BOREAS RSS-07 LAI, Gap Fraction, and fPAR Data

Summary

The BOREAS RSS-07 team collected various data sets to develop and validate an 
algorithm to allow the retrieval of the spatial distribution of LAI from 
remotely sensed images.  Ground measurements of LAI and FPAR absorbed by the 
plant canopy were made using the LAI-2000 and TRAC optical instruments during 
focused periods from 09-AUG-1993 to 19-SEP-1994.  The measurements were 
intensive at the NSA and SSA tower sites, but were made just once or twice at 
auxiliary sites.  The final processed LAI and FPAR data set is contained in 
tabular ASCII files.

Table of Contents

   *  1.  Data Set Overview
   *  2.  Investigator(s)
   *  3.  Theory of Measurements
   *  4.  Equipment
   *  5.  Data Acquisition Methods
   *  6.  Observations
   *  7.  Data Description
   *  8.  Data Organization
   *  9.  Data Manipulations
   *  10. Errors
   *  11. Notes
   *  12. Application of the Data Set
   *  13. Future Modifications and Plans
   *  14. Software
   *  15. Data Access
   *  16. Output Products and Availability
   *  17. References
   *  18. Glossary of Terms
   *  19. List of Acronyms
   *  20. Document Information

1. Data Set Overview

1.1 Data Set Identification

BOREAS RSS-07 LAI, Gap Fraction, and fPAR Data

1.2 Data Set Introduction

Ground measurements of Leaf Area Index (LAI) and the Fraction of 
Photosynthetically Active Radiation (FPAR) absorbed by the plant canopy were 
made in the BOReal Ecosystem-Atmosphere Study (BOREAS) Northern Study Area (NSA) 
and Southern Study Area (SSA) using optical instruments.  The instruments used 
were the LI-COR LAI-2000 and the Tracing Radiation and Architecture of Canopies 
(TRAC), which was developed at the Canadian Centre for Remote Sensing (CCRS).  

1.3 Objective/Purpose

The objectives of this project were to:

1. Obtain LAI and FPAR for the tower sites in both the BOREAS SSA and
   NSA.
2. Describe the spatial variability of LAI and FPAR for the sites.
3. Compare methods for indirect measurements of LAI and FPAR. The
   methods included the LAI-2000 plant canopy analyzer and a sunfleck-LAI 
   instrument, called the TRAC, recently developed at the CCRS.
4. Develop algorithms for retrieving LAI and FPAR from Landsat Thematic Mapper
   (TM) and Advanced Very High Resolution Radiometer (AVHRR) data.
5. Investigate the effect of plant canopy architecture on indirect
   measurements of LAI and FPAR.
6. Scale up LAI and FPAR measurements from submeter to km scales National
   Oceanic and Atmospheric Administration (NOAA) AVHRR pixel scale).

1.4 Summary of Parameters

The following parameters were used:

1. LAI-2000:  effective LAI
2. TRAC:  indirect LAI, foliage clumping index, FPAR, PAR albedo of forest floor
3. Destructive sampling:  ratio of needle area to shoot area

1.5 Discussion

Measurements of LAI were made using two or three units of the LI-COR LAI-2000 
plant canopy analyzer. Data were acquired along three 170-m - 300-m parallel 
transects separated by 10 m at the tower sites and along 50-m transects at the 
auxiliary sites.

On the same transects, the TRAC was also used to measure LAI, the clumping 
index, and canopy architectural parameters.

The clumping effect within shoots was determined from laboratory analysis on 27-
45 shoot samples for each conifer tower site using a video camera-computer 
system.

1.6 Related Data Sets

BOREAS RSS-04 1994 Southern Study Area Jack Pine LAI and fPAR Data
BOREAS TE-23 Hemispherical Photography for Calculating Radiative Transport, LAI
BOREAS TE-06 1994 Tower and Carbon Evaluation Site Allometry and Biomass Data

2. Investigator(s)

2.1 Investigator(s) Name and Title

Jing M. Chen, Ph.D.
Research Scientist

Josef Cihlar, Ph.D.
Senior Research Scientist

Margaret Penner, Ph.D.
Research Scientist

2.2 Title of Investigation

Retrieval of Boreal Forest Leaf Area Index From Multiple Scale Remotely Sensed 
Vegetation Indices

2.3 Contact Information

Contact 1
---------
Jing M. Chen
Ottawa, Ontario
(613) 947-1266  
Chen@ccrs.emr.ca 

Contact 2
---------
Josef Cihlar 
Ottawa, Ontario
(613) 947-1265
Josef.Cihlar@geocan.emr.ca

Contact 3
---------
Jaime Nickeson
Raytheon STX Corporation
NASA/GSFC
Greenelt, MD 
(301) 286-3373
Jaime.Nickeson@gsfc.nasa.gov

3. Theory of Measurements

Parameter definitions for background:

1) LAI

LAI is defined as one half the total green leaf area per unit ground surface 
area.  It has been demonstrated independently by Lang (1991) and Chen and Black 
(1992a) that this definition is correct for non-flat leaves (including conifer 
needles) of convex shapes, and it is incorrect to define LAI on the basis of the 
largest projected area as commonly done before.

It must be pointed out that this definition is given based only on radiation 
interception by leaves. Plant physiologists concerned with gas exchange and 
stomatal density and distribution may prefer staying with the total leaf area 
(in case of concave leaves) or the projected area.  It is therefore necessary to 
know the shape factors that convert between these areas.

2) PAI

PAI is defined as one half the total area of all above-ground plant materials 
per unit ground surface area.  The plant materials include leaves, branches 
(live or dead), boles, and attachments to plant parts such as lichen and moss.  
Without the knowledge of the contribution from each of the components, all 
optical instruments can measure only PAI rather than LAI.

3) Effective LAI (Le)

The term "effective LAI" was used by Chen and Black (1992b) in their earlier 
papers for the need to provide a measure for the effect of non-randomness of 
foliage spatial distribution on indirect measurements of LAI.  For conifer 
forest stands, the effective LAI is considerably smaller than LAI (usually 50%) 
because leaves are grouped together in tree crowns, branches, shoots, and so on.  
The grouping or clumping of foliage reduces the light interception and hence 
effectively reduces LAI derived indirectly from the measurements of canopy gap 
fraction using equipment such as the LI-COR LAI-2000, hemispherical photography, 
tram, or moving light sensors. The definition of the effective LAI is: 

Effective LAI = Foliage Clumping Index * LAI                                (10)

The foliage clumping index is smaller than unity for conifer and deciduous 
stands (usually 0.5).

The LI-COR LAI-2000 measures canopy gap fraction and derives LAI from the gap 
fraction under the assumption that the foliage elements are randomly distributed 
in space.  Therefore, it measures only the effective PAI (or loosely effective 
LAI) rather than LAI when the foliage is not random. It is therefore meaningful 
to report the popular measurements as effective PAI or LI-COR LAI. 

Although the effective LAI measured by the LAI-2000 is not LAI, the measurements 
are still very valuable for estimating the gap fraction and light interception 
(FPAR and Absorbed Photosynthetically Active Radiation [APAR]) by the canopy, 
and therefore they should be reported as raw data.

4) Direct LAI and PAI

Direct LAI and PAI are measured directly through destructive sampling.  In the 
measurements, relationships may be used between leaf area and leaf fresh or dry 
weight, between total leaf area in a branch and the branch diameter or branch 
weight, and between total leaf area in a tree and the tree diameter at breast 
height (dbh). In other words, some degree of indirectness may still be involved.

5) Allometric LAI and PAI

These are obtained using pre-established relationships between leaf area and dbh 
or sapwood area. Sometimes an additional parameter such as crown width, crown 
length, or an index related to the tree density is used.

6) Indirect LAI and PAI

Indirect LAI and PAI are measured indirectly using optical instruments or by 
other means. The effective LAI (or more precisely the effective PAI) measured 
using the LAI-2000 may be corrected to obtain the indirect LAI or PAI. Much 
research has been done on making such corrections for conifer stands. The 
corrections include:

   i) Needle-to-shoot area ratio (gamma): 
      Rationale:  Conifer needles are tightly grouped together in shoots (an 
      important scale of foliage clumping), and shoots can be treated as the 
      basic foliage units responsible for light interception.  This ratio 
      quantifies how much leaf area there is in an average shoot area (if a 
      shoot projection can be approximated by a sphere, it is half the sphere 
      surface area),  which is believed to be the quantity measured by the LAI-
      2000.  Gower and Norman (1991) successfully applied this type of 
      correction to conifer stands of several species.  Further investigation 
      has been made by Fassnacht, et al. (1994).  The only underlying assumption
      for making this correction is that shoots are randomly distributed in 
      space.

  ii) Shoot clumping index (omega)
      Rationale:  To consider the effect of clumping at scales larger than 
      shoots.  For open conifer stands, shoots are obviously grouped into tree 
      crowns; i.e., the assumption of random spatial distribution of shoots is 
      not met.  In this case, an additional parameter concerning foliage 
      clumping at scales larger than the shoot scale becomes very important
      (Chen and Black 1992a).

      Shoot clumping index accounts for the effect of foliage clumping at scales 
      larger than shoots.  It can be obtained from analysis of canopy gap size 
      information (Chen and Black, 1992b).  The TRAC, developed by RSS-07 at
      CCRS, is designed to measure sunfleck sizes along straight transects on
      the forest floor, from which a distribution of canopy gap size is 
      obtained.  Measurements using the TRAC show that the shoot clumping index
      is about 0.70-0.80 for most conifer stands.

 iii) Woody-to-total area ratio (alpha):
      Rationale:  Woody and other nonfoliage materials can have an important 
      contribution to light interception in the canopy, and optical instruments 
      can measure only PAI.

      Alpha is the percentage of total green foliage area to the total area of 
      above-ground materials. For closed stands, it is generally larger than 
      0.9, but for the open boreal stands, the value would be considerably 
      smaller (0.7-0.9).

In conclusion, the following formulae are proposed for calculating the indirect 
PAI and LAI:

PAI = Effective LAI * gamma/omega                                           (11)

LAI = (1-alpha)* PAI
i.e.,
LAI = (1-alpha)*effective LAI*gamma/omega                                   (12)

Gamma is about 1.3 to 1.5 (Gower and Norman, 1991; Chen and Black, 1992b; 
Fassnacht, et al., 1994; Deblonde, et al., 1994; and Chen 1996a).  It is 
obtained by directly measuring the total leaf area in a detached shoot and the 
total shoot area (4 times the average projected shoot area) using a computerized 
video camera system.

From equations 10 and 12, it can be shown that:

Foliage clumping index = Omega/gamma                                        (13)

7) 	FPAR

Green FPAR is the fraction of incident PAR that is absorbed by the green leaves 
in the canopy. It excludes the fraction reflected back to the space and the 
fraction absorbed by the background (moss, soil, and understory in forest), but 
it includes the small fraction that is reflected by the background and absorbed 
by the green leaves on the way back to space. The daily green FPAR is the final 
result reported here after applying a weighting scheme to the instantaneous 
green FPAR values (Chen, 1996b).
 
8) 	PAR Albedo of Forest Floor

This value is calculated as the ratio of the mean values, over a transect, of 
the transmitted total irradiance and reflected total PAR irradiance from the 
forest floor using the upward-facing and downward-facing hemispheric PAR sensors 
of the TRAC.

LI-COR LAI-2000:

There is a certain probability that a beam of radiation passing through some 
distance of a vegetative canopy will be intercepted by foliage.  The probability 
of interception is proportional to the path length, foliage density, and foliage 
orientation.  Therefore, if the beam transmittance is known, then it is possible 
to invert foliage information (Welles and Norman, 1991).

Noninterception (i.e.) transmittance [T]) is described by Beer's law:

T(zen,azi) = exp (-G(zen,azi) * u * S(zen,azi))                            (1)

where G(zen,azi) = fraction of foliage projected toward direction (zen,azi)
      u          = foliage density (m2 foliage/ m3 canopy)
      S(zen,azi) = path length through the canopy (m)
      zen        = zenith angle
      azi        = azimuth angle

Because the LAI-2000's optical sensor averages over azimuth, the azimuth angle 
(azi) is omitted from the following equations with the understanding that the 
various quantities are azimuthal averages.

Rewriting equation 1 yields

G(zen) * u = - (ln(T(zen)) / (S(zen)) = K(zen)                             (2)

K(zen) is the contact frequency, and is equivalent to the average number of 
contacts per unit length of travel that a beam would make passing through a 
canopy at zenith angle (zen).

The foliage density u is defined as
      p/2
u = 2  ?  K(zen) sin(zen) ?zen                                              (3)
       0

Foliage density is related to LAI by canopy height (z):

LAI = u * z                                                                 (4)

Path length S is related to canopy height (z) by zenith angle (zen):

S(zen) = z / cos(zen)                                                       (5)

Using equations 2, 3, 4, and 5, LAI can be defined in terms of canopy
transmittance:

        p/2
LAI = 2  ?  -ln[T(zen)] cos(zen) sin(zen) ?zen                              (6)
         0

Because canopy height cancels out of equation 6, it is numerically identical to 
equation 3 when S(zen)=1/cos(zen).  Thus, equation 3 can be used for either LAI 
or foliage density:  if the distances are 1/cos(zen), then the results should be 
interpreted as LAI; otherwise, foliage density is computed.

Once LAI is estimated from transmittance measurements, five values of G(zen) are 
determined using equation 2.  A straight line is fit to the data, and the slope 
of that line (?G(zen)/?zen) is used in the following equation to predict mean 
tilt angle:

MTA = 56.82 + 46.85(x) - 64.62(x2) - 158.69(x3) + 522.06(x4) + 1008.15(x5)  (7)

where x = ?G(zen)/?zen

However, it must be realized that the above inversion of LAI is based on the 
assumption that the foliage is randomly distributed in space. This assumption is 
not met for forest stands, where leaves are grouped into shoots, branches, and 
tree crowns. Because foliage of forest stands is generally more clumped than 
random, the LAI-2000 measures the effective LAI (Chen and Black, 1992b) rather 
than LAI.

TRAC (Tracing Radiation and Architecture of Canopies):

The LAI-2000 measures the canopy gap fraction from which to derive LAI.  The 
canopy gap fraction is the percentage of sky seen from underneath the canopy and 
carries no information on the actual gap size.  The TRAC is designed to obtain 
the canopy gap size information.  The instrument measures the transmitted direct 
light through the canopy at a high spatial density (1 sample/10 mm) on straight 
transects near the forest floor. The sunfleck size on the forest floor is thus 
obtained.  From the measured sunfleck size, the corresponding canopy gap size 
can be calculated after considering the penumbral effect (Chen and Cihlar, 
1995a).  The distribution of the canopy gap size is a description of the canopy 
architecture and can be used to quantify the effect of nonrandom foliage spatial 
distribution on the inversion of LAI from gap fractions.  The foliage clumping 
index is a measure of such an effect and serves as a correction to LAI-2000 
measurements.  Two methods are useful for deriving the foliage clumping index 
from a canopy gap size distribution.  One is developed by Chen and Black 
(1992b).  They derive the foliage (shoot) clumping index based on the 
assumptions that foliage elements (shoots) are randomly distributed within 
foliage clumps (tree crowns), and the foliage clumps are randomly distributed in 
space.  In natural stands, these assumptions are generally acceptable, but the 
method cannot be applied to plantations, where the assumptions are violated. The 
second method was recently developed by Chen and Cihlar (1995a). They use a gap 
removal approach to derive the foliage (shoot) clumping index.  In their 
approach, gaps appearing at probabilities larger than those predicted for the 
same gap size in a random canopy are truncated or partially removed from the 
total canopy gap fraction. For this project, Chen and Cihlar's method was used 
for processing the TRAC data. It is believed to be more accurate than Chen and 
Black's method because it does not require the assumptions made by Chen and 
Black.

4. Equipment

4.1 Sensor/Instrument Description

LI-COR LAI-2000:

The LAI-2000 plant canopy analyzer is composed of an LAI-2070 control unit and 
an LAI-2050 sensor head.  The control unit is 21 cm x 11.4 cm x 6.9 cm  and has 
connectors for two sensor heads, two connectors for other LI-COR sensors, and a 
connector for RS-232 communication.  The sensor head projects the image of its 
nearly hemispheric view onto five detectors arranged in concentric rings 
(approximately 0-13, 16-28, 32-43, 47-58, 61-74 degrees).  Radiation above 490 
nm is rejected.  Lenses are coated with MgF2 to improve transmission at high 
oblique angles.

For further information, consult the LAI-2000 plant canopy analyzer instruction 
manual (LI-COR, 1991).

TRAC:

The TRAC consists of three LI-COR quantum sensors (Model LI-190SB, LI-COR, 
Lincoln, NE) and a data logger (Campbell Scientific, Logan, UT, Model CR10).  
Two sensors measure, respectively, the total and diffuse photosynthetic photon 
flux density (PPFD) transmitted through the forest canopy, and one sensor 
measures the reflected PPFD from the forest floor.

4.1.1 Collection Environment

Most of the LAI-2000 measurements were made near sunset with the solar elevation 
angle below 15 degrees to minimize the effect of blue light scattering. The 
measurements were sometimes also made in overcast conditions. The TRAC was used 
on clear days only. Sometimes it was operated under sparse cloud conditions, but 
care was taken to ensure no direct cloud effects on the TRAC measurements. 

4.1.2 Source/Platform

LI-COR LAI-2000:

Hand held in a horizontal position at knee height

TRAC:

Hand-held in a horizontal position at knee height by a person walking on a 
straight transect on the forest floor.

4.1.3 Source/Platform Mission Objectives

The objectives were to measure and analyze LAI and FPAR taken at various BOREAS 
sites using the LI-COR LAI-2000 and TRAC instruments.

4.1.4 Key Variables  

From the LI-COR LAI-2000: Effective LAI. 

From the TRAC: Shoot clumping index.

From shoot sample analysis: needle-to-shoot area ratio.

From destructive tree sampling: foliage-to-total area ratio

4.1.5 Principles of Operation

LI-COR LAI-2000:

The amount of foliage in a vegetative canopy can be deduced from measurements of 
radiation attenuation as it passes through the canopy at several angles from the 
zenith.  Foliage orientation information can also be obtained.  The LAI-2000 
measures the attenuation of diffuse sky radiation at five zenith angles 
simultaneously.  A 90-degree mask was used all the time to prevent interference 
caused by the operator's presence.  The same mask was used for the reference 
sensor to reduce the influence of the Sun.

For further information, consult the LAI-2000 plant canopy analyzer instruction 
manual (LI-COR, 1991).

TRAC:

To obtain the canopy gap size distribution, the direct light transmitted through 
the canopy is measured at a high spatial density (one sample/10 mm) along 
straight transects.  From the canopy gap size distribution, the shoot clumping 
index is calculated, which is used as a correction factor for the LAI-2000 
measurements, in addition to the correction factor of shoot projection ratio.

4.1.6 Sensor/Instrument Measurement Geometry

LI-COR LAI-2000:

The LAI-2000 was hand-held in a horizontal position at knee height.  The LAI-
2050 (sensor head) has a near-hemispherical field-of-view (FOV).  The effective 
view area is:

           A = p * H2                                                      (8)

           where A  = area
                 p = 3.1416
                 H  = canopy height

The potential view area is larger than the effective because the effective range 
of view is reduced by foliage. The potential area viewed is:

           A = p * (3*H)2                                                  (9)

TRAC:

The TRAC was hand-held in a horizontal position.  Two sensors measure, 
respectively, the total and diffuse PPFD transmitted through the forest canopy, 
and one sensor measures the reflected PPFD from the forest floor. The view area 
of the TRAC is hemispherical for diffuse radiation.

4.1.7 Manufacturer of Sensor/Instrument

LI-COR LAI-2000:

LI-COR, Inc.
4421 Superior Street
P.O. Box 4425
Lincoln, NE  68504
(402) 467-3576

TRAC:

3rd Wave Engineering
P.O. Box 13460
Kanata, Ontario
Canada K2K 1X6

Contact: Mr. Mike Kwong
(613) 828-2195
(613) 828-9498 (fax)
email: mikek@3wce.com

4.2 Calibration

4.2.1 Specifications

LAI-2000:

The front lens of the LAI-2050 sensor head should be kept clean and dry for 
comparable readings.  Recalibration of the sensor head may never be necessary, 
as long as the optics within the sensor remain in place.  The detectors may have 
long term electrical drift, but this would not affect LAI determinations.

TRAC:

The LI-COR quantum sensor measures PPFD in the spectral range from 0.4 to 0.7 
micrometers.  A filter having the transmittance linearly increasing with 
wavelength is used for this purpose. The filter has sharp cutoffs at both ends 
of the spectrum.  The sensor has a time constant of 10 microseconds.

4.2.1.1 Tolerance

LAI-2000:

It is very difficult (if not impossible) to determine the precision and accuracy 
of LAI measurements. LAI is estimated by the LAI-2000 from all the light not 
intercepted by any object in the sensor's FOV (thus, foliage area index would be 
a more appropriate term).

Some assumptions must be met for accurate estimates of foliage amount and 
orientation when using the LAI-2000. The degree to which these assumptions are 
violated will affect the degree to which the calculations can be trusted.  The 
major assumptions are:

 1) The foliage is black.  It is assumed that the below-canopy readings do not 
    include any radiation that has been reflected or transmitted by foliage.  
    There is an optical filter in the LAI-2050 (sensor head) that rejects 
    radiation above 490 nm.  In this blue portion of the spectrum, foliage 
    typically reflects and transmits relatively little radiation.
 2) The foliage is randomly distributed within certain foliage-containing 
    envelopes.  These envelopes might be parallel tubes (a row crop), a single 
    ellipsoid (an isolated bush), an infinite box (turf grass), or an infinite 
    box with holes (deciduous forest with gaps).
 3) The foliage elements are small compared to the view area of each ring.  An 
    approximate guideline is this: the distance from the sensor to the nearest 
    leaf over it should be at least four times the leaf width.
 4) The foliage is azimuthally randomly oriented.  That is, it does not matter 
    how the foliage is inclined, as long as all the leaves are not facing the 
    same compass direction.
 5) The sky brightness is azimuthally uniform.
 6) Blockage of the sensor's FOV is the same amount for both incoming 
    and transmitted readings.

No canopy conforms exactly to the first four assumptions.  Foliage is never 
random, but is clumped along stems and branches, and is certainly not black. It 
was felt that in open boreal forests, the effect of light scattering caused by 
greyness of leaves is small, and that the LAI-2000 measures the canopy gap 
fraction or the effective LAI accurately.

TRAC:

The sensor after recalibration is accurate to 98%.  The major error arose from 
the difficulty of maintaining the sensor at a constant horizontal position 
during measurements.  A level is mounted on the holding arm close to the sensor.  
While walking, the level was watched and the holding arm was adjusted instantly 
to keep the sensor in a level position.  However, because the whole system moves 
at a walking pace, a slight deviation from the horizontal position is 
inevitable.  The deviation was generally kept within 2 degrees.

The TRAC measures the transmittance of the direct light by subtracting the 
diffuse fraction from the total irradiance in post-measurement data processing. 
The diffuse fraction was identified as a steady baseline appearing in the total 
irradiance plot for each 10-m section of the transect.  The transmittance can be 
determined with a 97-98% accuracy.

The inversion from the apparent sunfleck size to the corresponding canopy gap 
size was accurate for large gaps but less accurate for small gaps because of the 
penumbral effect.  A procedure is being developed to minimize this effect (Chen 
and Cihlar, 1995a).

4.2.2 Frequency of Calibration

LAI-2000:

Two LAI-2000 units were used, one in the forest stand and the other on the 
ground in an opening to be used as a reference for the above-the-forest-canopy 
radiation.  These two units were calibrated against each other under overcast 
conditions prior to the field measurements in each Intensive field Campaign 
(IFC).  The calibration procedures are given in the LAI-2000 Plant Canopy 
Analyzer Instruction Manual, Chapter 4-1 (LI-COR, 1991).

TRAC:

The sensing units, the LI-COR quantum sensors, were calibrated by the 
manufacturer. Before the 1994 experiment, the sensors were recalibrated against 
a new LI-COR quantum sensor maintained as a laboratory standard.

4.2.3 Other Calibration Information

Not applicable.

5. Data Acquisition Methods

1993:  In August, LAI-2000 measurements were made in the Old Black Spruce (OBS), 
Old Jack Pine (OJP), and Young Jack Pine (YJP) tower sites in both the SSA and 
NSA.  In each site, measurements were made on three transects parallel to one 
another and separated by 10-m.  The transects are from 170 m to 350 m long, 
running the flux tower at 135 (SE) and/or 215 (NE).  The measurements were 
made at 10-m intervals along the transects.  Two LAI-2000 units were used, one 
in the forest stands and the other in a nearby opening as the reference.  The 
reference unit was set in a remote logging mode at a sampling frequency of one 
sample per 15 seconds.  The measurements were made in the evening, shortly 
before and after sunset.  The TRAC was also used in the OJP tower site in the 
NSA and OBS, OJP, and YJP tower sites in the SSA.  The measurements were made 
along the middle transect among the three parallel transects for each site on 
clear days. The measurements were repeated several times in a day for the same 
site to obtain the canopy gap size distributions at different solar zenith 
angles.

1994: Similar LAI-2000 and TRAC measurements were made in IFC-1, -2, and -3 for 
the tower flux sites. Transect measurements were also made at the SSA-Old Aspen 
(OA) in a southwest direction from the tower for 300 m. In IFC-2 and -3, both 
instruments were used at 12 auxiliary sites on two transects oriented S-N and E-
W and orthogonal.

The LAI-2000 was used on overcast days or near sunset to minimize the effect of 
blue light scattering on LAI measurements. The TRAC was used on clear days or on 
sunny days when the duration of the full sunshine was long enough to permit 
complete transect measurements.

6. Observations

6.1 Data Notes

None.

6.2 Field Notes

Field notes recorded detailed weather conditions that might affect LAI-2000 and 
TRAC measurements.  These notes are not useful in using the data sets because 
the results presented here are final, with environmental effects minimized.  

7. Data Description

7.1 Spatial Characteristics

7.1.1 Spatial Coverage

Tower and auxiliary sites in the NSA and SSA were visited, although more 
measurements were concentrated at the forested tower sites.

The maximum length of the transects is about 300 m, which is long enough to 
obtain the mean value for the stand as long as the stand is homogeneous at large 
scales. The variation along the transect characterizes the spatial variability.

At the auxiliary sites, two 50-m transects were usually used for the TRAC and 
LAI-2000 that were perpendicular to each other and crossed in the middle to form 
a + shape.

The locations of the transects at each tower site are reported below relative to 
the micrometeorological flux tower.  All coordinates reported in this section 
are based on the North American Datum 1983 (NAD83).

Tower Site Coordinates
Transect        Site    grid ID    Latitude   Longitude   Zone
-------------  ------  ---------   ---------  ---------   ----
T-300SE        SSA-OA    C3B7T     53.62937   106.19819    13
150NW-T-150SE  SSA-YJP   F8L6T     53.87581   104.64529    13
T-200SE        SSA-OJP   G2L3T     53.91634   104.69203    13
T-300SE        SSA-OBS   G8I4T     53.98717   105.11779    13
T-300SE        NSA-OBS   T3R8T     55.88007    98.48139    14
170NW-T-260SE  NSA-OJP   T7Q8T     55.92842    98.62396    14
170NW-T-170SE  NSA-YJP   T8S9T     55.89575    98.28706    14
-------------------------------------------------------------
T-300SE        SSA-OA    C3B7T     53.62937   106.19819    13
150NW-T-150SE  SSA-YJP   F8L6T     53.87581   104.64529    13
T-200SE        SSA-OJP   G2L3T     53.91634   104.69203    13
T-300SE        SSA-OBS   G8I4T     53.98717   105.11779    13
T-300SE        NSA-OBS   T3R8T     55.87758    98.47765    14-
170NW-T-260SE  NSA-OJP   T7Q8T     55.92842    98.62396    14
170NW-T-170SE  NSA-YJP   T8S9T     55.89575    98.28706    14

Notes:
"150NW-T-150SE" means that the measurements were made on transects from 150 m 
northwest of the flux tower to 150 m southeast of the tower. T-300SE means that 
the measurements were made on transects from the tower to 300 m southeast of the 
tower.  There were always three transects parallel to one another and separated 
by 10-m.  LAI-2000 measurements were made at 10-m intervals, while TRAC 
measurements were made continuously (1-cm interval for the transmitted PAR) 
along the transects.

The auxiliary sites listed below were visited: 

SSA:
BORIS                    West       North     UTM        UTM      UTM 
Grid        notes      Longitude   Latitude  Easting   Northing   Zone
-----       ------     ----------  --------  --------  ---------  ----
F7J0P       JMH-5       105.05115  53.88336  496667    5970323.3   13
F7J1P       JMH-A2      105.03226  53.88211  497879.4  5970405.6   13
G2I4S       BMH         105.13964  53.93021  490831.4  5975766.3   13
G9I4S       BDL-20      105.11805  53.99877  492291.2  5983169.1   13
BMM-1       BMM-1aa     105.28275  53.65383  481312.5  5945044.9   13
BMM-2       BMM-1ab     105.28705  53.65411  481028.4  5945077.2   13
BMM-3       BMM-1ac     105.28807  53.65393  480960.9  5945057.4   13
G1K9P       JMM-6       104.74812  53.9088   516546.7  5973404.5   13

Note: BMM-1, BMM-2, and BMM-3 are Remote Sensing Science (RSS-07) sites (the 
RSS-07 team did not find the BOREAS auxiliary site BMM-1 (D0H6S), and therefore 
set up its own sites.  Darcy Snell later surveyed them with the global 
Positioning System (GPS) and reported them as BMM-1aa, BMM-1ab, and BMM-1ac.

NSA:
BORIS                    West       North      UTM       UTM      UTM 
Grid         notes     Longitude   Latitude  Easting   Northing   Zone
-----       ---------  ---------   --------  --------  ---------  ----
T2Q6A       TE Carbon   98.67479   55.88691  520342    6193540.7   14
T6R5S       BIH-9       98.51865   55.90802  530092    6195947     14
T7R9S       BDH-3       98.44877   55.91506  534454.5  6196763.6   14
T8Q9P       JIH-2       98.6105    55.93219  524334.5  6198601.4   14
T6T6S       BIL-2       98.18658   55.87968  550887.9  6192987.9   14
T8S4S                   98.37111   55.91689  539306.4  6197008.6   14
T8T1P       JDM-1       98.26269   55.90539  546096.3  6195795.3   14
T9Q8P       JIL-1       98.59568   55.93737  525257.1  6199183.2   14
T7T3S       BML-21      98.22621   55.89358  548391.8  6194505.6   14

7.1.2 Spatial Coverage Map

Not available.

7.1.3 Spatial Resolution

Not applicable for LAI-2000.  The spatial resolution of LAI measured by the TRAC 
is 100 mm, which is 10 times the measurement interval of 10 mm.  The height of 
TRAC measurements was lowered to 10-20 cm from the ground in SSA-YJP and NSA-
YJP, where trees are short (1-5 m), to include all foliage above ground.  The 
sensor height is less critical in mature stands, where trees are about 10 m and 
higher.

7.1.4 Projection

Not applicable.

7.1.5 Grid Description

Not applicable.

7.2 Temporal Characteristics

7.2.1 Temporal Coverage

Measurements with the LAI-2000 began at about 20 minutes before sunset or under 
overcast sky conditions. Measurements at a location typically took half a minute 
and about 30-45 minutes for a whole stand with about 90 measurement locations.

Measurements with the TRAC were made under clear sky conditions. 

In 1994, the LAI measurements were made for the same sites in IFC-1, -2, and -3 
to show the seasonal variation.

7.2.2 Temporal Coverage Map

Dates and Instruments Used at the Various Sites

dd/mm/yy	Site	LAI-2000	TRAC
--------	-----	--------	----
15-Aug-93	NOJP	x		x
16-Aug-93	NYJP	x		
17-Aug-93	NOBS	x
19-Aug-93	SOJP	x		x
20-Aug-93	SYJP			x
21-Aug-93	SYJP			x
22-Aug-93	SYJP	x
23-Aug-93	SOBS			x
24-Aug-93	SOBS			x
25-Aug-93	SOBS	x
25-Aug-93	SOJP	x
27-Aug-93	SOA	x		x

26-May-94	SOJP			x
27-May-94	SOJP			x
30-May-94	SOJP	x
31-May-94	SOBS			x
01-Jun-94	SOA			x
02-Jun-94	SOBS			x
02-Jun-94	SOA	x
03-Jun-94	SYJP	x
04-Jun-94	SOBS 	x
06-Jun-94	SYJP			x
07-Jun-94	NOJP			x
08-Jun-94	NOA (aux.)			x
09-Jun-94	NYJP			x
10-Jun-94	NOBS	x		x
11-Jun-94	NOA	x
11-Jun-94	NOJP	x
13-Jun-94	NYJP	x		x
28-Jun-94	W0Y5A	x
29-Jun-94	T4U9S	x
01-Jul-94	T8T1P	x
01-Jul-94	T8S4S	x
01-Jul-94	T6T6S	x

23-Jul-94	SOBS			x
24-Jul-94	SOJP			x
26-Jul-94	SYJP			x
27-Jul-94	SYJP	x
27-Jul-94	Sfen	x		x
28-Jul-94	SOA	x
29-Jul-94	SOBS	x
29-Jul-94	SOJP	x
31-Jul-94	Nfen			x
02-Aug-94	NYJP	x		x
03-Aug-94	NOA	x
03-Aug-94	NOJP	x
04-Aug-94	NOBS	x		x

30-Aug-94	NOJP	x
31-Aug-94	NOJP			x
31-Aug-94	NYJP			x
01-Sep-94	t7t3s,t7r9s			x
02-Sep-94	NOBS	x		x
03-Sep-94	Nfen, t6r5s			x
05-Sep-94	NYJP	x
06-Sep-94	Nfen	x
06-Sep-94	NOJP, t8q8p			x
07-Sep-94	NOJP	x		x
08-Sep-94	NOA	x
08-Sep-94	Aux Sites	x
	(t3u9s, t6r8s, t7r9s, 
	t7t3s, t8q9p)
10-Sep-94	SOJP	x
10-Sep-94	SYJP	x
10-Sep-94	Sfen	x
11-Sep-94	SOBS	x
12-Sep-94	Sfen			x
12-Sep-94	SYJP			x
12-Sep-94	SOJP			x
13-Sep-94	SOBS			x
16-Sep-94	Aux. Sites 			x
	(g1k9p, g2l7s)
17-Sep-94	SOA			x
18-Sep-94	Aux. Sites	x		x
	(g2i4s, g3i4m, 
	g9i4s, f7j0p, f7j1p)

In addition to these optical measurements, 27-45 conifer shoot samples were 
taken from each stand in each IFC 1994 for laboratory analysis of the needle-to-
shoot area ratio and other shoot properties. In IFC-3 1994, destructive sampling 
of LAI was made in NSA-OJP, SSA-OJP, and SSA-OBS.  All the above measurements 
were reported in Chen (1996a). Shoot angle measurements were made in IFC-3 1994 
in SSA-YJP, SSA-OBS, and NSA-YJP. These measurements are reported in Chen 
(1996b). 

7.2.3 Temporal Resolution

Measurements of the LAI-2000 began at about 20 minutes before sunset or under 
overcast sky conditions. Measurements at a location typically took half a minute 
and about 30-45 minutes for a whole stand with about 90 measurement locations.

7.3 Data Characteristics

Data characteristics are defined in the companion data definition file 
(r07elaid.def).

7.4 Sample Data Format
 
Sample data format shown in the companion data definition file (r07elaid.def).

8. Data Organization

8.1 Data Granularity

The LAI, Gap Fraction, and fPAR Data are contained in one dataset and effective 
LAI data are contained in a separate dataset.

8.2 Data Format(s)

The data files contain a series of numerical and character fields of varying 
length separated by commas.  The character fields are enclosed within single 
apostrophe marks.  There are no spaces between the fields.  Sample data records 
are shown in the companion data definition file (r07elaid.def).

9. Data Manipulations

9.1 Formulae

See Section 7.3.2. 

9.1.1 Derivation Techniques and Algorithms

Not yet available.  

9.2 Data Processing Sequence

9.2.1 Processing Steps

LAI-2000: In-stand files from one or two LAI-2000 units were merged with an 
above/outside-stand reference file from another LAI-2000 unit within the program 
c2000.com to calculate the effective LAI.
TRAC: The element (leaf for aspen and shoot for conifers) clumping index was 
calculated for each transect measurement. A canopy gap size distribution was 
first calculated from the stream of transmitted PAR data, and a gap removal 
approach (Chen and Cihlar 1995a) was used to calculate the clumping index.
TRAC: Measurements from the upward and downward-facing PAR sensors were used to 
calculate the mean transmitted PAR and the PAR albedo of the forest floor. The 
above-canopy incident PAR was taken as the PAR measurements outside the stand or 
in large canopy gaps. The stand PAR albedo was obtained on the top of the flux 
tower with the TRAC or stationary PAR sensors (Chen, 1996b).

9.2.2 Processing Changes

None.

9.3 Calculations

9.3.1 Special Corrections/Adjustments

A key correction to the final LAI results is the 15% increase in the mean value 
of the effective LAI from the LAI-2000, according to the finding of Chen 
(1996b), who found that the LAI-2000 underestimates the effective LAI by about 
15% in comparison with TRAC measurements, which are free from the light-
scattering effect. This correction was not made in the raw transect LAI-2000 
measurements but was made in the final LAI files.

9.3.2 Calculated Variables

See Section 3.0.

9.4 Graphs and Plots

None.

10. Errors

10.1 Sources of Error

LAI is estimated with the LAI-2000 from all light not intercepted by objects in 
the sensor's FOV so foliage area index would be a more appropriate term.  Some 
assumptions must be met for accurate estimates of foliage amount and orientation 
when using the LAI-2000.  The degree to which these assumptions are violated 
will affect the degree to which the calculations can be trusted.  The major 
assumptions are:

 1) The foliage is black.  It is assumed that the below-canopy readings do not 
    include any radiation that has been reflected or transmitted by foliage.  
    There is an optical filter in the LAI-2050 (sensor head) that rejects 
    radiation above 490 nm.  In this blue portion of the spectrum, foliage 
    typically reflects and transmits relatively little radiation.
 2) The foliage is randomly distributed within certain foliage-containing 
    envelopes.  These envelopes might be parallel tubes (a row crop), a single 
    ellipsoid (an isolated bush), an infinite box (turf grass), or an infinite 
    box with holes (deciduous forest with gaps).
 3) The foliage elements are small compared to the view area of each ring.  An 
    approximate guideline is this: the distance from the sensor to the nearest 
    leaf over it should be at least four times the leaf width.
 4) The foliage is azimuthally randomly oriented.  That is, it does not matter 
    how the foliage is inclined, as long as all the leaves are not facing the 
    same compass direction.
 5) The sky brightness is azimuthally uniform.
 6) Blockage of the sensor's FOV is the same amount for both incoming 
    and transmitted readings.

No canopy conforms exactly to the first four assumptions.  Foliage is never 
random, but is clumped along stems and branches, and is certainly not black.  
Many species exhibit some degree of heliotropism, which violates the azimuthal 
randomness assumption. However, the practical compromises that must be made are 
often not serious.  Many canopies can be considered to be random, and living 
foliage does have relatively low transmittance and reflectance below 490 nm.  
Offsetting errors may be common, such as when leaves are grouped along stems 
(increasing light transmittance), but arranged to minimize overlap (decreasing 
transmittance).  View restrictors on the LAI-2050 (sensor head) can reduce 
errors associated with assumptions 5 and 6 but at the potential cost of 
reduction of sample size.

The sensor after recalibration is 98% accurate.  The major error arose from the 
difficulty of maintaining the sensor at a constant horizontal position during 
measurements.  A level is mounted on the holding arm close to the sensor.  While 
walking, the level was watched and the holding arm was adjusted instantly to 
keep the sensor in a level position.  However, because the whole system moves at 
a walking pace, a slight deviation from the horizontal position is inevitable.  
The deviation was generally kept within 2 degrees.

10.2 Quality Assessment

10.2.1 Data Validation by Source

LAI values were compared with values obtained from different methods and values 
from other investigators, and the LAI results presented here have been validated 
with direct LAI measurements through destructive sampling (Chen et al., 1997b).  

10.2.2 Confidence Level/Accuracy Judgment

LAI-2000 measurements alone considerably underestimate LAI because of the 
foliage clumping; i.e., the effective LAI is usually about 50% of the true LAI 
for conifers and 75% of the true LAI for deciduous.  Hemispherical photography 
can provide only the effective LAI. The clumping index obtained from the TRAC 
and shoot sample analysis provides a critical improvement to bring optical LAI 
into agreement with destructive sampling results obtained by Terrestrial Ecology 
(TE-06). 

10.2.3 Measurement Error for Parameters

The measurement error for the final LAI is assessed to be within 25% of the 
reported value and daily green FPAR within 5%.

10.2.4 Additional Quality Assessments

Not available.

10.2.5 Data Verification by Data Center

BOREAS Information System (BORIS) staff has viewed the data and performed some 
basic checks before loading.

11. Notes

11.1 Limitations of the Data

The number of sites included in this investigation is too small for accurate 
assessment of the mean LAI and FPAR values for boreal forest. Remote sensing 
methods are used to extend these sites to the BOREAS region (see the document 
for RSS-07 AVHRR LAI and FPAR data sets).  The needle-to-shoot area ratio 
appears to have little variation between the stands and can be taken as the 
representative value for boreal forests, while the element clumping index varies 
greatly and is largely affected by stand density. This clumping index has to be 
assessed for individual sites using instruments like the TRAC.

11.2 Known Problems with the Data

See Section 10.1.

11.3 Usage Guidance

There can be considerable variability in LAI values, especially in natural 
ecosystems.  Grazing of trees can enhance the natural variability.  Extreme 
water stress causing leaf rolling could change the effective LAI.

11.4 Other Relevant Information

The LAI-2000 is definitely a field-proven instrument. It measures the canopy gap 
fraction accurately, from which the effective LAI is derived accurately.  No 
artificial influence can be easily introduced into the measurements. It is the 
state of the art for measuring the canopy gap fraction.

The TRAC is a recent development for measuring the canopy gap size distribution 
from which the effect of nonrandom foliage spatial distribution on LAI-2000 
measurements of LAI can be quantified.  The error in the foliage (shoot) 
clumping index derived using the TRAC is within 5%.

12. Application of the Data Set

To establish relationships between LAI, FPAR, and remotely sensed radiances and 
their transformations.

13. Future Modifications and Plans

14. Software

14.1 Software Description

None given.

14.2 Software Access

None given.

15. Data Access 

15.1 Contact Information

Ms. Beth Nelson
BOREAS Data Manager
NASA GSFC
Greenbelt, MD 
(301) 286-4005
(301) 286-0239 (fax)
Elizabeth.Nelson@gsfc.nasa.gov

15.2 Data Center Identification

See Section 15.1.

15.3 Procedures for Obtaining Data

Users may place requests by telephone, electronic mail, or fax.

15.4 Data Center Status/Plans

The RSS-07 LAI and fPAR data are available from the Earth Observing System Data 
and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed 
Active Archive Center (DAAC). The BOREAS contact at ORNL is: 

ORNL DAAC User Services
Oak Ridge National Laboratory
Oak Ridge, TN 
(423) 241-3952
ornldaac@ornl.gov
ornl@eos.nasa.gov

16. Output Products and Availability

16.1 Tape Products

None.

16.2 Film Products

None.

16.3 Other Products

Tabular ASCII files.

17. References

17.1 Platform/Sensor/Instrument/Data Processing Documentation

LI-COR LAI-2000 plant canopy analyzer instruction manual.  LI-COR, Inc., 
Lincoln, NE (1991).

LI-COR LAI-2000 plant canopy analyzer technical information.  LI-COR, Inc., 
Lincoln, NE  (1989).

17.2 Journal Articles and Study Reports

Chen, J.M. and T.A. Black. 1992a. Defining leaf area index for non-flat leaves. 
Plant, Cell and Environment. 15:121-129.

Chen, J.M. and T.A. Black. 1992b. Foliage area and architecture of plant 
canopies from sunfleck size distributions. Agric. For. Meteorol. 60:249-266.

Chen, J.M. and J. Cihlar. 1995a. Plant canopy gap size analysis theory for 
improving optical measurements of leaf area index. Applied Optics. 34:6211-6222.

Chen, J.M. and J. Cihlar.  1995b. Quantifying the effect of canopy architecture 
on optical measurements of leaf area index using two gap size analysis methods. 
IEEE Trans. Geosci. Remote Sens. 33:777-787.

Chen, J.M. and J. Cihlar. 1996. Retrieving leaf area index for boreal conifer 
forests using Landsat TM images. Remote Sensing of Environment. 55:153-162.

Chen, J.M. 1996a. Optically-based methods for measuring seasonal  variation in 
leaf area index of boreal conifer forests. Agricultural and Forest Meteorology 
80:135-163.

Chen, J.M. 1996b. Canopy architecture and remote sensing of the fraction of 
photosynthetically active radiation in boreal conifer stands. IEEE Transactions 
on Geoscience and Remote Sensing. 34:1353-1368.

Chen, J.M. 1996c. Evaluation of vegetation indices and a simple ratio for boreal 
applications. Canadian Journal of Remote Sensing 22: 229-242.

Chen, J.M., P. Blanken, T.A. Black., M. Guilbeault, and S. Chen. 1997a. 
Radiation regime and canopy architecture of a boreal aspen forest.  Agricultural 
and Forest Meteorology 86:107-125.

Chen, J. M., P. M. Rich, S. T. Gower, J. M. Norman, S. Plummer, 1997b, Leaf 
Area Index of Boreal Forests:  Theory, techniques, and measurements, Journal 
of Geophysical Research, BOREAS Special Issue, 102, 29429-29443.

Deblonde, G., M. Penner, and A. Royer. 1994. Measuring leaf area index with the 
LI-COR LAI-2000 in pine stands. Ecology 75:1507-1511.

Fassnacht, K.S., S.T. Gower, J.M. Norman, and R.E. McMurtie. 1994. A comparison 
of optical and direct methods for estimating foliage surface area index in 
forests. Agric. For. Meteorol. 71:183-207.

Gower, S.T. and J.M. Norman.  1991. Rapid estimation of leaf area index for 
forests using LI-COR LAI-2000. Ecology. 72:1896-1900.

Lang, A.R.G.. 1991. Application of some of Cauthys theorems to estimation of 
surface areas of leaves, needles and branches of plants, and light 
transmittance. Agric. For. Meteorol. 55:191-121.

Sellers, P. and F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment 
Plan. Version 1994-3.0, NASA BOREAS Report
(EXPLAN 94). 

Sellers, P. and F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment 
Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN 96). 

Sellers, P. and F. Hall. 1997. BOREAS Overview Paper. JGR Special Issue, 102.

Sellers, P., F. Hall, and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere 
Study: 1994 Operations. NASA BOREAS Report (OPS DOC 94). 

Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere 
Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96). 

Sellers, P., F. Hall, H. Margolis, B. Kelly, D. Baldocchi, G. den Hartog, J. 
Cihlar, M.G. Ryan, B. Goodison, P. Crill, K.J. Ranson, D. Lettenmaier, and D.E. 
Wickland. 1995. The boreal ecosystem-atmosphere study (BOREAS): an overview and 
early results from the 1994 field year. Bulletin of the American Meteorological 
Society. 76(9):1549-1577. 

Welles, J.M. and J.M. Norman.  1991.  Instrument for indirect measurement of 
canopy architecture.  Agronomy Journal 83:818-825.

17.3 Archive/DBMS Usage Documentation

18. Glossary of Terms
    
None.

19. List of Acronyms 

    APAR    - Absorbed Photosynthetically Active Radiation
    ASCII   - American Standard Code for Information Interchange
    AVHRR   - Advanced Very High Resolution Radiometer
    BOREAS  - BOReal Ecosystem-Atmosphere Study
    BORIS   - BOREAS Information System
    CCRS    - Canada Centre for Remote Sensing
    DAAC    - Distributed Active Archive Center
    dbh     - diameter at breast height
    EOS     - Earth Observing System
    EOSDIS  - EOS Data and Information System
    FOV     - Field of View
    FPAR    - Fraction of Photosyntheically Active Radiation
    GMT     - Greenwich Mean Time
    GPS     - Global Positioning System
    GSFC    - Goddard Space Flight Center
    IFC     - Intensive Field Campaign
    IPAR    - intercepted photosynthetically active radiation
    IRT     - infrared thermometer
    LAI     - Leaf Area Index
    NAD83   - North American Datum 1983
    NASA    - National Aeronautics and Space Administration
    NOAA    - National Oceanic and Atmospheric Administration
    NSA     - Northern Study Area
    OA      - Old Aspen
    OBS     - Old Black Spruce
    OJP     - Old Jack Pine
    ORNL    - Oak Ridge National Laboratory
    PAI     - Plant Area Index
    PANP    - Prince Albert National Park
    PBFD    - Photosynthetic Photon Flux Density
    RSS     - Remote Sensing Science
    SSA     - Southern Study Area
    TE      - Terrestrial Ecology
    TM      - Thematic Mapper
    TRAC    - Tracing Radiation and Architecture of Canopies
    URL     - Uniform Resource Locator
    UTM     - Universal Transverse Mercator

20. Document Information

20.1 Document Revision Date 

     Written:         29-Dec-1995.
     Last Updated:    01-Jul-1998

20.2 Document Review Dates

     BORIS Review:    10-Sep-1997
     Science Review:  24-Nov-1997

20.3 Document ID

20.4 Citation

Please contact the PI for more information when publishing this data and 
acknowledge the efforts of J.M. Chen, J. Cihlar, and M. Penner.  Please also 
make references to appropriate publications in section 17.

20.5 Document Curator

20.6 Document URL

KEYWORDS:

LAI
FPAR
LAI-2000
Effective LAI
Plant Area Index
Clumping Index
Vegetation Indices
Canopy Gap Fraction
RSS07_Ground_LAI_FPAR.doc
07/07/98