of crops to their multispectral reflectance properties. For example, 
it is essential to know in which regions of the spectrum information 
relating to variations in crop parameters is contained. This infor- 
mation is necessary for the optimum use of current Landsat technology, 
as well as for the design and development of future remote sensing 
systems. 
Differences among crop species and dynamic changes due to growth, 
development, stress, and varying cultural practices cause differences 
in the reflectance spectra of crops. 
Many of the factors affecting the reflectance properties of plant 
leaves have been identified and investigated utilizing laboratory 
measurements. The relationships of physical-biological parameters 
such as chlorophyll concentration, water content and leaf morphology 
to reflectance, transmittance and absorption have been well-established 
for leaves. Some of the papers and reviews describing these relation- 
ships include: Gates et al. (1965), Breece and Holmes (1971), Gausman 
et al. (1970), and Sinclair et al. (1971). 
Knowledge of the reflectance characteristics of single leaves is 
basic to understanding the reflectance properties of crop canopies in 
the field, but cannot be applied directly since there are significant 
differences in the spectra of single leaves and canopies. The reflec- 
tance characteristics of canopies are considerably more complex than 
those of single leaves because there are many more interacting vari- 
ables in canopies. Some of the more important agronomic parameters 
influencing the reflectance of field-grown canopies are: leaf area 
index, biomass, leaf angle, soil cover percentage, soil color, and 
leaf color. Differences in these parameters are caused by variations 
in many cultural and environmental factors, including planting date, 
cultivar, seeding rate, fertilization, soil moisture, and temperature. 
Solar elevation and azimuth angle and the view angle and direction of 
the sensor also affect the measured reflectance of crops and soils. 
The spectral and agronomic measurements which have been acquired 
during the three years of the LACIE field research program are being 
analyzed to provide an understanding of the relationship of reflectance 
to the biological and physical characteristics of crops and soils. The 
primary data analyzed to date are the spectrometer data acquired by the 
truck- and helicopter-borne systems. These data are particularly useful 
because the spectral data were acquired in 0.01 um wavelength intervals 
and are calibrated in terms of bidirectional reflectance. Having the 
entire spectrum from 0.4 to 2.4 um permits simulation of the response 
in any specified waveband. In other words, the analysis is not restricted 
to a fixed set of bands such as Landsat MSS or one of the aircraft scan- 
ner systems. Calibration of the data permits valid comparisons to be 
made among different dates, locations, and sensors. 
The overall objective of the analyses being conducted is to quanti- 
tatively determine the spectral-temporal characteristics of wheat, small