Section II.B), including an updated listing of 

the publications resulting froa this research (Section 11°C). 
Vkgure 1. SBARC prinenpal iaves%igatsra at %ha Third dnnaal @or%* 9 o~ the 

caggus of HIT sn January 30, 1985, The PPs ars lfro~t taw, Iefh 3 right1 

Drs* Badhear, Saikh, bxner, Berakf, Fang, KahBe; $a&csad row$ EElabg, Stvakler, 

Pesree, Paris, Cencl, Moore, long; (%hip& row) Ir~ns, nornan, Frsser, Lang, 

VnadcrbiPk; ($our&h row] &~ECB~ 
11. SRAEC PROJECT RESRABCH RESULTS 
11. A. PROGRESS AND ACCOMPLISHMENTS 

By the time of the Third Annual SRAEC Principal Investigator's Meeting the SRAEC Project was beginning its fourth year 

and most of the investigators had either completed or were 

nearing completion of their third year of research. It therefore 

seemed an appropriate time to look back on what had bean done, 

what progress had been made toward addressing the "research 

issues" that had been identified at the inception of the program, 

and what recommendation could be made now concerning the future 

directions of the program. 

A time for discussing the progress and accomplishments of 

the project was reserved on the agenda for the last day of the 

workshop to allow everyone to be updated on the progress of each 

of the investigations. Drs. Fawwaz Ulaby and Jim Smith accepted 

the responsibility for chairing these sessions and summarizing 

the results. 

Four questions were presented to the participants in the 

workshop; thres of which dealt with the success of the project 

and one which considered a topic of considerable interest to most 

of the scientists concerning the potential establishing a 

centralized facility for artificial plant canopy experiments. 

After some general discussion, each of the participants was asked 

to individually prepare a written response to four questions. 

The four questions are given below, and the summarized, selected 

responses are given on the following pages of this section. 

In his cover letter (Feb. 20, 1985) reporting on the 

responses, Dr. Ulaby summarized by stating, "...the SRARC program 
is regarded by its members as 'one of the most successful 

programs NASA has ever run'." The principal investigator 

responses that follow contain numerous suggestions and varied 

opinions regarding future directions. 

WSTION NO. 1 

Excluding your own contributions, what are the three 

most significant technical advances or developments 

that were accomplished under the SRAEC Project? 

The responses to this question have been 

categorized according to: 

(a) General Contributions 

(5) Specific Contrib.---Optical Region 

-1 Specific Contribe--Microwave Region 

QUESTION NO. 2 

What accomplishments have been made in the SRAEC 

Project relative to the goals defined in its inception 

document? Suggest changes in direction, approach, or 

administration. 

These responses have been grouped by: 

(a) Accomplishments Relative to Goals 

(b) Suggested Changes in Direction 

QUESTION NO& 

Are there "gaps" in the program? Should new areas be 

added? Should there be deletions? 

QUESTION NO. 4 

What are your views regarding the creation of a 

"National Canopy Facility"? 
QrreSTION # 1 

Excluding your own contributions, identify the three Qost 

significant technical advances or developments that were accomplished 

under the SRAEC Program. 

The answers may be grouped into two classes: (a) general staterilefits 

that address the overall technical direction of the program, and (b) specific 

statements relating to either the Optical or the Microwave portions of the 

program. 

(a) General Contributions 

"Remote sensing represents, in essence, an inverse problem. T'he 

characteristics of radiation fields are used to deduce surface properttcs. 

The two basic keys to the success of this are fundamental understanding of 

(I) the interactive properties of the target (the surface) and (2) the 

influence (if any) of the prapagatio~ medium. 

Efforts towards canopy modeling which have resulted in basic models 

for BRDFts and/or backscatter cross sections are therefore a very important 

component to our progress in attacking this inverse problem." 

"Create a nucleus of experts and expertise." 

"The program has helped to bring together investigators from both 

the optical and microwave areas. As a result, both group's knowledge has 

bccn strengthened by techniques used in the other area. Examples are: 

the optical people were using transport theory--now the microwave 

investigators are using it also. The microwave researchers were more 

aware of the coherence effects and the non-uniform ancular radiation 

properties of leaves and surfaces. The optical researchers are naw 

measuring the BKDP of leaves and surfaces. In addition, the conccntrntion 

11 
by the whole group on characterization of individual scatterers and 

the architecture of the canopy has led to an increased understanding 

of the relationships between measurements and biophysical parameters." 

"I and other optical modellers are moving toward better understanding of the microwave problem. We all are working toward wavelength 

independent solutions to the scattering/absorbing problem." 

11 Interdisciplinary interaction among various groups: optical and 

microwave, atmospheric and surface researchers; experimentalists and 

theoreticians with investigators who develop inversion algorithms." 

"Developing a better understanding of the interaction of radiant 

energy with surfaces, canopies, and atmosphere. Such knowledge enables 

development of better mcldels and inversion algorithms." 

"The bringing together of multiple disciplines has been useful in 

getting the optical surface people to think about atmospheric problems 

and microwave contributions, and vice versa. This has led to greater 

sophistication in scene characterizations." 

"Smith's phase function work helps build an important bridge 

between optical, microwave and atmospheric work." 

"I do think that a very important result was getting these diverse 

PI'S together and exposing them to each other's work. I think that the 

communication links that were formed and the sharing of common 
problems concealedinthedifferent terminologies of the sub&isciplines 

was most helpful and will pay benefits for a long time to come." 

"To an outsider just joining this group, there appears to be too 

heavy an emphasis on a few areas (modeling of broadband electromagnetic 

radiation interaction with a few vegetative canopy types and measuring 

of somg) to the exclusion of many other problems. 1 see little spectral 

work, no soils studies, no geology, no forestry, no mixing-model studies, 

no hydrology .... There are fundamental science problems in these areas, 

involving "SRAEC". Maybe nobody proposed to study them. Maybe announcement 

of opportunity needs to be more broadly written and distributed. 

The work that has been and is being done by this program appears 

to be excellent and important." 

"The development of a variety of computational tools for 

addressing thc multidimcnsional tcrrnin mcdia problem, principally 

canopies. " 

"The beginnings of a solid, unified, attack on combined 

theoretical modeling of microwave/optical interactions." 

- 

t'Establisl~ment of the com~~~unicatons channel among scic~rtists 

in optics and in microwave field. A fruitful and stimulating exchange 

is being developed. " 

"The potential unification of the theoretical frame work, which 

makes use of common mathematical approaches such as the radiative 

transfer theory .It 

13 
(b) Specific Contributions--Optical Region 

"I am impressed with progress being made in the visible-IR area in 

inversion to determine actual relevant plant canopy properties from data. 

I found Strahler's success with a simple model particularly striking." 

"Established common theoretical basis for systematic evaluation 

of land remote sensing issues, i.e., radiative transfer, BRDF, phase 

functions, cross-sections, etc. Combined surfacefatmosphere descriptions." 

I I Identified new and important sensitivitie~ of electromagnetic 

radiation (emitted or reflected from land surfaces) to intrinsic 

surface features, e.g., spatial lzeterogeneities and non-Lambertian 

angular signatures. I' 

"IdentiEied angular rcflcctinn Features that seem invariant 

to atmospheric effects." 

"Tremendous progress has been made in testing,-evaluating and 

then improving canopy reflectance models in a systematic way. And with 

a clear confidence in these models, key biophysical parameters have been 

extracted, The 'Holy Grail' of remote sensing, the solution of the 

so-called 'signature extension' problem has been shown to exist and the 

role of canopy models in providing an understanding of this solution is 

clearly identified." 

 h he complete atmospheric-canopy problem has been studied by 

transport methods. Investigators have made initial attempts at obtaining 

boundary conditions for this model. Atmospheric correction methods of 

an elementary form has been proposcd." 

14 
"The developments in atmospheric modeling coupled to the canopy 

reflectance models and measurements has ameliorated doubts; regarding 

capabilities to observe canopy BDRF's through the atmosphere. Therefore, 

satellite remote sensing remains a viable tool for botanical, land-surface 

climatology, and habitability types of research. 

"Sound practical approaches to atmospheric correction of digital 

image remote sensing data were discussed by Fraser and Dines (i.e., 

deblurring). The applied remote sensing community has been in desperate 

need for such an approach. I believe this development is immediately 

applicable. " 

"The fact that the canopy reflectance models are demonstrathly 

invertible is most cncournging. The continuing development of these models 

is probably the largest nccomplishment of the SRAEC program. 

"Tile most significant tccl~nical advance is that the effect of 

specularly reflected light is now being included in canopy models." 

"The atmosphere/canopy is being treated as one problem rather than 

two. Phase functions pecific to each are being included." 

"I believe that all of the research being done in the space 

program is addressing the goals of the inception document. The 

approaches of these studies are appropriate. The individual researchers 

have developed 6 strong ttteore tical background which .provides a sound 

basis for exploring extraction techniques of desired canopy characteristics. 

Thcsc 'dcsip,nsl qf canopy rharactcristics are varied for many similar 

problems inside and outside of NASA as we have discussed. I believe 

15 
this is the area which will give the SRA.EC program a great deal of 

publicity and future support. " 

"Significant advances appear to have been made in both measurernenr 

and characterization of BDRF's of a number of complex surface types." 

I I The potential merge of the vegetation canopy study and the 

atmospheric science, providing a complete framework for the study of 

the complete earth environment including earth terrain and atmosphere." 

11 The recognition at optical wavelengths, that besdies ectral 

signature, there are other observables which distinguish di, .rent crop 

canopies, i.e., angular reflectance signature, temporal greenness 

profile, or scene textural analysis. 

"The rrcognition that the information content of previous 

generation remote sensors (e.g., Landsat) is limited due to the 

restriction of nadir viewing. It appears that most interesting or 

useful effects appear at view angles greater than 45 degrees. A 

redirection of thinking to consider high off-nadir angles, taking into 

account the advantages as well as technical problems associated with 

such an approach, is a significant step. 

"Time dependency of canopy reflectances seems to be a reliable 

crop identifier. 

"Jim Smith improved his canopy phase function." 
"Angular patterns of reflectance is understood only qualitatively 

(bowl-shape, hot-spot, "invariant valley), but not quantitatively. An 

artificial canopy with the possibility to set LAI, leaf, sizes, etc, 

may give us the hint to quantitative expressions." 

"UnscrambLing pixels affected by the adjacency effect." 

-"Identifying distinctive features for remote sensing (hot spot, 

persistent valley, specular reflections in visible IR, branch structure 

and the like for millimeter waves. 

"Canopy reflectance models for inhomogeneous canopies." 

- - 

"More detailed models of canopy BKDF that consider leaf and 

soil URDF, partial cover and specular reflection." 

"Calculating ph;~se functions for canopy so general RTE code can 

be used to obtain BRDF predictions. Need to do better work reLacing 

this phase furiction to actual canopy architecture." 

- 

"The combined radiative transfer modeling, in a mu h more 

realistic way, of the atmospherelsurface problem with remote sensing 

implications. " 

"The potential merge of the vegetation canopy study and the 

atmospheric science, providing a complete framework for the study of 

the complete earth environment including earth terrain and atmosphere." 
(c) Specific Contributtons--Microwave --- Regj-on 

I 

"Improved theoretical descriptions that are beginning to take into 

account the actual geometries better." 

"Measurements of dielectric constants for materials and frequencies 

not well handlcd in the past." 

"By replacing stems with lossy dielectric rods and leaves with 

lossy dielectric discs, modeling techniques can be used to approximately 

reproduce observed experiments." 

"Rough surface effects have been incorporated into models 

showing that surfaces can exhibit strong backscattering at nadir angles." 

--- 

"Eluch better understanding of the dielectric properties OF a 

single leaf through measurements." 

"Much improved understanding of the relative contribution of the 

component parts of a canopy." 

"Scattering models with much wider ranges of applicability have 

been developed." 

"Ulaby's measurements fill a great need." 

"Different contributions of different canopy elements to the returned 

and transmitted signals in the microwave region, assessment of importance of 

those elements for microwave remote sensing." 
II Putting microwave sensing on a very firm mechanistic basis, 

especially in the work of Ulaby and Lang." 

"Trend towards understandable and usable models for backscattering 

in the microwave region. " 

"Some basic measurements like dielectric properties of soil, 

leaves, stalks, etc." 

"Microwave modelers considering leaf angle distributions and 

seems and branches." 
qmropr # 2 

the a*-lishmcnts of the SRAEC program relative 

to the goals defined in its i.ncept-on dent. Suggest changes 

in direction, approach, or ad mini st ratio^^. 

(a) Accomplishments Relative to Goals 

"As far as I know, little has been done under controlled conditions 

to solve the stress-response problem directly--yet this is one of the most 

important from an applications point of view. Ulaby has done a lot of 

work on seasonal variations, per se, as have the French and Dutch. 

It Ulaby has made extensive measurements of soil dielectric as part 

OF this and other programs. This is an accomplishmenir. 

"Coal 4 ('overriding necessity to relate to biophys parm.') 

is attacked by theory and experiment and may find culmination in work 

perceived For artificial canopy." 

- 

"Perhaps the most important justifi.cation for NASA to suppcrt 

SRAEC is to develop a strong scientific basis for the remote sensing 

programs being developed for the 1990s. The entire radiation spectrum 

that has high transmission through the atmosphere will be utilized." 

I4Relative to the accomplishments stated above, SRAEC program 

has made very significant progress towards the fundamental approach 

to the remote sensing science in unifying researchers from different 

disciplines, from different electromagnetic spectrum, from different 

schools of thought, and from both theoretical and experimental expertise." 
"The first years oE the SRAEC program have led to advances 

in developing the tools needed to address the question outlined in 

the inception document. While some of the questions may have not 

yet been answered, we are in a significantly better position to address 

them now than we werethree years ago. The flexibility of the program 

is a major plus, allowing researchers free freedom to pursue new ideas 

and not be rigidly held to their proposals." 

"I think the SRAEC research program has pretty well followed the 

goals objectives set out for the program at its inception.. The original 

document called for a very broad research program with many topics 

and needs listed. Although not all oE these areas have been attacked, 

the main thrust has clearly been along the lines of the plan. It seems 

to be funding a good balance of theoretical work, measurement, and work 

that is a bit more application-oriented. Except for the usual NASA 

bureaucratic problen~s (Eundlng delays, etc .) , the program has been 

well administered. I don't think it really needs much change." 

"Modelers should not start impacting the applied programs. 

A question like: 'what is the best CR model for a given vegetation?' 

I believe, should be addressed by the group." 

"Program is proceeding toward stated goals at a rapid pace and 

I would not change the approach or administration and would let the 

direction continue to be defined by the original document." 
"Much better than Z would have thought. While individuals may 

come and go, I believe it is important to keep some collective memory. 

I believe administration by NASA has been exemplary. Overall, a first. 

class group doing firs: class work under enlightened NASA enviornment 

fostering creativity and comraderie." 

"Relative to the accomplishments stated above, SRAEC program 

has made very significant progress towards the fundamental approach 

to the remote sensing science in unifying researchers from different 

disciplines, from different electromagnetic spectrum, from different 

schools of thought, and from both theoretical and experimental 

expert ies. " 
(b) Suggeeted Changes in Direct* 

"Perhaps the Inore glaring gaps in the program are filled with 

the induction of geologists into the group. We need better coverage 

on the properties of rocks and soils. We need thermal band coverage. 

These are addressed to some extent with the recent program addition. 

On the other hand, we have not, as a group, looked at snow or ice. 

We have not looked at the sea although use:ul observations might he 

possible, especially for coastal waters. 

"Little has been done to improve cross-polarized measurements. llse 

of circular reflectors of parabolic shape leads to significant cross 

polarization. Low-cross-polarization arrays or horns should be used 

in such measurements. Cross-polarized returns have signiiicnnt potent i- ' s, 

as demonstrated years ago with Ll~e Wcstingt~ouse 35 GlIz radar, and more 

recently with ERIN, CCIIS .~rld .IPI, r;~cl.lrs .I1 

"Nothirig Iias beclrl Jc~r~c~ in this program with regard to snow and 

ice dielectrics, although svnle othcr work relates to them. The problem 

is complex, and perhaps should be left to the Arctic and Air Force 

programs. " 

'I see no need for a change in direction." 

-- 

"I agree with Dr. Smith's statement that the SRAEC program needs 

to extend applications of radiative transfer theory to other terrestrial 

media. I am biased towards the study of soils. Other media obviously 

include snow, ice, exposed rock, and even water bodies (e.g., the 

turbid waters of the Great Lakes)." 
"Steps need to be taken to ensure the transfer of SRAEC accomplj.sl~mt~nts 

to applied remote sensors. In particular, these accornpliohments are of 

immediate and great utility to those scientists planning retrospective 

and field observations for ISLSP .'' 

"The greatest strength of the program is the heavy emp';liW.s on 

devrlopment of better understanding of the canopy radiation field using 

modeling as an approach." 

"As implemented, this emphasis has elevated determination of 

LAI, leaf angle distribution etc. (e.g., a very limited set of 

parameters) as an end objective. This is both good (we need to know 

them) but also bad (we must not lose sight of the goal to obtain 

information. The vJnri;~t)les or parameters mean nothing by themselves. .---- 

To be usc.Pr11, they ~us~ bt' put in some context and they must be used 

with other information. Thc modcling efforts tend to neglect these 

aspects. 

Thus, there is a need to better relate the modeling activities 

to basic botanical information." 

"SRAEC ir~vestigatior,~ should commence on all subjects that ore not 

now being done properly. Examples may be snow-ice, hydrology, wet 

lands, soil and shore erosion, etc. 

- - 

"There were almost no intercomparisons between different models 

addressed to the same topic .'I 
"Validation, verification and sensitivity analysis of existing 

models are still needed. This can be done by using numerico simulation 

in the case of rough soil surface and perform basic experiments on 

artificial canopy of known potenti-als in the case of vegetation layers." 

"Extension of the existing models to heterogeneous media is 

being done but ~ot yet completed." 

"To relate electromagnetic paramcaters to the classical 

biophysical descriptions--much progress has been made over recent 

years both experimentally and from mcdelling viewpoint." 

- 

"Stronger links between experimental programs and theoretical 

work ilre st ill dcsirabl(2. Should encourage joint cf forts or proposals 

from thcorcticians and expcrimentalists." 

-- 

"Basic mcasurcmcnt should now be de-emphasized. Some modcling 

effort be directed to check models against observations already made." 

- 

"SUEC program needs more research related to incoporating as 

many aspects of the soil-plant-atmosphere system as possible. We have 

emphasized radiation exchange, but numerous other processes are closely 

rela.:d to radiation exchange such as evapotranspiration and dry matter 

production and there should be some attempt to bridge this gap with as 

rigorous an approach as possible," 
"Further developments are needed in relating classic biophysical 

descriptors to e1ect::amagnetic parameters (e-g., Biomass needs to be 

estimated as opposed to LA1 and LAD). These needed developments, 

however, will likely follow from the current research direction." 

"One gap is in not using the theoretical radiation caoability 

assembled in SRAEC program to address problems of leaf BRDF as it 

depends on leaf structure - internal (cells, chloryplasts, air gaps, 

water, etc.) and external (epidermis, cuticle, surface irregularities, 

etc.) ." 

"Much - - more emph;lsis nceds to be placed on the inverse problem --- 

both in terms of rigoror~s tht'orcLica1 models and simple algorithms that 

can be usrd efficientlv on millions of pixels. This universe problem 

needs to include the a~rnosphrrt in tticl near future." 

--- 

"1 think there were not enough model intercomparisons . " 
QUESTION # 3 

Are there gaps in the program? Should new areas be added? 

Should there be deletions? 

"It seems to me that a gap exists in tying the microwave and vis-IR 

response together. The ulitmate application is going to involve sensor 

combinations with combined use of vis-IR and microwave when vis-IR 

is possible, and use of microwave alone when clouds obscure the ground." 

"If natural vegetation is the goal these days, it skems to me that 

we are not doing justice to some forms of natural vegetation. Specifically, 

I scc almost no effort on grassland and sparse desert a getation. Althou~h 

other programs arc addressing snow cover, sea ice, etc., at least some 

link to tliesc would l)c al~propriatc. Eloreover, urban areas arc a part of 

the environment--a very big part in some places--yet nothing seems to bc 

underway with regard to them except a tiny effort on-our part to look 

at radar :.ourccs in wooden buildings." 

"Another area that seems to be receiving too little emphasis is 

uncovered lithology. It is fine that it is starting in the thermal IR, 

but the visible and microwave regions are not being treated. We have 

done some work in the past that shows that one really can get lithologic 

signatures in the microwave, but the surface has barely been touched." 

"Much work needs to be done for grasses and forest canopies in 

both canopy models and hope to extract key biophysical variables. 

A clear need to attack (or combine) canopy reflectance models with 

at~nospheric models needs to bc done, though a start has been made 
"The important gap in the program is the lack of a systematic 

plan to verify individual models with carel:slly controlled- experiments. 

The experiments should be made on both real and artificial canopies. 

All investigators should be notified of the experime~f- in advance and 

have the opportunity to have ground truth that might need to be measured." 

I1 In the optical area, there is a need to have the individual 

scatterers in the canopy carefully modeled." 

- 

It Both in optics and microwaves, the inversion of present models 

should be carried forth. Since this is our ultimate goal, the groups 

should start TO address this porticn of the wcrk more seriously." 

-7 

II There ?re gaps in two areas. Tlierc is a crying need for 

research to pravide means to obtain the input 1,;lrnmctcrs needed Eor use 

in canopy radiation models. That is, we need better instruments to 

measure/cstimntc LAI, LAD, etc in a timely manner. At prescnt we are 

quite capable of collecting enormous amounts of spectral reflectance data 

on numerous fields but only limited amounts of supporting data on 

only n few fields. Thus we need a machine to masure the canopy 

geometry. We need support for collection of a limited amount cf scanner 

polarization data, preferably polarized AIS type data, in support of 

my area and other modellers. Without these data we will not be able 

to address these questions. 

(1) How is light, scattered and polarized by a plan canopy, transmitted 

through a disturbing atmosphere over a large area. (2) Is polarization 

data another independent source of information about the scene-- 

providing another 'channel' of informati~n for discriminating species 

,znd assessing the condition of the plant canopy on the ground." 

2 8 
"An error analysis needs to be made for the entire remote sensing 

system to determine the amount of research that is required for each 

component of the system. The system consists of the surface, canopy, 

atmosphere, sensor, processing the measurements, and finally inversions.. 

If the accuracy of only one component of the system is only five percent, 

say, then it may be unnecessary to achieve much greater accuracy for 

any other component. Sensors should not be built at great expense 

with greater accuracy than is justified by the accuracy of the remaining 

components in the sys tem. " 

"Lack of interaction between SRAEC investigators and meteorologists 

and climatologists." 

"Only che thermal region is missing in the existent programs." 

"lihe gaps in the program arc related to the issues addressed in 

question 1, which arc in fact tlic future directions that we should be 

concentrating on. It will be of Eundamclltal importance to unify the 

optics and the microwave approaches, to include earth terrain media 

other than vegetation canopy, and extend the atmospheric study to 

include both the lower and the upper atmospliere. With such 

interdsiciplinary approaches, we should be able to establish credential 

in accountability and applicability to NASA goals such as the global 

habitability studies. and at the same time remain in the domain 

of fundamental research ." 
"Gaps: The thermal is an obvious gap that has been mentioned. 

Snow surfaces are not being addressed, and should. New work in soils 

and rock spectra are extending our knowledge of scene radiation to 

jqclude phenomena beyond plant canopies. I think the program should 

continue to broaden in this way, but still keep its emphasis on 

fundamental research unknowns. 

"There is now a critical need for more coherent involvement 

of measurement and modeling. The so-called "National Canopy Facility" 

is all manifestation." 

"Inversion of modcls to obtain biophysical parameters from 

remotely sensed data." 

"Considering the Fllntls nvailnbic and the number of people involved, 

the program is very balanced. The biggest gap I see is a strong research 

program on modeling thermal IR phcnomcna." 

"Thermal IR studies of the surface, including multi-angular 

studies as well as investigation oE IR sounding to characterize the 

atmosphere." 

"The addition of someone in the lidar field would be useful, to 

get the optical passive and actj.ve communities talking to each other, 

as well as to give the laser community a better sense of the type of 

atmospheric information that is needed in order to correct images for 

atmospheric effects." 
"The gaps in the program are related to the issues addressed in 

Question 1, which are in fact the future directions that we should be 

concentrated on. It will be of fundamental importance to unify the 

optics and the micrawave approaches, to include earth terrain media 

other than vegetation canopy, and extend the atmospheric study to include 

both the lower and the upper atmosphere. With such interdisciplinary 

approaches,we should be able to establish credential in accountabilitl; 

and applicability to NASA goals such as the global inhability studics, 

and at the same time remain in the domain of fundamental research." 
QUESTION # 4 

What are your views regarding the creation of a Nationhl Canopy 

Facility? 

- 

"Considering the effort required to establish a chosen and 

various LA1 and LAD for a canopy of credible size (number of "leaves", 

etc), it would seem to me that it might be better to devote effort to 

devising rapid, comprehensive, and accurate techniques for measurement 

of the geometrical leaf descriptions than to constructing a hardware 

model of large scale. 

"T11e use of models in experiments is importarit in many investigations, but it is also important that individual experime~ters use simple 

models at their own sitcs to answer simple questions quickly. The whole 

job cannot be done effectively wit11 one or two massive models used by 

everyone. Perhaps these are dcsirablc for comparison purposes and for 

classes of experiments where simple models will not do." 

"~eornetric scaling should be possible for answering most modeling 

problems. This means that the models can be much snaller than the 

real world, which makes them easier to use in some ways. For microwaves 

this means that a higher Frequency must be used than the frequency that 

would be used with the real thing, but this is not hard to do. I see no 

real problems with doing this scaling in the optical-IR regime, aqd it 

should allow the models to be much more tractable. Moreover, for a dense 

canopy. there is no need to model the entire thickness, since the 

radiation will not penetrate beyond a certain depth anyhow!" 
"I recommend a very inexpensive, simple canopy at first to see 

if tnis idea is really worth putting the time and money into." 

"Absolutely necessary because (1) angular distribution (be~ides 

time variation) of canopy reflectance seems to be a valuable crop 

identifier and (2) angular pattern of reflectance is understood only 

qualitatively (bowl-shape, hot-spot, invariant valley), but not 

quantitatively. An artificial canopy with the possibility to set 

LAI, LAD leas sizes, etc may give us the hint to quantitative 

expressions." 

"1 bclicvt. thert. is n strong need to establish rt "controlled" 

facility for a variety of representative media (not just canopies). 

Sonic tests would be very sinlp~e/some complex. Considernble thought 

should go into such a program-wide resource--it is important to do it 

rigtit and assure that sufficient resources be allocated for a sustained 

effort--not a "one-shot" deal. I am reasonably confident that 

funds From other agencies could be identified to match NASA funds. 

I am quite concerned that such a facility be established and 

maintained by a group/groups that already have existing measurement 

expertise in microwave/optical regions. I think a combined facility 

could be beneficial. I need to think through some stepslways to get 

things going. I have some significant requirements for the op,-cal case 
"I believe there is well-defined value, over all programmatic 

interests, in the NCF: models are not verified in full as being 

invertible for enough distinctive canopy features, we need to 

understand "hidden variables" or hidden assumptions about canopy 

structure (especially pair cotrelations of leaves or other scattering 

structures). 

II I think that construction of a National Canopy Facility will be 

a total waste of scarce resources. For homogeneous and uniform canopies, 

CR models exist which represent the CR quite accurately (within the 

measurement accuracy). For complex canopies, the models are not as 

good but a complex artificial canopy wili be hard to make and will 

itsclf int rotlur.c unwi~ntcd artifacts .. 

T support the concept of an individual P. I. proposinv Ili 

artificial cnnopy cxpc.rirncnt as part of his/llPr proposal." 

-- - - 

"I favor ttic itlc>a of ;In artificial canopy being exp1orc.d. Ilowt~vc~r, 

there must be at least a promise of learning something from this that 

we do not already know. Also, I would hope that it is not so conceived 

and constructed that it becomes an end in itselt without contributing 

to the real vegetation remote sensing problem. 

I think that a significa:tt effort should be funded to explore 

designs for such a facility using expertise from a broad cross section 

of the biological and remote sensing communities. This would involve 

materials, questions, logistic questions, radar vs. optical, and outlines 

of some reasonable projects that it would be used for. 
After this one year or more of study, the question should be 

posed well enough to be evaluated in a peer review system. Whether 

this artificial canopy has naything to offer will depend strongly on 

the deslgn and we need to know specifics that are generated $,om a broader 

cross sect:tsn of potential users ." 

"I don't think large amounts of money should be spent on making 

an artificial canopy closely resembling plants when one couIa sp.~nd 

69~ on a seed packet and grow the real thing! To me, the utility of 

an artificial canopy would be to convincingly demonstrate that canopy 

properties can be recovered uniquely for relatively simple (but non-trival) 

geometries, because if that can't be done, then I don't see how crop 

situations can be inverted. Thus, there is no pressing need for the 

artifical canopy to rescmbly plants other than in some gross way. If 

such a simple canopy can't be constructed for under, say, $10,000, we're 

getting into dollar amounts that might be better spcnt elsewhere, 

especially in this time of budget limitations." 
1I.B. PRINCIPAL INVESTIGATOR SUMMARY REPORTS 

Each of the principal investigators was requested (see 

Appendix A) to bring to the Third Annual SRAEC Principal Investigator's Meeting a succinct summary research report that provided 

information on the 1) justification, goals and objectives; 2) 

experimental approach; and 3) study results, with up to three key 

figures to illustrate their findings. In addi~~on, a separate 

listing of publications and presentations on their research was 

also requested (see Section 1I.C.) 

The remainder of this section contains the individual 

investigator's summary research reports in the following order: 

Smith Reflectance Modeling (p.37) 

Norman 

Mimes 

Bidirectional Reflectance Modeling of 

Non-Homogeneous Plant Canopies 

(p.45) 

Understanding the Radiant Scattering 

Behavior of Vegetated Scenes (p.53) 

Vanderbilt Measurement and Modeling of the Optical 

Scattering Properties of Crop 

Canopies (p.59) 

Strahler Geometric-Optical Modeling of a Conifer 

Forest Canopy (p.66) 

Badhwar Crop Characteristic Research: Growth 

and Reflectance Analysis (p.71) 

Kahle 

Diner 

Ground Reflectance Measurements from 

Thematic Mapper Data (p.78) 

Thermal Infrared Geometric Remote 

Sensing Research (Co-I, 

Bartholomew) (p.85) 

Atmospheric and Scene Complexity Effects 

on Surface Bidirectional 

Reflectance (p.92) 
Fraser 

Pearce 

Gerstl 

Fung 

Kong 

Lang 

Moore 

Paris 

Atmospheric Effect on Remote Sensing of 

the Earth's Surface (p.99) 

The Characterization of Surface Variegation Effects on Remote Sensing 

(p.106) 

Multidimensional Modeling of Atmospheric 

Effects and-Surface Heterogeneities 

on Remote Sensing (p.113) 

Scattering Models and Basic Experiments 

in the Microwave Regime (Co-I, 

Blanchard) (p.119) 

Remote Sensing of Earth Terrain (p..125) 

Discrete Random Media Techniques for 

Microwave Modeling of Vegetated 

Terrain (p.129) 

Microwave Dielectric and Propagation 

Properties of Vegetation Canopies 

lp.135) 

Determination of Backscattering Sources 

in Various Targets (p. 148) 

Active Micowave Properties of Vegetation 

Canopies (p.147) 
Dr. 3ms A. Smith 

College of .?orestry & Natural Resources 

Colorado State University 

Fort Collins, Colorado 80523 

The overall goal of our work has been to develop a t of computational tools and media abstractions for the terrain bidirectional reflectance problem. The ndeling of soil and vegetation surfaces has been 

emphasized with a gradual increase in the comp1exit.y of the mdia 

geanetries treated. Pragmatic problems involved in the m-cbined modeling 

of soil, vegetation, and atmospheric effects have been1 of interest and one 

of our objectives has been to describe the canopy reflectance problem in a 

classical radiative transfer sense prmitting easier inclusion of our work 

by other workers in the radiative transfer field. 

Th? application of radiative transfer theory to soil and vegetation 

media requires an abstraction of the scattering and absorbing properties of 

the medium in terms of biogeophysical attributes, a specification of the 

geanetrical boundary of the medium, and a mthgnatical solution technique 

to the radiative transfer equations. We have abstracted our media to consist of a collection of discrete scatterers, e.?. leaf or soil facets, with 

individual diffuse and specular optical properties. Bulk proprties of the 

media are usually derived from suitable averaging ovex the statistical distribution of the individual elements within the mdium. For sirrp?le plane 

parallel nledia gecmetries, we are using classical solutions to the radiative transfer equations, e.g. the discrete ordinates/ finite difference 

method of Qlandrasekhar, the Adding method of Van de Hulsk, or the two 

stream method of Kaufm. For complex geanetries with irregular rough surfaces, we are employing Monte Carlo techniques. 

We will briefly sumr~rize three areas which have been addressed since 

the last SRAEC annual meeting. These are orthogonal expansion of our phase 

functions in terms of total scattering angle and example use with standard 

radiative transfer aode, e.g. Kaufm's two stream approximtion; our Monte 

Carlo reflectance rnodeling for oomplex soil surfaces which now include 

Frsnel facets; and our current work in modeling complex vegetation surf aces. 

Orthouonal, msion a Utilization of C.axgy .Phase Functions 

We have previously described our cakculational technique for averaging 

over leaf angle distributions and leaf optical properties to estimte the 

canopy scattering diagram as a function of the global incident and exitant 
angles. The phase functions we presented were given in terms of incident 

angles, p,rd and exitant angles, p1,8'. As Ross has indicated, it *pars 

that canopy phase functions, unlike me of the more symmetrical atmospheric cases, my not necessarily be explicitly formulated in tern of only 

a total scattering angle, 8. We have qent sane time pondering this circumstance. Recently, we have adapted an approach outlined by Liou for ice 

crystals whereby "averaget1 phase functions can be cornput&. The procedure 

essentf ally averages over ranges of p, 18 and p1 ,rdl which yield the same 

total scattering angle, @, i.e. 

cos 8 - p p' + (l-p11/~ (l-y'~~/~ cos [I& 4') (9) 

We tern the resulting scattering diagrams, nstylized" phase functions. 

We do not -believe the results are strictly correck in the fine details, 

because of both fundamental reasons and numerical. problems. Howeverp as 

Van de Hulst has indicated, for many calculations the fine details may not 

be all that inportant. Theoretically, the phase functions are milch more 

tractable and be expanded, in mendre polynanials, for example, as follaws: 

and, thence, into a variety of useful forms. The table below shows an 

example calculation for a spherical leaf angle distribution for visible and 

near infrared wavelengths. The phase funckion, and, hence, expansion me£-- 

ficients vary with the vegetation optical proprties. 

WI'E: % should be 1.0; sane measure of the numerical precision of the 

calculatioils is indicated by the deviations from this value above. 

Such expansions can be easily incorporated into standard radiative 

transfer code. We have used the above values in Kaufman's published modified two strean method-the program aade was obtained from the Atmospheric 

Science Department at Colorado State University. Figure 1 is a plot of the 

(spline - smoothed) stylized phase functions at the three wavelengths 

above. 
At last year's SRAEX: sm preliminary results from a Monte Caiclo mxlel 

for the reflectance of a rough soil were presented. The thr~st of our work 

in this area over the past year has been to extend the usefulness sf this 

model to surfaces having non-%ambertian elmental rdleetance properties, 

In particular, we were concerned with the effect of a distribution of 

Fresnel facets superinposed on macroscopic surface irregularities . The 

reflectance properties of an element of area of surface covered by these 

facets was determined theoretically, and then this reflectance fuaction was 

substituted for the original Limbertian one in the Monte Carlo mdel. 

In the substitution of reflectance functions into the Monte Carlo 

model it was desirable to allow the most general forms possible. For this 

reason two alternatives were investigated: the approximation of the reflectance functions in te~m of spherical harmonics, and the use of a lookup 

table generated from the value of the reflectance functioris at discrete 

angles. Mter sane preliminary testing it appears that the former approach 

is slightly better when the reflectance function in question is sinple, 

however for mre complex functions, and in particular for the functions 

arising from clistrjd3utions of Fresnel facets, the lookup table approach is 

the only reasonable one. 

Thus far, we have only considered the case when the Fresnel facets 

have a uniforrn distribution of inclination angles. An exanqle of the sort 

of results obtained for a surface with a sirnpLe cosine undulation is given 

in Fig. 2a. In this case light was incident on the surface at a zenith 

angle of 45 degrees and an azimuth prpendicaar to the direction of the 

rows. The results are given by plotting mntours of equal r~,'lectance factor on a polar plot in which distance £ram the center indicates the zenith 

view angle, and the azimuth of the view corresponds directly to that on the 

plot. Figure 2b shows the bidirectional reflectance distribution function 

for the same surface possessing purely Lambertian elemental scattering properties. 

After reviewing the bidirectional reflectance distribution modeling 

work for vegetation media currently underway in the SRAEC fundamental 

research effortr we concluded that it would be useful to attack the problem 

of reflectance from a rough surface vegetation layer from a multiple 

scattering, radiative transfer perspective. The approach we chose is an 

~utgrcrwth of Nom2's work and eornplements Strahler's geanetric optics 

approach utilizing stylized structures for tree crowns. Basically, we are 

adapting a Monte Carlo code by utilizing probability of gap expressions 

which take into acmunt the varying optical path length through vegetation 

layers as a function of canopy densityr macro-structure and look angle. 

Gecmetrical routines are used to compute required parameters f ran a canopy 

height profile. In practice we gnploy Fourier series expansion of canopy 

height profiles. Later we may examine statistical structures inherent in 

the data via power spectra analysis and formulate appropriate mdels. 

These ideas are partially generated from same thermal deling work we are 

performing over a forested site at Oak Ridge National Laboratory and we are 
capitalizing on the canopy structure &ta available for this site. 

This work is in preliminary stages, but briefly our approach follows: 

1. An adapted version of our Monte Carlo vegetation reflectance model 

will be used to handle the multiple scattering calculations. 

2. Probability of gap expressions are computed for photon interactions by 

considering both micro (i.e. leaf angle distributions) and macro 

(canom height profile) structure. Specifically, 

Po (8) = exp - IN*$ (8) *D (8) /h (3) 

where g( 8 1 is the mean canow projection in direction 8, LA1 is leaf 

area index, and D( 8 is the gemetric path length from the bottan of 

a canopy late1 to the top profile in direction 8, and h is the canopy 

layer thickness. 

3. Appropriate geometrical computatioml. routines have been developed to 

calculate D(8) for an arbitrary canopy height profile. We have 

applied these routines to sample data transects from the Oak Ridge 

Site. In practice, the canopy height profile data are first 

"detrended" using least squares regression, and the the pier spctra 

computed for the detrended data in order to develop Fourier series 

representations for the calculation routi.nes. Figure 3 shows a sample 

detrended height profile, and schematically illustrates the varying 

path lengths through this canopy layer as a function of look angle. 

Multiple voids in the canopy are correctly handled. 

The min significance in our work is an increased understanding, 

expressed via a variety of computational procedures, of terrain bidirectional reflectance properties. To our knawledge, there were no macro soil 

reflectance models for amplex surfaces incorporating the complete rnultiple 

scattering solution and accounting for shadowing effects. Our calculation, 

treatment, and utilization of canopy phase functions also appears to be 

smewhat novel, although we have built upon the efforts of earlier workers. 

Extensions could be made to our work to include, for example, the incorporation of media subelement models to account for physiological or polari- zation properties. 

In the eight months remaining of our third year of funding the final 

step in our research focus will be to complete a tractable treatment of 

complex vegetation surfaces amendable to our Monte Carlo canorpy reflectance 

modeling techniques. In addition, we will more gracefully complete several 

loose ends in our completed work including the generation of orthogonal 

expansions of our canopy phase functions and the utilization of the mdels 

developed under this study to illustrate soil/vegetation/atmospheric 

effects in such applications as AWEU+derived vegetation index calculations. 
I 1 1 

'h, 0.55 micrometers 

'1 0.80 

\ r. 

--\ 

5 s s 

Scattering Angle 

Figure 1 . Sty1 ized Canopy Phase Functions 3s a 

Function of Scattering Angle fur 

wavelengths of 0.55 and 0.80 micrometers. (Normal ization is incomplete) 
gji~uv@ 2d- Do? JT rsq~t of hidifactiona'l ref1 ectance distribution 

fur.re,t,jon froi;n ~023 soil ~urface ~itk ~adrtia11y specularly 

ve9""8ee,t1nrj Fresnel facets, Sun is &t 45 degvees a&th 

dz 71'1tith zjerglt -4 ic~l 21' &rl me5, Kler$~en%al ~ef 3 ectance 3 s 

285, , 
Figure 2b. ?olar plot of bidirectional reflectance distribution 

function from a row soil surface witn strictly 

Lambertian elemental ref1 ectance properties. 
Figure 3. Detrended height profile for forest transect and probability 

of gap calculation for path length as a function of look angle. 
BIDIRECTI'JNAL WFLECTANCE MODELING OF NON-HOMEENEOUS PLANT CANOPIES 

John M. Norman 

University of N2braskil 

Lincoln, NE 685Pj 

Objective 

The objective of this research is to develop a 3-dimensional radiative 

tran.- fer model for predicting the bidirectional reflectance distribution 

function CBRDF) for heterogeneous vegetation canopies. The model (named 

BIGhP.) considers the angular distribution of leaves, leaf area index, the 

location and size of individual subcanopies such as widely spaced rDws or 

trees, spectral and directional properties of leaves, multiple scattering, 

solar position and sky condition, and characteristics of the soil. The model 

relates canopy biophysical attributes to down-looking radiation measurements 

for nadir and off-nadir viewing angles. Therefore inversion of this model, 

which is difficult but practical, should provide surface biophysical 

propertizs from radiation measurements for nearly any kind of vegetation 

pattern; a fundamental goal of remte sensing. Su2l-i a mdel also will help to 

evaluate atmospheric limitations to satellite remote sensirig by providing a 

good surface boundary condition for many different kinds of canopies. Further 

this model can relate estimates of nadir reflectance, which is approximated bj 

TMS~ scitellites, to hemispherica? reflectc~cc, -..+ich is zccczrrr;. In the 

energy budget of vegetated surfaces. 

Technical Approach 

The approach to this research requires developnent of the mathematical 

equations and computer coding of the heterogeneous-canopy model, better 

characterization of leaf and soil properties which are a serious limitation et 

the present time, and finally comparison of made1 predictions with field 

measurements that are obta.ined from other investigators. The Bidirectional 

General Array Model (BIGAF?) is based on the concept that heterogensous 

csnopies car, be described by a combination of many subcanopies, dlich contain 

all the foliage, and these subcanopy envelopes can be characterized hy 

ellipsoids of various sizes and shapes. The foliage within an ellipsoid may 

be randomly positioned or non-randonly positioned. Estimtes of multiple 

scattering are obtained by transforming each point of interest in a particular 

ellipsoidal canopy to an equivalent one-dimensional canopy and solving the 

radiative transfer equations for this simple case. The BR3F for individual 

leaves has been measured so that appropriate leaf properties can be. used in 

the model. The BRDF for several soils has been measured and modeled with a 

simple block-modeling approach to provide a reasonable Power boundary 

carldition for the canopy model. Fieia masurements of corn and soybean caaopy 

BRDFs are canpared with -&el predictions. 
- Research Results 

The results of this study are three fold: 1) A simple soil BRDF model 

tested with measuranents, 2) laboratory measureinents of leaf BRDFs for live 

corn and soybean plants grown in the greenhouse and the field, and 3) the 

developnent and validation of a 3-dimensional canopy BRDF model of 

heteroge.neous vegetation that combines soil, leaf, and canopy-architectural 

information. 

The simple soil BRDF model approxhates a soil aggregate by a single 

rectangular block placed on a fixed lot area with a fixed orientation reletive 

to the sun azimuth. The relati-ve reflectance factor in any view direction is 

computed fsom projections of block faces and the shadow of the block on the 

horizontal. Fig. 1 contains a comparison of model results with measurements 

in the solar waveband over a rough surface that was recently plowed from sod 

with furrows approximately 15 crn deep. The RMS difference between thc 

surfaces is 2.2% in reflectance. The simple-black-model predictions fit 

measurements from smooth (0.5-1 cm gravel) and medium rough (2 to 5 cm clods 

from multiple tillages) even better with 1% RMS differences in reflectance. 

kcif BR3F ~iaastirments were mde at 3 source incidence angles (20, 45, 

70) and about 50 view angles for intact corn and soybean leaves attached to 

their respective plants. The distribution visible and near-infrared, 

reflectance and tra~~s~ittance factors is shown in Fig. 2 for a 45 degree 

suurce inci&'l~e a~~12. The leaf hemispherical ref leccance, which is 

essential to all models of vegetation radiation exchange, was calculated from 

the integral of the BRDF (Teble 1). Clearly normal incidence valves which 

currently are being used in other models may not be appropriate since mean 

leaf-sun angles for mfxt canopies are between 45 and 60 degrees and not near 

normal incidence. 

The 3-dimensional bidirectional reflectance general array model (BIGAR) 

predictions have been compared to measurements on corn and coybeans that were 

obtained from the Laboratory for Applications to Remote Sensing (LARS), 

Purdue, University, West Lafayette, Indiana as part of the AGRISTARS program. 

An example of how ellipsaids are used to represent a young corn canopy is 

shown in Fig 3 and a comparison of measured and modeled results is in Fig.4. 

In general the model predictions agree very well with measurements considering 

that soil BRDF measurements cannot: be made for the same site as the vegetation 

BRDF measurements. 

R simple 3-ten empirical equation has been derived to fit measured and 

modeled, soil and canopy BRWs over a wide range of wavelengths. The FW3 

reflectance difference hetwEerr the 3-term empirical equation and modeled or 

measvred distributions (including view zenith angles from O to 60 degrnes) is 

about 0.2% in the visible and 2% in the near infrared for soybeans and several 

soils; a remarkably good fit. 
Significance of Re~ults 

Significant research results from this study impact on vegetation remote 

sensing in three ways: 1) relation of soil BRDF to roughness and sun angle, 2) 

interactions between soil 3RDF and canopy reflectance properties that lead to 

confounding the discrimination of sparse vegetation using angle-of-view 

observations, and 3) interpretation of leaf BRDF measurements to provide more 

suitable leaf spectral properties for models of vegetation radiative transfer. 

The very simple block model, which has beem verified with field 

rneasurenents, relates the soil BWF to roughness. Unfortunately the roughness 

is a relative roughness and thus not the erne kind of "roughness" used by soil 

physicists, Ttlus a disked field and a gravel lot can have similar relative 

roughnesses (ratio of size to spacing) and BRDFs but represent very different 

roughnesses to the soil physicist. 

Tne RRDF of sparse vegetation is not as different from soil as is 

desirable for discrimination based on view angle observations. However the 

structure of sparse canopies may be distinguishable from each other or soil 

backgrounds with zenith view angels of 60°. Unfortunately this is not 

possible from satellites. In addition we nmy understand how a BRDF is 

different for a s~il below a canopy than a soil in the open even though their 

physical characteristics are identical, Tne 3-term eupirical equation fits 

soil and vegetation BRDFs so well that it my greatly simplify extraction of 

canopy properties from off-nadir observations for natural surfaces so that use 

or' s~ck ;Laid my bade practical. Perhaps it may even reduce rile r~m.ber oi 

off-nadir angles needed for obtaining canopy properties from satellite 

observations. 

During this study we have measured leaf BRDFs for corn and soybean; a 

rather formidable task that few have attempted. From this work have 

learned that models bzsed on normal-incidence integrating sphere leaf spectral 

properties, and to date nearly all leaf spectral property data is for norms1 

incidence, are using underestimates of leaf reflectance znd overestimates of 

transmittance. Using the more appropriate leaf spectral properties may change 

canopy reflectance by 5 to 15X of the reflectance value. Tt?e improved 

estimates of leaf spectral properties will also improve estimates of campy 

wEter use anci photosynthesis. In fact the reduced water use of an isogenic 

line of dense pubescence (dense hairs) soybeans could only be explained by the 

leaf BRDF and not normal incidence integrating sphere measurements. 

Future Work 

Future research should emphasize the inversion of 3-dimensional 

vegetation-soil bidirectional reflectance factor models and develop siqier 

inversion algorithms from exercising these conrplex nmdels. Both a~zu'lar (view 

direction) and wavelength information should be combined in the inversion 

process to extract the maximum amunt of information; perhaps inverting the 

distribution of normalized-difference with view angle may hold promise. The 

logical extension of this 3-D model is to include more complex canopoy 

architecture such as conifer trees, and also extend the wavelength band to the 

thermal. 
Table 1. Hemispherical reflectance and transmittance of corn and soybean 

calculated 'by integrating the results of leaf BRDF measurements. 

Incidence Visible IZIR 

Crop Angle Ref1 (%) Trans (2) R3f1 (2) Trans (%) 

Corn 0 7.3 3.9 - - 

Soybean 0 8.3 4.9 .. - 

20 9.3 4.3 41.7 30.9 

45 9.6 3.7 44.9 33.2 

70 15.3 3.1 51-6 32.0 
Fig. 1. Soil BRDF predicted fro= simple model (H=0.4, L=0.85 

kT~0.1, =0.67) and measured for a rough plowed soil 

witl-. 15 cm furrows zni .:lads for a solar zenith angle 

of (6) 63O and (b) 28'. The RlIS difference between 

measured ar.2 rodeled for (a) is 2.2% and for (b) is 1.1% 

in reflectance units. Plaximum zenith vier angle is 60' 

0 (outer rbm), cer~ter is nadir azld sun azimuth is 0 . 
14 I R SUN ZEN=45 VISIBLE SUN ZEf.J=45 

CORN LERF #18 CORN LE5F +I" 

SOY BEaN LERF# 1 1 ies 

." 15- 

w--:-, , . .., +zz:]\ .-... , \ ', i 'I '. 

/-y / . ; i I. 1; /,? ),) , /.. ;--. ---.--" -..... . . ......- .- 4 ..... . :k/ /: ;'- I:! . ,.' . 

5% / '/ ./ ,, /., /' /, 

'",- ... . -. . -S-r. I ...h5 -'-. 

3.5 -/ / .' 

WEFLECTRNCE 'TRRNSMITTANCE REFLECTRNfZC TRRNSMITTFITJiE 

Fig. 2. Leaf BRDP and bidirectional transmittance distribvtion function 

at a source incidence angle of 45' and azkugh of 0' for (a) corn 

at near infrared wavelengths, (b) Cora fit visible wavelengths, 

(c) soybean at near infrared wavelengths, and (d) soybean at 

visible wavelengths, 51 
Fig. 3. Sketch of a corn canopy with LAI= 0.4 including the 

ellipsoids used to approximate the canopy envelope. 
, a- i" > .. '~,~ei'b.Jd. .u.*- L-Y . - .. ha,, 

OF POOR QUALEY 

8 MODEL 1 

Fig. 4. Comparison of measurements and model predictions for a 

corn canopy of TAI = 0.4 having north-south rows. (a) 

solar azimuth = 7O, solar zenith = 18' (b) solar azimuth= 

276', solar zenith = 47'. South is 00: Marioum view 

zenith angle is 60" (outer rim) and nadir view is at 

the center. 

53 
UNDERSTANDING THE RADIANT SCATTERING BEHAVIOR OF VEGETATED SCENES 

Daniel S. Kimes 

NASA/GSFC 

Fundamental kncwledge of the physics of the scattering behz,vior of 

vegetation as gained in this study is important. This growing body of 

knowledge will ultimately serve the remote sensing and earth science 

community in many ways. For example, it will provide (1) insight and 

guidance in developing new extraction techniques of canopy characteristics, 

(2) a basis for better interpretation of off-nadir satellite and aircraft 

data, (3) a basis for defining specifications of future earth observing 

sensor systems, and (4) a basis for defining iniportant aspects of physical 

and hi01 ogical processes of the plant system. Such fundamental know1 edge 

is very important to the long term advancement of remote sensing and eartli 

science programs. The overall objective of the three-year study is to 

improve our fundamental understanding of the dynamics of directional 

scattering properties of vegetation canopies through analysis of field 

data and model simulation data. The specific objectives were to (1) collect 

di rectional ref7 ectance data coveri ng the erlti re exi tance hemi sphere for 

several commn vegetation canopies with various geometric structilre (both 

homogeneo~rs and row crop structures), (2) develop a scene radiation model 

with a general mathematical framework which will treat 3-D variability in 

heterogeneous scenes and account for 3-D radiant interactions within the 

scene, (3) conduct validations of the model on collected data sets, and 

(4) test and expand proposed physical scattering mecharrisms invol ved i n 

refl ectance distribution dynami cs by analzyi ng both field and modeling data. 

Using a !lark I11 3-band radiometer, directional reflectance distributions 

spanning the enti re exi tance hemi sphere were measured of natural vegetation 

canopies ranging from bare soils to complete with 100% ground cover. NOAA 

7/8 AVHRR bands 1 (0.58-0.68 w) and 2 (0.73-1.1 wn) were used in data 

collection. The cover types reported were corn, soybeans, grass lawn, 

orchard grass, alfalfa, cotton row crops, pine forests, hardwood forests, 

plowed fields, annual grassland, steppe grass1 and, hard wheat, salt plain, 

and irrigated wheat. All measurements were taken from the ground except 

the forest canopy measurements which were taken from a helicopter. Leaf 

area index, leaf angle orientation distributions, probability of gap functions, 

1 eaf refl ectance and transmittance, and soi 1 refl ectance were measured on 

some of the canopies. 

A three-dimensional radiative transfer model was developed (Fig. 1 ) 

and is unique in that it predicts (1) the directional spectral reflectance 

factors as a function of the sensor's azimuth and zenith angles and the 

sensor's position above the canopy, (2) the spectra'l absrsrption as a function 

of location within the scene, and (3) the di rectional spectral radiance as 

a function of the sensor's location within the scene. It is one of two 

existing models with such general three-dimensional capabilities. This 3-D 

model was expanded to i ncl'ude the ani sot r'npic scatteri ng properties of 

leaves as a function of the leaf orientation distribution in both the zenith 

and azimuth angle modes. The model was applied to complete vegetation 

canopies of various leaf orientations-"erectrophi le (mostly erect 1 eaves), 
pl anophil e (mostly horizontal leaves), spherical (equal probability of a1 1 

leaf orientations), and he1 iotropi e (sun tracking leaves). The model was 

also validated and analyzed for agricultural crop canopies, natural 

grassland canopies and forest canopies. The model was used to explore the 

radiative transfers that take place in these various scenes. 

The analysis of the field data and model simulations yielded significant 

information on the radiant scattering hehavi or of the vegetation canopies. 

The results showed unique reflectance distributions ranging from bare soil 

to complete vegetation canopies for agricultural crops and natural grasslands. 

Physical mechanisms causi ng these trends were proposed based on scattering 

properties of soi 1 and vegetatian. Soi 1 exhibited a strong backscatteri ng 

peak toward the sun (Fig. 2). Complete vegetation exhibited a "bowl" 

di~tribution~withe mi nimum reflectance near nadi r (Fig. 3). Sparse 

vegetation canopies showed shifting of the minimum reflectance off of 

nadir in the forward scattering direction because both the scattering 

properties of the vegetation and soil were being observed. In addition, 

sparse canopies exhibited the strong backscatter peak 6f the soil at 

relatively small solar zenith angles. The largest variations in reflectance 

with changing view angle occurred at large solar zenith angles for canopies 

with very 1 ow vegetation covers. As vegetation densities increased and 

the solar zenith angle decreased, reflectance variations decreased. The 

dynamics of the directional reflectance distributions were analyzed and 

physi cal pri nci pl es responsible for the observed dynami cs were proposed. 

Past studies have demonstrated that the normalized difference transformation 

[AVHRR (Band 2 - Band l)/(Band 1 + Band 2)1 is useful in monitoring green 

vegetation biomass. A difficulty in utilizing AVHRR data that scans out 

to 56O is that the signal for any particular target can change significantly 

with various view angles. It was demonstrated that this transformation 

generally decreased the li rectional variation of the signal. However, 

there were exceptions. For each remote sensing application the user should 

be aware of these variations for the specific cover types being studied, 

solar zenith angle and scanning direction of the sensor with respect to 

the solar azimuth. It was found that complete canopies with different 

leaf orientation distributions (erectophil e, spherical, planophil e, and 

heli otropic) had unique ref1 ectance di stri bution characteristics. The 

dynamics of these distributions were physically explained by directional 

scattering effects of two mechanisms. The first mechanism causes the 

characteristics "bowl" shape of complete canopies that is--increasing 

reflectance with increasing off-nadi r view angle for azimuth directions. 

It is caused by shadowing gradients and view projection gradients within 

the canopy. The second mechanism is the primary directional scattering of 

the leaves (phase function) due to leaf orientation, source direction, and 

leaf transmittance and reflectance values. The combination of these two 

mechanisms in the various canopies are responsible for the dynamics of the 

overall shape of the directional reflectance distributions. 

The results showed that the scattering behavior of relatively dense 

forest canopies is very sirni far to the scattering behavior of agricultural 

crops and natural grasslands. Only in more sparse forest canopies with 

significant spacing between the tree crowns (or clumps of tree crowns) does 

the scatteri ng behavior deviate from homogeneous agricultural and natural 

grassland canopies. This clumping of vegetation material has two effects 

on the radiant transfers within the canopy. (A) It increases the probability 
of gap to the understory and/or soil layers which increases the influence 

of the scattering properties of these lower layers and (0) It increases 

dark shadows within the scene causing increased backscatter and decreased 

forward scatter to occur relative to the homogeneous case. Both phenomenon 

tend to increase backscatter relative to forward scatter. For typical 

forest canopies, the peak backscatter reflectance can be increased as much 

as 30% relative to an equivalent homogeneous canopy due to phenomenon A and 

35% due to phenomenon B. The combined effect of phenomenon A and B can 

cause typical increases of 65% or higher. It is hypothesized that these 

phenomenon are especially important in sparse conifer forests such as the 

boreal forest which account for 50% of the world's forest area. 

The understanding of the radiant scattering behavior of vegetated 

scenes gained in this studied can lead to intelligent techniques for 

extracting canopy parameters from remotely sensed data. For example, 

estimating the hemi spherical refl ectance (a1 Redo) of terrestri a1 surfaces 

is of great importance in studying biospheric and atmospheric processes. 

It is proposed that satellite borne instruments represent the only practical 

means of obtaining global estimates of surface a1 bedo data at reasonable 

time resolution; the problem being how to relate the nadir or directional 

reflectance observations from such sensors to the integrated hemispherical 

refl ectance. This study investigated (1) the relationships betwen 

di rectional reflectances and hemispherical reflectance and (2) the effect 

of solar zenith angle and cover type on these relationships. The results 

showed that errors in inferring hen~i spherical reflectance from nadi r 

reflectance can be as high as 45% for all cover types and solar zenith 

angles. By choosing a solar zenith angle between 30°-40° the same error is 

reduced to less than 20% in both bands. For both bands a view angle of 60° 

off-nadir and +90" from the solar azimuth reduces this error to less than 

11% for all sun anyles and cover types. A technique using two specific view 

angles red~jces this error to less than 6% for both bands and for all sun 

angles and cover types. These techniques may yield considerable di vi dends 

in terms of more reliable estimation of hemispherical reflectance of natural 

surf aces. 

These fundamental research efforts have improved our physical 

understanding of radiant scattering in vegetation canopies. This has been 

accomplished through the analysis of both model simulation data and field 

directional reflectance data in the visible and near i nfrared wavelengths. 

The directional scattering behavior of vegetation has been described and 

explained for various solar zenith angles, and various canopies with 

different densities, leaf orientation distributions, and optical properties. 

The work has been in response to providing an intelligent basis for defining 

specifications of earth ohservi ng sensor systems and for inferring important 

aspects of physical and biological processes of the plant system. 
Y Figure 1. Three dimensional framework of the model showing the cell matrix, cell 

coordinate system, diffuse solar sources (only rne is illustrated), and 

the direct solar source. The diffuse and direct solar sources are extended down to the surface of each cell on the top surface of the cell 

mar;rix. Any 3-D scene can be represented by "filling" the cells with 

various materials with different densities and scatt,ering pfoperties. 
BARE SOIL - VISIBLE BAND 

0600 MST 

0 

0946 MST 

0 

1 

0740 MST 

0' 

I 

1Q45 MST 

Q' 

? 80 I 180' 

Figure 2. Polar plots cf isolines of percent directional reflectance in t h e v i s i b l e band for bare soil. The distance 

from the origin represents the off-nadir view angle of the sensor and the azimuth angle represents the 

sensor's azkclth. The solar azimuth is always 180°. A sensor with O0 azimuth looks into the sun, the dashed 

lines represent 15' increments of off-nadir view angle (0"-90'). The solar posltion is shown as a small 

starred circle on each plot. 
GRASS LAWN - VISIBLE BAND 

0640 EST 

0 

1 

0753 EST 

*--- 

0900 EST 

0 

-- .. 

Figure 3. Polar plots of isolines of percent directionai reflectance in t h e v i s i b l e band for a grass I.awn. 

Symbols follow 
MEASUREMENT AND MODELING OF THE OPTICAL SCATTERING 

PROPERTIES OF CROP CANOPIES 

V. C. Vanderbilt 

Laboratory for Applications of Remote Sensing 

Purdue University 

I. Justification of Research 

The amount of sunlight specularly reflected by such plants as sunflower, 

corn, sorghum, wheat, and grass is often so large that canopies of these plants 

appear white instead of green when viewed obliquely toward the sun. 

Specular reflections from the shiny leaves of plants ~r~iginate at the 

interface between air and the cuticle wax layer. Unlike the diffuse portion of 

tbe light reflected by a leaf, the specular portion of the reflected light is 

reflected at the first surface it encounters; it never enters the leaf. From 

the Fresnel equations of optFcs, the light reflected by such a shiny surface is 

po2arized. The polarized csrt;ion of the reflectance may be species dependent 

and related potentially to tile physiological status and development stage of the 

canopy - to such botanical variables as leaf age and plant water status and 

temperature regime. 

All of this suggests that reaotely sensed polarization measurements of a 

plant canopy will contain information about the leaf surfaces -- information 

independent of that already identified in the light reflected from the interior 

of the leaves measured in the various spectral regions. The information is 

independent because the polarized portion of the reflected light does not enter 

the leaf to interact with cell pigments, walls or water. 

Polarization measurements, althodgh certainly a potential source of useful 

information about the earth, have never been acquired routinely by satelliteborne imaging sensors as part of earth observation research. The reason is 

simple; the research area is virgin. Hard evidence in the form of physicallybased theories l~upported by actual data has only recently begun to demonstrate 

the actual -- not merely potential -- information ifi such data. More evidence 

is needed before a dedicated satellite-borne sensos system would be justifiable. 

11. Research Objectives 

The overall objective is to investigate the potential information in the 

polarization data of both single leaves and plant canopies. This research is 

measuring, analyzing, and mathematically modeling the specular, polarized, and 

diffuse light scattering properties of several plant canopies and their 

component parts (leaves) as a function of view angle and illumination angle. 

The potential. of these bidirectional radiation properties for ground cover 

diserimination and condition assessment is being evaluated. 

111. Approach 

The research approach has proceeded in both empirical and theoretical 

directions. Measurements performed at our laboratory demonstrate the 

relationship betweec polarization data and various optical and botanical 

properties of both pieces of foliage and plant canopies. The data provide a 

basis fop gaining fundamental understanding of how light is scattered and 
polarized by a plant canopy. A mathenlatical model has been developed for 

predicting the specular and polarized light scattering properties of plant 

canopies. By exercising the model we have developed better understanding of the 

potential information in polarization data. 

The empirical part of the approach has involved demonstrating our new 

technique for determining specular, polarized, and diffuse components of the 

reflectance factor of both leaves and plant canopies. Applying this new 

technique to our field measurements, we have determined the specularly scattered 

and polarized light from a plant canopy as a functjon of view and illumination 

directions. To these reflectance data, we have appendqd the ancillary data of 

the plant canopies for use by ourselves and other investigators developing and 

testing light-canopy interaction models, such as our specular 

reflection/polarization model. 

A polarization photometer was developed to investi~ate the potential 

information in the mean and standard deviation of the polsrized/diffuse 

components of the reflectance factor of leaves. .,,ezsurec individually in Vivo at 

six wavelengths at the Brewster angle. Measur-~~er.ts wcre made (1) in a survey 

of plant species and varieties representing crops, forests, "weeds," and 

horticulture, including as factors (when appropriate) ~eaf pigmentation, 

development stage, position of leaf on plant, and positron of instrument on 

leaf, (2) of a corn canopy as a function of its moisture stress, and (3) of a 

greenhouse-grown wheat innoculated with wheat rust. 

IV. Results 

We present three results of our research, (1) a theoretical model of the 

specular-polarized light scattered by a plant canopy, (2) data demonstrating a 

linear relationship between the relative water content of a leaf and its nonpolarized reflectance, and (3) data demonstrating the importance of the 

variable, angle of incidence, in explaining the polarization of light scattered 

by plant canopies. 

A. Theoretical Model 

A model was developed for predicting the amount of light specularly 

reflected and linearly polarized by the leaves of such plant canopies as wheat, 

corn, and sorghum. The model is based upon the morphological and phenolcgical 

characteristics of the canopy and upon the Fresnel equations which describe the 

light reflection process at an optically smooth boundary separating two 

dielectrics. 

The theory demonstrates that, potentially, measurements of the linearly 

polarized light from a plant canopy may be used as an additional feature 

discrimination. Examination of the model suggest that, potentially, satellite 

polarization measurements may be used to monitor plant development stage, leaf 

water content, leaf area index, hail damage, and certain plant diseases. The 

modeling results show that the angles of the polarization analyzer on a 

radiometer or satellite-borne sensor measuring a ground scene may be predicted 

from the view and illumination directions. 

Applicability of the model of the canopy specular reflectance should extend 

to many species because leaves - which specularly reflect sunlight - are 

ubiquitous, unconfined by geography or climate. 

The modeling results, Fig. 1, show that for the predictions from the model 

the single variable, angle of incidence (on the leaf) of the sunlight specularly 

reflected to the sensor, explains much of the variation, as a function of view 

direction (both zenith and azimuth), for a plant canopy with a uniform 
(spherical) leaf angle probability density function. For exangle, at any 

specific angle of incidence, 30 degrees, for example, the predicted R , Fig. 1, 

changes little for zenith view angles less than about 40 degrees, only changing 

significantly for angles approaching 90 degrees. The physical interpretation of 

this prediction, Fig. 1, is that at any given angle of incidence there are more 

specularly reflecting leaves in the field of view of the sensor at large zenith 

view angles near 90 degrees than near 0 degrees. For example, for the sun on 

the horizon in the east and for view directions varying from 0 deg~lees up to the 

horizon to the north, the angle of incidence will be constant at 45 degrees in 

all these view directions; however, the number of specularly reflecting leaves 

in the field of view of the sensor will be least at 0 degrees zenith view angle 

and greatest at the horizon. 

9. Leaf Moisture vs. Reflectance 

To investigate if relationships exist between reflectance and moisturestressed vegetation, measurements were acquired on the leaves of corn, grown in 

a field under moisture-stressed conditions. (A physiological disturbance of a 

plant usually retqults in an increase of reflectance in the visible portion of 

the spectrum.) Twenty-four hours prior to reflectance measurements, a portion 

of the field was flood irrigated. Leaves for reflectance measurements came from 

(a) this irrigated treatment, (b) the field-grown, stressed conditio.~~, and (c) 

leaves excised from plants subjected to rapid desiccation. The water status of 

each individual leaf was quantified by measuring the relative water content of 

each leaf sampled for leaf ref'lectance measurements. 

Fig. 2 depicts the reflectarce ia ;he red wavelength band (650 nm) as a 

function of relative water con+ . The results, Fig. 2a, show that when 

the RWC of these corn leaves i . , the reflectance factor, R, tended to 

decrease. But within this range uf relative water contents sampled (between 50% 

and loo%), the variaton in the reflectance factor is great - making the 

usefvlness of the reflectance measurements Tor predicting the relative water 

content slight. Fig. 2b shows there is no relationship between the polarized 

component of the reflectance factor, R , and relative water content. 

But there is a relationship betweeg the non-polarized component of the 

reslectance factor and relative water content, Fig. 2c, which increases linearly 

(R = 0.77) with decreasing relative water content, This rela tionship -.ippeai-ed 

valid even for relative water contents greater th:n 80%, a moisture regime for 

which other investigators have found hemisphf:rical leaf reflectance '> be a poor 

estimator of relative water content. The ran-polarized component of +' 2 

reflectance factor thus appears to be a bztter predictor of relative water 

ccntent than the reflectance factor. 

C. Plant Canopy Angle of Incidence 

In field experiments designed to provide comparisons between the model 

predictions and polarization data, we measured two plant canopies, each in a 

variety of view directions as the sun moved, providing illumination in a 

continuum of directions. More than 200 spectra were acquired on two wheat 

canopies in the boot (preheaded) and dough (headed) stages of' development, and 

on each date in each of 33 view directions. 

The degree of linear polarization (Fig. 3) at a wavelength of 9,66 urn is 

plotted for 19 June and 17 July for four view zenith angles and angle of 

incidence, gamma. Regardless of zenith or azimuth view angles, the data points 

for June 99 fall within a narrow region defining an :ire. On July 17 the scatter 

in the dataois generally greater, although those data acquired at a view zenith 

angle of 60 define a fishhook-shaped curve. 
Fig. 3 shows that most of the variation on June 19 in linear polarization as 

function of the two variahies, view zenith and view azimuth angles, is explained 

by the single variable, angle of incidence, a prediction of the 

specular/polarization model. The angle of incidence is computed knowing that a 

small area of shiny leaf must be uniquely directioned to spec1uld21y reflect 

sunlight to an observer. For the headed wheat of July 17, the angle of 

incidence explains the variation in the linear polarization at a zenith view 

angle of 60' (albeit the arc-shaped relationship of June 19 is a fishhook on 

July 17) but less well at smaller zenith view angles. The decrease in the 

0 degree of linear polarization at large angles of incidence for 60 zenith view 

angles on July 17 (the hook of the fishhook) is due to the heads (poor specular 

reflectors) decreasing the visibility of the flag leaves to the radiometer. 

V. Conclusions 

The specular reflection process has been shown to be a key aspect of 

radiation transfer by plant canopies. Polarization measurements have been 

demonstrated as the tool for determining the specular and diffuse portions of 

the cznopy radiance. The magnitude of the specular fraction of the reflectance 

is significant compared to the magnitude of the diffuse fraction. Therefore, it 

is necessary to consider specularly reflected light i.n developing and evaluating 

light-canopy interaction models for these two wheat canopies. Models which 

assume Leaves are diffuse reflectors correctly predict only the diffuse fraction 

of the canopy reflectance factor. The specular reflectance model, described 

here, when coupled with a diffuse leaf model, would predict both the specular 

and diffuse portions of the reflectance factor. The specular model predicts and 

the data analysis confirms that the single variable, angle of incidence of 

specularly reflected sunlight on the leaf, explains much of variation in the 

polarization data as a function of view-illumination directions. 

Design of hardware to remotely sense the polarization of the light reflected 

by a canopy under a clear sky is simplified by the results of this research. 

First, the lack of fine structure in wavelength in the polarization spectra 

suggests that a design with a single wavelength band covering the entire visible 

wavelength is a possibility. Second, the angle of the polarizaelon analyzer on 

the polarization sensor does not depend on the data but solely on 

view/illumination directions and can be set prior to data acquisition. 
0 10 20 30 40 50 60 70 80 90 

Angle of Incidence (degrees) 
100 58 108 50 

Relative Water Content (%) 

(b) 
Linearly Polarized Light Reflected by Wheat Canopy 

(0.66prn) 

Preheaded Headed 

\ 

a 0 20 40 60 0 20 4Q 60 

E Angle of Incidence (degrees) 
GEOMETRIC-OPTICAL MODELING OF A CONIFER FOREST CANOPY 

Alan H. Strahler 

Principal Investigator 

Hunter College 

City University of New Yozk 

The primary objective of this research is to explo r~ 

how the geometry of trees in forest stands influences the 

reflectance of the forest as imaged from space. Most plant 

canopy modeling that has been carried out thus far views the 

canopy as an assemblage of plane-parallel layers on top of a 

soil surface. For these models, leaf angle distribution, 

leaf area index, and the angular transmittance and reflectance of leaves are the primary optical and geometric parameters. Such models, and their derivatives, are now sufficiently well developed to explain most of the variance in 

angular reflectance measurements observed from homogeneous 

plant canopies. However, forest canopies as imaged by airborne and spaceborne scanners exhibit considerable variance 

at quite a different scale. Brightness values vary strongly 

from one pixel to the next primarily as a function of the 

number of trees they contain. At this scale, the forest 

canopy is nonuniform and discontinuous. 

This research focuses on a discrete-element, geometric-optical view of the forest canopy. Trees are considered 

to be solid objects casting shadows on a contrasting plane. 

The brightness of a pixel is then a function of the background brightness, the number of trees in the pixel, the 

size and shape sf the trees and the individual shadows they 

cast, and the chance overlapping of shadows and tree crowns 

that occurs when trees fall close together. This model of 

the forest canopy presents an alternative approach to canopy 

modeling that is well suited to applications of multispectral imaging by aircraft and spacecraft. 

The primary objectives of this research are: (1) 

mathematical formulation of a discrete-element, geometricoptical model to explain the mean and pixel-to-pixel variance in reflectance of sparse to dense forest canopies; (2) 

testing of the formulation through Monte Carlo simulations 

and real image data; and (3) development of an inversion 

procedure to allow remote estimation of size, shape and 

spacing of trees from imagery when the imagery is too coarse 

to permit identification and aeasurement of individual 

trees. 

As developed, the model considers conifers as cones 

(Fig 1 . Parallel-ray geometry is used to describe the 
Geometric-optical Modeling 

illumination of the three-dimensional cone and the shadow it 

casts on the background. Cones are assumed to be randomly 

placed and freely overlapping; their heights are assumed to 

be ognormally distributed. Both these assumptions are supported by literature studies and field work, For the initial model, the cones are assumed to be of a fixed shape 

determined by the apex angle; however, in application, the 

apex angle is allowed to vary and an effective apex angle is 

determined for the stand as a whole. 

The research has been carried out in four overlapping 

phases, all of which are nearly complete. The first phase 

involved development of the basic mathematical model 

explaining the distribution of reflectance values expected 

for stands with given size, s\ape, and spacing parameters 

under fixed conditions of ill~,,mination. This phase included 

the development of an importan*t general theorem in geometric 

probability describing the expected variance in random overlapping of shapes in the plane. 

The second phase utilized Monte Car10 simulations of 

forest stands both to confirm the general theorem and empirically calibrate some parts of the model. As one part of 

the Monte Carlo modeling effort, the bidirectional reflectance of a pixel consisting of Lambertian cones on a background was simulated. The result (Fig. 2) showed many of 

the features of bidirectional reflectance distribution functions that have been observed for real forests. 

The third phase involved assembling Landsat 80-m and 

SPOT simulation iG-E digital imagery for two test sites in 

northern California, and visiting the sites to collect 

ground data for model calibration and verification. The two 

sites contrasted a rather open stand of smaller, broader 

trees {pines) with a dense stand of taller, more narrow 

trees (red firs) . Field measurements included recording the 

diameter and location of every tree within 12-16 circular 

subplots arranged on a grid at each site, as well as the 

collection of accurate heights and apex angles for a random 

subsample of trees within each subplot. 

The fourth phase included the development of an inversion procedure to estimate stand parameters of tree size, 

shape, and spacing remotely through the observed distribution of brightness values for a stand, as well as the checking of the results against the field observations. For the 

two stands tested, the inversion procedure yielded good 

results. The 80-m imagery was less accurate for the denser 

of the two stands, whereas the 10-m imagery was generally 

better. The contrasts between the two stands emerged 

strongly at both resolutions in spite of sonne differences in 

observed and calculated parameter values. 

SRAEC Report 
Geometric-optical Modeling 

The significance of this research is twofold, First, 

it establishes firmly that the three-dimensional geometry of 

ground scenes alone can explain much of the variance in 

digital imagery seen at resolutions typical of present and 

planned sensing instruments, This observation is widely applicable beyond forests to many other types of natural 

plant communities, as well as to any other scenes imaging three-dimensional objects, such as urban areas, suburban 

developments, etc. Second, it provides a method to directly 

parameterize the shape, size, and spacing of ground objects remotely even when such objects are below the level of resolution of the sensing instrument. The most obvious example 

is the remote estimation of forest biomass, which is a 

direct fundtion of the shape, height, and density of the 

trees. Used in conjunction with quantitative relationships 

between spectral reflectance and leaf area indexistanding biomass now being developed by other researchers, as well as 

with a stratified sampling procedure, this technique could 

greatly aid global understanding of carbon flows and cycles. 

The future development of this research will have two 

mcin thrusts, First, more mathematical modeling is necessary to incorporate new crown shapes and mixtures of shapes, 

as well as to account for terrain effects. Second, more 

field testing is necessary to confirm the utility of the 

inversion procedure and extend the technique to vegetation ty2es bey~nd conifer stands. These developments will not 

only .improve our basic understanding of remotely sensed 

scenes, but also allow the direct extension of that improved 

understanding to relevant problems in remote sensing and 

global habitability. 

SRAEC Report 


CROP CHARACTERISTIC RESEARCH: 

GROWTH AND REFLECTANCE ANALYSIS 

G. D, Badhwar 

Johnson Space Center 

Houston, TX 77058 

Justification, Goals, and Objectives 

Much of the early research in remote sensing follows along developing 

'spectral signatures" of cover types. It was, however, found that a 

signature from an unknown cover class could not be matched to a catalog 

value of known cover class. This approach was abandoned and "supervised 

classification" schemes followed. These were not efficient and required 

extensive trainiog. It has been patently clear that data acquired at a 

single time could not separate cover types. 

A large portion of the proposed research has concentrated on modeling the 

temporal behavior of agricultural crops and on removing the need for any 

training data in remote sensing surveys--the key to which is the solution 

of the so-called "signature extensioni1 problem. 

A clear need to develop spectral estimaters of crop ontogenic stages and 

yield has existed even though various correlations have been developed. 

Considerable effort in developing techniques to estimate these variables 

was devoted to this work. 

The need to accurately evaluate existing canopy reflectance model (s), 

improve these models, use them to understand the "crop signatures," and 

estimate leaf area index was the third objective of the proposed work. 

The next section gives a synposis of this research effort. 

Technical Approach 

The technical approach consisted of first developing an accurate model that 

would describe the temporal development of various spectral transforms with 

tirne, henceforth called a profile, that would depend primarily on crop 

characteristics. It would thus permit features to be extracted from real 

spectral data that describes a specific crop and would not depend on external 

variables such as row direction, sun zenith angle, the atmospheric state, 

etc. Having extracted a very small set of features use the canopy reflectance 

model (s) to gain (a) better understanding and 1 imitations of existing canopy 

models, (b) use the model (s) to accure a deeper physical understanding of 

why these features permit crop separation and develop method (s) of deciding, 

a priori, what features would permit crop separation, and (c) explorate the 

appl i cabi 1 i ty of these model s to natural forest communities . 
Results 

The current research effort has shown that the Kauth-Thomas (K-T) greenness, 

ir the spectral space of both the multispectral spectya! scanner or the 

thematic mapper, can be described by a model of the form, 

a/ 2 

a 

~(t) = p0 3 (P, - Po) ( t:) (t - to Exp [-~(t - (1 ) 

where p(t) the K-T greenness as a function of time, p,, the maximum value of 

greenness reached at time of peak greenness 

p0 the value of soil greenness at times at and before emergence, to, and a 

and B are two crop and condition specifics constant. These two constant are 

related to the inflection points of the profile 

This research effort has established that the peak greenness above the soil 

line, GqaX = pm - PO, the separation 

and the time of peak greenness, tp,'are three characteristics or features 

that carry 95% of all information (Fisher information criteria') available 

in both spectral and temporal data and has led to a drastic reduction in 

the number of variables and a simp1 ification of classifier design. 

Figure 1 shows the power of these features in sep3rating two summer crops, 

corn/soybeans, based on data extracted from the tnematic mapper. The axis 

out of the plane of paper is the number sf pixels, the other two axes being 

Gmax and a in days. The distributions are more or less qaussian and provide 

excellent separability. Not onlj has it been shown that these features (Gmax, 

o, and tp) are applicable to different sensor systems but are truly 

"signature extendable" over vast areas in the United States and, for the 

first time ever in remote sensing, to areas in Argentina. In particular, 

it has been found that, (i) Gmax (soybeans) > Gmax (corn), (ii) a (soybeans) < 

o (corn), and (iii) tp (soybeans) > tp (corn). 
It has been shown that the cardinal points ti, tp, and t2 are related to 

three specific ontogenetic stages of a crop. This has been shown to be 

case for wheat, barley, corn, and soybeans and appears to be true for 

rice also. This, then permits, a priori, calculation of these stages from 

an agrometeorol ogical model and in complete automati on of crop classification. 

It has also been shown that integral, 

which acts in a manner very similar to the leaf area duration, is strongly 

correlated to yield in the case of both corn and soybeans. More research 

in this dikction is called for; hoblever, the potential of a true integrated, 

automatic, and objective crop production system applicable to global corn 

and soybean> areas seem within grasp. 

In order to understand the reasoning behind why Gmax (soybeans) > Gmax (corn) 

almost uni versely, the existing canopy reflectance models were used. Figure 

2, shows a two dimensional histogram of the Gma, and leaf area index, 

calculated using the SAlL model, The distribution for each crop was obtained 

by varying soil types (12 covering the world soil reflectances) and fourteen 

diffetmewt leaf angle distribution for a total of 168 different calculations 

in each distribution. These calculations show that if the lea; area index 

of these crops is greater than about 4, the primary reason of their 

separability is because corn is Cq plant and soybeans is C3 plant and their 

leaf reflectance and transmittance are i ntri nsi cai ly different . Differences 

in soil type and leaf angle distribution simply require a somewhat larger 

differexe in the two leaf area indices to get the same separation. These 

results have also established that if the input to the canopy model such as 

leaf optical properties, soil reflectance, etc. for two crops is known, a 

transform and optimum observation period to provide a given level of 

separability can be calculated, a priori . The existing canopy reflectance models had not been subjected to a good 

test, particularly for off-nadir view angle. In order to acquirz 3 degree 

of confidence in the models and their predictions, the homogenous SUITS, 

SAIL, and CUPID canopy reflectance models wC-e very carefully evaluated for 

canopies of corn and soybeans. All of these models captured the salient 

features of the canopy reflectance, with the SAIL model showing the best 

overall performance. However, it was found that it is necessary to include 

the specul ar di rectional characteristics of 1 eaves into these models. 

Figure 3 shows the performance of the SAIL model before and after the 

inclusion of leaf specular reflectance systematic angular deficiencies of 

this model are substanti a1 ly removed. This should improvs :.IF \iseful ness 

of these models, to valuate key biophysical parameters, s r> ?is leaf area 

index. Considerable effort has been devoted in evaluating ;'it35 models for 

coni Perous canopies such as Gl ack Spruce, Jack Pi ne, Red Pine, White Pine, 

and Ponderosa Pine with 1 ittle success, partly due to lack of input data on 

key input parameters; however, their performance on Aspen and Birch canopies 

appear to be much better. We have also found that the temporal profile of 

an Aspen canopy can be adequately represented by an equation sf the form 

(1 ). The meaning of the tl, tp, and o would of course be very different. 
Si gni f i ca,m -- 

(1) For the first time in remote sensing, crop features have been found 

that are truly "signature extendable." In case of corn and soybeans 

they have been sh~wn to be applicable to vast geographic regions of 

the United States for four years 1978, 1979, 1980, an3 1982 and are 

extendable to Argentina. Based on SAIL canopy reflectance model, the 

reasons for this appl i cabi 1 i ty have been understood. 

(2) It has been shown that critical ontogenetic crop stages can be estimated 

from spectral data. Based on this work and more detailed work, it is 

suggested that it may be more accurate to estimate crop phenology 

using spectral data than current methods. 

(3) Preliminary evidence suggests that the area of greenness profile from 

ti (when new leaf development stops) to t2 (dent) is strongly correlated 

to yield. 

The above three results have made it possible to seriously consider an 

automati c and objecti vn crop production system. 

(4) An improved canopy ref1 ectance model has been developed that includes 

the leaf specular component. 

(5) The effectiveness of these models in estimation of leaf area index 

of wheat, corn, and soybeans and recently in studj of forest species 

separation and aspen leaf area estimation has been demonstrated. 

Future 

Most of the current work on feature extraction, ontogenetic stage and yield 

has been done on corn and soybean. Some start was made on wheat, barley, 

and oats. The work on spring grains should be intensified. Currently, 

no technique cxists to separate the three crops. Additional work on 

ontogenetic stagc and yield of corn and soybeans still needs to be done. 

The performance of existing canopy models on forest canopies has been found 

to be sadly lacking, much more so for coniferous forest than for decidous 

f~nst. Major improvements in these models are called for and a corresponding 

adequate input data set must be collected. Techniques to estimate leaf 

area index or phytomass of vegetation cannot be developed realiably without 

such an effort. 


8.10 

0 20 40 60 80 100 120 140 160 180 200 220 240 260 

RELAiivE AZIMUTH 

(DEGREES) 

0 20 $0 60 80 100 120 140 160 180 200 220 24U 260 

RELATIVE AZIMUTH 

(DEGREES) 

7& FIGURE 3 
GROUND REFLECTANCE EIP,- PROM 'IIlEMATIC MAPPER DATA 

J7-des E. Cone1 

Jet Propulsion Laboratory 

Pasadena, California 9 1109 

1. Background - Satellite radiance data are measures of solar radiation 

that has been reflected by the Earth's surface and scattered and absorbed by 

atmospheric gases and aerosols. Of concern to geologists are the surface 

reflectance and the degrading effects on surface resolution and albedo 

contrast introduced by atmospheric phenomena. The objects of the presentlydescribed research have been to: (1) provide an empirical relationship 

between scanner radiance and ground reflectance allowing interpretation of the 

satellite data in terms of the surface parameter, (2) assess the precision 

with which surface spectral reflectance may be recovered from Landsat-4 !Dl 

data in the presence of pezturbing atmospheric and instrumental factors. Our 

approach is field-oriented, and utilizes ground observations of surface 

spectral reflectance with portable spectrometers and radiometers to develop 

the required empirical relationships. 

2. Method - For a satellite scanner system over locally uniform ground 

w-fth homogeneous atmosphere above the upward directed rcidiance is given %y 

(Chandrasekhar, 1960; Gordon, 1976; Pearce, 1977). 

where the first term (1 ) represents radiation from the atmosphere alone, and I the second term radiation that interacts both with the atmosphere and the 

surface. R is the uniform Larnbertian surface reflectance, s is a parameter 

describing the overall probability of backscatter from the atmosphere after 

reflection by the ground, and I2 the overall probability OF transmission by 

the atmosphere after reflectj-on by the ground. All quantities in (1) are 

functions of wavelength. me detemination of R from equation (1) requires 

measurement of the functions 11, I , and s. In principle this may be carried 

out by theoretical study of moiel atmos pheres , provided in£ ormation is 

available on concentration and distribution of aerosols as well as the 

absorbing gas species present. These data are not however generally available 

for the times and places of satellite data acquisition. 

We illustrate here an alternative method wherein the required parameters 

of equation (1) are determined empirically using ground-based measurements of 

spectral reflectance. 'Ihe image data set used is the nJI scene for Wind River 

Basin, Wyoming (acquired November, 1982). me scene covers an area of 32,400 

km2 of central Wyoming. Ihe atmosphere is largely free of clouds and haze, 

whfch is typical of scenes ordinarily used for geologic remote sensing. Snow 

blankets higher parts of mountains surrounding the basin. 

3. Results -- for -- Surface Spectral Reflectance - Field spectral 

measurements of surface bidirectional reflectance were made for selected 

targets throughout the Wind River TM scene using a portable reflectance 

s pectrometer ( Canel, et ale, 1985). Image radiance values, expressed in 

digital number (3N) were determined for each of the field siees. Scatter 

plots of image DN versus surface reflectance averaged over bandpasses of the 
'I'M were prepared and are shown in figure 1. After conversion of the DN to 

energy units the term is obtained as the intercept value at R = 0, and the 

value of I2 from the slope. These plots are found to be linear with 

correlation coefficients of 0.96 or greater for all channels of the TM. It is 

also possible to obtain good fits using parabolic equations. Quasi-parabolic 

functional bet-,avior would indicate a contribution to the radiance from the 

multiple reflection factor -Rs) and would provide a means for 

determination of s directly from the curvature term. Based on statistical 

analysis of these various pssible fits to the data, the presence of nonlinear 

terms in equation (1) cannot be established. For the atmospheric conditions 

prevailing during time of satellite data acquisition we conclude that the term 

s is negligible compared to unity, and that the linearized form of equation 

(1) is appropriate. 

To illustrate application of the method for recovery of ground 

reflectance outside the calibration areas we present a comparison between 

image-derived spectra and measured field reflectance spectra for five areas 

throughout the Wind River IM scene (Figure 2). 'Ihe chronology of events for 

gathering the data was as follows: (1) the original TM scene was obtained in 

November, 1982, (2) field measurements were obtained in November of 1983 and 

used to construct the calibration lines of Figure 1, (3) field measurements 

using portable spectrometers and a hand-held broadband radiometer of the 

additional "unknown" areas were obtained in July, 1984. Thus the comparisoris 

involve measurements spanning a period of approximately two years. Agreement 

between the two sets of observations is excellent to good. It is expected 

that the comparisons could be improved if the time interval between satellite 

and field measurements could be shortened. Two additional fhctors undoubtedly 

contribute to the differences observed. First, field sites were chose1 that 

were homogeneous and (except for Riverton High School lawn) unvegetated. 

Despite precautions the best natural targets are always inhomogeneous at the 

level of a few prcent reflectance, and we must rely upon a limited sampling 

to provide representative reflectance data. Second, some targets are small 

and it is often difficult to locate them accurately in the images. Factors 

that are likely to contribute second order effects include those of so-called 

adjacency effects, phaco effects in the surface reflectance, and the 

compa~ison of bi-directional versus Lambertian surface reflectance 

funct-ions. Adjacency effects reduce contrasts between contiguous areas of 

differing surface reflectance. Kaufman and Jose& (1982) have provided some 

numerical examples. These problems can be minimized by making measurements 

far from the edges of large areas of differing albedo, but this is not usually 

possible in practice. For optically thin conditions (optical Cepth on the 

order of 0.2 or less?) the effects may amount tn a relative change in 

brightnebs of a percent (see Uufman and Joseph, 1982). Relative effects of 

this magnitude will be difficult to detect (see below) let a~one correct for 

in image data. Ihtse effects may influence both the calibration relationships 

as well as the determined brightness values for isolated pixels in the 

scene. Phase effects in the surface reflectance can be minimized by taking 

field measurements at the same phase angle and solar elevation as characterize 

the satellite observations. Ihe third problem of interpreting satellitedetermined reflectance as bi-directional is not considered serious for the 

present observations since the atmosphere, especially at longer wavelengths, 

was optically thin. 
Consid.ering the possible complications, agreement between measured and 

satellite-determined reflectance properties is remarkably good. This lends 

support to the assumption, implicit in Equation 1, of homogeneity of the 

atmosphere over large areas of the scene during the time of satellite data 

acquisition. The measured surfaces also appeared to have been stable over the 

time span of satellite and field data acquisition. 

4. Sensitivity -- of the TM-derived measurements of reflectance - By 

differentiating Equation (1) with respect to R (Gordon, 1976) a basis is 

provided for determining what differences in spectral reflectance AR may be 

obtained from 'IM scanner data, including effects of both atmosphere and 

precision of scanner irradiance measurements AI. The 'IM system signal-tonoise ratio (i.., I/AI~ for all visible and near infrared bands can be 

expressed as a linear function of the irradiance I (Barker, et al., 1.983), 

i.e., I/AI~ = A f BI where the A and B are known constants, and AIN is the 

noise-equivalent f rradiance of the scanner. An expression for AR including 

the signallnoise ratio can then be written down. Figure 3 shows the results 

of calculations for such noise-limited reflectance differences for all bands 

of the 7M scene of Wind River Basin. The values of I1 and I2 are derived from 

the data given in Figure 1. Based on these calculations, the intrinsic 

sensitivity of the 'IM system to detection of changes in reflectance everywhere 

in the scene less than about 1%. 

The actual detectable reflectance differences may be limited by 

instrumental gain. These differences AR' are given by AR' = l/(d~N/d~), which 

is the reciprocal slope of a calibration line in Figure 1. The values of hR' 

obtained in this way for the calibration data in Figure 1 are comparable to 

those obtained accounting for the measured pre-flight signai/noise ratio of 

the TM system together with the atmospheric attenuation factors (Figure 3). 

The present gain settings of the 'IM system are thus consistent with the actual 

noise characteristics of the TM. 

5. Significance of Results - We have employed an approximate analysis of 

the real terrestrialatmosphere and surface (embodied in Equation 1) to 

investigate the question of recovering surface reflectance from TM radiance 

data, and to estimate the uncertainties present in such determinations. It 

was shown that the surface reflectance could in the best examples be recovered 

to within a few percent, and it is expected that these estimates could in 

principle be improved by better sampling procedures. 'Ihe theoretical limit on 

such determinations was shown to be about a percent for the TM system. 

Equation 1 and its empirica.11~ determined constants can be used in conjunction 

with sharp edges in the image to estimate the atmospheric portion of the 

system modulation transfer function (MTF). I1 arid I2 in Equation 1 can be 

thought of as functions of the optical depth and phase function for a 

homogeneous model, and the numerical values obtained as slope and intercept 

use6 to estimate these parameters for an optically thin atmosphere. These 

determinations have been made for the present data set, but space has not 

permitted a discussion of the results. They along with other results will be 

set out in forthcoming papers. It also appears possible to provide 

independent estimates of optical depth and scattering albedo using the socalled "two-halves" method of Kaufman (1982), which will provide an 

interesting comparison with the present results. 
6. Future Research - Despite emp1;asis placed on interpretation of 

satellite-acquired scanner data, aircraft sckilner systems like TMS and AIS 

continue to provide essential data sets for the study of many geologic and 

geobotanical problems. The ?.ircraft: observations provide useful high spatial 

resolution and (for TMS) encom;~,:. 2 wide range of surface viewing 

directions. We will study the prob l..-m of correcting aircraft data for 

atmospheric effects, and provide metho*'.: for looking at directional properties 

of the surface independent of the atr~ctsphere for one or two test sites. me 

a pproach will emphasize "field" detem-ination of atmospheric parameters along 

lines indicated above, together with observation of directional atmospheric 

scattering from the aircraft data themr;elves as inputs to modeling programs. 

7. References 

Baker, J.L., D.L. Ball, K.C. Leung, and J.A. Walker, 1983, Abstracts -- of Early 

Results Symposium, ~ASA/Goddard Space Flight Center, Greenbelt, MD. 

Chandrasekhar, S., 1960, Radiative Transfer, Dover, New York. 

Conel, J.E., H.R. Lang, E.D. Paylor, and R.E. Alley, 1985, IEEE Trans. Geosci. 

and Remote Sensing, in press. -- 

Gordon, H.R., 1976, AppS. Opt. 15(8), 1974-1979. 

Kaufman, Y.J., 1982, -- J. Geophys. -- Res., 87(C6), 1437-1447. 

Kaufman, Y.J., and J.H. Joseph, 1982, -- J. Geophys. Res., 87(C2), 1287-1299. 

Pearce, W.A., 1977, Rep. 004-77, EG&G/Washington -- Anal. Serv. Center, 

Riverdale, Maryland, 136 pp. 

8. Figure Captions 

Figure 1: DN vs. Reflectance Calibratioi; Curves. TM-4, Wind River Basin, 

Wyoming, Nov., 1982. 

Figure 2: Comparison of TM-4 and Field Spectra, Win6 River Basin, Wyoming. 

Flgure 3: Noise-Limited Uncertainty W Derived from LM-4, Wind River Basin, 

Wyoming. 
200 

180 

160 

140 

120 

I, loo 

80 

60 

40 

40 6o 1 &-I RANGE - 

I I I I I I I I " 

- 2 - 

( 0.52-0.60 pm - - 

- - 

- - 

- - 

- 

- 

I-0-iMEAN 

y4 RANGE 

SURFACE REFLECTANCE, PERCENT SURFACE REFLECTANCE, PERCENT 

a Figure 1 
COMFssiRISOM OF TM-4 AND FIELD SPECTRA, 

WIND RIVER BASIN, WY. 

.-- 5- 7- 

TM BANDS SANDY LOAM, ADAPAHOE RANCH. WYD 

70 f TM-4 DERIVED REFLECTANCE 

MEAN AN0 RANGE OF 9 PIXELS 

PFRS, RANGE OF FIELD 

60 SPECTRA, 7 SITES 

E sot A ic~ue VEGETATION COVER I 

:0° 

% 80 W 

70 

-12 

13210 

3 

0 

4 0 5 

1 

7 

- 

- 

- 

- BENTONITE, RATTLE SNAKE GULCH,WYO - *, TM-4 DERIVED REFLECTANCE 

- 1 HHRR, MEAN AND RANGE. 7 SITES 

I I I 

90-123 

-9 - 

4 

c=3 

5 

0 

7 - ALLUVIUM, FREMOMT COUNTY. WYO 

- TM-4 DERIVED REFLECTANCE 

*,a ROAD BED 

WAVELENGTH, p~ WAVELENGTH, pm 

loo 90p7'31 -ta m 

LAWN. RIVERTOt HIGH SCHOOL.WY0 s 80 w o TM-4 DERIVED REFLECTANCE 

:.:jj..:::.:.: : ..;,:..:::::i.i:s:. ..,., . PFRS, RANGE OF FIELD SPECTRA, 

7 SITES I TM-4 IMAGE CALIBRATION, NOV., 1983 

FIELD SPECTRAL DATA REQUIRED JULY, 1984 

Figure 2 
R, PERCENT R, PERCENT 

1.1 

I- 1 .o 

5 0.9 

0.8 

0*7 

k 0.6 

4 0.5 2 oaa 0.3 

0.2 

0.1 

- BAND 1 - 

- (0.45-0.52 ,am) - 

- - 

- 

/ - - 

- - 

- - 

- - 

- 

- - 

- - 

- - 
Thermal Infrared Geologic Remote Sensing Research 

at the Jet Propllsion laboratory 

Wry Jane Bartholomew and Anne B. Kahle 

January 29, 1985 

JUSTIFICATION 

Remotely sensed thermal in£ rared spectral data have great ptential to 

improve rock type discrimination if the factors that control thermal infrared 

spectral. reflection and emission can be better understood. Improved rock type 

discrimination in turn leads to better and more efficient geologic mapping 

which is carried out in the exploration, assessment and documentation of 

mineral resources and geologic hazards. Geologic map; also contribute 

significantly to the understanding of the natural history of the earth and 

neighboring planetary bodies. 

The particular goal is to study the spectral emission and reflection 

behavior of rock materials (rocks, rock weathering products and soils) as a 

function of earth-like environment and occurance. Some of the important 

environmental variables that influence the earth's near surface thermal regime 

and hence its thermal emission are sky temperature, sky field of view, 

microclimatology, time of day and season of the year. In addition, chemical 

and physical factors, mineralogy, prticle size, surface roughness, presence 

of desert varnish and rock weathering, play a role. 

APPROACH 

The approach involves both field and laboratory investigatioos. The 

field work is divided between airborne and ground based studies. Remotely 

sensed mid-infrared spectral data of the earth can be acquired by the airborne 

Thermal Infrared MuZtis pect ral Scanner (TIMS) (Kahle and Goetz 1983; Palluconi 

and keks, 1985). TIMS measures normal spectral radiance of the earth's 

surface. It has six channels from 8 to 12 pn and is flown in a NASA Lear 

Jet. (Within this range the transmission of the earth's atmosphere is good 

and intense absorption features are present in surface silicate materials.) 

Computer image enhancement research is a signtficant part of TIMS 

investigations. 

he ground based field work is carried out with the Portable Field 

Emission Spectrometer (PFES) which is used to make normal spectral radiance 

measurements from 3 to 14 ~m. This JPL-built instrument is mounted and 

carried by backpack. The PFES has a spectral resolution of approximately 

.2 pm which makes it an important tool that can be used in interr:~. ting TIMS 

data. 

However, some scientific questions in this subject require the kind of 

experimental control that can only be providsd in the laboratory. For 

example, the influence of earth-like near surface thermal gradients, desert 

varnish, rock we 'hering, particle size and surface roughness on the spectral 

emission of rock nnterials ~eeds to be understood and can only be studied in 
an environment that is free from variations in sky temperature, 

microclimotology, and sky field of view and uneffected by the season of the 

year or the time of day. 

Therefore, we are developing thn capability to measure in the laboratory 

the normal lpectral radiance or rock materials at ambient temperatures (-. 

20'~). 'Ihis involves the careful design and construction of a sample 

accessory, called the emissivity cold box, for a commercial Fourier Transform 

infrared spectrometer that allows control and stabilization of sample 

tcqperature while shielding it from bactcground radiation, (Brown and Young, 

1975; Aronson and Enslie, 1973; Logan and Hunt, 1970; Conel, 1969; Low and 

Coleman, 1966; Lyon, 1965). A schematic diagram of the sample accessory is 

shown in Figure 1. 

Liquid nitrogen will be used to control the temperature of the walls of 

the cold box and dry gaseous nitrogen will control the sample temperature. 

The temperature of the gaseous nitrogen will be controlled by a liquid bath. 

A separate liquid bath will be used to control the temperature of gaseous 

nitrogen that plrges the spectrome ter' s optic bench. 

he cold box will take the place of the spectrometer's source mirror 

during the measurement oE sample radiance. Flodifications to the spectrometer 

that allow this are already complete. Furthermore, the spectrometer's 

standard pyroelectric detector has been replaced by a more sensitive liquid 

nitrogen cooled mercury-cadmium-telluride detector. 

With this configuration the sample radiance at the detector can he 

characterized as 

where L(X,T1) = radiation at detector 

TI = temperature of sample 

K( A) = instrument resonse function 

E(X) = emissivity of sample 

W(X,T1) = black body radiation at temperature TI 

R(X) = radiation reflected by sample 

S(X) = background radiation 

then by making these additional measurements, 
where T2 = temperature of sample different from T1 

TLN2 = temperature of liquid nitrogen 

B(X,T1) = radiation at detector from blackbody at 

temperature T1 

the sample emissivity can be calculated as follows. 

All values in equation 5 are either measured or calculated from Plank's Law 

once the temperature of the sample is known. 

techniques will be used to determine the sample's temperature. 

First, thermocouples will be located on or near the top and bottom surfaces of 

the sample. Second, the surface temperature will be computed from the 

radiance at the sample's Christiansen frequency (Conel, 1969; Arenson et al., 

1969). 

RESULTS 

An example of TIMS data from Death Valley, California is given in Figure 

2. These images show variation in emittance across part of the Panamint 

Mountains, valley floor and part of the Funeral Mountains. The light areas 

indicate high emittance and the dark low emitt~nce. The values upn which the 

images are based were calculated from Platik's Law and TIMS data. These data 

have been used to make lithologic map of bedrock and alluvial fans in Death 

Valley (Kahle and Goetz, 1983; Gillespie, Kahle and Palluconi, 1984). 

Figure 3 shows PFES data from Death Valley. The silicate absorption 

doublet from 8 to 10 pm can be clearly seen in the quartzite sp2ctt-a. This 

feature is only hinted at in the spe.ctra of the volcanic rocks. The presence 

of the absorption features at 6.5 and 11.5 clearly indicate the carbonate 

nature of the dolomite example. 

FUTURE PROSPECTS 

We will evaluate the geologic utility of multispectral thermal infrared 

data using TIMS, and we will determine the lithologies that can be effectively 

discriminated on the basis of TIMS measurements, either alone or in 

combination with other remotely sensed data sets. Our laboratory studies will 

be directed towards understanding the spectral emission behavior of Earth 

surface materials so as to optimize the interpretation of TIMS data. 
I 

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FIG~IRE 3- NORMAL SPECTRAL RADIANCE AND SPECTRAL EMITTANCE OF 

ROCKS FROM DEATH VALLEY. CALIFORNIA. AS DETERMINED BY THE PFES- 
REFERENCES 

Aronson, J.R., and Fmslie, A.G., 1973. Spectral reflectance and emittance of 

particulate materials. 2: Application and Results. A.p. Optics, 12, 

p. 2593-2584. 

Aronson, J.R., Emslie, A.G., Rooney, T.P., Coleman, I. and Horlick, G. 1969. 

Spectral emfttance and reflectance of powders. Ap. Optics, 8, p. 

1639-1643. 

Brown, R.J., and Youong, B.G., 1975. Spectral emission signatures of ambient 

temperature objects. Ap. Ot. 14, p. 2927-2934. 

Conel, J.E., 1969. Inf rared emissivit.ics in silicates : experimental results 

and a cloudy atmosphere model of spectral emission from condensed 

particulate medians. Joun. Geophy. Res., 74, p. 1614-1634. 

Gillespie, A.R., Kahle, A.B., and Palluconi, F.D., 1984. Mapping alluvial 

fans in Death Valley, California, using multichannel thermal 

infrared images. Geophysical Res. Letters, 11, p. 1153-1156. 

Kahle, A.B., and Goetz, A.F.K., 1983. Mineralogic information from a new 

airborne thermal infrared multispectral scanner. Science, 222, p. 

24-27. 

Logan, L. , and Hunt, G.R., 1970. Emission spectra of prticulate 

silicates under simulated lunar conditions. J. Geophys. Res. 75, 

6539-6548. 

Low, M.J.D., and Coleman, L,, 1966. Measurement of the spectral emission of 

in£ rared radiation of minerals and rocks using multi ple-scan 

interferometry. Applied Optics, 5, 1453-1455. 

Lyon, R.J.P., 1965. Analysis of rocks by spectral infrared emission 18 to 25 

microns. Econ. Geol., 60, 715-736. 

Palluconi, F.D., and Meeks, G., 1985. In preparation. 
AT?IOSPHERIC AND SCZNE COKPLEXITY EFFECTS ON SURFACE BIDIRECTIONAL REFLECTBNCL 

David S. ~inerl (Principal Investigator) 

John V. Ffartonchikl 

William D. smythel,2 

Charles 'dessom2 

l~et Propulsion Laboratory, California Institute of Technology 

2~niversity of California at Los Angeles 

1. Justification and Objectives 

Among the tools used in passive remote sensing of Earth resources in the visible and near-infrared spectral regions are measurements of spectral signature and 

bidirectional reflectance functions (BDRFs). Determination of surface pr3perties 

using these observables is complicated by a number of factors, including (a) mixing 

of surface components, such as soil and vegetation, (b) multiple reflections of 

radiation due to complex geometry, such as in crop canopies, and (c) atmospheric 

effects. Differences in surface conditions, spectral coverage, viewing and illumination geometry, and atmospheric conditions make comparison of observations obtained 

in the laboratory, in the field, and from aircraft and spacecraft extremely difficult. In order to bridge the diversity in these different approaches, there is a 

need for a fundamental physical understanding of the influence of the various effects 

and a quantitative measure of their relative importance. In particular, we consider 

scene complexity effects using the example of reflection by vegetative surfaces. 

The interaction of sunlight with a crop canopy and interpretation of the spectral 

and angular dependence of the emergent radiation is basically a multidimensionai 

radiative trsnsfer problem. In the first step of the radiation historp, sunlight 

is directly and diffusely transmitted downward through the Earth's atmosphere. The 

downward radiation field then interacts with the plant canopy. Each element of the 

canopy (leaves, srems) reflects (and transmits) light according to its intrinsic 

bidirectional reflectance (and transmittance) properties. The comylex canopy geometry, underlying soil cover, and presence of diffuse as well as collimated illumination will modify the reflectance characteristics of the canopy relative to those 

of the individual elements. Finally, upwelling radiation emergent £rum the canopy 

will be directly and diffusely transmitted by the atmosphere to space, and some 

contamination of the spectral signature with radiation reflected from neighboring 

surface regions will occur due to scattering associated with the adjacency effect. 

The intent of this research program is to develop some of the tools needed in order 

to achieve a quantitative understanding of such phenomena, using a combination of 

experimental and theoretical methods. 

2. Technical Approach 

The tools which are needed in order to study this radiative transfer problem 

include (a) knowledge of the bidirectional scattering properties of individual 

canopy elements, primarily leaves, as well as of the canopy as a whole, (h) a 

model describing the intaraction of radiation wich the canopy, and (c) a radiative 

transfer algorithm for describing the interaction of a nonuniform radiation field 

with the atmosphere. In order to obtain realistic leaf bidirectional ref 1-ectance 

functions for incorporation into canopy and scene models, we are using laboratory 

spectrogoniometry to study the intrinsic scattering properties of individuai leaves. 

These measurements provide a data set which obviates the need for nonphysical model 

assumptions, such as Lambertian leaf BDRFs. We have been using a goniometer located 
at the University of California, Los Angeles to obtain spectra of individual leaves 

for a variety of illumination and viewing geometries. The instrument operates in 

the spectral range 0.4 to 2.5 ym. The illuminating source may be placed at an 

inclination of 0 to 90' relative to che surface normal and essentially the entire 

range of emission and azimuth angles may be measured, inclading near-zero, grazing, 

and high phase angles. An important attribute is the ability obtain data out o 

the principal plane of scattering. The leaf BDRFs obtained in this manner will be 

made available to other researchers for incorporation into canopy models. With 

regard to atmospheric effects, including extinction (absorption and scattering); 

addition of path radiance; multiple reflections between atmosphere and ground; and 

adjacency effects (whereby radiation reflected from surface regions not in the 

field of view are scattered into the line of sight), we have been developing comprehensive computational tools for solving multidimensional radiative transfer problems. Our technique incorporates a two dimensional spatial Fourier transform of 

the radiative transfer equation, and the resulting expressions for each Fourier 

component of the radiation field are computed. The full 3-D intensity field is 

then reconstructed using the inverse Fourier transform. The mathematical description is of general form so as to include consideration of non-Lambertian BDKFs. 

Our technique has been specifically designed to overcome some of the approximations 

employed in previous methods and has been implemented on a minicomputer. The method 

is nearly as general as Monte Carlo but has the advantage of providing deterministic 

solutions for the upwelling and downwelling radiations fields at many altitudes, 

zenith argles, and azimuths from a single computer run. 

3. - Research Results 

Experimental data have been acquired using the UCLA goniometer on camellia, 

cuc~mber, and cauliflower leaves. In order to aonitor the effect of using cut lea.?es 

versus leaves still attached to the plant, the reflectance of a cucumber leaf was 

monitored for several hours fqllowing clipping. Xeflectivity at 0.98 pm increased 

during this period, indicating sater stress and a decrease in the strength of the 

water band. To study spectral dependence of leaf BDRF, we obtained spectra of a 

camellia leaf at view angles of 0 and 30 degrees for illuminati-on at normal incidence. The ratio of these spectra in the 0.4 - 0.9 ym region is displayed in Fig. 

1. The increased noise level at the short wavelength end is due to lower detector 

response and decreased source light levels. This plot shows that the leaf BDRF 

deviates markedly from Lambertian behavior in a spectrally dependent fashion. The 

greatest departure from Lamber:ian reflectance is observed in the 0.68 um chlorophyll absorption feature, possibly as a result of a decrease in the amount of 

multiple scattering within the leaf. 

As an example of the success .:.f our multidimensional radiative transfer algorithm, we consider the albedo step function problem, in which two semi-infinite 

fields of differing albedo are adjacent to 3ne another. This model is useful in 

that it provides (a) an evaluarion of :he diffusion of radiation across the sharp 

albedo boundary separating the two regions, and (b) the ability to verify that the 

solution asymptotically appr.3aches the correct result For a homogeneous surface at 

large distances from the boundary. This surface model nay be considered to represent a coastal boundary, in which s lnrge expanse of low llbedo water borders a 

broad land area of higher reflectivity. We compare results obtained using the 

?ourier transform method with Monte Carlo results for an atmospheric model consisting of 3 clear atmospher? with a scale height of 8 km and an optical depth of 0.189, 

corresponding to Rayleigh scattering at 0.47 urn. The ti10 half-planes are Lambertian 

with albedos of 0.0 and 0.6, and the solar zenith angle is 40°. This set of condi- 
tions is referred to as Model 1. Figure 2 shows the .~,ults of calculations for 

Model 1 using the Fourier transform technique, along wit1 selected points from the 

Nonte Carlo results. The total upwelling intensities are shown as the sum of the 

diffuse (multiply scattered) radiation field and the direct field, which consists 

of photons transmitted to space without being scattered. The agreement between 

the two methods appears to be excellent. We also show at large distances from the 

boundary the intensities calculated using the one-dieensional matrix operator 

method for uniform albedos of 0.0 and 0.6, demonstrating that the Fourier transform 

results approach the expected values away from the boundary. In the vicinity of 

the boundary, the adjacency effect is apparent. Due to scattering within the atmosphere, the upwellirig intensities on either -'ide of boundary are affected by photons 

reflected from the gurface on the opposite side of the boundary and then scattered 

into the line of sight. In effect, the atmosphere "blurs" the boundary with a point 

spread function whose width is a few kilometers. The Fourier transform technique 

is useful in that its underlying mathematical formalism demonstrates how the atmosphere filters high spatial frequency information from the upwelling radiation 

field. This filtering can be described by the computation of atmospheric modulation 

transfer functions (MTFs). Figure 3 is a comparison of MTFs calcillated using our 

technique for a Rayleigh atmosphere and an aerosol laden (hazy) atmosphere, each 

of total optical depth 0.3 and 5 km scale height. These MTFs indicate that the 

more highly forward scattering haze phase function results in a greater observability of the adjacency effect. 

Another area in which the 3-D radiative transfer algorithm is proving useful 

is in the development of a technique for determining atmospheric transmittance 

from surface inages acquired at off-nadir view angles. The basis of the nethcd is 

as follows: As shown in Fig. 2, the total upwelling radiance is the sum of a direct 

and diffuse component. Radiation directly transmitted to space is proportional to 

the surface albedo distribution, and a sharp discontinuity in the surface albedo 

gives rise to a similar discontinuity in the direct field. The diffuse field, on 

the other hand, while exhibiting a qualitative similarity to large scale variations 

in surface albedo, exhibits a much smoother character, owing to che filtering effects 

of the atmosphere, as discussed above. The direct field, which is also proportional 

to atmospheric transmittance exp(-~/~), where T is the optical depth and p is the 

cosine of the view angle, thus has a very different spatial character from the 

diffuse field. If we compute the spatial Fourier transform of upwelling radiances 

within an image, the spatial "smoothness" of the diffuse field means that it will 

make a negligible contribution at high spatial frequencies. Thus, if we eliminate 

iow frequency Fourier components we are left with a measurement tnat is directly 

proportional to the atmospheric transmission factor exp(-T/~). By obtaining images 

of the same surface region at several view angles, it should in principle be possible 

to solve for T, provided non-Lambertian surface effects can be minimized. Our calculations suggest that acqaisition of images in the vicinity of 60" off-nadir should 

be sufficient to accomplish this and recover atmospheric transmittance with an accuracy of 5-LO%. 

4. Significance of Results and Future Directions 

Xany investigators have studied the spectral properties of a wide variety of 

crop samples. The spectral reflactance of the foliage is modified by changes in 

the internal structure of the leaves associated with various forms of stress, such 

as water or mineral stress. The specularity of the reflected radiation increases 

at wavelengths where increased absorption occurs, presumably due to reduced depth 

of penetration of the incident radiation into the leaf resulting in fewer multiple 
reflections between layers. Therefore, we expect changes in leaf structure resulting from stress to affect the angular as well as spectral reflectance properties. 

Thus, it is important to incorporate realistic (non-Lambertian) leaf bidirectional 

reflectance functions into canopy and scene models. The spectrogoniometric leaf 

measurements will provide such data. 

The Fourier transform radiative transf~r algorithm which we have developed is 

a useful tool for studying the effect of the atmosphere on high spatial resolution 

imaging of the Earth's surface. As discussed above, the sharpness of the adjacency 

effect in the vicinity of albedo boundaries is dependent upon the vertical distribution of the atmospheric scatrsrers. We are using our radiative transfer method to 

perform a systematic study of the variation of atmospheric point spread functions 

with aerosol vertical distribution, phase function, single scattering albedo, and 

optical thickness. The results of such calculations will permit evaluation of the 

possibility of observing atmospheric blur directly in high resolution images of 

the Earth's surface, with the goal of determining aerosol properties. Conversely, 

these calcuilations will lead to techniques for removing spectral contadnation 

associated with the adjacency effect. 

Further work is necessary in order to demonstrate thc feasibility of implementing the multiple view angle optical depth retrieval techiiique on a space platform. 

The major uncertainty at present is the manner in which the unknown angular reflectance properties of the surface should be taken into account. For the model BDRF we 

used in our simulations, off-nadir imaging near 600 appears appropriate to compensate 

for lack of a prioriknowledge of the shape of the surface BDRF. Whether this range 

is appropriate for natural surfaces can only be determined by experimentation in the 

field. A number of portable field spectrometers are available for obtaining BDRF 

measurements. The success of this technique would be significant because it provides 

a means of monitoring tropospheric opacity, which is important not only for atsospheric studies brrt also because it is one of the most important parameters governing the effect of the atmosphere on surface images. An extension of the optical 

depth retrieval technique is to near infrared spectral regions where water vapor 

absorption occurs. In its current form, the technique relies on the assumption that 

atmospheric transmittance variesias exp(-~/~). In the water vapor bands, any finite 

bandwidth spectral channel will incorporate many individual lines and this law may 

not be foll.owed. In order to study the view angle dependence of transmittance in 

such regions, we are developing a radiative transfer algorirhm which permits calculation of broadband radisnces for channels containing uany absorption lines in the 

presence of aerosol scattering. 

Finally, we plan to investigate the applicability of our 3-D radiative transfer method to scattering in plant canopies. In principle, our algorithm is applicable to heterogeneous media and has the advantage of providing a true solution 

to the multidimet~sional radiative transfer equation. In addition, solutions are 

obtained at many view and illumination angles and azimuths, thus providing the 

fr~ll canopy BDRF. Variation of the BDRF of the individual leaves will permit 

study of the effect of changing reflectanc? ?roperties of the individual canopy 

dements on the canopy angular and spectral reflectance as a whole. Such calculations will mesh nicely with the goals of the experimental portion of this investigation. 
CAMELLIA LEAF 

Fig. 1. Ratio of reflected intensity at 30' view angle to 0' view angle for camellia leaf. 
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FREQUENCY (cycleslkm) 
ATMOSPHERIC EFFECT ON REMOTE SENSING 

OF THE EARTH'S SURFACE 

Principal Investigator: 

Robert S. Fraser 

Goddard Laboratory for Atmospheres 

NASA/GSFC, Greenbelt, MD 20771 

Co-Investigator: 

Yoram J. Kaufman 

University of Maryland and 

NASA/GSFC, Greenbelt, MD 20771 

I. INTRODUCTION 

The Earth's atmosphere has a significant bearing on the quality of images of the Earth's 

surface as observed from space by reflected sunlight. This atmospheric effect is caused by absorption and scattering of sunlight by molecules and aeroso!~. The molecular effects can be accounted 

for, but the aerosol effects are variable and poorly known during satellite observations. The optical parameters used to compute the atmospheric el'lfects are: its optical depth to determine the extinction of light; the sing!e scattering albedo, which is the fraction of light scattered from total extinction; and the scattering phase function giving the probability of scattering in a particular 

direction. 

The atmosphere tends to make dark surfaces appear brighter and bright surfaces darker, but 

the resultant effect depends on the surface reflectance pattern itself. Atmospheric scattering diffuses the boundaries between adjacent fields. This effect, called the adjacency effect, is due to 

light reflected from the ground surrounding a sensor's field-of-view and then scattered into the 

field-of-view. The adjacency effect depends on the above mentioned opticai parameters and on the 

depth of the aerosol layer. 

Theoretical analyses of atmospheric effects, ground-based measurenients of atmospheric 

parameters, and analysis of satellite data are reported on here. This work occurred during the 

period 1982-4. 

2. JUSTIFICATION, OBJECTIVES, AND APPROACH 

2. I. Justification 

Recently developed theoretical models of radiative transfer in the atmosphere can be used to 

perform atmospheric corrections for known aerosol characteristics. The developnlent of correction 

algorithms requires testing the models against measuremerits to investigate the main atmospheric 

characteristics that affect certain remote sensing techniques, and to develop methods to measure 

these characteristics from ground and from space. 
2.2. Objectives 

To study the atmospheric effect on remote sensing by theoretical niodeling and to measure 

this effect. To relate the effects of the atmosphere to the aerosol characteristics in order to determine which are the main characteristics that affect a given remote sensing function. The specific 

goals are: 

a. Laboratory simulation and analysis of field measurement of the atmospheric effect to study 

the effect and to validate theoretical models. 

b. Development of a theoretical model that can simulate the atmospheric effect over any variable 

surface. 

c. Study the atmospheric effect on the spatial resolution of satellite images of the surface and on 

classification of surface features. 

d. Analyze the relative importance of zerosol scattering and absorption on remote sensing of the 

surface in order to determine if atmospheric corrections based on the optical thickness alone 

are feasible. 

e. To measure the atmospheric characteristics that are important for atmospheric corrections: optical thickness, path radiance, scattering phase function, and single scattering albedo, and find 

the relations between them in order to establish the minimum information required for atmospheric corrections, 

2.3 Approach 

a. In order to measure the atmospheric effect and test theoretical models, a field and controlled 

laboratory experiments are performed in the presence of nonuniform surface reflectance. 

b. The simulation of the atmospheric effect over a general varying surface reflectance is performed by the calculation of the atmospheric Modulation Transfer Function (MTF) and application 

of two-dimensional Fourier Transforms for the calculation. 

c. Analyze the aerosol effect on spatial reduction and classification by means of the atmospheric 

MTF and application of the 2-D Fourier Transform technique. 

d. Radiative transfer computations are used to derive the relative importance of aerosol scattering 

and absorption on remote sensing of the surface albedo, vegetation index, and classification. 

e. A system is developed to measure simultaneously from the ground the optical thickness, the 

path radiance, the scattering phase hnction, and the single scattering albedo. The covariance 

between these parameters is studied. Inversion procedures are developed to derive from the 

observations the aerosol optical-thickness, scattering phase function, and absorption. 
3. RESEARCH RESULTS 

3.1. Measurement of the atmospheric effect 

A laboratory experiment [6] was conducted in which a half white, half black plate represented the nonuniforn~ surface and a dish with hydrosol of latex spheres represented the hazy atmosphere. A solar simulator irradiated the dish and a detector scanned the upward radiance across a 

line perpendicular to the border between the white and black area. Fig. 1A shows an example of 

the measured radiance and the theoretical fit [I] as a function of the distance from the boundary 

X (normalized by the hydrosol height H). In this experiment the adjacency effect (the effect of a 

bright object on the radiance above a nearby dark object) was measured as a function of hydrosol 

optical thicknesses for nadir and off nadir observation directions. Good agreement was found between theory and experiment. The measured adjacency effect had an amplitude 20% higher than 

the theoretical one, and a range 25% shorter than in theory. 

A field experiment was also conducted [8] in which the upward radiance above and below the 

haze layer was measured simultaneously with ground and airborne measurements of the atmospheric characteristics. Fig. 1B shows an example of the upward radiance from the nadir below 

and above the base. The radiances are measured over the dark water as a function of the distance 

from the bright vegetated land (the wavelength is 773 nm). The reflectance of the vegetated surface 

was approximately 0.35. A comparison with theory shows similar good agreement as in the 

laboratory study, with the adjacency effect somewhat stronger and narrower than in theory (as 

was found in the laboratory study). This difference can be due to the approximations in the theory 

and due to errors in accounting for very large particles. 

3.2. Resolution and classification 

The experimental verification of the radiative transfer theory and the application of Fourier 

Transform [7] to generalize the theory so that the upward radiance can be simulated for any 2-D 

varying surface, enables the application of the theory to study the atmospheric effect on spatial 

resolution and classification of surface features [3], [5] and [7]. It was found (see Fig. 1C) that the 

atmospheric effect reduces the spatial resolution substantially. For the Thematic Mapper (TM) the 

spatial resolution of 30m (defined for Modulation transfer value of 0.35) is reduced to lOOm by a 

hazy atmosphere (aernsol optical thickness =0.5, X= 550nm). An atmospheric correction that ignores the adjacency effect can correct the resolution to 50m. Similarly, significant effects were 

found on classification of surface features [3] and on separability between field classes [7]. 

3.3 Scattering versus absorption 

A theoretical study was conducted 19, 121 to test the comnion hypothesis that the atmospheric 

effect depends mainly on one atmospheric parameter-the optical thickness (TA). An increase in 

the amount of aerosol tends to brighteo dark surfaces and darken bright surfaces (see Fig. 2A). In 

the brightening process aerosol scattering has a dominant effect and absorption is of secondary 

importance; but in the darkening process the absorption has an important role. For a given bright 

surface the atmospheric effect car] be of brightening or darkening depending on the ratio of 

aerosol scattering and extinction optical thicknesses (w,). A reliable estimate of such effects can 

not be made until more is known about atmospheric absorption and its variability. However, Fig. 

2B shows that remote sensing of contrast such as vegetation index is weakly affected by absorption, but still affected by changes in the optical thickness. The vgetatiori index is a function of the 

slope of a line in this figure and thus does not change appreciably with absorption (from model I 

to 2 and from model 3 to 4). Figure 20 also shows how the reflectance of the earth-atmosphere 

system is altered by the atniospliere. 
3.4 Grouad-based experinlent 

In order to learn about the optical characteristics of the atniopshere as they affect remote 

sensing, a ground experiment is being performed in order .to collect and analyze a substantial data 

base. Sin~ultaneous measurements in the visible and near infrared spectrum are made of the solar 

transmission, the sky radiance in the direction of the North Star and also in the almucantar 

through the sun and the degree of polarization of the skylight. The aerosol optical thickness is 

derived from the solar transmission. The path radiance is measured in the direction of the North 

Star in order to minimize geometric effects and observe changes associated with aerosols. During a 

day the angle between the observer, sun, and North Star is essentially constant, 

Attempts have been made to relate atmospheric corrections to only one parameter-namely 

the aerosol optical thickness, in only one spectral band. Figure 3A shows the strong correlation 

between path radiance (at 870nm) and optical thickness (at 610nm). 94 percent of the radiance 

variance is associated with optical thickness variance for these wavelengths. The correlation between the radiance at 870nm and the optical thickness at 610nm was bigger than the correlation 

with optical thickness at 870nm. This is due to a different size dependence of the radiance and the 

optical thickness. The correlation between path radiances in two spectral bands (Fig. 3B) shows 

the accuracy of estimating the path radiance in one band from that : another band. The radiance 

at 870nm can explain 74 percent of the radiance variance at 48011s kid 62 percent of the radiance 

variance at 1670nm. 

The aerosol scattering phase function is derived from the radiance of the skylight in the solar 

almucantar. The inversion proceeds by an iterative method to account for molecular and multiple 

scattering. An inversion of radiances computed for a model atmosphere is shown in Fig. 3C. The 

true aerosol phase function of scattering angle is given by P,. P would be the estimated phase 

function derived from the radiance, if only molecular scattering was accounted for. Po is the first 

guess of the aerosol phase function, which is used to estimate the radiance of multiple scattering. 

This value is subtracted from the measured value to obtain the PI-estimate of the aerosol phase 

function. The procedure is repeated with this new value of the phase function (PI). After two 

more such iterations, the curve P, is obtained, and it is nearly identical to the true value (P,). 

Although the simulated radiances are free of errors, an analysis of the error budget has been 

made. This inversion method has been applied to measured radiances. Eventually, these functions 

will be compared with those derived from solar transmission data. 

5. CONCLUSION 

Radiative transfer theory (RT) for an atmosphere with a nonuniform surface is the basis for 

understanding and correcting for the atmospheric effect on remote sensing of surface properties. 

In the present work the theory was generalized and tested successfully against laboratory and field 

measurements. There is still a need to generalize the RT approximation for off-nadir directions 

and to take into account anisotropic reflectance at the surface. 

The adjacency effect results in a significant n~odification of spectral signatures of the surface, 

and therefore results in modification of classifications, of separability of field classes, and of 

spatial resolution. For example, the 30m resolution of the Thematic Mapper is reduced to lOOm by 

a hazy atmosphere. The adjacency effect depends on several optical parameters of aerosols: optical 

thickness, depth of aerosol layer, scattering phase function, and absorption. Remote sensing in 

general depends on these parameter, not just adjacency effects, but they are not known well 

enough for making accurate atmospheric corrections. It is important to establish methods for 

estimating these param-eters in order to develop correction methods for atmospheric effects. Such 

estimations can be based on climatological data, which are not available yet, correlations between 

the optical paranieters and meteorological data, and the same satellite measurements of radiances 

that are used for estimating surface properties. Our knowledge about the atmospheric parameters 

important for remote sensing is being enlarged with current measurements of them. 
L 

Fig. 1: Measurement of the atmospheric 

effect on remote sensing over a nonuni- . - 

fprmi ty in the surface ref1 ectance. SPATIAL FREQUENCY (CIKM) 

Fo is the solar spectral irradiance 

and eo=arccosine(~o), the solar 

zenith angle. 

- A - Laboratory si~nulation for optical thickness 0.3, nadir observation. The 

theoretical fit (.,. .) and the surface reflectance (- - -) are indicated. X is 

the distance frorn the bright area and H the hight of the scattering medium. 

B - Field measurernents for aerosol optical thickness 0.5. The aircraft measurements T-) and theory (. . . . ) are indicated. 

- C - The atmospheric effect on spatial resolution of the Landsat Thematic Mapper (M). 

The modulation transfer functions for the TM(-) alone, with atmospheric effect (. . . .) 

and with correction that ignores the adjacency effect (- - -) are shown. The original 

resolution (30m) is reduced to 50m by the adjacency effect and to lOOm by the total 

atmospheric effect. 
RADIANCE (L1- CLEAR DAY 

Fig. 2: A - Scatter diagram of the radiance from a 

Landsat iinage on a hazy day as a function of the 

radiance on a clear day taken over Washington, DC; 

for 700-800nm band. The radiance is normalized to 

ref 1 ectance units. 

RADIANCE (820) 

B - Hadiance of models of the earth-atmosphere system. 

The surfaceoconsists of dense alfalfa. The solar zenith 

angle is LO ; the direction of observation is given by 

the polar angle 0 ,and azimuth 4 froin the direction of 

propagation of incident sunlight. The number besides 

the plotted points refer to the aerosol models: 

JI1UDEL - uo ~~60nm T A (820nrn I1 0.96 U. 487 0.200) - J 

12 0.88 0.287 0.200 1 

13 0.96 0.861 0.600 1 

14 0.88 - 0.861 0.600 L 
RADIANCE/F, (870 nm) 

C 

1 02 

50 1 00 

ANGLE 

LT 0.0 

0 

K 

.O 0.03 0.06 

RADIANCE/F, (870 nm) 

I1 RADIANCE/F, (1 670 nm) 

Fig. 3: Exarnl~le of dndlysis of ground ~neasclrernents of the sky radiance. 

- A - The relation between the optical thickness T, at(610nm) and the sky radiance (at. 870nm) 

in the direction of the North star. Each symbol represents a different observation da,~. 

- U - The correlation between the sky radiance at 480nm and 870nm; and 870nm and 167nnm. 

- C An example of inversion of the alniucantar simulated radiances for the aerosol scatterinn 

phase function. 
THE CHARACTERIZATION OF SURFACE VARIEGAT1,ON EFFECTS 

ON REMOTE SENSING 

William A. Pearce 

EG&G Washington Analytical Services Center, Inc. 

5000 Philadelphia Way 

Lanham, Maryland 20706 

Improvements in remote sensing capabilities hinge very directly 

upon attaining an understanding of the physical processes contributing 

to the measurements. In order to devise new measurement strategies and 

to learn better techniques for processing remotely gathered data, we 

need to understand and to characterize the complex radiative 

interactions of the atmosphere-surface system. In particular, it is 

important to understand the role of atmospheric structure, ground 

reflectance inhomogeneity and ground bidirectional reflectance type. 

Our goals, then, are tc model, analyze, and parameterize the observable 

effects of three dimensional atmospheric structure and composition and 

two dimensional variations in ground albedo and bidirectional 

reflectance. 

To achieve these goals, we employ a Monte Carlo radiative 

transfer code to model and analyze the effects of many of the 

complications which are present in nature. We can, for 'example, treat 

finite clouds as well as vertical atmospheric structure. We can model 

the effects of two dimensional structure in ground albedo and 

directional reflectance. We can examine alternate data acquisition 

strategies perhaps involving variations in detector viewing direction, 

solar illumination direction, or polarization sensitivity. Most 

importantly, for the purposes of analysis and characterization, we can 

divide the detected radiance into components. The radiance transmitted 

directly through the atmosphere from the ground to the detector is the 
component which carries the most significant information about the 

character of the surface. The radiance arising solely from atmospheric 

scattering is a term which, in effect, should be subtracted froro. the 

data as it has no bearing on the surface character. Lastly, there is a 

ground diffuse component comprised of radiation which, having scattered 

from the ground, is atmospherically scattered prior to detection. This 

last term is responsible for non-local adjacency effects. Its influence 

on the data usually may be described by an atmospheric spread function. 

Specifically, thn objectives of the present study are to 

5.nves tigate the sensitivity of the radiance components and the 

atmospheric spread function to: variations in the vertical aerosol 

profile; variations in the aerosol size distribution (and, hence, its 

scattering distribution); variations in the detector look direction and 

solar illumination direction; variations in ground reflectance type and 

bidirectional reflectivity; the presence of clouds in the vicinity of 

the point of view. 

RESULTS 

As the modal radius of the atmospheric aerosol size distribution 

increases, the associated scattering phase function is enhanced both in 

the forward and backward directions. For remote sensing, it is the 

changes in the forward scattering peak which are more important. Our 

simulations show significant sensitivity in the inner regions of the 

spread function (within 250 meters of the point of view). Figure 1 

illustrates this, showing the atmospheric modulation transfer function, 

or MTF (the Fourier transform of the atmospheric line spread function) 

for three log-normal size distributions with modal radii of 0.13, 0.26, 

and 1.04 micrometers (bottom curve, middle curve, and top curve, 

respectively). 
For Lambertian ground reflectance, there is relatively little 

sensitivity to detector nadir angle for nadir angles less than about 

40 degrees. For larger nadir angles, however, the atmospheric line 

spread function becomes asymmetric and depends upon the illumination 

angle. Figure 2 shows the atmospheric line spread function for a 

detector nadir angle of 50 degrees (detector pointing roughly into the 

sun), while the dashed curve is for 180 degree receiver azimuth. The 

solar zenith angle for both cases is 47 degrees. The line spread 

function here is computed from the gradient of the intensity in a scan 

across a. fixed albedo boundary. The asymmetry is due primarily to the 

forward-backward asymmetry of the aerosol scattering phase function. 

Variations in the form of the vertical aerosol density profile 

tend to scale the range of the atmospheric spread function. This 

scaling appears to be roughly linear in the average aerosol altitude. 

Clouds in the vicinity of the point of view can influence tile 

detected radiance. In particular, the shadow of a cloud produces much 

the same intensity gradient when scanning across its edge as is obtained 

for a high contrast ground albedo boundary. Figure 3 shows a detailed 

comparison of the radiance components for two cases. The solid lines 

show (from top to bottom on the right side of the Eigura) total 

radiance, ground direct radiance and atmospheric radiance as detected 

from nadir while scanning across a Lambertian albedo boundary (albedou 

0.4 and 0.07). The symbols correspond to a similar scan across a cloud 

shadow boundary (the ground albedo is 0.4, the solar zenith angle ia 

47 degrees, and the altitude of the cloud top is 7 km.). The p'liiacs 

indicate total radiance; the solid squares show the ground direct 

radiance; the open squares show the ground diffuse component; and tlw 

crosses mark the atmospheric radiance. Here, the atmospheric component 

varies because the cloud shades the scattering atmosphere as well as tire 

ground. The ground direct radiance varies less abruptly on the dark 

side of the shadow due to cloud transparency and translucence, The 
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FIGURE 3. 
MULTIDIMENSIONAL MODELING OF ATMOSPHERIC EFFECTS 

AND SURFACE HETEROGENEITIES ON REMOTE SENSING 

S.A.W. Gerstl, C. Simmer, and A. Zardecki 

Theoretical Division 

Los Alamos National Laboratory 

The overall goal of this project is to establish a modeling capability that 

allows a quantitative determination of atmospheric effects on remote sensing 

including the effects of surface heterogeneities. This includes an improved 

understanding of aerosol and haze effects in connection with structural, 

angular, and spatial surface heterogeneities. One important objective of our 

research is the possible identification of intrinsic surface or canopy characteristics that might be invariant to atmospheric perturbations so that they 

could be used for scene identification. Conversely, an equally important 

objective is to find a correction algorithm for atmospheric effects in satellite-sensed surface reflectances. 

Our technical approach is centered around a systematic model and code 

development effort based on existing, highly adva-ced computer codes that k-re 

originally developed for nuclear radiation shielding applications. 

Computational techniques fo~ the numerical solution of the radiative transfer 

equation were adapted on the basis of the discrete-ordinates finite-element 

method which proved highly successful for one- and two-dimensional radiative 

transfer problems with fully resolved angular representation of the radiation 

field . 

Results of the initial phases of our research project, namely, the 

implementation and verification of computer codes and modern atmospheric data 

bases, have been published and proved highly successful. In the next step, a 

coupled atmosphere/canopy model was developed that allowed us to perform a 

sensitivity analysis and to quantify how satellite-sensed spectral radiances are 

affected by increased atmospheric aerosols, by varying leaf area index, by 

anisotropic leaf scattering, and by non-Lambertian soil boundary conditions: 

Our numerical results allow the following conclusions: 

1. Atmospheric perturbations are the major contributors to 

Landsat PISS bands 1 and 2 (visible), while they play only a 

minor role in MSS bands 3 and 4 (near-IR) for remotely 

sensed images of vegetative surfaces. The Kauth-Thomas 

greenness parameter is found nearly proportional to the 

atmospheric optical depth over uniform vegetative surfaces. 

2. The inclusion of anisotropic leaf scattering characteristics in our canopy model is significant to explain 

reflectance measurements directly above the canopy but 

produces only negligible effects on satellite-measured data 

above the atmosphere at nadir. 
3. Non-Lambertian and specular surface reflectance characteristics (BRDF) affect satellite measurements at nadir only 

insignificantly but can make large differences for off-nadir 

observations. 

TRe details of these results are also published and led us to our most recent 

investigations of how typical non-Lambertian angular canopy reflectance characteristics may be used for scene identification. 

Identifiers for horizontally homogeneous vegetated surfaces that may be 

used in remote sensing are the spectral distribution and the angular 

distribution of radiances above the canopy. The spectral distribution is 

determined by the optical properties of the constituents of the particular 

canopy, e.g., leaves and stems, while the angular distribution is created mainly 

by the canopy architecture. While the spectral characteristics of most canopy 

components are very similar for most plants, the canopy architecture aay be most 

dissimilar. This fact leads to intrinsic canopy angular reflectance patterns 

that may be typical for certain classes of plant canopies. Thus, the 

atmospheric perturbations of the angular reflectance pattern of a Lambertian, a 

mixed Lambertian/specular surface, and of the measured BRDFs of savannah and 

coniferous forest canopies were studies using aerosol-free and polluted 

atmospheres. 

Two typical results of our calculations are shown in Figs. 1 and 2, where 

measured angular reflectance patterns above real canopies are computationally 

"transported" through a mildly aerosol-loaded atmosphere to a hypothetical offnadir satellite sensor. These results show that maxima, like the canopy "hot 

spot" (a dominant peak when viewing in the direction of the sun with the sun at 

observer's back), are still detectable above the atmosphere even if observed 

through heavily aerosol-loaded atmospheres. It appears that especially those 

patterns that vary with the azimuth angle are better preserved than variations 

with view zenith angles. Note, in particular, how the shape of the reflectance 

pattern along the 180° azimuth changes when transported through the atmosphere, 

while variations with the azimuth along the 30' zenith remains basically the 

same. The underlying cause for this effect is obviously the constant path 

length through the atmosphere for all directions with the same view zenith 

angle. Thus, strong azimuthal variations typical for any surface or canopy 

reflectance pattern undergo only minor perturbations by the atmosphere, while 

the angular patterns for varying view zenith angles are much more perturbed by 

atmospheric effects. This finding suggests that off-nadir satellite 

observations with varying view azimuth angles may contribute significant new 

data that is expected to be valuable for crop identification. 

In our search for an effective new atmospheric correction algorithm, we are 

presently performing exploratory calculations with the objective of reconstructing, from radiance distributions above the atmosphere, a typical angular 

reflectance pattern as measured directly above a canopy. Figs. 1 and 2 

demonstrate clearly the severe atmospheric perturbations that are cumulatively 

added to the upwelling radiance distributions, especially in the visible 

wavelength region and for large view zenith angles. However, we show in Fig. 3 

the result of a simple correction algorithm applied to the coniferous forest 

data (see also Fig. 1) for an aerosol-polluted, rural atmosphere of horizontal 

visual range of 23 km, equivalent to vertical optical depth at 0.55 pm of 0.45 
for the entire atmosphere. The top half of the iso-radiance contour plots give 

Kriebel's measured data directly above the forest canopy while the bottom half 

shows our reconstructed radiance distributions from values above the atmosphere 

but corrected for atmospheric perturbations. This correction is based on a 

simple subtraction of the atmospheric path radiance component as determined from 

an independent additional radiative transfer calculation assuming purely 

Lambertian surface reflectance but with the same albedo as that of the real 

canopy. For our forest canopy, we have a = 11% at 0.85 pm. The comparison in 

Fig. 3 shows an agreement within approximately 10% between the measured and reconstructed radiance distributions for view zenith angles lower than 60' and all 

view azimuth angles. The hot spot is almost perfectly retrieved after this 

simple atmospheric correction. These results are both surprising and 

encouraging, because the correction apparently works very well even at the 

visible wavelength where atmospheric effects dominate the canopy signal by far. 

The next logical step in our research project must be a two-pronged 

approach. First, the analysis of our (as yet) simple atmospheric correction 

algorithm must be broadened and studied in depth. Secondly, our physical 

understanding of how certain typical canopy reflection patterns are correlated 

with measurable biophysical canopy parameters must also be deepened. To achieve 

this latter goal, we propose to build a simulated vegetative canopy structure 

using only artificial (non-living) structure elements for leaves, stalks, 

branches, etc., that provides a weil-defined and fully reproducible testbed for 

verification and testing of instruments and theoretical models in remote 

sensing. Since every natural vegetation canopy changes through growth, and its 

canopy components and architecture are intrinsically variable, reproducibility 

is seriously limited and measurements of biophysical parameters, such as leaf 

area index and leaf angle distributions, are prone to large uncertainties. In 

contrast, the artificial canopy provides a facility for "ground truth" measurements, testing and calibration of instruments, verification, and sensitivity 

testing of theoretical models as well as specific instruments. A synopsis of 

this proposal is attached. 

If our preliminary findings about the invariance of typical local extremes 

in surface reflectance patterns to atmospheric perturbations can be further 

substantiated, then important conclusions should be drawn for the operation of 

future earth observing satellites. This result leads to the recommendation that 

off-nadir satellite observations in the near-infrared may contribute additional 

valuable information to crop identification as well as other scene identification when enough non-Lambertian (e.g. specular) reflectance is present. For 

crop identification it might be sufficient to swing an MSS or TM type scanner 

into the downward sun direction to observe the hot spot, and then rotate the 

instrument around a 360° azimuth for the constant solar zenith angle. 
Las Aianos Calculations, B~rsnber 2,98h, ConifcreusFnres,t: Beet@% haundary csndlrIon i~ aeasurcd 

Bidirect iardl ~e~ieclance ~istributian Funcrion ('BRDF) at eoaifarsus Esresr by KriebrT f 1977). 

ALaasgkerit madel: Mid-latitude sumaer, PU~OI boundary layer aerasag btPtk vtsu~t range 23 km, 

totar optical depth af atmosphere r e 0,45, Surfacps retcr to 0.0, $.a, ad 76 km f~8~f b~kkda 

ra tap, Surfaces shn-4 the up-welling radisnce dtsrriburian at 0,&5 Qlef~l and 0.85 fright) far 

solar zani tl~ rngie 29.3'. Sundirectidn and dlr~crion opposite to sun ere indicated by + ("hot 

spot") a~d Q, +CSIJ$C~~VE%V. 
Sun Zenith Angle 

Figure 2. Los Alamos Calculations, November 1984, Ssvannah: Bottom boundary conditicn is measured Bidirectional 

Reflectance Distribution Function (BRDF) of Savannah by Kxiebel (1977). Atmospheric model: Fid-latitude summer, rural boundary layer aerosol with visual range V, = 50 km, total optical depth of atmosphere 

T = 0.25. Surfaces refer to 0.0, 1.0, and 70 km from bottom to top. Surfaces show the up-welling radiance distribution at 0.65 (left) and 0.85 pm (right) for solar zenith angle 29.3'. Sun direction and 

/ direction opposite to sun are indicated by f ("hot spot") and 0 , respectively. 
(D 

0 

VISIBLE (0.65 p~) 

I 

0 

0 

NEAR-INFRARED (0,85 VM) 

Figure 3. Upwelling radiance distribution of coniferous forest at surface (upper half) compared with 

radiance ~t top of the atmosphere, corrected for the atmospheric perturbation (lower half). 

Vo = 23 km. 
SCATTERING MODELS AND BASIC EXPERIMENTS 

IN THE MICROWAVE IVGIME 

Fung, A.K. and A.J. Blanchard 

Wave Scattering Research Center 

Electrical Engineering Department 

University of Texas at Arlington 

Arlington, Texas 76019 

The objectives of the research over the next three years are: 

(1) To develop a rarldomly rough surface scattering model which is 

applicable eve-r the entire frequency band. 

(2) To development computer simulation method and algorithm to 

simulate scattering from known randomly rough surfaces,Z(x,y). 

(3) To design and perform laboratory experiments to study 

geometric and physical target parameters of an inhomogeneous layer. 

(4) To develop scattering models for an inhomogeneous layer which 

accounts for near field interaction and multiple scattering in 

both the coherent and the incoherent scattering components. 

(5) Comparison between theoretical models and measurements or 

numerical simulation. 

Although various new approaches in rough surface scattering 

have appeared in the literature,they are generally restricted to 

either low or high frequency regions becausedof the simplifying 

assumptions used. General theories which are not restricted by 

such simplifying assumptions are so complex that either no 

explicit solutions are available or only the scattered field is 

available because the average scattered power is too involved to 

compute. In order to obtain a general scattering model for 

randomly rough surface which is explicit and simple to use it is 

necessary to determine a sufficiently accurate surface current 

including just enough multiple scattering terms tc have the 

correct behavior over the entire frequency band but not too 

involved to deny an explicit solution. This is our goal for a 

rough surface scattering model. In volume scattering problems 

most theories are restricted to either a sparsely populated medium 

or coherent scattering in a dense medium. Incoherent scattering 

which is of major interest in remote sensing has been investigated 

mainly by either the Born or the distorted Born approximation 

in the field approach and the radiati~e~transfer formulation in the 

intensity approach. Other methods are needed to include multiple 

incoherent scattering in the field approach and techniques are 

needed to determine the autocorrelation function in the coherent 

field calculation in dense inhomogeneous medium. Currently, the 

use of Percus Yevick approximation and the associated pair 

distribution function for hard spheres in coherent scattering 

computation leads to nonphysical results when the volume fraction 

of the medium is around 0.6. 

All theoretical scattering models involve some simplifying 

assumptions. To verify these models it is best to have 

controlled experiments so that target parameters can be varied and 
any given experiment can be repeated. In the case of random 

surfaces it is possible to use computer simulation. This is not 

only eost effective compared with full scale field measurements 

but it is also more convenient to change target parameters than 

in any controlled experiment. 

2. Approach 

The approach to be used to develop the proposed random sutface 

model is to use the integral equation method. We have used this 

method successfully to develop a scattering model for a perfectly conducting surface in the past year and we intend to generalize it 

to dielectric surfaces. To perform computer simulation for the 

rough surface problem we intend to investigate first the 

generation of a two- dimensional random surface with specified 

autocorrelation function. This is a major effort because 

algorithms and techniques for this purpose have been restricted to 

one-dimensional surfaces. From the numerical point of view this 

is also a large job requiring large capacity computer. Past 

experience on a one-dimensional surface indicates that it is 

desirable to have at least a 10,000 point surface to insure 

convergence of statistical parameters and it is desirable to have 

a 50,000 point surface to allow scattering computation at 

different frequencies. Once the surface is available the standard 

moment method will be used for scattering coefficient 

computations. Here again it is necessary to generalize from one kn 

two dimensions and numerically this is a problem because we cannot 

allow the computation-size to increase like a square. 

The measurement program will be divided into two majar 

tasks, (1) the design and construction of a versatile volumetric 

target structure, and (2) the measurement of radar backscatter 

cross section as a function of system and target parameters. The 

target is designed and constructed to simulate vegetation type 

structures. The target can be used to provide a variety of both 

geometric and electrical characteristics to include, leaf density in three dimensions, leaf orientation and location, leaf size and 

shape,and permittivity characteristics of the volumetric: 

structure including relative permittivity and conductivity. The 

target is designed to allow a number of different parameters to 

be evaluated while maintaining the basic target shape. 

Measurements will include the effects of leaf distribution, 

shape, orientation and location on radar backscatter. Initial 

experiments will minimize the effects of the stalk structuresl 

however, future measurement programs could include these 

interaction effects as well. The measurements will be made ili 

an indoor Radar Cross Section Range. The measurements will 

include amplitude and phase measurements at X band,K band, 

incident angles from 0 to 50 degrees, and the four li~renr 

transmit/receive polarization states. 

In view of the difficulties with the current theoretical 

approaches as stated in the introduction to the volume scattering 

problem, we propose to use the eikonal approximation for incoherent 
scsees~dng co~pu+ak%on snd tha sslutlon sL kha maaeag equakion Ear 

det%r~Sn%nq a mag& real $@tic autaco~bcl&tfon funceian, It sksufd 

ha nsted that the pain d$&km%bution Eunctian wss dari~ed far BBP 

fn a dyaaa5s msdlom ~ucb &% fladd, Wsnc@@ far a medium with 

rando% bat f %gid distrPhutisns oB p&rtfclas it is nak apprapr iak@ 

and 4oes lea4 to nonphy%ic&% mesalt&, 

QVEE tR@ pa%% year ws have dav~2sged w, scattaring l*+ad@IX. $8~ 

&n fnhowtaganaaua layer asnkt?rlnlng nsadls- shaped Ieave%, Ws &&PC 

made ccowtp&ri~~na bekwsorp ~cakksriag $gem such a Payer sad (sansther 

l%y%r asratieainf ng d$sc-abap@$ ts;&va%, 4frhe ~fgtg~L%beank dif E@%len~@ 

bakwasn the &wo types aF vcgakakian fa that tba baekscakterfng 

&agulae: carve far $he disc=-type has a hump in the mid awqrrla~ 

pegion y%piJte the ?:@@dl@-kype hag dip kin the saxrta regfo~ whaxr the 

aiz@ of tRc 4savas ie cawp&fabl@ &he $nciBent wnvelengkh% sec 

P%gates % and 21, Pa addiction, study has alga been carrigd auk 

to datcrm$n@ %he eff@ct& of Pra~nel phaae in k&e scattsrfng phase 

makr f ces aft ~~*7lbtter~~1~ that$& a~1 GOFS~BE*S~~~%B t;o khe in~idemt 

uavclangkh but ans much ~mall~r %ha% ei e wav~f cnqtb in at least 

awe dimenaian, The canclusi~n is ghat he $n@ZusLsn of the 

Fresnal phaaa qfvea a mo~& accurate fkgquancy krcnd depen4enas $as@ Leer4984 b , Alas studlsd is the effcek oZ clos$-<r spacings 

b~kweew s@at%er@ra accsunled far in khc aeaktcring pkavc matrix, 

Results Indieake kh~t a mare a~cosakc target garam~k@r c&n be 

fnfarred Pram such a ~sdcl than is passfb$a asfnq a standard 

radL&tkve tranafer mekhsd (Pung and Eam;2une,198&), The inversfsn 

Irom @easuz@ment& far albeda and agtdea1 dspkh was skudied hy Punq 

and Earn kAug@a%,fP84f vitb the conc2us%an that &% least B 

Sis~t-o~dsr thaory mu@% ba used in the zadSatlvc tranafe~ 

fsrrrruf&tion Ear emnfsaksn E~am an dnf:amog@n~aa% lay@&., 

A acatkcting mad93 far a perfectly conducting, randomly rsuqh 

surface hna been devaBspad which $R ~akkd over the cnkire 

frequency band kPantl934), at has b~an demsnstrated analytically 

thae Lhc genera2 solution obkalned reduce% car~ecely ko the 

gcamekrical optico solukfsn in the hgqb f~cquency PImIQ and to the 

firak-order small psr8urbation &~Xu%Asn in Bhc la% Eseqreancy 

Iimft, Pn the 3n%@rtrredriak@ region ft has a behavior whieka can be 

spe~y 3iff~renk from ci$hs~ 1B:nitinq solutfsn but ia IiahSLg to be 

afsfntssprekad 2% ens or the other, Tba raazan La thak it could 

re&@~hX@ tba low f~equency so5utfon in pal&rirati~w behavior hue 

EsXPow the general angular %rend aE the Rfrehhoff sa4u%ion{see 

FAgu~a 91, Al%s develaped was the scattering model for a pertu~bad 

sfnusaddal Burface Ea@ and Fa~g,19841, This waa done 6a account 

Eof: ~ai% aa~Ea@e~ with ~sw Bheckxiana2 degendeaace, 

a pXaski@ mod@l for a Layer of Xeavea QE eithe~ sfreulax ar 

el&%p%%c %haps has been Besigned which permits khe %&aP angular 

dAatrfhukion, leaf size, leaf dcnsleyr leaf &Se$@ekmfc valwo, and 

paw d%~@ctl~n eEE@cka ta b@ studied under labsratamy candft2* rls, 

xt $B expacead %hat m@a%ugcmsnta conducked vfth this karge% will 

be able ts p~avidc ~cBiable data far the vcrificatfon of cxisking 

valume ~eattsrgwg aodals, 

&=a$, X lca 

******+arsq,ra*r e.3 ,@@em 

F 1 & 2 ?_lzE srl:EJsX@Kxea: QF St-;EDB,T:*SWi3R:ip VFCL fj<Tfli?< (,I= Y;I~LQ%/ l'x l~~gth aa 

needle b 
FIG 3 Comparison of iNEQ with FOSP and KM (ka=l.O and kt=2.79). 
REMOTE SENSING OF EARTH TERRAIN 

Jin Au Kong 

Massachusette Institute of Technology 

1. Objective 

The objective of this research is to develop theoretical models that are useful and 

practical in the remdte sensing of the earth environmect including the earth terrain, the 

lower and the upper atmospheres. We have been very successful in developing various models applicable to the microwave remote sensing of vegetation, snow-ice, md atmospheric 

precipitation. We shall extend such studies to the higher frequency range to unify the 

optical band and the microwave theoretical foundations. We shall also extend our study, 

which had an emphasis on vegetation canopy to include all terrain media, <and the whole 

earth environment. A data base will be developed to generate scene radiation characteristics which will benefit the studies of global inhabitability, meteorological applications, and 

crop yield. 

2. Technical A~proach 

The radiative transfer theory has been fully developed to treat the volume and rough 

surface scattering effects. The combined random rough surface and volunle scattering effects have been studied by employing a Gaussian random surface and applying the slnall 

perturbation methods which are modified with the use of cumulant techniques. The rough 

surface effects are incorporated into the radiative transfer equations by modifying the 

boundary conditions for the intensities. The T-matrix method, which utilizes vector spherical wave functions for the expansion of incident, scattered, and surface fields is used to 

derive the extinction niatrix and the phase matrix for the radiative transfer equations. 

Densely distributed spherical dielectric scatterers is studied with the qlxmtum mechanical 

potential approach. The quasi-crystalline approximation is applied to truncate the hierarchy of multiple scattering equations and the Percus-Yevick result is used to represent 

the pair distribution function. The modified radiative transfer theory is studied with the 

Feynman diagrammatic representation. Atmospheric precipitation is also studied with the 

vector radiative transfer equations by making use of the Mie scattering phase functions and 

incorporating the rain-drop size distributions. To study scattering by anisotropic medium 

modelling sea ice arid vegetation field with row structures, the dyadic Green's function is 

first derived and used in conjunction with the first-order Born approxilnation to calculate 

the backscattering coefficients. 
3. Research Results 

In active n~icrowave remote sensing, a two-layer anisotropic random mcdium model 

has becn developed to investigate the anisotropic effect of sea ice in which, due to the 

flow of sea water, the brine ilclusions are tilted 'and to study the aziniuthally anisotropic 

behavior of vegetation canopy which is attributed to the orientations of the vegetation 

stalks. In this scheme, the dyadic Green's function for a two-layer anisotropic medium is 

developed 'md used in conjunction with the first order Born approximation to calculate the 

backscattering coefficients. It is shown that strong cross-polarization occurs in the single 

scattering process and is indispensablc in the interpretation of radar measurements of sea 

ice at different frequencies, polarizations, and viewing angles. The effects of anisotropy on 

angle responses of backscattering coefficients are also illustrated. For passive microwave 

remote sensing of a two-layer anisotropic random niedi:lm, the principle of reciprocity is 

invoked to compute the brightness temperatures. The bistatic scattering coelficients are 

first calculated with Born approxilnation and then integrated over the upper hemisphere 

to be subtracted from unity, in order to obtain the ernissivity for the random medium 

layer. The theoretical results are illustrated by plotting the emissivities as functions of 

viewing angles and polarizations. They are used to interpret remote sensing data obtained 

from vegetation canopy where the aniostropic random mediunl model applies. Field measurements with corn stalks arranged in various configurations with preferred azimuthal 

directions arc successfully interpreted with this model. 

The problem of microwave scattering from periodic surfaces is solved by using a rigorous niodal technique which conserves energy, obeys reciprocity, and takes into account 

the multiple scattering and shadowing effects. The theorctical results have been applied 

to the calculation of the radar backscattering cross sections in active remote sensing and 

the brightness temperatures in passive rernote sensing, and used to match field data from 

soil moisture measurements. The angular behavior of the brightness temperatures has 

becn cxplaincd with the threshold phenomenon 'oy considering the appearance and disappearance of the various Floquet modes. The Kirchhoff approximation is used to study 

the scattering of electuronlagnetic waves from randomly perturbed quasi-periodic plowed 

fields. The narrow-band Gaussian random variation around the spatial frequency of the 

sinusoidal variation is used to introduce the quasiperiodicity. The physical optics integral 

is evaluated to obtain closed form solutions for coherent and incoherent bistatic scattering cocficiex~ts. In the geometrical optics limit, it is shown that the bistatic scattering 

coefficients are proportional to the probdbility of the occurrence of the slopes which will 

specularly reflect the incident wave into the observation direction. The theoretical results 

are illustrated for the various cases by plotting backscattering cross sections as a function of the incident angle. It is shown that there is a large difference between the cases 

where the incident wave vector is parallel or perpendicular to the row direction. When 

the incident wave vector is perpendicular to the row direction, the nlaximunr value of the 

backscattering cross section does nut necessarily occur at normal incidence. The scattering 

coefficients can be interpreted as a convolution of the scattering patterns for the sinusoidal 

and for the random rough surfaces. For the backscattering cross sectiolis we observe the 

occurrence of peaks the re'iative magaitudes and locations of which are explained in terms 
of the scattering patterns for sinusoidal surfaces. The combined random rough sc~face 

and volun~e scattering eifects have been studied by en~ploying a Gaussian random surface 

and applying the small perturbation methods which are modified with the use of cumulant 

techniques. The rough surface effects are incorporated into the radiative transfer equations 

by modifying the boundary conditions for the intensities. The radiative transler equations 

are then solved nunlerically using the Gaussian quadrature method and the results are 

illustrated and compared with experimental data. 

The radiative transfer theory is applied to calculate the scattering by a layer of randomly positioned and oriented nonspherical particles. The scattering amplitude functions 

of each individual particle are calculated with M'at,erman's T-matrix method, which utilizes vector spherical wave functions for the expansion of Incident, scattered, and surface 

fields. The orientation of the particles is described by a probability density fu~lction of the 

Eulerian angles of rotation and a rotation matrix is used to relate the T-matrix of the principal frame to that of the natural frame of the particle. The extinction and phase matrices 

for the radiative transfer equations are expressed in. terr~ls of the T-matrix elements. The 

extinction matrix for nonspherical particles is generally nondiagonal. It is shown that; there 

are only two attenuation rates in a specified direction of propagation. The scattering of a 

plane wave obliquely incident on a half space of densely distributed spherical dielectric scatterers is studied with the quantur~l ~nechanical potential approach. Tlre quasi-crystalline 

approximation is applied to truncate the hierarchy of multiple scattering equations and 

Pertus-Yevick result is used to represent the pair distribution function. While results at 

high frequencies are calculated numerically, closed form solutions are obtained in the low 

frequency limit for the effective propagation constants, the coherent reflected wave and the 

bistatic scattering coefficients. 

In the strong fluctuation theory for 2 bounded layer of random discrete scatterers, the 

second liloments of the fields in the second order distorted Born a,pproximation me obtained 

for co-polarized fields. The backscattering cross sections per unit area are czlculated 

by including the mutual coherence of the fields due to the coincident ray paths, and 

those due to the opposite ray paths, corresponding to the ladder and cross terms in the 

Feynma~~ diagrammatic representation. It is proved that the contributio~~s fro111 laclder 

and cross term for the co-polarized backscattering cross sections are the same, while the 

contributions for the cross-polarized backscattering cross sections are of the same order. 

The bistatic scattering coefficients in the second order approximation for both the ladder 

and cross terms are also obtained. The contributions from the cross terms explain the 

enhancelnent in the backscattering direction. 

Both passive and active remote sensing of atmospheric precipitation are studied with 

the vector radiative transfer equations by making use of the Mie scattering phase fucctions 

and incorporating the rain drop size distributions. For passive remote sensing we enlploy 

the Gaussiali quadrature method to solve for the brightness temperatures, 'and for active 

renlote sensing an iterative approach carryied out to second order in albedo is used to 

calculate the bistatic scattering coefficients and the backscattering cross sections per unit 

volume. 
4. Significance of Results 

The anisotropic medium model that has been developed is now able to account for 

the like as well as cross polarization measurements of the backscattering cross sections in 

active remote sensing of sea ice. The same model applies to the interpretation of data 

from the passive remote sensing of vegetaiion field. Extending this two-layer medium 

model to multilayered configuration will facilitate the interpretation for more complicated 

scene radiation characteristics. 

The strong fluctuation theory has been successfully developed to account for the 

volume scattering effects, not only for earth terrain media such as vegetation and snow-ice 

fields, but also for the remote sensing of atmospheric precipitation. The periodic rough 

surface theory provides a rigorous approach that satisfies both the principle of reciprocity 

and the principle of energy conservation. 

5. Next Maior Steps 

There are three major steps: 1) To extend our study to include the effects of the upper 

atmosphere such as the troposphere, the ionosphere, and the magnetosi>here. Our initial 

snccess with the usage of the random medium model applied to atmospheric precipitation 

serves as a solid starting point. 2) To extend our study to other earth terrain medium 

co~figurations such as canopy-covered soil moisture investigation, snow-covered fields, and 

layered-medium model including both volume scattering and rough surface scattering effects. 3) To extend our study to unify the theoretical foundation for the microwave and 

the optical spectra. The starting point is the application of the radiative transfer theory, 

which has been developed in both frequency ranges rather independently. 
DISCRETE RANDOM MEDIA TECHNIQUES FOR 

MICROWAVE MODELING OF VEGETATED TERRAIN 

Roger H. Lang 

Department of Electrical Engineering 

end 

Computer Science 

George Washington University 

Washington, D.C. 20052 

1. Introduction 

Microwave remote sensing of vegetated terrain has been studied. 

Vegetation is modeled so that backscattered radar signals can be used to 

infer parameters which characterize the vegetation and underlying 

ground. The vegetation is modeled by discrete lossy dielectric 

scatterers with prescribed characteristics. The goal of the modeling 

effort is to remotely sense vegetation type (classification), growth 

stage, and plant/qround moisture. This information can then be used as 

input into agricultural, forestry and global circulation models. The 

microwave frequency spectrum, particularly L and C bands, are especially 

appropriate for this purpose since the wavelength is comparable to plant 

leaf and stem size. The resulting resonant interaction leads to 

backscattered data highly depend on plant shape and orientation. In 

addition, the transparent nature of the atmosphere in this frequency 

regime allows for algorithm development which requires no atmospheric 

correction. 

2. Technical Approach 

The modeling approach characterizes the vegetated terrain as a 

layer of plant growth over a possibiy rough surface. The plants are 

viewed as composites of leaves and stems which are modeled by dielectric 

discs (not necessarily circular) and rods. The discs and rods are 

placed at random locations throughout the layer; their size and 

orientation statistics are chosen to correspond to the vegetation being 

modeled. 

Once the discrete stochastic model has been specified, the average 

backscattering coefficients are computed for both like and cross 

?olarizaticrns. The calculation is made amenable to analysis by the 

presence of a small parameter - the fractional volume of vegetation. It 

is then possible to employ the distortad Born approximation or transport 

theory (depending on albedo size) to calculate the backscattering 

coefficients. This constitutes the formulation of the discrete probleni, 

i.e., given the distribution of scatterer sizes and orientations, the 

backscattered power can be computed. The final step in the procedure to 

obtain a remote sensing algorithm is to invert this direct problem. The 

performance of the inversion assumes that the backscattering coefficient 

is given as a Function of angle of incidence and/or frequency. From 

this data, the statistical characteristics of the scatterers are 

computed. This calculation is often numerically ill-condi t ioned and 

needs special treatment. 
3. Research Results 

Over the three year period, results have been obtained in all areas 

needed for algorithm development. Electromagnetic modeling of plant 

elements has been addressed, bac kscattering coefficients have been 

calculated and inversion algorithms have been developed. 

Simple plant canopies such as soybeans can be modeled by replacing 

the plant's leaves an3 stems by dielectric discs and rods respectively 

as is shown in Fig. 1. The relative dielectric constant used for the 

discs and rods is the equivalent dielectric constant of the plant 

material. The use of this equivalent dielectric neglects scattering 

effects caused by internal variations within th~e plant. This is small 

however, because of the long wavelength involved. 

Scattering amplitudes have been computed for both the disc and stem 

elements. The resulting formulas for the scattering amplitudes are 

particularly simple because they take advantage of the small ratio of 

thickness to radius in the case of the discs and radius to length in the 

case of the rods. The simple formulation is particularly important 

since the results must be averaged over both inclination and size 

distributions. 

Backscattering from the modeled plant canopy has been treated by 

two techniques: the distorted Born approximation and the transport 

theory. The two methods are equivalent when the albedo of the 

scatterers is small and no coherent (planar) boundaries are present. It 

has been shown for the case of a flat ground that the transport theory 

neglects certain coherent interference terms which are taken into 

account by the distorted Born approximation. It should be noted that 

this effect is a law frequency (L-band) phenomenon because at higher 

frequencies the surface appears rougher, and as a result, coherence 

effects disappear. Since the distorted Born method is applicable in the 

L band frequency regime, since it contains the interference terms and 

since it is relatively simple in formulation as compared to vector 

transport theory, it has been used almost exclusively, to calculate the 

backscattering coefficients. 

Application of the distorted Born theory to the modeling of crops 

such as soybeans has yielded interesting results. Fig. 2 shows some of 

these results for a frequency of 1.5 GHz. The figure is a plot of cr;, 

versus angle of incidence. An examination of the figure shows that for 

vertical-like polarized returns the leaves are dominant at low angles 

and the stems are most important at large angles of incidence. This is 

not surprizing since the electric field is aligned with most stems at 

large angles of incidence. 

The model whose resu1.t~ are shown in Fig. 2 consists of leaves 

having radii of 2.5, 3.5 and 5.0 cm. Each of these leaf types has a 

density of 333/m . The stems are all taken to be 20 cm long and with a 

density of 1000/m . The leaf and stem size characteristics were 

obtained by the principal investigator who made on-site measurements at 

Beltsville. 

Although Fig. 2 just shows the vertjzal-vertical backscatterinq 

coefficient, simple expressions were obtained for the 

horizontal-horizontal case as well as the cross polarized returns. 

These appear t,o be valid for frequencies below 4 GHz as long as the 

correct dielectric constants For the discs and rods are used. The deLoor formula has been used for the calculation of disc and stem 

dielectric constants however, at lower frequency (= 1-2 GHz) a 

conductive contribution should be included. 
The final step in any remote sensing problem is the inversion 

process. Results in this area have beed obtained this year. Attention 

has been focvsed on the relationship between the backscattering 

coefficient 5hh and the joint probability density of disc radii and 

inclination angles. The expression derived by the distorted Born 

approximation has been used. An examination shows that it is nonlinear 

in nature. The relationship has been linearized in the 1-2 GHz region 

where the skin depth is large. The linearized expression (a Born 

approximation) is a Fredholm integral equation of the first kind. 

Inversion problems of this type are usually ill-conditioned and must be 

regularized. 

To simplify the inversion procedure further, it has been assumed 

that the radii and inclination angle densities are independent. IV it 

is assumed that the density of one variable is known, then the other can 

be found through the integral equation with the knowledge of the 

backscattering coefficient for various angles of incidence. Such an 

inversion is shown in Fig.3. Here the leaves have fixed radius of 4 cm. 

The inclination angles density is shown by the solid line in Fig. 3. 

The combined joint density is then used to generate for various 

angles of incidence. The calculated values of the backscattering 

coefficient are corrupted by noise and a Phillips-Twomey inversion 

algorithm is used to compute the inclination angle density at certain 

discrete points. The results, which are good, are shown by small 

circles, squares and stars in Fig. 3. 

The Phillips-Twomey mehhod has also been applied to the inversion 

of the complete two-dimensional density of radii and inclination angles. 

Here it has been assumed tht backscattering data is known at different 

angles of incidence and for different frequencies. 

4. Significance of Results 

The results just presented provide a direct relationship between 

the backscattering coefficient and the detailed parameters that 

characterize the scatterers. This means that by remote L band radar 

measurements at different angles of incidence and for different 

frequencies, such quantities as leaf inclination angle distribution and 

leaf area distribution can be determined. These distributions can then 

be directly used to estimate growth stage by knowledge of the area 

density of leaves and to estimate stress, due to lack of water, by 

knowledge of the inclination angle density. 

5. Future Work 

The model developed thus far has been directed towazd leafy 

agricultural crops such as soybeans. By incorporating other scattering 

types of a more complex nature, other crops and forests can be modeled 

and inversion algorithms developed. Future scatterer development should 

include the modeling of non-planar leaves, branches and stalks with 

periodic nodes (corn) . An experiment should be planned so that the theoretical 

developments can be tested. The experimental approach is particularly 

important in the inversion algorithm development since equipment 

limitations can force consideration of different inversion techniques 
Fig. 1. Vegetation Layer Modeled by Leaves and Stems 


Hf CROUAVE DI ELECTRIC AND PROk-fiGATZOg 

PROPERTIES OF VEGEThrr%8H GAHQPFP:S 

A vcgetsrfsn csnapy i~ a highly inhamageneous medxum .&E 

mrcravsvc Eregueecics, and beesuse ~hc scat Eering e%emeaes 

Ql~svexs, s&alks, &rui~s, and branches1 have s uganwniforaw 

dl~tribuEisn in srienkatfon, the canopy is Ixke'Ly &a exhibit 

nant%okropie aEEenuatxsn propescics, Hn some canopies, chc 

sl;&lk may csnt&in khe okr@rwheh$$hing majority of the plank's 

biasns~s, which s~ggosts thaL aa incidew81 8. iar wave wsufb be 

dkEFeren&isliy aEtefiuatcd by ehe canopy d~pe~drng an ehe 

direction of Che incxdan6 eXecrrtc Eistd relskive to the otsXk~" 

orfeneation, The propagataon prapercaes of w vegetseian canagy 

play a ccntral role in mode*% ing $o&h Lhs hackscaktering kehav~ar 

~bserv&d by &fi imaging radar and th& anzsszan observed by s 

radiomek~r, These propaga&ion pro~ergies are in turn governed by 

$he di.ale@&f%e properties and @he sax*, shape, and 

alsgadis$+ibo&ions aF khs scst&erdzrs, Ln spice of thc ctiCacak 

nscd for csnspy prapagskisn models nnd experxmentsl data, very 

few investigstions had h~en cawduetsd lpriat to this study b bo 

QeCermina the extinction prnpefriea of vegckarion cannpics, 

ef&her by c~n~t;ikuenL &ype <l%sf1ves, atslkr, etc, B or aa a whale, 

W shree-Eacered &ppra&ch *as tiwdertaksn in kkis sedy 

cansiscing sf comp&xwen&asy Ifivcstigskions vxth ear11 providing 

Bnsuers ko speckFi~ s~pe~ts af the overall queskdorl, The Flryt 

Facet caasise~d af Qie'le~trlc meaaarernentg that were coaduc&ed 

aver %he 1-10 GHz $ant,? Ixo daE~rrrr~ne khe v&rrstions of the 

die3.sctric permittiviey and Pas$ Facear a$ s Functxon aE vaeer 

content and asXiniky, Dx&L~ctrkc mixing modef 3 were ci~veloped 

&nd evaluate$ agsin%& the ewpc~imentaE dacs for indzvzdual pfanC 

part3 bZe~%se%, dkalks, E~-u'it> QF ~%?~a?rsZ hjfJ*PBS sf planks (wh~ak, 

carn, and soybeansl, 80 example is shawn xn Fig, I., 

$he saeo~8 facet of the study conaisged a& dxrecc 

me&%uremankg oE canopy aLbenuaIxxsn, Usxng truck-mounted radars 

as transmitting sources pssikxunsd above the canopy, and small 

recci aakefinas asunEed on f%&sr$Xass +fa 11% underneaEA &he 

esnopy $ow the sail surfaced, at&cnusKisn msaswrements #ere 

conducked aa a EuncEion oE incidence angle Crelative $a nadir%, 

mierawave Freyueney, snd polarization canExgutarisn, In 

a&dil;ian, %lpecic92 Eaperlm@nr% weyo ~aada~ked t~f $%rkgluatb &he 

r@%aE.iue csntribatEona af the various canspy csnseituents Che 

tabal loss for akcanaakaanb f~ctor a$ &he canopy, Thesc ineXudc8 

wheak decspf%a&isn axpecimewla, in which massaremcnes aE the 

canopy lass factor wea@ madc $@Ease and after cukting aff &nd 

removing rhe vhe~t hesds, and saybean defslrat~on expErirnengs 
which prsvidsd camysarx%on af The ~xt.snc$iorn Idttss due ?.a kha 

~ka2ks alone wiXh %he to&&%% loas du~ ?.eo the skalk~ and leavgs 

cogsther, Accardzng Eo Pig, 2, &he ~Ea'Iks accounk for &he 

rnajarkky of ehe propagBtion Loss aw a soybean8 canopy for 

vcrCics2ly palarized waves, whereas Ehe leavss are %ha domiw%n% 

sbsorbers $or horizantal polarizakion, 

a cEznspy pYOp%gB% kBW model id&$ c~Qv@~Q~@Q~ COREZ~L 0% three 

$a?rms: {a1 ZlcegE lorm that acso-punts far sbsorption hy rawdrlassrly 

orien&ad disc-ah~pcd leaves, <$I a stalk kerm tha% &ccrjunts far 

abaorpkion by a unzsxssf crystal cafisisting OF Chis, vertsca2, 

lsasy cylsndor~ in sn air background, and Cc) a branch term e hat 

account8 Far tane Iss% by a msdirtrn contaxning randamly orxeneed 

needle-shaped branches, The Elrst and khrrd terms are 

go$ariz&k.~on-inCil~p~fid~fet and vary with iocxdea~~ angle ;r% sdc 3: . The s&alk term has a slrong d~pendsnce on bath pnlarizafisn and 

insrdenca angle, The mads% uss found to be tn goad agreement 

whth @wp@ram@nt&% ab5s9-wations. One or $he key p&ramakem.& in the 

madgk is the dzckeetric conscan8 aF the vegek8x&ian rnakerxal, 

which was caleulatc~ u%xng Lhe tllahectrrc rrn~axing ~lodels devclhgpcd 

in Zh@ first Escet af %his investig&lion, The csmbxnstisn sf kha 

dae1ecF.ri.c mixing made2 and the csnapy propagarisn madel provides 

&he means ro esmputc she lass factor of khe canegy iF given ehe 

w~ker canbent% and v&kume Frd~Eian~ bf the ~aa~py uunstatuents 

sod %he canopy he%gh&, Thc model aceaunt?s far the dependence an 

f asc idance angXe, polar azer non anti wavelength, 

fn khe nex% facet oB ehis ycudy, we sttemptvd to rslaLc t,ha 

resul&s obtained abovg Lo ~hc remo8e sensine prob1@m, In order 

to Eecus the study era ehe canopy itse"t and avozd prablems 

agsocaated wi%h uari~'tisas in the sail bsckgrnund, it was decid~d 

&a caver &he sail sucEace with screen wire and mekg pwssive 

macrsuave ala@rvatsons as a fuactlon of trme over Fhe growing 

cyc'lo, The scnae~ ware, wh-ale 1% has no d~~~etg"8ib-sle eE8-~~tfi 

&h~ graukh BF the pldnt~, ~CEB a6 8 CC>~~QIC$, in% su~fdcc with a 

near-z~ro emiasivity, Thus, sari rnozsrure vsriaerons exercrse na 

1n5luance an the cahapy emrssron, Thxs technique was used ta 

hwvsstig~te %he vsrlakian a& the Rsashtnexs temperakut~ of the 

csnapy with look drreertlort brclarmve t~9 the row d~r~cglasnl, 

ancideactz snglc, a~d pnf@r~zwt.ion confxgura&ron Bar wheat, 

soybeans, and corn canopies, A radia~ivc Lransfer model we5 aged 

to re%ate &he brightness t@mperaturc ta bxaphysical pnrametets uE 

the canopy thrsugk the canspy loss factor, vxgurc 3 shows GhaL 

the experrmenkal ahscrvstions are in good agreeaenz wzCh T~E 

model predieeions, A second see aF radzometcr sbs@rval%one were 

made For canopies under naturwl condtgzons (nu screen used8, The 

radxatxve LP SnsFcr msdet was err$enc1~d to include :l sorid-mlraiaEurc 

berm CARL ~CCOU~~TS for tk~ emisstan and rcFlac&ean by the sox1 

surEacc, Again goad agreement, wss found between theory swd 

expa'rrme?n&, 

The majsriky 0% rnkcrouavc scatLcr xng snd emtss ion models 

rspurted kn Che Ti%~raLux=~ have Lceated the canopy as wn 

isots~plc medium, This rmglies thwt the &rtenuat.scm coeff/cren$ 

i s in~;fepenficnC of pd41ar t ZA~SO$%+ 3 iOc i~1~8ar&tl awgle, srrd lask 

dxrect~on t nn a%lmuLh), The yses@?wk study has shown @..hat. an mwsr 
cases, none of the above assumptions are valid. Consequently, 

modelers will have to incarpgrate the anisotropic character of 

the canopy in their models, which is likely to lead to more 

applicable models for the backscattering and emission from 

vegetation than now exists. 

The work conduct-ed to data has established the overall 

functional relations between the propagation coefficients of a 

vegetation canopy and its biophysical and geometrical properties. 

The results, however, are based on a number of specific 

experiments that were conducted for a specific set of crops at 

specific stages of growth. The goal of the next phase of this 

study is to develop a general propagation model that may be 

applied to a wide range of canopy types and conditions. The 

experimental component of the study will be designed accordingly. 
Figure 1. Measured Dielectric Behavior of corn 

1 cakes . 
mQIATED 

H ~QLARIZATION ............................................. DoY 188 

FACTOR, 

dB 

V POLARIZATION 

10 1 ,.-.- ............. Dey la&.. .............................. 

LOSS , ................................ 

FACTOR, ...... dB D€FOLIATED 

.). ............................................................................... 

Figure 2. Comparison of attenuation measurements 

made for soybeans canopy before and 

after defoliation for vertical and 

horizontal polarizations. 
Figure 3. Coriparison of the tetzporal record of the brightness temperature 

of soybeans canopy with model prediction. 

- 

- 

- 

- 

F fy/ I E. A i_l 'a x 

.' m 

SOYBEANS OVER SCREEN 

2.7 GHz 

I v polarization j ? e= 10 

Measured 

A Predicted ILIIlIll~ IIII 111111111111l1 

5G 175 200 225 250 275 300 

DAY OF YEAR 
DETERMINATION OF BACKSCATTERING SOURCES IN VARIOUS TARGETS 

R.K. Moore, Principal Investigator 

R. Zoughi and L.K. GJu, Co-Investigators 

Remate Sensing Laboratory 

University of Kansas Center for Research, Inc. 

Lawrence, Kansas 66045-2969 

OBJECTIVES 

The objectives of this research are to identify the primary corltributors 

to 10-GHz radar backscatter from various natural and man-made surfaces and 

ojjects, and to use this information in developing new and better models for 

the scatter. When the true sources are known for the scattering that leads to 

variation in intensity on radar images, the images (and sets of them) may be 

interpreted more meaningfully in terms of the variation of parameters of 

interest for science or application. For example, better interpretation of 

vegetation images may be possible for yield forecasting and stress detection. 

APPROACH 

Backscat tering coefficient (a0) measurements from crops, soil, snow, etc. 

have been conducted for over three decades, but only a minimal effort has been 

focused on determining the sources of backscattering in those targets. Tlsing 

a pulse radar, Graf and Rode 119821 in Germany used a solitary fir tree to 

determine its major sources of backscattering. Tllaby et al. [1982], using a 

defoliation technique, conducted scattering measurements on several types of 

crops. The only previously reported extensive direct measurements of sources 

of scatter have been conducted by the Remote Sensing Laboratory at the University of Kansas through this research in 1983 [Zoughi et al., 1885; Wu et al., 

13851. The approach and the results of these experiments provided the primary 

guidelines for the 1984 experiments. 

To measure the relative backscattered energy from various constituents in 

a target (i.e., corn cob, stalk, leaves), a radar system with a fine range 

resolution and a small footprint at the target range is required. Measurements conducted during 1983 utilized an available FM-CW radar system adapted 

so that its transmitted frequency swept over a wide band to produce a range 

resolution of about 11.0 cm. A focused parabolic-reflector antenna system was 

used to provide narrow beamwidths in both the azimuth and the elevation directions; this resulted in a footprint of 15 x 18 cm at the range of 4 m. Associated with this system were relatively high range-sidelobe levels which made 

target detection ambiguous at times. Therefore, funding for a specialized 

radar system was requested and zpproved. Consequently, a short-range veryfine resolution FM-a4 radar system was designed and built. This radar system 

(SOURCESCAT) also provides a range resolution of 11 cm, but its range-sidelobe 

levels are appreciably reduced. The same focused antenna system used in 1983 

was used with the SOURCESCAT. 

Targets examined during the 1984 growing season included corn, soybeans, 

wheat, alfalfa, short grass, tall prairie bluegrass and several types of 

trees. To determine the main sources of backscattering in these targets, 

constituent defoliation (i.e., for corn and trees) and layer-by-layer defoliation (i.e., soybeans and tall grass) were implemented. All the measurements 

were conducted at incidence angles of 30' and 50'. 
RESULTS 

For an individual corn plant, backscattered energy is mainly due to the 

heaves; scattering from the cobs and the stalk is negligible, as shown in 

Figure 1. For a canopy, echoes from the upper 1 - 1.5 m portion of the plants 

dominate the total echo. Energy returned from the ground is insignificant due 

to the two-way attenuation of the radar signal through the canopy. 

So;rbeans are very lossy volume scatterers. The two-way loss through one 

row of plants ranges from 20 to 15 dR at 30° and 50°, respectively. Backscattered energy from the upper 30 cm of the plant dominates the returned signal. The energy returned from this portion is about the same at both incidence angles. Layer-by-layer defoliation indicates that the unattenuated 

hackscattering from various leaves in the canopy is about the same. 

The backscatter from wheat is dominated by the heads in both the early 

and late stages of the growth. Hackscatter from heads remains almost constant 

at different stages, but attenuation through the heads is considerably more at 

the early stages of growth due to its higher moisture content at this stage. 

This shows backscat ter Lnsensitivity to moisture content but direct loss due 

to moisture content of the heads. 

Individual alfalfa plants of about 40 cm tall were observed with no 

defoliation performed. In the presence of the plants, the returns due to the 

entire plants dominated the radar signal (individual parts of the alfalfa 

plants are too small to resolve). The returns in this case were slightly 

higher at 30' than at 50" incidence angles. With the plants removed, backscatter from the roots was observed at the depth of 5 to 12.5 cm beneath the 

ground. 

Two different tall prairie grasses (50 crn high) were examined. The first 

site was an undisturbed and natural site which contained the dead grass maternial from the previous year on top of the soil. The second site had this dead 

material intentionally burnt off the soil before the growing season. Therefore, the latter site containe4 Pcss soi? moisture than the former site. The 

results of our measurements were also in agreement with this fact. In both 

cases, a volume of grass about 15 cIn thick and about 25 cm above the soil gave 

the strongest backscattered energy. This experiment was conducted in collaboration with investigators from Kansas State llniversity. 

For pine trees, the needles showed the strongest backscatter, and caused 

the strongest attenuation in the radar signal, Cones, elthough insignificant 

contributors to the total backscatter, exhibited more backscattering than 

attenuation propertfes. Figure 2 illustrates these results. 

Four types of deciduous trees were examined. Leaves were a strong cause 

of backscattering and attenuation. However, removing the leaves and keeping 

the leaftails and small twigs and branches reduced the backscattered energy 

very little. Theref ore, their contribution to the total backscatter cannot be 

ignored. 

These results are in great agreement with the results of the 1983 exper<- 

ments, but there is mote confidence in these results because a greater number 

of independent samples were observed and the ambiguities caused by range 

sidelobes were much less. 
nISCITSSION 

To obtain a complete understanding of the wave-target interaction process, experiments need to be conducted and models developed in each of the 

following areas : 

(1) Target Dielectric Properties: To model a vegetation canopy, the 

dielectric constant of canopy constituents (leaves, stalks, fruits, 

etc.) as a function of temperature and water-volume fraction needs 

to he known. 

(2) Target .- Attenuation Properties: For media such as snow, forests, and 

vege;:tttion canopies, attenuation properties of the medium are essential in modeling. 

(3) Target Volt.xn$ Geometry: Methods need to be developed to measure the 

three-dimensional statistical distribution of orientation and density of scstterers within the volume. 

(4) Target Scattering Properties: Extensive measurements need to be 

conducted on the scattering behavior of (a) targets under natural 

conditions, and (b) target constituents. 

Information from all of these four areas enter into a scattering model. 

The existing scattering models in many cases assume or estimate the contribution of some of these parameters to the whole model. To develop complete 

models, these assumptions and estimations must very closely coincide with the 

true state of these parameters. This can only he achieved through sound 

experiments in the above areas. 

By modeling the scattering properties of target constituents sfid using 

our experiment results to cross-check the models, we may be able to model 

correctly the scattering properties of the target as a whole. 

A method-of-moments solution is proposed to compute the scattering from 

the individual plant parts, which may be modeled as dielectric cylinders, 

ellipsoids or smooth-curved dielectric slabs of arhitrary shapes. The 

analysis is based on the LeVine-Schwinger integru-diffe.:ential equation, 

derived from the equivalent polarization current. The solution for the total 

field is obtained numerically. The far-zone approximation is applied to the 

integral equation. Given the total field inside the dielectric scatterer, we 

can calculate the scattered Eield and, therefore, the scattering crosssection. 

Vore concentrated experiments and research in this area are needed to 

answer all the related questions raised and those that may be introduced as 

the research progresses. Experiments on mote natural targets and man-made 

targets (such as buildings) will continue in 1985, along with extensive 

efforts on developing scattering models. 
REFERENCES 

Graf, G. and R. Rode, "Radar Scattering from a Solitary Fir Tree," Digest of 

IGARSS182, TA-1, vol. TI, pp. 8.1 - " .6: Munich, West Germany, 1982. 

Illaby, F.T., et al., "Review of Approac. c.s t !ie Investigation of the 

Scattering Properties of Material Media, Digest of IGARSS182, TA-1, vol. 

11, pp. 1.1 - 1.5, Munich, West Germany, 1982. 

Wu, L.K., et al., "Preliminary Results on the Determination of the Sources of 

Scattering from Vegetation Canopies at 10 GNz, Parts I and I1 ," to be 

published in International Journal of Remote Sensing, 198.5. 

Zoughi, R., et al., "Determination of Fackscatter Sources in Surface Type 

Targets," to be published in International Journal of Remote Sensing -' 

1985. 


Sack F, Paris 

CaILfamLs Xnatikute of Teehnolagyi 

Jet Fectpulafon kboratctry 

Juseltf$catfon, Boteaeial users of radar imgery need a better farndansentaf. 

uadere tanding sf the capabilit fee OF radar systems for vegetatlan a tudies than 

paae studies provide, &e approach is the use ctf thearekieal odel la te, predfet 

obeasrvatiPle active derswaoa prapertfea aF vegetation, %fa In turn raquires 

Beetarate a'trsa~v~ztlorms e,f backscattering eaeff ieieats and aeher active ntirrowalse 

propertiea in fh&d researcks studfa%, The bekground dostarn~nt Car the SRABC 

program empkasi~ 9 the need to relate electrowgnecfc parameter$ to alas~ical. 

bLapFsyaical dcscrigitars anel Lo bonderstand the kale of pt>%ariratfon, e@peeialfy 

erass-pokaritatlsn. Coals* The bread goat sf sttxdy is to increas~ the 

understanding of the ef feets of canopy atttssture ors the act ive mfcomave 

propertfes ctf vegetation cenopfes, with parciearlar atkeslkfon to po~ariaarbon. 

En the first yearl I studied alre~efk radar $GatEQrOWt@r 

atrraaurewnta of earn and soybean ffelds fn Iowa re, detertnfne the propertkes of 

these mttsse field8 st L-band 619 ent) and C-baad (6 cnt) arid at sensor Lookangles fro% 5 to 50 dagrese, kag the secctfld year, X used the Cloud Model 

(Ref, 1) with a set of X-band <J em) and K-bkaad (2 cnt) truck-based radar 

ecatterooteter like-potazfzatiaosa deea far corn fa Kana@@ to extend the ntode$ and 

to relate the mdel parastreters trs bictphy$icaI characterf~ties of tht* corn. Far 

the third end ctsrrent year, Z uaed a 6-bn.8 dual-palari~atian trtxek scatteroweer at the Untvarslty of CaliCoraka Gamey AgrkeuktoxsaX Canter to masure 

the actlve ntlsrctwave properties ~f trees in ~~~f%ard~a Using the @loud Xadel, 1 

was able to eatimte no: lmly the hckscattering coefficient, btxt also the 

attenuation coefficfent, the density of backscattering cross sectiamla, and the 

transmittermee, Ttre research asrivity lead ta s new procedure irm using aoxrh 

trsetlk-based radar scatteraet:er data for thick, vot~~~1@ aeatterlng nsedia, 

Pirat Icar, In the first year, 1. found that mttxre corn and soybean Fields 

esuld best separated with eke use of C-band cross-polarization [RV"tata at 

90 dagreas, Ho separatioa exfated for C-band like-palarkzatiav (HR), At 

1,-band, thp taeparatfon of earn and soybeans was best for Ifke-palari~atfctrm (%(8>, 

baxt was% not a% goad as It wa8 far C-'brano W dear E;Bo separatia~~ exi~ted in 

L-baa& croaa-polart~atm dat~, I rsksk~rved significant row directfarm effect@ 

for aeneor laok-eagle near IS degrees when like-pctlarizatfo.81 was used# These 

effec*~ @ere strangest: at Z-band* 220 rw diz@etiorr ef feets existed for crosspolarfzation far either had, PiaaZly, 1 observed that the presence rsf wet soil 

and/c~r wet canopy due ko rain reduced the separations of corn and soybeans and 

pradaxeed ~d%(nlfieant fncreatae isr hckscatter, especfafly near 15 degr~es. 

deeand "fear. Xn alzslgaining the Cloud Bodel, T found tha4 he wdeL form was 

eignfffeantXy different For eross-palarlzatkan than it For usual Xikepolarf~ntioo formulatian, Alaa, E Found that the use of the ratfss sF backscattering enefficdents for the various poParfzatPon eomhinatlona (VV, NH* W 

%ad W) could Lead to the isalaeion of canopy angular orkentation .rapertte&, 
I%$@ allowed a new interpretarlon aX the eorn end soybean data atudlied in the 

fl rst yaarr Similar separatians existed f n the dcpolarizat 2oa rat2 a {eras&- 

palasfaation divided by like-polari~atian) such as existed independently En the 

Xratter of rhe two ~hanniels. Ftnally, by applying the Gleltdt Modal to thraughthe-aeagon, tswek-based radar acatterumeter masuresnent8 * T eaexld estimate the 

baekbaestt~ring end extlrrct ton cross 8ectPorrs af average Icavas, X. Partnd that 

the loraex mi+ a s1~p4e pazjer-law Eatncti~n of corn Leaf area br2 of D,9?') 

tkrroetghnut the season, 

Tkfrrd x%&r, I: used the Mierawave Scatteromtar C-band (WBC), ol loan from the 

mahasm Spac~l Center, mounted on ia .WL tlcrpck. (height of if. m) to make field 

m@asureeet.rte, %is Znstcttmt?x~~t ubteins @&lihraLecf r@l$ar &ek@earkarinig eoeFEicient data in tha fieldt flawever, lt samples a volrsms that is limited tn size 

due to the finitlz range-reasI:txtlen and the fdnite beam-idth, Xt abtainc data 

at both like-polari~at fan and cross-polarf zatlanr %raatgb the age uf the rangIn& capability of the HSC: 8nQ tha Claud Wodel, 1 wns able estisaate the active 

aterawove properties of vegetatlan cana fes, as Pallavs: Q E f the true, 

sorrztted backscatt~rirrg r;ne%f&*.it;at, S 8 T; .I%) the volume a tfrp Elon eeeffieiant 

R (m 1; (3) the backscartering cross st?ctlon density, F (nfmm5,; (4, the fwaway ttansaittanC1? of the canopy, 1: t (1 and j stand far lit or V ttu dencre the 

paZarlzatior~ cambina&.f on used 1; &%I tie 'Ytxll ea~spy" hekscat. turin coeff iclent, s"~; and <6) the distrfbutlan af soureea wlt!t rasaRe, Bcr a given 

ve~rzeatkura canopy these active mi crowave eharacterlaties vary vf tki palarfxatf an 

or pal~rfzatfon camhinet tan, 

PlJustratZon OX the Hew Pt-kreedurc. The proccda$ra ea obeatn tkese paraseters is 

t"~uatrstacl bekw far an ideal eaee where tha canopy proparttea are ksnapsn- 

@cut;, %e view of the Cloud Hadel is that the a~srrved biackscnttsri9yg cosffickeot is given by 

fur the o~ne-Xwer camr where th~anopy efements are Found batween the rarges, 

RX an$ R2 (%I, with tht? refleeted Canirror Img~) ektnapy extendin& to cererge 

g3 <@I* 

f2 EI rij cws (TI exp g-(Mb + K ) fR2 - Rl )j 1 631 

exp (-CKp + Kj) tff - M21j 

wher,. Y is the aeneor look-eagle (degrees 1, ri Is the surfae~ ref lectaace 

Qessameed. to specular hn baic eharactea) for pdlarfzatfon $1, nnQ R f9 the raage 

Qa)* 
We $ate$ration sf (13 over the entire range From PI to R3 with the 

exprea8fons in $23 and f3) Zeeds to the true canopy backscattering coeiffeieot, 

ohre is the surface BackacatCerfnp c~effi cient r 

Rowever, fox the HSI: &or any $cat1:erometar faav-tng a small, finite range resolution), &he senaor Beasuses oxsly a fraction of the to1:al back~~~aEEarttng* P call 

this the part fa1 Backseatterfng eaef $2 cfarst (measured) &fch is related to the 

%uneE tan i by 

&tidP a ,ff dR laver the range resolution, AR) (31 

Since AR fs saal1 $1: is poa~~ible ta eatlmate the Ft~nctiasn f by 

Figore I $haw th~ eomparpaan becueerr. the %%yen (true) value of f and the 

eskiaated value ax? F as ohtaf ntld Prm a raodeled prediction of the "gmeasured" 

partial backscattering ~oeffieie~lt (see Pipare 2). %e e~timated Z i& e%ase to 

the gives f for soma ranges hut not for 121 ~ange~a Now, %t is poaeible to 

perfarm a anaerieel integration ta e%EimCe the tfue value of beckscatterfng 

coefficient as indicated in Eq. (If above, For chick vegatatfsn canopies, the 

true value ls efgniffcantly higher than the largest partial value, Thus, this 

pracedure fs requtred For such ot tuat fona* 

Since the warlatian of % with range Is a decaying expanentfal fufickf~d, the use 

of the kogarlthm sf f (or alternatively, expression sf f in dsciBels, dB1 leads 

t.0 a straight line portioa of the f (dB) versus crrrve (see Ffgure 33r Passing 

a strafght line througlr psfrit~ brs thfd segment allowe esttaation of both & and K 

E fRi see (T) and X slope/(-8.686) (61 and (7) 

Nth the estimated valoe asi K rlrsd the knswan slant range thickness of eke canopy, 

k$ t cars be eati~&ed~ Using rrsugh erstfaekes sf r and eurfcrce backacatt~riag 

t.bxefJicient, one can ctstla~ate kndependeatly the value far 8, B"lr$a value rthould 

be clsse to thee eatlmated far Eq, ('61, Mith the nav values far R axld K it: 19 

possible to eskilr;arske the "'iu11 canapy" hckscatterinp coefficient frona 

1% &tar; eeconlf (refleeted1 portion af the f [dl) versus W curve can h detected, 

it fa paasihle to extrapalate the tua strafght lines (one froa rangee leas thaa 

the range ts the surface, and oaa for ranges greater thaa the rang@ ta the surface-.) ba the surface range values of fL dleft side) and fg fright side) a~ld 
C~~CUZACI 2 by PR/PLe Since the estimated value of P al Rq ~taksg be I~igher than 

the average value of ft and kM due to the contrtbution of atteatuated surface 

becksrattering, f t ie possi b%a to estisuate the surface 'hackecattering eeef Pfsient, 

Reserlrs with brcharde, Pfpure 4 shows &he p&rti@a backseatterinp coefffcients 

versus range TOP a young peach orchard (see Pigure 5 which indicates the tree 

structure), Hoke that near the top of the canepy the radar return fs do~insted 

by the VV where kt%% dnrssfnates thc return near the Base af the Canapga After the 

noise Plaoc l% estimated and aubtrsct@d, the data were ataed to estfwtr f [dB) 

as ahnm J'n Ftgure 6, The actfve radar parameters show In Table 1 are obtained 

From tlaese data using the &bow procedure, 

The ttrrec; year strtdy shows chat, in many casesj., sroespaZarizattan or n comb%nation of WM, VV andlor cross-palar~eation yeilds Informat ion on the angular orienkatioa of vegetatf nn canopies. Rat fos of' channels 

shoutd be used to $$nlwce such Informkfan from other vepetat Ian eharacteristica 

sttch as total araal 'biama~s etr water content. Furthermore, with the proper use 

of simple rralcrowawe scattertng models, ~ctx as the Cloud Pbdel, and accrrrate 

radar scarterawetes date, tt Is possible to @$itmate the tatat backscattering 

coeiflf cient , the attentus t tan cnafff ciant , the transmit tanre , and average seatterrirtg and exki~ctian radar cross seations aP seettering elem@nt@, These data 

ofiattld prove u~efldl for verb fication OF modeling approaches and Bar thr development of adequate uuzderstandfng of the Lnformatikm content of radar sensor data 

gosh a8 From the synthetic aperture rk~der {SARI imagecl~r, 

Example af E~asur~d Active Mlcrnwave Properties 

trF Orchard8 IIS.irosxp&a Analysis OF Truck Fb~dat" 

Scetterometer Measurements at @-Band and 66 Degrees 

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1I.C. LIST OF PUBLICATIONS AND PRESENTATIONS 

The following pages list the refereed journal articles and 

other publications and presentations that report on the results 

of the research performed under the SRAEC Project. The 1isti.n~~ 

are presented as provided by the principal investigators and are 

arranged in the same order as the summary reports presented in 

Section 11.8. 

SRAEC Pro,ject scientists have produced approximately 80 

refereed scientific journal papers during the first three years 

of the program as well as dozens of additional writings in the 

form of theses, dissertations, symposium and conference proceedings, and special documents. 
K, D, Cooper and 2, A, Smf.th. W Mont~k..a;rZo Wfbe&m Node1 fox 

C-1113~ Sail t3.1tEaces. 3.985. Im5."6t& ko O 

8 .E@&I. *%mt.) 

A, H. Strahler, C. E, WoCaCOCka andf J. Ac ?SM%W, On the Nature OE 

Plo&2s Li amate SsminglP 3985, k3dmitted ta JEEg 

J32Q&&e It;r m. J*%c) 

J. A. Mat K. Dm COO~II~ and A* HI StraMer. 1384. Eleckro-opki6aE 

Terrain Ref~ecrl=ance Modeling: Same Pesspct5ves, me 

SgggiME.!ttirnC Nash. D, Clp 475: 12-117. (fwited paper for 

Critical RBW~WS oE Bcholqy Sesbes in Remote mnsing3 
$TDIRECTIONAL REFLECIIANCE mODELIMG OF NON-HOI4QGENEOUS PLANT CANOPIES 

John M. Norman 

University of Nebraska 

Lincoln, NE 68583 

Publicat ions 

Norman, 3, M. and J. W. tJelles. 1983. Radiative transfer in an array 

of canopies. krone 3, 75:481-488. 

IJaltha3.1, C. L., 3. M, Norman, J. 31. Welles, G. Campbell and B. L. 

Blad. 1985. A simple equation to approximate the bidirectional 

reflectance from vegetated surfaces, ,AppXC O,pt$csc (to be 

published Feb. 19835). 

Norman, 3, IS., 3, M. Welles and E, A. Walter. 1985. Contrasts among 

bidirectionax reflectance of leaves, canopies and soils. IEEE 

Trans. GeoSci. Remote sen sin^^ Submitted. 

Kimes, D. S,, 3, M, Norman aisd C. L, WaltEsall. 1985. Piodeling the 

radiant transfers of sparse vegetation canopies. IEEE TransA 

- GeoSci. Rmote Senstnk Submitted. 

Norr;,,w, 3. ;s:~, J. Speclit, Z, L, Bldd and 3. E.I. Wefles. 1982, Tile 

ef feet of pubescence on soybean leaf and canopy reflectance. An~er. 

Soc. Agron. Abstracts, Madison, WIS. 53706, p. 17, 

Norman, 3. M. 1984, Using canopy reflectance properties to estiroate 

some parameters essential to macroscale Et predict ions. Amer, 

Geophys, Union Abstracts, Fall, 1985, AGU, Washington, D. C. 

Norman, J. IS., J, M, Tqelles, E, A, Walter and G, S, Campbell. 1984. 

A bidirectional reflectance model for heterogeneous plant canopies. 

Amer. Soc. Agron. Abstracts, Madison, WSS. 53706. p. 15. 

Walter, E. A,, 5, Mo Norman, J. M. Welles and B. L. Blad. 1984, Leaf 

bidirectional reflectance measurements in corn and soybean. Amer. 

Soc. Agron, Abstracts, Madison, WIS. 53706, p. 19. 

Present at ions 

982 Volunteer paper - The effect of pubescence on soybean leaf 

and canopy reflectance. Amer. Soc, AgrOn, Annual Neering, 

Anaheim, CA,, Now. 28-Dec. 3. 

1984 Znvited paper - Using canopy reflectance properties to estimate 

some parameters essential to macroscale Et predictSons. 

Hydrology Symposium on Evapotranspiration Modeling, Fall Arner. 

Geophys. Union Meeting, San Francisco, CAY Dee. 3-7, 
1984 Volunteer paper - A bidirectional reflectance model for heterogeneous plant canopies. her. Soc. Agron, Annual Heet ing, 

Las Vegas, NEV, , Nov. 25-30. 

1984 Invited to present research results at Fundamental Research 

Project Briefing at NASA Headquarters for Dr. Shelby Tilford 

and Br, Burton Edelson, Washington, Du C. Mar. 16, 

1984 Invited seminar - Bidirectional reflectance in heterogeneous 

plat canopies, Monthly seminar series jointly sponsored by 

U. of Maryland RSSL and MASA/GSFC, Washington, DOC. July 19. 
Understanding the Radi ant Scattering Behavior of 

Vegetated Scenes 

Danlei S. Kimes 

1) Refereed Journal Publ3cations 

Kimes, D.S. and J.A. Kirchner, 1982, I1Irradiance Measurement Errors Due to 

the Assumption of a Lambertian Reference Panel ,It Remote Sensisoq.Fqi ronment, 

12: 141-149 

Kimes, D.S and J.A, Kirchner, 1982, "Radiative Transfer Mode1 for 

Heterogeneous 3-0 Scenes, " Applied Optics ,t 21 (22) :4119-4129. 

Kimes D,S. and J,.L Kirchner and J.E. McMurtrey III, 1982, "Variation of 

Di rectional Reflectance Factors with Structural Changes of a Devel opi ng 

Alfalfa Canopy, " App1 i ed Optics, 22: 3766-3774, 

Kiws, D.S. and J,A. Kirchner, 1983, "Directional Radiometric l'feasuremcnts 

of Rw-Crop Temperaturess" Int, J, Remote Sensing, 4(2):299~311. 

Kimes, D.S., 1983, "Remote Sensing of Row Crop Structure and Component 

Temperatures Using Di rect lonal Kadi omet ri c Temperatures and Inversion 

Techniques, Remote Sensing of Environment, 13:33-55, 

Kimes, D.S. and J.A. Kirchner, 1983, "Diurnal Variations of Vegetation 

Canopy Structure, " Int. J. Remote Sensing, 4(2):257-271. 

Kimes, D.S., 1983, "Dynamics of Direct iona'i Refl ectance Factor Distributions 

for Vegetation Canopies, 'I Applied Optics, 22:1364-1372. 

Kimes, D.S., J .A. Ki rchner and tl .We Newcomb, 1983, "Spectral Radiance E rro~s 

i n ~enote sensing Ground Studies Due to Near by objects," Applied Optics, 

22: 8-10. 

Kimes, D.S., B.N. Holben, C.J. Tucker and WOW. Newcomb, "Optimal Directrat~al 

View Angles for Remote Sensing Missions, " Int. J. - Remote Sensing, 5:887-908. 

Kimes, D.S., W.W. Newcomb, J.B. Schutt, P.J. Pinter, Jr., and R.D. Jackson, 

"Dl recdional reflectance factor distributions of a cotton row crops, 'I - Int. 

J. of Remote Sensing, 5:263-277, 

Kimes, D.S., "Modeling the Directional Refl ectance from Comgl ete Homgeneous 

Vegetation Canopies with Various Leaf Orientation Distribution, I' ?ps.fnal of 

the Qptieal Society of America -9 1: 725-737. 

Kimes, D.S., W.W. Newcomb, C.J. T~rcker, I.S. Zonneveld, W, Van Wij~;g6or*d~n, 

G.F. Epema, and J. DeLeeun, "Directional Refl ectance Factor Distributions 

for Cover Types of Northern Africa in NOAA 7/8 AVHRR Bands 1 and 2," -- Remote 

- Sensing of Environment, in press. 
Kimes, D,S,, d,M, %orman, and C,L, Valthall, 1985, 'IModeIi ng the Radiant 

Transfers of Sparse Yegetatton Canopfes," IEEE Transaction on Geoscience 

and Remote Sensing, suhmi tted. 
I4EASUREE";ENTS AND MODELING OF THE OPTICAL SCATTERING 

PROPERTIES OF CROP CANOPIES 

V. C. Vanderbilt 

Publications 

32fereed Journal Publications 

*:anderbilt, V.C., L. Grant, and C.S.T. Daughtry, "Polarization of light 

scattered by vegetati~n,~~ P1*uceedings IEEE, (in press). 

*Ianderbilt, V.C. and L. Grant, "Plant canopy specular reflectance mode1,v 

(submitted to IEEE Transactions on Geoscience Electronics and Remote 

Sensing), 

Sanderbilt, V.C., L. Grant, L.L. Biehl, and B.F. Robinson, "Specular, diffuse 

and polarized light scattered by two wheat canopiesllI (Accepted by Applied 

Optics. 

7anderbilt, V.C., "Measuring plant canopy ~tructure,~ (submitted to 

Photogrammetric Engineering and Remote sen sin^). 

Sonference Presentations 

':anderbilt, V.C. and L. Grant, "Light polarization measurements: a method to 

deeermine the specular and diffuse light-scattering properties of both leaves 

and plant canopies,~ Conference paper presented ta the International 

Colloquium on Spectral Signatures of Objects in Remote sensing, September 

1983, Bordeaux, France. LARS Technical Report 09 1 683. 

:rant, L., V.C. Vanderbilt, and C.S.T. DaughLcy, vMeasurements of specularly 

reflected radiation for individual leaves," Agronomy Abstracts, vol. 75, 

p. 12, 1983. 

Vanderbilt, V.C., L. Grant, L.L. Biehl, and B.F. Robinson, "Specular and diffuse 

reflectance of two wheat canopies measured at many view angles," (Abstract) 

International Union of Hadio Scienc!e. January 1983. 
GEOMETRXC-QP'PXCA'Cr MODELXNG QF A CONSFER FOREST CANOPY 

Alan He Btrahler 

Hunker Col2ege 

Franklinr Janet, Je MichaeZsona and A. H. StrahLer, 1985. 

Spatial pattern in coniferous forest stands, VeaetaWt submitted. 29 ms. pp. + 7 fig. + 3 tab, 

Lit Xiaowent and A, H. Strahler, 3985, Geometric-optical 

modeling of a conifer Eorest canopy, SEEE m. QQ 

Geoscience Remate Sensjnq, submitted. 54 ms. ppe 4- 

16 fig. + 4 tab. 

Strahlerp B~M Be; C, E, t?~a6cock~ and J. A, Smith, 1985, 

On the nature of models in remote sensing. IEEE Trans, 

rn Geoseience & Remote Sensing, submitted. 42 ms. 

PP 

Smith, a. A., K. D, Cooper, and A. H, Strahler, 9984, 

Electra-optical, terrain reflectance modeling: A perspective. m. $? Tech. m.? m. 1984.r pp. 12- 

17 

Strahler, Alan Hop X. Li and J. Franklinr 1985. 

Spatial/spectral modeling of conifer forest canopies. 

Modeling E.buJatiorl, Yolum U0 Proc. Fifteenth 

Ann, Pittsburgh Canf. on Modeling and Simulation, April 

19-20r 1984, ppc 19-21. I 

Strahler, Alan Her C. El Woodco~k~ X. hir and D. Z. B. JUppr 1984. Discrete-object modeling of remotely sensed 

scenes, Proc* Ei th Irate m. QQ Remote Sensing 

Esni.ronwr P%~~"France, act. l-!jr 1894f in 

press, 10 pp. 

Straklerr Alan H, and X, Lit 1984. Spatial/spect~al modeling of conifer forest reflectance. Proc. otgd AustraJasian Remote Sensing w., GQld Coastp Qtseen~land,~ 

,fiuskralia, &Qy 21-25, 5986, pp. 88-90. 
PranIcXinr aaneC, 3.983, & E iricaJ, Study: a &Jxe 9~atiaI 

Pattern nf Poniferous sea. En A. Thesis, Univ. of 

Californiar SanCa Baxbarar Sune 3.985r 99 pp. 

Lit Xiaawen, 3.985, Geomw-Qpticak Modeliw & g iloniget.0~5 Forest S:ilno~-* Zlh. D. Dissert*, Univ, of California, Sanka Barbara, March 3.985, 78 j?p. 
CROP CHARACTERISTIC RESEARCH: 

GROMTH AND REFLECTANCE ANALYSIS 

G, D, Badhwar 

Johnson %ace Center 

PUBLICATIONS 

Journal Arti cl es 

1. G. D. Badhwar, ld. Verhoef, and N. J. J. Bunni k: Comparatiw Study of 

Suits and SAIL Canopy Reflectance Model s, Remote Sensing of Envi ronment, 

vol 17, 1985. 

2. E, Reyna and G. D, Badhwar: Inc1 usion of Specular Ref1 ectance in Canopy 

Models: IEEE Geosci ence and Remote Sensingz 1985, 

3. G. Do, Badhwar: Multitemporal Classification of Corn and Soybeans 

Using Thematic Mapper Data: Remote Sensing of Environment, ~rol l6, 

pp 175-182 (1984). 

4. G. D. Badhwar and K. E. Henderson: Application of TM and Simulated 

TM Data to Estimate the Der~joprnent Stages of Corn and Soybeans: 

Remote Sensing of Envi ronment, vol 1 7 (1 985). 

5. G, D. Bsdhwar and K. E. Henderson: Relationship of ProfSle Inf?ection 

Points to Crop Development Stage and Yield: Agronomy Journal, 1985. 

1. G. D. Badhwar and S. S. Shen: Techniques for the Estimation of Leaf 

Area Index Using Spectral Data: 10th International Symposium on 

Machine Processing of Remotely Sensed Data, June 12-1 4, 1982. 

2, G. D. Badhwar, R. Re MacDonald, F. G. Hall, and J. G. Carnes: 

Spectral Characterization of Bi ophysi caf Characteristics in a Boreal 

Forest: Re1 ati onshi p Between Thematic Mapper. Band Ref 1 ectance and 

Leaf Area Index for Aspen: Proceedings of IGARSS084 Symposium, 

August 27-30, 1984, pp 111-11 5. 

A member of AgR'ISTARS documents describing the data produced. 
David J. Diner (Pri~ltcipal Xnvastigator) 

Refereed Journal PtrbLications 

1. Diner, D. J. and Martonchik, J. V. (2984). Atmospheric transfer of radiation above an inhomogeneous non-Lambertian reflective ground. X. Theory. 

J. Quant, Spectr. Rad. Transf. 31, 97-125. 

2. Diner, D. J. and Martonchik, J. V. (1984). Atmospheric transfer of radiation above an inhomogeneous non-Lambertian reflective ground. 11. Computational considerations and results. 3. Quant. Spectre Radc Trans£. 32, 279- 

304 e 

3. Martonchik, J. V. and Diner, D. J. (1985). 3lhsee-dimensional radiative 

transfer using a Fourier transforrnmatrix operator method. J. Quant. Spectr. 

Rad. Trans£*, in press. 

Symposium Papers 

1. Diner, D. J. (3.983). Atmospheric influence upon obser-vation of surface bLdirectional refletances. Mational Radio Science Neeting, Boulder, CO. 

2. Diner, D. J. and tiartonchik, J. V. (1983). Atmospheric radiative transfer 

above a surface of nonuniform albedo: The planetary problem in 3-D. 15th 

Annual American Astronomical Society, Division for Planetary Sciences 

Xeeting, Ithaca, M. 

3. Diner, D. J. and Martonchik, J. V. (1985). Remote sensing of atmospheric 

opacity using multiple view angle imaging. Optical Society of America Meeting on Optical Remote Sensing of the Atmosphere, Incline Village, NV. 
REFERENCES 

Robert S. Fraser - Principal Investigator 

Yoranl 3. Kaufnlan - Co-investigator 

Referred Journal Publications 

I. Y. J. Kaufman, 'Solutian of the equation of radiative transfer for remote sensing over twodimensional surface reflectivity', J. Geoph. Res., 20, 413704447, 1982. 

2. Y. Mekler and Y. J. Kaufman, 'Contrast reduction by the atmosphere and retreival of 

nonuniform surface reflectance', Applied Optics, 21, 3 103 16, 1982. 

3. 'Y, J. Kaufman and R. S. Fraser, 'The effect of finite field size on classification and atmospheric correction', Remote Sensing of Environment, 15, 95-1 18, 1984. 

4. Y. J. Kaufman and R, S. Fraser, 'Different atmospheric effects in remote sensing of uniform 

and nonuniform surfaces', Adv. Space Res. Vol. 2, pp. 147-1 55, 1983. 

5. Y. J. Kaufman, 'Atmospheric effect on spatial resolution of surface imagery', Applied Optics, 23, 3400-3408, 1984. 

6. Yu. Mekfer, Y. J. I'aufman and R. S. Fraser 'Reflectivity of the atn~osphere-inhomogeneous 

surf~ca sysiem. Laboratory simulation.' J. kemos. Sci., 41, 2595-2604, i984. 

7. Y, J. Kaufman, 'The atmospheric effect on separability of field classes measured from 

satellite', accepted for publication in Remote Sensing of Environment, 1984. 

8. Y. J. Kaufman, T. W. Brakke and E. Eloranta 1985, 'Field experiment to measure the 

radiative characteristics of a hazy atmosphere', in preparation. 

9. R. S. Fraser and Y. J. Kaufman 1985, 'The relative importance of aerosol scattering and absorption in remote sensing', submitted for publication in IEEE Transactions on Geoscience 

and Remote Sensing. 

Symposium and Conference Presentations 

10. Y. J. Kaufntan and R. S. Fraser, 'Different atnlospheric effects in remote sensing of uniform 

and nonuniform surfaces,' paper presented at the COSPAR 24th Planetary meeting, Ottawa, 

Canada, 1982. 

11. Y. J. Kaufman, 'Atmospheric effects on spatial resolution and classification of surface imagery', paper presented at the 21st Aerospace Sciences Meeting, Reno, Nevada. 1983. 

12. ' R. S. Fraser and Y. J. Kaufman, 'The relative importance of aerosol scattertng and absorption 

in remote sensing', V Conf. on Atm. Radiation, BaItimore, MD, 1983. 

13. Y. J. Kaufn~an, 'Atmospheric effects on remote sensing of surface reflectance,' Paper 

presented at the SPIE Crytical Review of Remote Sensing, Crystal City, Virginia, 1984. 

14. Y. J. Kaufnlan, T. W. Brakke and E. Eloranta, 'Field experinlent to measure the radiative 

characteristics of a hazy atmosphere', V. Conf. on Atm. Radiation, Baltimore, MD, 1983. 
PUBLICATIONS 

William A. Pearce 

William A. Pearce, "Monte Carlo Study of the Atmospheric Spread 

Fun~tion,~ submitted to Applied Optics, 

William A, Pearce, "Cloud Shadow Effects on Remote Sensing," submitted 

to IEEE Transactions on Geoscience and Remote Sensing. 
MULTIDIMENSIONAL MODELING OF ATMOSPHERIC EFFECTS 

AND SURFACE HETEROGENEITIES ON REMOTE SENSING 

PI: - S.A.W. Garst1 

A. Refereed Journal Publications 

1. S.A.W. Gerstl and A. Zardecki, "Discrete-ordinates finite-element method for 

atmospheric radiative transfer and remote sensing," Appl. Opt. 24, 81-93 

(1985) + 

2. S.A.W. Gerstl and A. Zardecki, "Coupled atmosphere/canopy model for remote 

sensing of plant reflectance features," Appl. Opt. 24, 94-103 (1985) 

3. C. Simmer and S.A.W. Gerstl, "Remote Sensing of Angular Characteristics of 

Canopy Reflectances," submitted to IEEE Transactions, Special Issue, to 

appear Sept. 1985. Also, Los Alamos National Laboratory report LA-UR-85-31 

(Jan. 1985). 

4. A. Zardecki, S.A.W. Gerstl, and J.F. Embury, "Multiple scattering effects in 

spatial frequency filtering," Appl. Opt:. 23, 4124-4131 (1984). 

5. A. Zardecki, S.A.N. Gerstl, W.G. Tam, and J.F. Embury, "Image quality degradation in a turbid medium under prrtially coherent illumination," J. Opt, 

Soc. Am., accepted for publ, Dec. 1984. 

B. Symposia and Conference Presentations 

1. C. Simmer and S.A.W. Gerstl, "Influence of the Atmosphere on Remotely Sensed 

Reflection From Vegetation Surfaces," Topical Mtg. on Opt. Remote Sensing of 

the Atmosphere, Lake Tahoe, NV, January 14-18, 1985. 

2. C. Simmer and S.A.W. Gerstl, "Modelled Atmospheric Effects on Remotely 

Sensed Bidirectional Reflection Distribution Functions (BRDFs)," Am. 

Geophys. Union 1984 Fall Mtg., San Francisco, CA, Decembcr 5-7, 1984. 

3. A. Zardecki and S.A.W. Gerstl, "Modulation Transfer Functions Computed with 

Multiple Scattering Radiative Transfer ~heory," 12th Znt. Laser Radar Conf., 

Aix-en-Province, France, August 13-17, 1984. 

4 S.A.W. Gerstl, A. Zardecki, and J.F. Embury, "Image Degradation and MTF 

Computation for Turbid Atmospheres," 1984 Annual Mtg. Opt. Soc. Am., San 

Diego, CA, October 1984. 

5, S.A.W. Gerstl, "Atmospheric Effects in Satellite-Sensed Vegetative Surface 

Features," As~oc. Nat'l. Radio Science. Mtg. (URSZ), Nat'l, Acad. Sci. and 

Eng. and Nat.'l. Res. Council of the U.S., Bauldar, CO, January 5-7, 1983. 
Lee,R,K,, Scattering from an inhomogeneoua layer, PhD. 

dissertationr Electrfcal Engineering Department, University of 

Kanfias, Lawrence, Ks,66045, August, 1934, 

PantG,Wer The fntegra2 equatson method for rough surface 

scattering, PhD, dissertation, Electrical. Engineering 

Department, University of Kansas, Lawrence, Hs.66045, AU~US~~ 

1984, 

Fungr A.K,,and H,5, Eom, Estimation of albedo and optjlcal thickness with the radiative transfer method, TG&RSS,84, 

Strasbotxrg, France, August, 1984, 

Eom,H,J.and A,K.Fungr Backscattering coefficient of a perturbed 

sinusoidal surfacer XEEE Trans, Ant, and Prop, vol, 32, no,3 

pp,291-295, March 1984, 

Fung,A,K, and H,J,Eomr W study of backscattering and emission from 

closely packed inhomogeneous media, National Radio Science 

Meeting, EostonrMass. June 1984 
1. f assivs, md active remote sensing of atmophcric precipitEleion (Y. Q. Jin asld 3. 

A. Mong), -, vo1,22,2535-2545, September 1983. 

A2. Dyadic Green's functions for layered anisotropic medium (J. K. Lela md 5. A. 

Kong)* @ectromg,getics, ~01.3, 111-188,1983. 

A3, Wave scattering and guidmce by dielectric waveguides with periodic surface (8. L. 

Chuang md J. A, Mong), Journal of the Qltical Society of Anlericg, ~01.73, 669- 

679, May 1983. 

A4. Scattering of ellectromagnetic waves from a half-space of densely distribntcd dielectric scatterers (L. Tsmg md J. A. Kong), gadio Science, ~01.18, 12S0-1272, 

Nov-Dec. 1983. 

A5. Strong fluctuation theory for electromagnetic wave scattering by a Iayer of random 

discrete scatterers (Y. Q. Jin and J, A. Kong), Journal of Amlied Physics, ~01.55, 

1364-1369, March 1984. 

A6. Microwave thermal emission of periodic surface (5. A, Kong, 5. L. Lin, and S. 

L. Chuang), IEEE TrCmsactions on Geoscience and Remote Sensin., vol. GE22, 

377-382, July 1984. 

A?, Scatterin6 ~f electromagnetic waves from a randomly perturbed quasiperiodic smface (R. 2'. Shim J. A. Kong), Sournd of Applied Physics, ~01.56, 10-21, July 

1984. 

A8. Radiative transfer theory for active remote sensing of a layer of nonspherical paticles (L. Tsang, J. A. Kong, and R, T. Shin), Eadio Science, vol.lS, 629-642, 

Mach-April 1984. 

A9, Ladder and cross terms in second order distorted Born approximation {Y. $, Jin 

and J. A. Kong), J. Mathematical Phvsics, accepted for publication, 

A10. Wave approach to brightness temperature from a bounded layer of random discrete 

scatteress (Y. $. Jin), Electro~~~annetics, accepted for p11b~ic~ti.0~3.. 

All. Active microwave remote sensing of as misotropic rarndoln layer (J. IC. Lee afsd J. 

A. gong), SEE33 Transactions on Geoscience and Remats Sensing, submitted for 

publication. 
C6. 

CW. 

Passive microwave remote sensing of an anisotropic random medium layer (J* K, 

Lce and J, A. Kong), DEE Bmscntions on Geoscimote Su, mb 

mitted for publication, 

Theoretical models for microwave remote sensing of vegetation and soiI moistrxre 

(3. A. Kong), -, Houston, Texasts, December 1-2, 1982. 

Thermal microwave elrrission from a scattering medium with rough surfaces (R. 

Shin and J. A, Kong), URS'J:osiua, Boulder, Colorado, Jmuary 6-7, 1983, 

Remote sensing of soil moisture and vegetation (3. A. Kong, S. L. Lin, S. L. Clxumg, 

md R. T', Shin), YRSI Syl~lposiztq, Boulder, Colorado, January 5-7, 1983. 

Mie scattering ~f electromagnetic waves by precipitation (Y. $. Jin, and J, A. 

Kong), O~tical Societv of America TopicaI Meetinn on Optical Tecbniuues fo~ 

&&, Lake Tahoe, Nevada, January 10-12,1983. 

Scattering of electromagnetic waves from a half-space of densely distributed dielectric scrctterers (L, Tsang and J. A. Kong), XEZE,/APS Svmn~~sium asad rm Jag1, T 

Meeting, I-Iouston, Texas, May 23-26, N83. 

Theory of microwave remote sensing of dense medium (L. Tsang and J, A. Kong), 

URSI Symposium, San Francisco, 1983, 

Wave scettsring by a bounded layer of random discrete scatterers (Y. Q. Jin and 

J. A. I<ang), National Radio Science Meeting, Boulder, Colorado, Januaay 11-13, 

1934. 

Scattering of electromagnetic waves by a randomly perturbed quasi-periodic surface (R. T. Shin and J. A. Kong],National Radio Science Meeting, Boston, Massachusetts, June 25-28, 1984. 

Modified radiative transfer equation in strong fluctuation approach (Y, Q. Jin md 

3. A. Mong], National Radio Science Meeting, Boston, Massachusetts, June 25-28, 

1984. 

Active and passive microwave remote sensing of layered misotropic random 

medium (J. K, Lee and 3. A. Moag), National Radio Science Meeting, Boston, 

Massachusetts, June 25-28, 1984. 

Strong filzctuation theory of rmdom medium and applications in remote sensing (Y. 

Q. Sin <and J. PI. Kang), InternationaI Ssm~osium on Antennas EM Theory 

{ISAEj, Beijing, China, August 24-26, 1985. 
TI. 

T2. 

T3, 

T4, 

TS. 

Emissivity of a two-layer random medium with anisotropic correlation function, 

(E, T, Shin ad J. A. Kong), Technical Report No. EWT-RS-41-8303, MlTI 1983. 

Estimation of snow depth with measured brightness temperatures (11. 2. Wang), 

Techical Report No. EWT-RS-43-8304, MXT, 1983, 

Estimation of snow dcpth from backscattering cross scction obtained from active 

microwave remote sensing (H. Wmg), ~echniccll Report No. EWT-RS-45-8306, 

MfT, 1983. 

Extended boundary condition approach to wave scattering by periodic structures 

(S, L. Chumg and 3. A. Xo~lg), Technical Report No. EWT-RS-55-8312, MXT, 

6983. 

h4icrowave remote sensing of a scattering medium with rough surfaces (R. T, Shin 

and J. A, Kong), Technical Report No. EWT-RS-84-8402, MIT, 1984. 

Modified radiative transfer equation in strong Buct~tatition approach (Y. Q. Jin md 

3. A. Kong), Technical Report No. EWT-RS-67-8406, MIT, 1984. 

Active microwave remote Sensing of an canisotropic ranclom ~nediu~n layer (J. K. 

Lee and J. A. Kong), Technical Report No, EWT-RS-68.8407, MIT, 1984. 

Behavior of circularly polarized waves in active remote sensing of two-layer random 

media (F. C. Lin), Technical Report No. EW'f-RS-70-8410, MIT, 1984, 

Wave approach to brightness temperature from a bounded layer of random discrete 

scatterers (Y. Q. Jin), Technical Report No. EWT-Its-71-8412, MI'S, 6984. 

Lin, Sching Lih, cTMicrowave thermal emission from a periodic surface," S.M. Thesis, May 1983. 

Park, Dongwsok, "Passive remote sensing of layered random media with strong 

permittivity ~uctuations," S.M. Thesis, May 1984. 

Shin, Robert Tong-ik, "Theoretical models for microwave remote sensir;lg of earth 

terrain," Ph.D. Thesis, September 1984. 

Jin, Ya-qiu, "Strong fiuct~lation theory for a bounded layer of random discrete 

scatterers," Pb.D. Thesis, Januaty 2985. 

Lee, Jay Kyoon, "Electroilzagnetic wave propagation and scattering in layered 

misotropic random medium," Fh.D. Thesis, Jan~iizry 1985. 
BISCRE'TE RANDOM MEDIA TECHNIQUES FOR 

MICROWAVE MODELING OF VEGETATED TERRAIN 

Roger N. hang 

Referred Pub1 icat ions 

Electromagnetic Backscattering horn rt Layer of Vegetation: A Di screte 

Approach, with 3,s. Sidhu, IEEt-GE-21, p. 62-71, 1983. 

Scattering Prom Arbit rarkl y Oriented Dielectric Disks in the Physieal 

Optics Regime, with D.M. LeVine, R. 19enegI.rini, S.S. Seker, JOSA, 73, p. 

1255-1 262 1983. 

Scattering From Thin Dielectric Disks, with CeV ine, Schneider and 

Carter, NASA TM 86155, 1984. To be submitted to IEEE-APS, 1985. 

Microwave Inversion of Leaf Area and Inclination Angle Distributrions 

From Sackscattered Data, with H.A. Saleh, submitted for publication in 

Special Issue of IEEE Trans. on GeoSci. and Remote Sensing, 1985. 

Vector Solution for the Mean Electromagnetic Fields in a Layer of Random 

Particles, with Seker and LeVine, to be submitted to Radio Science, 1985 

Present at ions 

Backscattering from a Vegetation Layer - A Multiple Campanent Madel, 

with LeVine, presented at URSI, Boulder, CO, 1983. 

Mean Wave Propagation in a Trunk Dominated Forest, with A. Schneider and 

S. Seker , presented at IEEE/URSI Symposium, Houston, TX, 1983. 

Backscattering from a Vegetation Layer-Coherent and Incoherent Models, 

presented at URSI Commission F Symposium on Microwave Signatures in 

Remote-Sensing, Toulouse, France, 1984. 

Discrete Scattering Models for Remote Sensing, seminar at NASA Goddard 

Space Flight Center, Greenbelt, MD, 1984. 

Scattering From Thin Dielectric Disks with D. LeVine - presented at 

IEEE/AP§ URSI Meeting, Boston, MA, 1984. 

Inverse Solution for a Slab of Randarn Dielectric Discs: Orientation and 

Area Distributions, with H. Saleh, to be presented at IEEE/APS URSI 

Meeting, Vancouver, Canada, 1985. 

The Relationship Between the Field Correlation Function and the Specific 

Intensity, with A. Ghuniem, to be presented at: IEEE/APS URSI Meeting, 

Vancouver, Canada, 1985. 
MEASURING AND MODELING OF THE DIELECTRIC 

PROPERTIES AND ATTENUATION OF VEGETATION 

Fawwaz T. Ulaby 

Refereed Journal Publicarions 

Ulabv, F. T.. and R. P. Jedlicka, "Microwave Dielectric 

~ro~krties oi! Plant Materials, I' IEEE Transactions on Geoscience 

and Remote Sensin$, CE-22, pp. 406-414, July 1984. 

Brunfeldt, D. R., and F. T. Ulaby, "Measured Microwave Emission 

and scattering in Vegetation canopies, " IEEE Transactions on 

Geoscience and Remote Sensing, GE-22, pp. 520-524, November 1984. 

Ulaby, F. T., Me Razani, and M. C. Dobson, "Effects of Vegetation 

Cover on the Microwave Radiometric Sensitivity to Soil Moisture," 

IEEE Trans. on Geoscience and Remote Sensing, GE-21, N.l, pp. 

51-61, January 1983. 

Brunfsldt, D. R., and F. T. Ulaby, "Microwave Emission from Row 

Crops," submitted to IEEE Trans. on Geoscience and Remote Sensing. 

Ulaby, F. T., and E. Wilson, "Microwave Attenuation Properties of 

Vegetation Canopies," submitted to IEEE Trans. Geoscience and 

Remote Sensing SRAEC Special Issue. 

Allen, C. T., and F. T. Ulaby, "Modeling the Polarization 

Dependence of the Attenurtion in Vegetation Canopies," submitted 

to IEEE Trans. on Geoscience and Remote Sensing. 

Symposia 

Jedlicka, R. P., and F. T. Ulaby, "Measurements of the Microwave 

Dielectric and Attenuation Properties of Plants," National Radio 

Scfence Meeting (URSI Commission F), University of Colorado, 

Boulder, January 5-7, 1983. 

Brunfeldt, D. R., and F. T. Ulaby, "Measured Microwave Emission 

and Scatter in Vegetation Canopies," IEEE International 

Geoscience and Remote Sensing Symposium (IGAKSS '83), San 

Francisco, California, August 31 - September 2, 1983. 
Ulaby, F. T., "Microwave Properties of Vegetation Canopies: An 

Overview," International Colloquium on Spectral Signatures of 

Objects in Remote Sensing, Bordeaux, France, September 13-16, 

1983. 

Ulaby, F. T., R. P. Jedlicka, and C. T. Allen, "Measurements of 

the Sources of Scatter from Vegetation," Microwave Signatures in 

aote Sensing (URSI Commission FIa Toulouse, France, January 

5-20, 1984. 

Brunfeldt, D. R., F.T. Ulaby, and M. C. Dobson, "Active and 

Passive Observations of Vegetation Canopies," Microwave 

Signatures in Remote Sensing (URSI Commission F), Toulouse, 

France, January 16-20, 1984. 

Allen, C. T., and F. T. Ulaby, "Modeling the Polarization 

Dependence of the Attenuation in Vegetation Canopies," LEEE 

International Geoscience and Remote Sensing Symposium (IGARSS 

'84) , Strausbourg, France, 27-30 August, 1984. 

Brunfeldt, D. R., and F. T. Ulaby, "The Effects of Row Direction 

on Microwave Emission from Vegetation Canopies," IEEE 

International Geoscience and Remote Sensing Symposium (IGARSS 

'841, Strasbourg, France, 27-30 August, 1984. 
PUBLICATIONS AND PRESENTATIONS 

Determination of Backscntterina Sottrces in Various Targets 

R .K. Noore, principal Investigator 

1. Refereed Journal Articles 

"Determination of Rackscatter Sources in Surface Type Targets," R. Zoughi, 

R.K. Moore, L.K. \?u, F.T. Illaby and A. Afifi, to be published in 

International Journal of Remote Sensix, 1985. 

"Preliminary Results on the Determination of the Sources of Scattering from 

Vegetation Canopies at 10 GHz," L.K. Wu, R.K. bloore, R. Zoughi, F.T. 

Ulaby and A. Afifi, to be published in International Journal of Remote 

Sensing, 1985. 

"SOURCESCAT: A Very-Ff ne-Resolution Radar Scat terometer , " R. Zoughi , L.K. Wu 

and R.K. Moore, submitted to Microwave Journal, 1984. 

2. Conference and Symposia Presentations 

"Measurements of the Sources of Scatter from Vegetation," R.R. Moore, R. 

Zoughi, E.K. Wu, A. Afifi and F.T. Ulaby, presented at the llRS7: 

Specialists Symposium, Toulouse, France, January 1984. 
APPEND XX 
APPENDIX A. THIRD ANNUAL PRINCIPAL INPRSTIGATOR WORKSKOP-- 

INVITATION LETTER AND AGENDA 
National Aeronautics and 

Space Administration 

Goddard Space Flight Center 

Greenbelt, Maryland 

20771 

Reply to Attn ot 623 

Dear Col league: 

Trivia question No. 1: "Which state of the original thirteen was 

the sixth admitted to stateliood in 1788 and has a land area of 8,257 

square miles?" Trivia question No, 2: "Which city in that state 

has we1 l-known institutions of higher learning that were established 

? ,r 1636 and 1861?" Trivia question No. 3: "When and where is the 

thi rd annual qRAEC PI 's meeting going to be he1 d?" The annual 

gabhering of the NASA Fundamental Remote Sensing Science Research 

P~ogram' sScene Radiation and Atmospheric Effects Characterization 

Project's principal investigators is not a trivial event, this 

year especially, as each of you will be reporting the results and 

significance of three years of research! This letter is to 1) 

confirm the time and place for the meetping, 2) advise you concerning 

fol 1 ow-up communications concerning the meeti ng, and 3) inform you 

of the preparations that you should make for this meting. 

As you have been informed via telecon, the third annual SRAEC PI'S 

meeting will be held on the campus of the Massachusetts Institute 

of Technology in Cambridge during the last three days of January 

(29, 30, and 31) 1985. Dr. Jin Kong has graciously offered to host 

this meeting and is making the necessary local arrangements and 

finalizing the agenda for the meeting. Dr. Kong will be sending 

you further details concerning these items within the next few 

days. It might be useful to mention at this time however that a 

special hotel room rate has been negotiated and a block of rooms 

have been reserved for our group at the nearby Sonesta hotel. 

I'm very pleased that at this time it appears that we may have a 

100% P.I. participation at this meeting. I want to encourage you 

to make every effort to attend the entire three days of the meeting. 

We are planning to take a group photo at this meeting and I would 

like everyone in the picture. More important, however, is that we 

want full participation in the results reporting and research issues 

di scussi ons. 
This meeting, and your individual reports, will be focused on summarizing 

the significant contributions that these past three years of fundamental 

research have made to the remote sensing scientific community. In addition 

Lo learning about the more technical details and specific progress that has 

been made in your more focused research activity, we all together need Lo 

be able to summarize the new insights that have been gained, the remote 

sensing problems that have been solved and, in general, what benefit this 

project has provided to NASA and the remote sensjng and broader scient.1 fic 

communities, Gle need to collectively address a few key research issues and 

what are the new research priorities, based on what we have learned. Thus, 

we need to spend some "qua1 ity time" that wi 11 help both direct and defend 

thi s program. 

In addition to bringing your body and mind to this meeting, I need you to 

bring with you a brief written summary of your research that will be compiled 

with the summaries from all of the PIS into an annual report. This year I 

am asking for a single written report that fa1 1s somewhere between the 

"investigation Summary Results Abstracti' and the "Investigation Synopsi st' 

that you prepared last year. I need a succinct report that is introduced 

by a paragraph on the justification, goals and objectives for your research 

(the broader two or three year plan). This should be followed by a paragraph 

describing your technical or experimental approach. A discussion of the 

research results should then follow and can use up to three key figures to 

illustrate your findings. The final one or two paragraphs should high1 ight 

the significance of your results and (briefly) what the next major step 

should be in the logical progression of your research focus. This report 

should be a minimum of two and a maximum of four single-spaced typewritten 

pages, excludi ng figures, Figures should be suitable for reproduction 

(clearly readable) at one-half of full size as submitted to me on 8 112" x 

11' paper. As the heading at the top of the fi rst page you should include 

the descriptive title of your study (all capital letters), your name (first) 

and then any co-investigator's names, and your institutional affi 1 iation 

beneath the names. 

On a separate page (typed single-spaced with a double space between entries) 

you shou? d i nc? ude your 1 .C st of pub1 i cat i ons and presentat i on2 that have 

resulted from your funding f ram the SRAEC Project. You should give your 

study title and your name (as PI) only at the top of this page followed by 

a separate listing of 1) refereed journal publications and 2) symposia and 

conference presentat ions. 

Please adhere to the limi ts given above ir! preparing your report. Remember 

that this report is not a journal paper hut rather is intended for a 1 ess 

technical readership (i .e, , scientists from other di sci pl ines and research 

program managers ) and should be written to provide an interesting overview 

of your work. Your journal papers are available for anyone who needs or 

wants a1 1 the details and highly speci Picltechnical results. He1 p me put 

together a report that will enable us to keep this program alive and well 

within NASA during this era of significant government budget cutting. 

Your oral report' should be prepared as last year, a1 lowi ng 15-20 minutes 

for presentation and 20 minutes for discussisn. One final topic concerns 

the IEEE Transactiui?~ on Geoscience and Remote Sensing "Special Issue on 

Scene Radiation and Atmospheric Effects Characterization". For various 
reasons the communication concerning the dead1 i nes for thi s special transactions has not been what it should have been. Nevertheless, the current "deadline" 

for you to submit five copies of your paper (to Bob Murphy) for the September 

1985 specical issue is December 15, 1984 (moved back from the original September deadline). However, I have spoken with the editor and he has 

indicated that they can be submitted later than this date but the probability 

of their being reviewed, revised and re-submitted in final form in time 

for this special issue decreases with each week past this deadline. Probably 

early January will be sufficient time. Please submit your paper as soon 

as possible, as we would like a paper Prom each one of the PIS in the 

SRAEC project. 

Shank you for your eagerness to participate and future help in making this 

year's meeting a success. If you have further questions please feel free 

to call me at (301) 344-9186 or Jin Kong at (617) 253-5625, as appropriate. 

I look forward to seeing you again in January. 

Sincerely, 

\ 

Donald W. fleering \. 

Earth Resources Branch \ 

Laboratory for Terrestri a1 Physics 

P.S. Answers to Trivia Questions: 

1. Massachusetts 

2. Cambridge (Harvard, MIT) 

3. January 29-31, 1985; Cambridge, MA 
Third Annual Meetiaag of the NASA Rmdmemtd Research Sccxae Brndiat:on 

and Atmospheric Effects Characterization 

January 29-31,1985 

Tuesday, January 29, 1985 

09:OO-09:20 MIT Welcome (Jon Allen) 

09:20-09:50 NASA Welcome and Meeting Objectives (Don Deering) 

09:SO-10:30 Invited Speaker Men Hardy on applications of satellite data for meteorological analysis . 10:30-11:OO Coffee Break 

10:OO-12:OO - PI Reports (Gerst1,Diner) 

Lunch 

13:OO- 15:OO PI Reports (Fraser,Pezl~ce,Badhwar,VanderbiIt) 

15:OO- 1 5:30 Coffee Break 

15:30-3 7:OO PI Reports (Kimes,Smith,Strahler) 

18:OO Reception, MPT Faculty Club 

Wednesday, January 30, 1985 

09:OO-I 0:30 PI Reports (Norman ,Paris,U!aby) 

lo:30-10:15 Coffee Break 

10:45-12:15 PI Reports (Fung,Kong,Moore) 

Luncli Photo opportunity 

13:OO-15:(10 PI Reports (Lang,Conel,Irons,Kahle) 

15:OO-15:3O Coffee Break 

15:30- 16:OO Canopy model inversion (Goel) 

16:OO-17:30 Presentation and discussion on proposed artificial canopy experiment 

(Chair: Gerstl) 

Thursday, January 31, 1985 

09:OO-09:30 Invited Speaker Dave Staelin on Retrieval Techniques for Atmospheric Profiling 

09330-1 0:OO Report on ISLSCP-FIFE (John Norman) 

10:OO-10~30 NASA Headquarter Management Perspective (Bob Murphy) 

Coffee Break- - 

Discussion on project accomplishments 

tions (Chair: Smith and Ulaby) 

and future research direcLunch 

13:OO-14 :30 Research topic discussions and working papers 

14:30-15:OO Coffee Break 

15:OO-17:OO Written summary for project accomplishments and. future research 

recommendations 
APPENDlX Be THIRD ANNUAL MBETING PARTICIPANTS-- 

LIST AND PBOTO 
TBXRD ANHUAL MEETING OF THE NASA FUNDMN3AL RESEARCH 

SCENE RADIATLON AND ATMOSPHERIC EFFECTS CHARAC!PERIZATTQN 

Jonathan Allen 

Dlxector 

Research Laboratory 

for Electxonics 

Massachusetts Institute 

of Technology 

Room 36-143 

Cambridge, MA 02139 

Gautam Badhwar 

NASAlLyndon B . Johnson 

Space Center 

Code SN3 

Houston, TX 77058 

Mary Jane Bartholomew 

Geologist 

NASA/Jet Propulsion Laboratory 

4800 Oak Grove Drive 

MS 183-501 

Pasadena, CA 9 '1 109 

James E. Cone1 

NASA/Set Propulsion Laboratory 

Mailstop 183-501 

4800 Oak Grove Drive 

Pasadena, CA 91109 

Donald W. Deering 

NABA/Goddaxd Space Flight Center 

Code 623 

Greenbelt, MD 20771 

Uavid J. Diner 

NASA/Jet: Propulsion Laboratory 

Mailstop 183B-365 

4800 Oak Grove Drive 

Pasadena, CA 91109 

Robert E. Fxaser 

NASA/Goddard Space Flight Center 

Code 613 

Greenbelt, MD 20771 

Adrian K. Fung 

Electrical Engineering 

Department 

University 02 Texas 

at Arlington 

BGX 19016 

Ilrlington, TX 76019 

Siegfried A.W. Gerstl 

Theoretical Division 

Los Alamos National Laboratory 

MS-B279 

Los Alamos, NM 87545 
Narendra 9. Goel 

Aster Consulting Associates, Xnc . 4245 Plarietta Drive 

Binghamton, NY 13903 

Vince Gutschick 

Staff Henaker 

Loa Alamos National Laboratory 

P.0. BOX 1663 

EfSF 371 

Los Alamos, PTM 87545 

Ken Hardy 

Division Chief 

Geophysics Laboratory 

Hanscoln Air Force Base 

Lexington, EIA 02173 

Jim Xrons 

NASA/Goddaxd Space Flight Center 

Code 623 

Greenbelt, MD 20771 

Anne B. Kakle 

MASA/Je t ~rcupuls'ion Laboratory 

Mailstop 183-501 

4800 Oak Grove Drive 

Pasadena, CA 91 109 

Daniel S. Kimos 

N&SA/Goddard Space Flight Center 

Code 623 

Greenbelt, MD 20773 

J&n-Au Kong 

Research Laboratory 

gor Electronics 

k4essachusetts Xnstitute 

of Technology 

Cambridge, MA 02139 

Roger H. Lang 

Department of ElectrlEal 

Engineering 6 Computer Science 

George Washington University 

Washington, DC 213052 

Richard K. Moore 

Center fox Research 

University of Kansas 

2291 Xrving Hill Drive - Campus 

Lawrence, KS 66045 
John 8. Noman 

Department of Agronony 

UnivereiQ? oE Nebraska 

LfncoZn, NE 68583 

;Tack P. Paris 

NASA/Jet Pr:opaSsion Laboratory 

Ihilstop 183-701 

4800 Oak Grove Drive 

Pasadena, CA 91109 

WillYau A. Pearoe 

EG&G Washizrgton Ana2yticml 

Services Center X 

6801 KenSlworth Avenue 

Riverdale, NO 20757 

Cletrrea Simer 

Staff Member 

Los Alamos National Laboratory 

P.0. BOX 1663 

MSP 371 

Los Alamos, NM. 87545 

James A. Smith 

College of Poresfry & 

Natu?aZ BsQu~C88 

Colorado State Ui~iversi ty 

Fort ColZins, CQ 80523 

David H, Staelin 

Professor 

Electrical Engineering €4 

Coaputer Scf ence 

Massachursetfa Znslitutrs 

of Technology 

Room 26-339 

Canbridge, MB 02139 

Alan H. StrahZer 

Department of Geography 

Hunter CoSlege 

695 Park Avenue 

Box 1513 

New York, NY 10021 

Fawwaz T. Ulaby 

RadiatSon Laboratory 

The University of Michigan 

Wpartraent efi' Eleelrfcar 6i 

Compueer Engineering 

4072 East Engfneering Building 

Ann Arbor, ML 48109 

Vernan @. Vaadexbilt 

XIARS/Purdue University 

West LafayetLe, 3W 17907 
Pigsre 1-1, Partiefpaats st the Third Anngal %P&BC Pf Vartahap oa the e&%pu@ sf 

%1T an 3aa~@ry 3Q, E985% The gark%ciga%tr spa; ~lefl tc r%@ktj %a%@ tcaghf, 

Vine@ Quksehxek, Boa B&ariag, 3fa Srith, It%%&, Xary 9~ne larthafs~ew, Peesag 

UtaBy, goqtr &&=a, aautaa ladhua~~, Cleres Sa%ser, Je&n #erg&%, Bia~ Biaer, Yarn 

Va~derbilt, S%agfsied Gdk&%l, &%X>F% Qoc~$ %1Xl P6a~ee, &n% Bbhle* Biek @OQ~C~ 

Jaek Paris, Ji@ Iraas, &&r%aa Fun&, Jia Csn~?, Dawn& StacXf&, Jfn longs hLaa 

Strahiar, Beb Praaer* 
APPBNDfX C. MESSAGE TO F3s FROM DR. MURPHY 
Posted: Tflu Jan 31, 1985 10:28 AM FST 

From: REMURPHY 

To: DDEERING 

Subj: RE: Message to SRAHC PIS 

DON, Please read this note to the troops for me. 

Msg: XGIF-1963-1511 

I am sorry that I am not able to be with you at the 4th (can it really 

be the 4th?) meeting of the SRAEC principal investigators. My new job has had 

me on the road more than half of the time. I just couldn't do this one, both in 

terms of the backlog at my desk and the impact on my family. 

I just returned from Geneva where I secured the blessing of the World 

Meteorlogical Organization for the International Satellite Land Surface 

Climatology Project (better known to its progeniters as ISLSCP). This was a 

major step forward in the process of orienting NASA's program to scientific 

goals. There is a description of ISLSCP activities in the current Space Science 

and Applications Notice which you should all have received. If you didn't see 

it, 0on Bering, Bob Fraser and John Norman know everything you need to know 

about ISLSCP. There are also several reports by working groups which are 

availrtbte from Ron Witt (for retrospective studies) or Piers Sellers (for the 

field experiments). Both are at Goddard, That program should provide some of 

the focus for the application of the your SRAEC efforts in the future. (You may 

recall ehae 1 said that cultural crops where not the focus anymore. Here is one 

of the alternatives.) 

We are attempting to generate some other foci for the program. Berrien 

Moore of the University of New Hampshire is chairing a subcammittee of the 

Earth System Sciences Committee which deals with the Land Processes. We had a 

very successful meeting at UNH in November, and Jim Smith is organizing a 

follow-on meeting next month at Goddard to discuss measurement and modeling 

strategies. The Berriens committee meets again in March at Oregon State. Out of 

these meetings I expect some more fruitful directions. 

The work of the SRAEC group will be at the center of all that we will 

be doing. I hope to have a meeting of all PI'S in the total program sometime 

later this year so that all can benefit from the type of interaction you are 

having now. 

A not quite pleasant topic to bring up is the IEEE special issue. A few 

of you (and you know who you are!) still owe me your papers. Soon! (please?) 

What we have so far looks great. 

To return to pleasant things, I will be looking forward to receiving 

your renewal proposals over the next few months. There is much left to do, and 

you guys can do it. If you have questions about the nature of desireable work 

you can talk with Don or me. I will conduct the peer review from NASA HQ, but 

will do so in close coordination with Don and I will look to him for 

programatic guidance. 

As for the future of the Land Processes Program, I think that it looks 

good. This year we are (I hop) at the nadir of our funding with 5M$ less than 

fiscal year 84. Total useful funding this year is about 12 M$ for Geology, 
Ilydrology, Terrestrial Ecosystems, Remote sensing Science (thats you) and 

Applications. For next year, we have received high priority within NASA for an 

augmentation. Listen to President Reagan's budget message next week and see if 

he mentions us by name (HA!). 

If we do receive that augmentation their can be some improvemect in our 

average funding levels as well as the addition of new activites and some 

further upgrading of facilities. Things like the artificial canopy can proceed 

out of our existing funding base if someone redirects their curent work if we 

don't get the augrnenaition, or it can Ix an add on if we get it. (This, of 

course, asumes that it passes muster in terms of the programatis and peer 

review. Your input through Don from this workshop will shap the programatis; 

peer review will be according to pur usual capricious standards!) 

As you know, we had a successful shuttle flight this past year. While 

we got only a fraction of the SIR-I3 data that we hoped for, there is much good 

science ahead in the analysis of it. SIR-B will be reflown in early 1987 and 

SIRC will follow about a year later. We are hopeful of flying the Shuttle 

Imaging Spectrometer Experimet (STSEX) also in the 80's. Our aircraft 

capabilities are gradulaly being upgraded and we know have semi- operational 

bidirectional measurement capabilities from the air as well as the Airborne 

Imaging Spectrometer (AIS) , the Thermal Imagging Mapping Spectrometer (TIMS), 

a quad-pol SAR and a 4 beam L-Band pushbroom radiometer. 

I know I've left somethings out, and I am typing this while I am in 

transit to yet another meeting. So please excuse the rambling and incomplete 

nature of it. Keep up the good work. I hope to see you next year if not sooner. 

Perhaps at the IGARS meeting at UMASS. 

Bob 
BfSLEBGRleaPHIC DATA SHEET 

arth Resources Branch 

ASA Goddard Space Flight Center 11. Contract or Grant No. 

reenbelt, ~aryland 20171 

13. Type of Report 

2. Sponsoring Agency Name and Address 

ASA Readquarters 

ashington, DC 14. Sponsoring Agency Code 

I 1 

I 15. Supplementary Notes I 

The Scene Radiation and Atmospheric Effects Characterization 

SRARC) Project was established within the NASA Fundamental 

emote Sensing Science Research Program to improve our underLanding of the fundamental relationships of energy interactions 

etween the sensor and the surface target, including the effect 

f the atmosphere. The current studies are generalized into the 

ollowing five subject areas: optical scene modeling, earthpace radiative transfer, electromagaetic pmperties of surface 

atesials, microwave scene modeling, and scatterometry studies. 

his report has been prepared to provide a brief overview of the 

RAEC Project history and objectives and to report on the 

cientific findings and project accomplishments made by the 

inateen principal investigators since the project9s initiation 

ust over three years ago. This annual summary report derives 

rom the most recent annual principal investigators meeting held 

anuary 29-31, 1985. 

17. Key Words (Selected by Author(s1) 1 18. Distribution Statement I 

cene radiation 

tmoopheric effects 

icrovaave 

~t ical-r.ef lect ive I 

9 curiey. qsif (of this report) 20. Securi y Classif (of t is page) unc?aseassx?red uncrassifzea 

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