The application of C-band polarimetric SAR for agriculture: a review

Agricultural targets are very dynamic throughout the growing season, and thus remote sensing is an attractive approach to mapping and monitoring applications. Research performed with synthetic aperture radar (SAR) satellite systems such as European Remote Sensing Satellites ERS-1 and ERS-2, Japanese Earth Resources Satellite 1 (JERS-1), and RADARSAT-1 has demonstrated the potential of using this approach for a wide variety of applications. These satellites all have single-channel radars, however, and the research often concluded that additional channels and multitemporal observations were required. Spaceborne imaging radar C/X-band synthetic aperture radar (SIR-C/X-SAR) demonstrated this approach but was limited to two flight periods for data collection and a relatively small number of sites. RADARSAT-2 will have multipolarization and polarimetric modes and higher resolution than RADARSAT-1. ENVISAT advanced synthetic aperture radar (ASAR) also has a multipolarization capability. These sensors will allow further development of applications in agriculture, particularly crop-type mapping and condition assessment, soil tillage and crop residue mapping, and soil moisture estimation. Research has demonstrated that the additional polarizations will increase the information content in a SAR dataset similar to using multispectral approaches in the optical region. The value of the phase information and the polarimetric parameters that can be derived from these data is less certain. However, this information does help in understanding the scattering mechanisms and target interactions that are occurring, leading to a better approach to data processing and information extraction. Integrating C-band SAR with data acquired at other radar frequencies, or with data acquired by optical sensors, can provide additional crop and soils information. This paper reviews the use of C-band polarimetric and multipolarization data for agricultural applications with an emphasis on the potential of the upcoming RADARSAT-2 system.