OTTER Perkin-Elmer Spectrophotometer Data
	        OTTER Data Description

INVESTIGATOR:

	Lee F. Johnson
	Research Scientist
	TGS Technology Inc.
	NASA/Ames Research Center
	Moffett Field CA  94035

	Requested Acknowledgement:  Co-Author or Citation


INTRODUCTION:

	Hemispherical reflectance of leaves throughout the 400-
2400nm region has been measured as an aid to understanding 
remotely sensed spectral data collected at approximately the same 
point in the growing season.  Obtaining leaf spectra in the laboratory 
reduces or eliminates the confounding effects of atmosphere, 
platform instability, understory, exposed soils, mixed species, and 
canopy architecture which influence aircraft data.  Of particular 
interest is the spectral influence of biochemical absorption by  
nitrogen, lignin, chlorophyll, starch and cellulose.  Also of interest is 
examination of gross spectral properties such as the near-IR/red 
ratio and chlorophyll red-edge characteristics.  These data may 
identify spectral regions upon which to concentrate aircraft data 
analysis, provide an input to leaf-level radiative transfer models, or 
provide a check for aircraft data which have been processed into 
reflectance.  

	Five foliage samples were collected by shotgun or pruning pole 
from mid-upper canopy at each of the following OTTER sites:  Scio 
(control/fertilized Western hemlock), Warings Woods (Douglas fir), 
Cascade Head (Western hemlock/red alder).  Collection date was 3-4 
June 1991.  Each sample was separated into two portions, one for the 
spectral analysis reported here and another for chemical assay as 
part of the official Òoverflight dataset.Ó  The chemistry data (TN, TP, 
amino acids, sugar, starch, chl-A, chl-B) and description are available 
through the Forest Science Data Bank at Oregon State University.  
Each spectral analysis sample was immediately inserted along with a 
wadded-up wet paper towel into a transparent plastic bag and sealed 
airtight.  These were in turn inserted into black plastic bags to shield 
from light exposure, and stored either in ice chest or refrigerator 
until removed for spectral measurement.  These measurements were 
made during the period 14-18 June 1991.  The nearest Multisensor 
Aircraft Campaign to this time period occurred 15-22 May 1991.



EQUIPMENT:

 	Instrument:
			The spectrophotometer used was a Perkin-Elmer 			330 resident at  the Ecosystem Science and 				Technology Branch at NASA/Ames.  
			Manufacturer:
	
			Perkin-Elmer Corp., Analytical Instruments
			Main Ave. (MS-12)
			Norwalk CT 06856

	Key Variable:  
			Hemispherical Reflectance --
			Spectral Range:  400-2400nm
			Bandwidth:  6nm
			Sampling Interval:  2nm

	Calibration:

		One reflectance calibration standard, three wavelength 	
		standards, dark current, and background were measured.  
		Standards manufactured by:

			Labsphere, Inc.
			Box 70
			Shaker Street
			North Sutton, NH  03260

		  

DATA  MANIPULATION:

	For each sample, several needles including twig (or in the case 
of the alder, one entire leaf) were placed in the instrument sample 
holder, and scanned.  The instrument produced raw reflectance for 
each scan by comparing target response with that of an aluminum-
oxide standard of unknown (to the investigators) characteristics.  
Absolute reflectances reported to PLDS were developed by adjusting 
raw reflectance per channel by use of a spectralon reflectance 
standard (Labsphere SRS-75-020-4582-E) of known reflectance 
factor as follows:

		p(abs) = p(std) * [(x - xo) / (r - xo)],

		where:

		p(abs) = absolute reflectance of sample
		p(std) = reflectance factor of standard
		x = raw reflectance of foliage
		r = raw reflectance of standard
		xo = raw reflectance of dark current


	A localized smoothing operation was performed on each spectrum 
at about 875nm, to remove a spike which occurs due to detector change.
	

QUALITY ASSESSMENT:

		The absolute reflectance reported to PLDS includes both 
diffuse and specular reflectance from leaf. The conifer samples typically 
covered 90-95% of the sample port; thus these measurements will include 
a component of direct reflectance from the background (which is on the 
order of 4% throughout the spectral range).  No background was exposed 
to the detector during the alder scans.

	Because of the slow scan time (~20 minÕs/per scan), only one 
scan was taken of each sample.  Therefore the standard deviation at 
each channel is unknown.

	No objective effort was made to control for either biomass or 
architecture presented to the instrument.  This could account in part 
for variations in reflectance magnitude observed among scans.  
Particularly high variation is evident in the scans from the Warings 
Woods site.

	A residual effect of the spike described above may remain at 
about 875nm.

	These data are very noisy at wavelengths greater than 1900nm.

	The elapsed time between harvest and scan may have caused 
some biochemical differences to arise between the spectral samples 
and the corresponding assay samples.  

	Wavelength accuracy was shown by the spectral calibration to be 
plus or minus 2 nm throughout the spectral range, and no 
adjustment was made to the measured spectra.