67-1 A Diurnal Reflectance Model Using Grass: Surface-Substrate Interaction and Inverse Solution.



Monday, October 17, 2011: 1:05 PM
Henry Gonzalez Convention Center, Room 213A, Concourse Level

Mostafa Shirazi, US-EPA(Environ. Protection Agency), Corvallis, OR and Minocher Reporter, Botany & Plant Pathology, Oregon State University, Corvallis, OR
ABSTRACT

We report an analysis of canopy reflectance (ρ) experiment, using hand-held radiometer to measure distribution of biomass in a grass field. The analysis: 1) separates the green-fraction from thatch and soil background, 2) accounts for the changing diurnal ρ with the sun elevation angle, and 3) predicts plant biomass in a model directly from a new ρ observation, which is the inverse solution of the original experiment. Previous studies addressed one or more of these needs separately. Because reflectance components are inter-dependent, difficulties remain in obtaining a combined inverse solution. We combined a conditional probability method with a novel experimental procedure to predict grass dry weight (dw). Using the ratio of the Near Infrared and Red wavebands, that is, Simple Ratio, (SR)=(NIR)/Red that varied with the normalized time T = (local time-sunset)/(day length), we predicted the difference in grass dry weight (Δdw= dw1-dw2) of two grass patches. SR1 and dw1 defined the first patch which included a background and the second, SR2 and dw2, a pre-defined background. The inverted solution for Δdw was an ellipse with axes formed by the diurnal reflectance SR1 and SR2 coordinates. It described previously studied “soil line” and the zone of canopy-canopy-ground interactions. The standard error of predicting Δdw was 17%. We separately tested for plant height SR=f(h) or fresh weight SR=f(fw) as functions of SR and for dry weight as a function of normalized difference vegetation index NDVI=f(dw). SR=f(dw) produced superior results. Potential applications include predicting other biophysical plant properties in a single or in hyper-spectral bidirectional reflectance in agronomic and ecological remote sensing.

See more from this Division: ASA Section: Climatology & Modeling
See more from this Session: Soil-Plant-Water Relations: Modeling and Measurements