A Review of Multitemporal Synthetic Aperture Radar (SAR) for Crop Monitoring
Synthetic Aperture Radars (SARs) transmit and receive energy at microwave frequencies. The response recorded by these sensors is largely a function of the structure and dielectric properties of the target. The structure of a canopy is different among crops, and changes as crops grow. SARs respond very well to these structural differences and thus these sensors are able to accurately identify crop type and have proven sensitive to several crop biophysical parameters (Leaf Area Index, biomass, canopy height) Although optical sensors have traditionally been used for crop monitoring, advances in SAR applications research coupled with availability of SAR data at different frequencies and polarizations has raised the profile of these sensors for agricultural monitoring. And the "all weather" capability of SARs makes their use in operational activities of particular interest. Advancements in SAR applications development, continued improved access to data, and a push to transfer SAR research methods to monitoring agencies will lead to an increased role of SAR in monitoring agricultural production. This chapter reviews SAR research as it relates to crop type and acreage estimation, as well as determination of crop condition and crop bio physical properties.