Modeling Biophysical Factors for Grasslands in Eastern Kansas Using Landsat TM Data

Abstract

Objective of this study was to evaluate the relationships between grassland biophysical factors and spectral reflectance patterns recorded by the Landsat Thematic Mapper (TM) in eastern Kansas. Grasslands were stratified by cool and warm season life-forms, as well as grazed, hayed, and Conservation Reserve Program (CRP) management practices. Strength of the relations was examined using the raw TM reflectance values, and various vegetation indices (i.e., Normalized Difference Vegetation Index, brightness, vegetation greenness, wetness). Results indicated significant relationships between aboveground biomass and spectral variables and between plant moisture and spectral variables. Aboveground biomass also was correlated highly with plant moisture (r = 0.76). Total vegetation cover was correlated moderately with spectral data (r < 0.55). The relative cover by grasses was uncorrelated, whereas forb cover was correlated with spectral data suggesting that variation in forb composition among grassland types is a significant factor affecting spectral reflectance. Regression analysis results suggest that TM data are better predictors of aboveground biomass than any other biophysical factors (adjusted R2 = 0.77). Relationships between the spectral variables and many of the biophysical factors were improved significantly when the models were developed for the individual grasslands types. The use of the TM vegetation indices did not significantly improve the ability to predict biophysical factors.