NASA/TMm2000-209891, Vol. 51

Technical Report Series on the

Boreal Ecosystem-Atmosphere Study (BOREAS)

Forrest G. Hall and Jaime Nickeson, Editors

Volume 51

BOREAS RSS-7 LAI, Gap Fraction,

and FPAR Data

Jing Chen

Canada Centre for Remote Sensing, Ottawa, Ontario, Canada

National Aeronautics and

Space Administration

Goddard Space Flight Center

Greenbelt, Maryland 20771

July 2000

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NASA/TMm2000-209891, Vol. 51

Technical Report Series on the

Boreal Ecosystem-Atmosphere Study (BOREAS)

Forrest G. Hall and Jaime Nickeson, Editors

Volume 51

BOREAS RSS-7 LAI, Gap Fraction,

and FPAR Data

Jing Chen

Canada Centre for Remote Sensing, Ottawa, Ontario, Canada

National Aeronautics and

Space Administration

Goddard Space Flight Center

Greenbelt, Maryland 20771

July 2000
NASA Center for AeroSpace Information

7121 Standard Drive

Hanover, MD 21076-1320

Price Code: A17

Available from:

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

Price Code: A10
BOREAS RSS-7 LAI, Gap Fraction, and FPAR Data

Jing M. Chen

Summary

The BOREAS RSS-7 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).

Page 1
1.3 Objective/Purpose

The objectives of this project were to:

• Obtain LAI and FPAR for the tower sites in both the BOREAS SSA and NSA.

• Describe the spatial variability of LAI and FPAR for the sites.

• 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.

• Develop algorithms for retrieving LAI and FPAR from Landsat Thematic Mapper (TM) and

Advanced Very High Resolution Radiometer (AVHRR) data.

• Investigate the effect of plant canopy architecture on indirect measurements of LAI and FPAR.

• 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:

• LAI-2000: effective LAI

• TRAC: indirect LAI, foliage clumping index, FPAR, PAR albedo of forest floor

• 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-06 Allometry Data

BOREAS TE-06 NPP for the Tower Flux, Carbon Evaluation, and Auxiliary sites

BOREAS TE-23 Canopy Architecture and Spectral Data from Hemispherical Photos

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

Page 2
2.3 Contact Information

Contact 1:

Jing M. Chen

419-588 Booth St.

Ottawa, Ontario

K1A 1Y7 Canada

(613) 947-1266

Chen@ccrs.emr.ca

Contact 2:

Josef Cihlar

415-588 Booth St.

Ottawa, Ontario

K1A 1Y7 Canada

(613) 947-1265

Josef.Cihlar@geocan.emr.ca

Contact 3:

Jaime Nickeson

Raytheon ITSS

NASA GSFC

Code 923

Greenbelt, MD 20771

(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 nonflat 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) Plant Area Index (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 nonrandomness 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

Page 3
derivedindirectlyfrom themeasurementsof canopygapfractionusingequipmentsuchastheLI-COR

LAI-2000,hemisphericalphotography,tram,or movinglight sensors.Thedefinitionof theeffective

LAI is:

EffectiveLAI = FoliageClumpingIndex* LAI (1)

Thefoliageclumpingindexis smallerthanunity for coniferanddeciduousstands(usually0.5).

TheLI-CORLAI-2000measurescanopygapfractionandderivesLAI from thegapfractionunder

theassumptionthatthefoliageelementsarerandomlydistributedin space.Therefore,it measuresonly

theeffectivePAI (orlooselyeffectiveLAI) ratherthanLAI whenthefoliageis notrandom.It is

thereforemeaningfulto reportthepopularmeasurementsaseffectivePAI or LI-CORLAI.

AlthoughtheeffectiveLAI measuredby theLAI-2000isnotLAI, themeasurementsarestill very

valuablefor estimatingthegapfractionandlight interception(FPARandAbsorbedPhotosynthetically

Active Radiation[APAR])by thecanopy,andthereforetheyshouldbereportedasrawdata.

4) Direct LAI and PAI

DirectLAI andPAI aremeasureddirectlythroughdestructivesampling.In themeasurements,

relationshipsmaybeusedbetweenleafareaandleaffreshordry weight,betweentotalleafareain a

branchandthebranchdiameterorbranchweight,andbetweentotalleafareain atreeandthetree

diameteratbreastheight(dbh).In otherwords,somedegreeof indirectnessmaystill beinvolved.

5) Allometrie 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.

Page 4
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 PAl and LAI:

PAI= Effective LAI * gamma/omega (2)

LAI = (1-alpha)* PAI

i.e.

LAI = (1-alpha)*effective LAI*gamma/omega (3)

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 (4)

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)) (5)

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 5 yields

Page 5
G(zen) * u =- (ln(T(zen)) / (S(zen)) = K(zen) (6)

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

u=2

_12

/

0

K(zen) sin(zen) adzen (7)

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

LAI = u * z (8)

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

S(zen) = z / cos(zen) (9)

Using equations 6, 7, 8, and 9, LAI can be defined in terms of canopy transmittance:

LAI = 2

I_72

/

0

-ln[T(zen)] cos(zen) sin(zen) 8dzen (10)

Because canopy height cancels out of equation 10, it is numerically identical to equation 7 when

S(zen)=l/cos(zen). Thus, equation 7 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 6. A straight line is fit to the data, and the slope of that line (SG(zen)/Szen) 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) (11)

where x = OG(zen)/O 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

Page 6
ontheinversionof LAI from gapfractions.Thefoliageclumpingindexis ameasureof suchaneffect

andservesasacorrectionto LAI-2000measurements. Twomethodsareusefulfor derivingthefoliage

clumpingindexfrom acanopygapsizedistribution.Oneis developedby ChenandBlack (1992b).

Theyderivethefoliage(shoot)clumpingindexbasedontheassumptionsthatfoliageelements(shoots)

arerandomlydistributedwithin foliageclumps(treecrowns),andthefoliageclumpsarerandomly

distributedin space.In naturalstands,theseassumptionsaregenerallyacceptable,but themethod

cannotbeappliedto plantations,wheretheassumptionsareviolated.Thesecondmethodwasrecently

developedby ChenandCihlar(1995a).Theyuseagapremovalapproachto derivethefoliage(shoot)

clumpingindex.In theirapproach,gapsappearingatprobabilitieslargerthanthosepredictedfor the

samegapsizein arandomcanopyaretruncatedorpartiallyremovedfrom thetotalcanopygap

fraction.For thisproject,ChenandCihlar'smethodwasusedfor processingtheTRACdata.It is

believedto bemoreaccuratethanChenandBlack'smethodbecauseit doesnotrequirethe

assumptionsmadeby ChenandBlack.

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 cmx 11.4 cmx 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.

Page 7
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 = pi * H 2 (12)

where A = area

pi = 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 = pi * (3"H)2 (13)

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

Page 8
TRAC:

3rdWaveEngineering

P.O.Box 13460

Kanata,Ontario

CanadaK2K 1X6

Contact:Mr. Mike Kwong

(613)828-2195

(613)828-9498(fax)

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:

• 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.

• 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).

• 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.

• 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.

• The sky brightness is azimuthally uniform.

• Blockage of the sensor's FOV is the same 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.

Page 9
TRAC:

Thesensorafterrecalibrationisaccurateto 98%.Themajorerrorarosefrom thedifficulty of

maintainingthesensorataconstanthorizontalpositionduringmeasurements. A levelismountedon

theholdingarmcloseto thesensor.Whilewalking,thelevelwaswatchedandtheholdingarmwas

adjustedinstantlyto keepthesensorin alevelposition.However,becausethewholesystemmovesat

awalkingpace,aslightdeviationfrom thehorizontalpositionis inevitable.Thedeviationwas

generallykeptwithin 2 degrees.

TheTRACmeasuresthetransmittanceof thedirectlight by subtractingthediffusefractionfrom

thetotalirradiancein postmeasurement dataprocessing.Thediffusefractionwasidentifiedasa steady

baselineappearingin thetotalirradianceplotfor each10-msectionof thetransect.Thetransmittance

canbedeterminedwith a97-98%accuracy.

Theinversionfrom theapparentsunflecksizeto thecorrespondingcanopygapsizewasaccurate

for largegapsbut lessaccuratefor smallgapsbecauseof thepenumbraleffect.A procedureis being

developedto minimizethiseffect(ChenandCihlar,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.

Page 10
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 of 1983 (NAD83).

Tower Site Coordinates

Transect Site grid ID Latitude Longitude Zone

T-300SE SSA-OA C3B7T 53

150NW-T-150SE SSA-YJP F8L6T 53

T-200SE SSA-OJP G2L3T 53

T-300SE SSA-OBS G814T 53

T-300SE NSA-OBS T3R8T 55

170NW-T-260SE NSA-OJP T7Q8T 55

170NW-T-170SE NSA-YJP T8S9T 55

.62937 106

87581 104

91634 104

98717 105

88007 98

92842 98

89575 98

19819 13

64529 13

69203 13

11779 13

48139 14

62396 14

28706 14

T-300SE SSA-OA C3B7T 53

150NW-T-150SE SSA-YJP F8L6T 53

T-200SE SSA-OJP G2L3T 53

T-300SE SSA-OBS G814T 53

T-300SE NSA-OBS T3R8T 55

170NW-T-260SE NSA-OJP T7Q8T 55

170NW-T-170SE NSA-YJP T8S9T 55

62937 106

87581 104

91634 104

98717 105

87758 98

92842 98

89575 98

19819 13

64529 13

69203 13

11779 13

47765 14

62396 14

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.

Page 11
Theauxiliarysiteslistedbelowwerevisited:

SSA:

BORIS West

Grid notes Longitude

North UTM

Latitude Easting

F7JOP JHH-5 105

F7JIP JHH-A2 105

G214S BHH 105

G914S BDL-20 105

BMM-I BMM-Iaa 105

BMM-2 BMM-Iab 105

BMM-3 BMM-Iac 105

GIK9P JMM-6 104

05115 53

03226 53

13964 53

11805 53

28275 53

28705 53

28807 53

74812 53

88336 496667

88211 497879

93021 490831

99877 492291

65383 481312

65411 481028

65393 480960

9088 516546

UTM UTM

Northing Zone

5970323 3 13

5970405 6 13

5975766 3 13

5983169 1 13

5945044 9 13

5945077 2 13

5945057 4 13

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 (DOH6S), and therefore set up its own sites. Darcy

Snell later surveyed them with the Global Positioning System (GPS) and reported them as BMM-1 aa,

BMM-lab, and BMM-lac.

NSA:

BORIS West North UTM UTM UTM

Grid notes Longitude Latitude Easting Northing Zone

T2Q6A TE Carbon 98

T6R5S BIH-9 98

T7R9S BDH-3 98

T8Q9P JIH-2 98

T6T6S BIL-2 98

T8S4S 98

T8TIP JDM-I 98

T9QSP JIL-I 98

T7T3S BML-21 98

67479 55

51865 55

44877 55

6105 55

18658 55

37111 55

26269 55

59568 55

22621 55

88691 520342

90802 530092

91506 534454

93219 524334

87968 550887

91689 539306

90539 546096

93737 525257

89358 548391

6193540

6195947

5 6196763

5 6198601

9 6192987

4 6197008

3 6195795

1 6199183

8 6194505

7 14

14

6 14

4 14

9 14

6 14

3 14

2 14

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 ram,

which is 10 times the measurement interval of 10 ram. 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

Page 12
conditions.Measurementsat alocationtypicallytookhalfaminuteandabout30-45minutesfor a

wholestandwith about90measurementlocations.MeasurementswiththeTRACweremadeunder

clearskyconditions.In 1994,theLAI measurementsweremadefor thesamesitesin IFC-1,-2,and

-3 to showtheseasonalvariation.

7.2.2 Temporal Coverage Map

Dates and Instruments Used at the Various Sites

Date 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

27-May-94 SOJP

30-May-94 SOJP

31-May-94 SOBS

01-Jun-94 SOA

02-Jun-94 SOBS

02-Jun-94 SOA

03-Jun-94 SYJP

04-Jun-94 SOBS

06-Jun-94 SYJP

07-Jun-94 NOJP

08-Jun-94 NOA

09-Jun-94 NYJP

10-Jun-94 NOBS

ll-Jun-94 NOA

ll-Jun-94 NOJP

13-Jun-94 NYJP

(aux)

x

x

x

x

x

x

x

x

x

x

x

x

x

x x

x

x

x x

28-Jun-94 WOY5A

29-Jun-94 T4U9S

01-Jul-94 T8TIP

01-Jul-94 T8S4S

01-Jul-94 T6T6S

x

x

x

x

x

Date Site LAI-2000 TRAC

23-Jul-94 SOBS

24-Jul-94 SOJP

26-Jul-94 SYJP

27-Jul-94 SYJP x

27-Jui-94 Sfen x

28-Jui-94 SOA x

29-Jui-94 SOBS x

29-Jui-94 SOJP x

31-Jui-94 Nfen

02-Aug-94 NYJP x

03-Aug-94 NOA x

03-Aug-94 NOJP x

04-Aug-94 NOBS 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,

tSq9p)

10-Sep-94 SOJP x

10-Sep-94 SYJP x

10-Sep-94 Sfen x

ll-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

(glk9p,g217s)

17-Sep-94 SOA x

18-Sep-94 Aux Sites x x

(g2i4s,g3i4m,

g9i4s,f7j0p,

f7jlp)

Page 13
In additionto theseopticalmeasurements, 27-45conifershootsamplesweretakenfrom eachstandin

eachIFC 1994for laboratoryanalysisof theneedle-to-shootarearatioandothershootproperties.In

IFC-3 1994,destructivesamplingof LAI wasmadein NSA-OJP,SSA-OJP,andSSA-OBS.All the

abovemeasurementswerereportedin Chen(1996a).Shootanglemeasurementsweremadein IFC-3

1994in SSA-YJP,SSA-OBS,andNSA-YJP.Thesemeasurementsarereportedin Chen(1996b).

7.2.3 Temporal Resolution

Measurementsof theLAI-2000beganat about20minutesbeforesunsetor underovercastsky

conditions.Measurementsat alocationtypicallytookhalfaminuteandabout30-45minutesfor a

wholestandwith about90measurementlocations.

7.3 Data Characteristics

7.3.1 Parameter/Variable

The parameters contained in the data files on the CD-ROM are:

LAI, Gap Fraction, and FPAR Data:

Column Name

SITE NAME

SUB SITE

START DATE

END DATE

OP GRID INFO

SOLAR ZEN ANG

DAILY GREEN FPAR

LAI STD METHOD

EFFECTIVE LAI

ELEMENT CLUMPING INDEX

FOLIAGE TO TOTAL AREA RATIO

NEEDLE TO SHOOT AREA RATIO

PLANT AREA INDEX

FOREST FLOOR ALBEDO

CRTFCN CODE

REVISION DATE

Effective LAI

Column Name

SITE NAME

SUB SITE

DATE OBS

TIME

TRANSECT

DISTANCE

EFFECTIVE LAI

CRTFCN CODE

REVISION DATE

Page 14
7.3.2 Variable Description/Definition

The descriptions of the parameters contained in the data files on the CD-ROM are:

LAI, Gap Fraction, and FPAR Data

Column Name Description

SITE NAME

SUB SITE

START DATE

END DATE

OP GRID INFO

SOLAR ZEN ANG

DAILY GREEN FPAR

LAI STD METHOD

EFFECTIVE LAI

ELEMENT CLUMPING INDEX

FOLIAGE TO TOTAL AREA RATIO

NEEDLE TO SHOOT AREA RATIO

PLANT AREA INDEX

FOREST FLOOR ALBEDO

CRTFCN CODE

REVISION DATE

The identifier assigned to the site by BOREAS,

in the format SSS-TTT-CCCCC, where SSS

identifies the portion of the study area: NSA,

SSA, REG, TRN, and TTT identifies the cover type

for the site, 999 if unknown, and CCCCC is the

identifier for site, exactly what it means will

vary with site type.

The identifier assigned to the sub-site by

BOREAS, in the format GGGGG-IIIII, where GGGGG

is the group associated with the sub-site

instrument, e.g. HYD06 or STAFF, and IIIII is

the identifier for sub-site, often this will

refer to an instrument.

The date on which the collection of data

commenced.

The date on which the collection of the data was

terminated.

The site identifier used by this RSS team during

the execution of field operations. This is used

to further link data to site information

contained elsewhere.

The angle from the surface normal (straight up)

to the sun during the data collection.

Fraction of photosynthetically active radiation

absorbed by green plant material over the course

of a day.

Leaf angle index calculated by the standard

method with the LICOR LAI-2000.

A measure for the effect of non-randomness of

foliage spatial distribution on indirect

measurements of LAI

An index of the amount of grouping or clumping in

tree crowns, branches, and shoots

The ratio of total green foliage area to the

total area of above-ground materials.

The rates of needle to shoot area which

quantifies how much leaf area there is in an

average shoot area

The plant area index is defined as half the total

area of all above-ground plant materials per unit

ground surface area

The albedo measurement of the forest floor.

The BOREAS certification level of the data.

Examples are CPI (Checked by PI), CGR (Certified

by Group), PRE (Preliminary), and CPI-??? (CPI

but questionable).

The most recent date when the information in the

referenced data base table record was revised.

Page 15
Effective LAI

Column Name Description

SITE NAME

SUB SITE

DATE OBS

TIME

TRANSECT

DISTANCE

EFFECTIVE LAI

CRTFCN CODE

REVISION DATE

The identifier assigned to the site by BOREAS,

in the format SSS-TTT-CCCCC, where SSS

identifies the portion of the study area: NSA,

SSA, REG, TRN, and TTT identifies the cover type

for the site, 999 if unknown, and CCCCC is the

identifier for site, exactly what it means will

vary with site type.

The identifier assigned to the sub-site by

BOREAS, in the format GGGGG-IIIII, where GGGGG

is the group associated with the sub-site

instrument, e.g. HYD06 or STAFF, and IIIII is

the identifier for sub-site, often this will

refer to an instrument.

The date on which the data were collected.

The Greenwich Mean Time (GMT) when the data were

collected.

Designation for transect identifier within site.

Distance from the tower along the transect.

A measure for the effect of non-randomness of

foliage spatial distribution on indirect

measurements of LAI

The BOREAS certification level of the data.

Examples are CPI (Checked by PI), CGR (Certified

by Group), PRE (Preliminary), and CPI-??? (CPI

but questionable).

The most recent date when the information in the

referenced data base table record was revised.

7.3.3 Unit of Measurement

The measurement units for the parameters contained in the data files on the CD-ROM are:

LAI, Gap Fraction, and FPAR Data

Column Name Units

SITE NAME [none]

SUB SITE [none]

START DATE [DD-MON-YY]

END DATE [DD-MON-YY]

OP GRID INFO [none]

SOLAR ZEN ANG [degrees]

DAILY GREEN FPAR [unitless]

LAI STD METHOD [unitless]

EFFECTIVE LAI [unitless]

ELEMENT CLUMPING INDEX [unitless]

FOLIAGE TO TOTAL AREA RATIO [unitless]

NEEDLE TO SHOOT AREA RATIO [unitless]

PLANT AREA INDEX [unitless]

FOREST FLOOR ALBEDO [percent]

CRTFCN CODE [none]

REVISION DATE [DD-MON-YY]

Page 16
Effective LAI

Column Name Units

SITE NAME [none]

SUB SITE [none]

DATE OBS [DD-MON-YY]

TIME [HHMMSS GMT]

TRANSECT [none]

DISTANCE [meters]

EFFECTIVE LAI [unitless]

CRTFCN CODE [none]

REVISION DATE [DD-MON-YY]

7.3.4 Data Source

The sources of the parameter values contained in the data files on the CD-ROM are:

LAI, Gap Fraction, and FPAR Data

Column Name Data Source

SITE NAME

SUB SITE

START DATE

END DATE

OP GRID INFO

SOLAR ZEN ANG

DAILY GREEN FPAR

LAI STD METHOD

EFFECTIVE LAI

ELEMENT CLUMPING INDEX

FOLIAGE TO TOTAL AREA RATIO

NEEDLE TO SHOOT AREA RATIO

PLANT AREA INDEX

FOREST FLOOR ALBEDO

CRTFCN CODE

REVISION DATE

Effective LAI

Column Name

[Assigned by BORIS]

[Assigned by BORIS]

[Controller]

[Controller]

[Designation given by BORIS or PI]

[Calculated]

[TRAC]

[LAI-2000 and TRAC]

[LAI-2000]

[TRAC]

[Destructive tree sampling]

[AgVision camera-light table system]

[LAI-2000 and TRAC]

[TRAC]

[Assigned by BORIS]

[Assigned by BORIS]

Data Source

SITE NAME

SUB SITE

DATE OBS

TIME

TRANSECT

DISTANCE

EFFECTIVE LAI

CRTFCN CODE

REVISION DATE

[Assigned by BORIS]

[Assigned by BORIS]

[Controller]

[Controller]

[PI designation]

[Measured by PI]

[LAI-2000]

[Assigned by BORIS]

[Assigned by BORIS]

Page 17
7.3.5 Data Range

The following table gives information about the parameter values found in the data files on the

CD-ROM.

LAI, Gap Fraction, and FPAR Data

Minimum Maximum

Data Data

Column Name Value Value

Missng Unrel Below Data

Data Data Detect Not

Value Value Limit Cllctd

SITE NAME NSA-9BS-9TETR SSA-YJP-FLXTR None None None None

SUB SITE RSS07-LAI01 RSS07-LAI01 None None None None

START DATE 09-AUG-93 17-SEP-94 None None None None

END DATE 29-AUG-93 19-SEP-94 None None None None

OP GRID INFO N/A N/A None None None None

SOLAR ZEN ANG 32.4 50.9 None None None Blank

DAILY GREEN FPAR .38 .93 None None None Blank

LAI STD METHOD 1.06 5.37 None None None Blank

EFFECTIVE LAI 0 2.75 None None None Blank

ELEMENT CLUMPING 1 1.52 None None None Blank

INDEX

FOLIAGE TO TOTAL .7 .95 None None None Blank

AREA RATIO

NEEDLE TO SHOOT .68 .97 None None None Blank

AREA RATIO

PLANT AREA INDEX 1.61 5.74 None None None Blank

FOREST FLOOR ALBEDO 5.2 ii None None None Blank

CRTFCN CODE CPI CPI None None None None

REVISION DATE 31-OCT-96 26-JUN-98 None None None None

Effective LAI

Column Name

Minimum Maximum Missng Unrel Below Data

Data Data Data Data Detect Not

Value Value Value Value Limit Cllctd

SITE NAME NSA-OBS-FLXTR SSA-YJP-FLXTR None None None None

SUB SITE RSS07-EFL01 RSS07-EFL01 None None None None

DATE OBS 30-MAY-93 13-JUN-94 None None None None

TIME 134330 221611 None None None None

TRANSECT A TRAM None None None None

DISTANCE 0 300 None None None None

EFFECTIVE LAI .51 3.79 None None None None

CRTFCN CODE CPI CPI None None None None

REVISION DATE 06-NOV-96 06-NOV-96 None None None None

Minimum Data Value -- The minimum value found in the column.

Maximum Data Value -- The maximum value found in the column.

Missng Data Value -- The value that indicates missing data. This is used to

indicate that an attempt was made to determine the

parameter value, but the attempt was unsuccessful.

Unrel Data Value -- The value that indicates unreliable data. This is used

to indicate an attempt was made to determine the

parameter value, but the value was deemed to be

unreliable by the analysis personnel.

Below Detect Limit -- The value that indicates parameter values below the

Page 18
Data Not Cllctd

instruments detection limits• This is used to

indicate that an attempt was made to determine the

parameter value, but the analysis personnel determined

that the parameter value was below the detection

limit of the instrumentation•

-- This value indicates that no attempt was made to

determine the parameter value• This usually

indicates that BORIS combined several similar but

not identical data sets into the same data base table

but this particular science team did not

measure that parameter•

Blank -- Indicates that blank spaces are used to denote that type of value•

N/A -- Indicates that the value is not applicable to the respective column

None -- Indicates that no values of that sort were found in the column•

7.4 Sample Data Format

The following are sample records from the data file on the CD-ROM:

Effective LAI

SITE NAME, SUB SITE, DATE OBS,TIME,TRANSECT,DISTANCE EFFECTIVE LAI,CRTFCN CODE

REVISION DATE

NSA-OBS-FLXTR'

NSA-OBS-FLXTR'

NSA-OBS-FLXTR'

NSA-OBS-FLXTR'

NSA-OBS-FLXTR'

NSA-OBS-FLXTR'

RSS07-EFL01

RSS07-EFL01

RSS07-EFL01

RSS07-EFL01

RSS07-EFL01

RSS07-EFL01

10-JUN-94 200227 'C

10-JUN-94 200349 'C

10-JUN-94 200949 'C

10-JUN-94 201029 'C

10-JUN-94 201050 'A

10-JUN-94 201106 'C

i0 2.34, CPI

20 2.49, CPI

30 2.46, CPI

40 2.23, CPI

i0 3.04, CPI

50 2.45, CPI

06-NOV-96

06-NOV-96

06-NOV-96

06-NOV-96

06-NOV-96

06-NOV-96

LAI, Gap Fraction, and FPAR Data

SITE NAME, SUB SITE, START DATE,END DATE,OP GRID INFO, SOLAR ZEN ANG,

DAILY GREEN FPAR, LAI STD METHOD,EFFECTIVE LAI,ELEMENT CLUMPING INDEX,

FOLIAGE TO TOTAL AREA RATIO,NEEDLE TO SHOOT AREA RATIO,PLANT AREA INDEX,

FOREST FLOOR ALBEDO,CRTFCN CODE,REVISION DATE

'SSA-YJP-FLXTR', 'RSS07-LAI01',24-MAY-94, 05-JUN-94, 'FeL6T',32•4, •68,2•86, i•51

1.43, .72, .95,2.98, , 'CPI',31-OCT-96

'SSA-YJP-FLXTR', 'RSS07-LAI01',24-MAY-94, 19-SEP-94, 'FeL6T', , , , , , , , , 6.2, 'CPI',

26-JUN-98

'SSA-9OA-FLXTR', 'RSS07-LAI01', 02-JUN-94, 02-JUN-94, 'C3B7T',32•4, •74,2•26,2•02 i•0,

•77, .92,2.63, , 'CPI',31-OCT-96

'NSA-9BS-9TETR', 'RSS07-LAI01', 06-JUN-94, 16-JUN-94, 'T6R5S',33•0, •86,4•29 ......

'CPI', 1 I-NOV- 96

8. Data Organization

8.1 Data Granularity

The unit of data tracked by the BOREAS Information System (BORIS) is all the data collected at a

site on a given day or for a given time period.

8.2 Data Format(s)

The Compact Disk-Read-Only Memory (CD-ROM) files contain American Standard Code for

Information Interchange (ASCII) numerical and character fields of varying length separated by

Page 19
commas.Thecharacterfieldsareenclosedwith singleapostrophemarks.Thereareno spacesbetween

thefields.

Eachdatafile ontheCD-ROMhasfourheaderlinesof Hyper-TextMarkupLanguage(HTML)

codeatthetop.Whenviewedwith aWebbrowser,thiscodedisplaysheaderinformation(dataset

title, location,date,acknowledgments, etc.)andaseriesof HTML links to associatedatafilesand

relateddatasets.Line 5of eachdatafile is alist of thecolumnnames,andline 6 andfollowinglines

containtheactualdata.

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.

9.4 Graphs and Plots

None.

Page 20
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:

• 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.

• 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).

• 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.

• 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.

• The sky brightness is azimuthally uniform.

• 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 rim. 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.

Page 21
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

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

These data can be used to establish relationships between LAI, FPAR, and remotely sensed radiances

and their transformations.

None given.

13. Future Modifications and Plans

Page 22
14.1 Software Description

None given.

14.2 Software Access

None given.

14. Software

15. Data Access

The RSS-07 LAI, gap fraction, 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).

15.1 Contact Information

For BOREAS data and documentation please contact:

ORNL DAAC User Services

Oak Ridge National Laboratory

P.O. Box 2008 MS-6407

Oak Ridge, TN 37831-6407

Phone: (423) 241-3952

Fax: (423) 574-4665

E-mail: ornldaac@ornl.gov or ornl@eos.nasa.gov

15.2 Data Center Identification

Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory

(ORNL) Distributed Active Archive Center (DAAC) for Biogeochemical Dynamics

http://www-eosdis.ornl.gov/.

15.3 Procedures for Obtaining Data

Users may obtain data directly through the ORNL DAAC online search and order system

[http://www-eosdis.ornl.gov/] and the anonymous FTP site [ftp://www-eosdis.ornl.gov/data/] or by

contacting User Services by electronic mail, telephone, fax, letter, or personal visit using the contact

information in Section 15.1.

15.4 Data Center Status/Plans

The ORNL DAAC is the primary source for BOREAS field measurement, image, GIS, and

hardcopy data products. The BOREAS CD-ROM and data referenced or listed in inventories on the

CD-ROM are available from the ORNL DAAC.

16. Output Products and Availability

16.1 Tape Products

None.

16.2 Film Products

None.

16.3 Other Products

These data are available on the BOREAS CD-ROM series.

Page 23
17. References

17.1 Platform/Sensor/Instrument/Data Processing Documentation

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

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

17.2 Journal Articles and Study Reports

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. 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. 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., 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, and S. Plummer. 1997b. Leaf area index of

boreal forests: Theory, techniques, and measurements. Journal of Geophysical Research 102(D24):

29,429-29,443.

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 Cauthy's theorems to estimation of surface areas of

leaves, needles and branches of plants, and light transmittance. Agric. For. Meteorol. 55:191-121.

Page 24
Newcomer,J.,D. Landis,S.Conrad,S.Curd,K. Huemmrich,D. Knapp,A. Morrell, J.Nickeson,

A. Papagno,D. Rinker,R.Strub,T. Twine,F. Hall, andP.Sellers,eds.2000.CollectedDataof The

BorealEcosystem-AtmosphereStudy.NASA. CD-ROM.

Sellers,P.andF.Hall. 1994.BorealEcosystem-AtmosphereStudy:ExperimentPlan.Version

1994-3.0,NASA BOREASReport(EXPLAN 94).

Sellers,P.andF.Hall. 1996.BorealEcosystem-AtmosphereStudy:ExperimentPlan.Version

1996-2.0,NASA BOREASReport(EXPLAN 96).

Sellers,P.,F. Hall, andK.F. Huemmrich.1996.BorealEcosystem-AtmosphereStudy:1994

Operations.NASA BOREASReport(OPSDOC94).

Sellers,P.,F. Hall, andK.F. Huemmrich.1997.BorealEcosystem-AtmosphereStudy:1996

Operations.NASA BOREASReport(OPSDOC96).

Sellers,P.,F. Hall, H. Margolis,B. Kelly, D. Baldocchi,G. denHartog,J.Cihlar, M.G. Ryan,B.

Goodison,P.Crill, K.J.RansomD. Lettenmaier,andD.E. Wickland. 1995.Theboreal

ecosystem-atmospherestudy(BOREAS):anoverviewandearlyresultsfrom the1994field year.

Bulletinof theAmericanMeteorologicalSociety.76(9):1549-1577.

Sellers,P.J.,F.G.Hall, R.D.Kelly, A. Black, D. Baldocchi,J. Berry, M. Ryan,K.J. Ranson,P.M.

Crill, D.P.Lettenmaier,H. Margolis,J.Cihlar, J.Newcomer,D. Fitzjarrald,P.G.Jarvis,S.T.

Gower,D. Halliwell, D. Williams, B. Goodison,D.E.Wickland, andF.E.Guertin.1997.BOREAS

in 1997:ExperimentOverview,ScientificResultsandFutureDirections.Journalof Geophysical

Research102(D24):28,731-28,770.

Welles,J.M. andJ.M.Norman.1991.Instrumentforindirectmeasurementof canopyarchitecture.

AgronomyJournal83:818-825.

17.3 Arehive/DBMS Usage Documentation

None.

None.

18. Glossary of Terms

APAR

ASCII

AVHRR

BOREAS

BORIS

CCRS

CD-ROM

DAAC

dbh

EOS

EOSDIS

FOV

FPAR

19. List of Acronyms

- Absorbed Photosynthetically Active Radiation

- American Standard Code for Information Interchange

- Advanced Very High Resolution Radiometer

- BOReal Ecosystem-Atmosphere Study

- BOREAS Information System

- Canada Centre for Remote Sensing

- Compact Disk-Read-Only Memory

- Distributed Active Archive Center

- diameter at breast height

- Earth Observing System

- EOS Data and Information System

- Field of View

- Fraction of Photosynthetically Active Radiation

Page 25
GIS

GMT

GPS

GSFC

HTML

IFC

IPAR

IRT

LAI

NAD83

NASA

NOAA

NSA

OA

OBS

OJP

ORNL

PAI

PANP

PPFD

RSS

SSA

TE

TM

TRAC

URL

UTM

YJP

- Geographic Information System

- Greenwich Mean Time

- Global Positioning System

- Goddard Space Flight Center

- HyperText Markup Language

- Intensive Field Campaign

- Intercepted Photosynthetically Active Radiation

- Infrared Thermometer

- Leaf Area Index

- North American Datum of 1983

- National Aeronautics and Space Administration

- National Oceanic and Atmospheric Administration

- Northern Study Area

- Old Aspen

- Old Black Spruce

- Old Jack Pine

- Oak Ridge National Laboratory

- Plant Area Index

- Prince Albert National Park

- Photosynthetic Photon Flux Density

- Remote Sensing Science

- Southern Study Area

- Terrestrial Ecology

- Thematic Mapper

- Tracing Radiation and Architecture of Canopies

- Uniform Resource Locator

- Universal Transverse Mercator

- Young Jack Pine

20. Document Information

20.1 Document Revision Date

Written: 29-Dec- 1995

Last Updated: 26-Jul- 1999

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.

If using data from the BOREAS CD-ROM series, also reference the data as:

Chen, J.M., J. Cihlar, and M. Penner, "Retrieval of Boreal Forest Leaf Area Index From Multiple

Scale Remotely Sensed Vegetation Indices." In Collected Data of The Boreal Ecosystem-Atmosphere

Study. Eds. J. Newcomer, D. Landis, S. Conrad, S. Curd, K. Huemmrich, D. Knapp, A. Morrell, J.

Nickeson, A. Papagno, D. Rinker, R. Strub, T. Twine, F. Hall, and P. Sellers. CD-ROM. NASA,

2000.

Page 26
Also,citetheBOREASCD-ROMsetas:

Newcomer,J.,D. Landis,S.Conrad,S.Curd,K. Huemmrich,D. Knapp,A. Morrell, J.

Nickeson,A. Papagno,D. Rinker,R.Strub,T. Twine,F. Hall, andP.Sellers,eds.CollectedDataof

TheBorealEcosystem-AtmosphereStudy.NASA. CD-ROM.NASA, 2000.

20.5 Document Curator

20.6 Document URL

Page 27
REPORT DOCUMENTATION PAGE FormApproved

OMB No. 0704-0188

Public reporting burden for this collection of informationis estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this

collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson

Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

July 2000 Technical Memorandum

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Technical Report Series on the Boreal Ecosystem-Atmosphere Study (BOREAS)

BOREAS RSS-7 LAI, Gap Fraction, and FPAR Data 923

6. AUTHOR(S) RTOP: 923-462-33-01

Jing Chen

Forrest G Hall and Jaine Nickeson, Editors

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS (ES)

Goddard Space Flight Center

Greenbelt, Maryland 20771

9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS (ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

8. PEFORMING ORGANIZATION

REPORT NUMBER

2000-03136-0

10. SPONSORING / MONITORING

AGENCY REPORT NUMBER

TM--2000-209891

Vol. 51

11. SUPPLEMENTARY NOTES

J. Chen: Canada Centre for Remote Sensing; J. Nickeson: Raytheon ITSS

12a. DISTRIBUTION / AVAILABILITY STATEMENT

Unclassifie_Unlimited

Subject Category: 43

Report available from the NASA Center for AeroSpace Information,

7121 Standard Drive, Hanover, MD 21076-1320. (301) 621-0390.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

The BOREAS RSS-7 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.

14. SUBJECT TERMS

BOREAS, remote sensing science, LAI, FPAR, LAI-2000, TRAC.

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OF REPORT

Unclassified

NSN 7540-01-280-5500

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