Synthetic Aperture Radar (SAR) radiometric characterization

The Synthetic Aperture Radar (SAR) is increasingly gaining acceptance as an important sensor with military and commercial applications. Characterization of the SAR sensor is paramount for interpreting the data and developing new applications. This paper reports on work done at the Naval Air Development Center (NADC) to quantify and correct the P3 SAR imagery data for various system effects. Among the major factors that affect SAR images is the antenna pattern. For the P3 SAR the antenna effect is particularly apparent at X band, where the imaged area is comparable in extent to the area illuminated by the main beam. The antenna pattern introduces a gain attenuation away from the main axis, as well as gain modulations due to pattern interactions with the aircraft structure. Additional factors that affect SAR images include range attenuation, range dependent processing gain, system non-linearities, and others. The paper presents integrated SAR radiometric calibration procedures developed at the NADC, that build on previous work done in this area by researchers at the Environmental Research Institute of Michigan (ERIM). The procedures enable relation and comparison of SAR imagery collected at different times and conditions, and provide for actual radiometric evaluation of SAR data. Tests were carried out to evaluate the proposed methods using targets of known radar cross section. The test results confirm the feasibility of the calibration process.