ABSTRACT
Remote sensing has provided valuable insights into agronomic management over the past few decades. The use of remote sensing for determining crop physiological and phenological status has its roots in the pioneering work by William Allen, Harold Gausman, and Joseph Woolley [1-3], who provided much of the basic theory relating morphological characteristics of crop plants to their optical properties. These pioneering works have led to the understanding of how leaf reŸectance changes in response to leaf thickness, species, canopy shape, leaf age, nutrient status, and water status. Leaf chlorophyll content and its absorption in the visible spectrum provide the basis for utilizing reŸectance as a tool either with broadband radiometers typical of current satellite systems or hyperspectral sensors that measure reŸectance at narrowbands. The basic understanding of leaf reŸectance has led to the development of various vegetation indices (VIs) that have been extended to crop canopies and have been used to quantify various agronomic parameters (e.g., leaf area, crop cover, biomass, crop type, nutrient status, and yield). These tools are still being developed as we learn more about how to use the information contained in reŸectances from a range of different sensors.
