Application of Spectral Remote Sensing for Agronomic Decisions

Remote sensing has provided valuable insights into agronomic management over the past 40 yr. Th e contributions of individu- als to remote sensing methods have lead to understanding of how leaf refl ectance and leaf emittance changes in response to leaf thickness, species, canopy shape, leaf age, nutrient status, and water status. Leaf chlorophyll and the preferential absorption at diff erent wavelengths provides the basis for utilizing refl ectance with either broad-band radiometers typical of current satellite platforms or hyperspectral sensors that measure refl ectance at narrow wavebands. Understanding of leaf refl ectance has lead to various vegetative indices for crop canopies to quantify various agronomic parameters, e.g., leaf area, crop cover, biomass, crop type, nutrient status, and yield. Emittance from crop canopies is a measure of leaf temperature and infrared thermometers have fostered crop stress indices currently used to quantify water requirements. Th ese tools are being developed as we learn how to use the information provided in refl ectance and emittance measurements with a range of sensors. Remote sensing continues to evolve as a valuable agronomic tool that provides information to scientists, consultants, and producers about the status of their crops. Th is area is still relatively new compared with other agronomic fi elds; however, the information content is providing valuable insights into improved management decisions. Th is article details the current status of our understanding of how refl ectance and emittance have been used to quantitatively assess agronomic parameters and some of the challenges facing future generations of scientists seeking to further advance remote sensing for agronomic applications.