Leaf Area Index Estimates for Wheat from LANDSAT and Their Implications for Evapotranspiration and Crop Modeling1

Abstract

Ground measurements of leaf area index (LAI) are tedious and costly. If they could be estimated spectrally from earth observation satellite data, evapotranspiration and photosynthesis models that use LAI as inputs could be implemented for large areas. Thus, we related LAI measurements of winter wheat (Triticum aestivum, L.) made in Kansas during the 1974–1975 and 1975–1976 growing seasons to three spectral vegetation indexes in the literature: transformed vegetation index (TVI), green vegetation index (GVI), and perpendicular vegetation index (PVI). The three vegetation indexes were each significantly linearly correlated (r = 0.70** to 0.95**) with measured LAI from the time LA1 was ≃ 0.3 until plant senescence, and their seasonal time courses were similar to those of directly measured LAI. Thus the indexes capture information on crop development and growing conditions manifested by LAI. We conclude that LAI can be calibrated in terms of the vegetation indexes to provide crop model inputs for as many fields as are of interest, or can serve as an independent check on model calculations when not used as a direct input to physical and physiological process models affected by the amount of vegetation present.