A study on radiometric calibration of next generation spaceborne SAR

With the new demands for SAR (Synthetic Aperture Radar), such as variable off-nadir and SCAN SAR, phased array radar technology is required for most of the next generation spaceborne SARs. Radiometric calibration of active phased array type SARs, however, is a very complicated task, because they have hundreds of active devices and phase shifters to be calibrated. In this paper, the authors have conducted a study on the internal calibration method for phased array type SAR. First, they derive the error sources of such kind of SARs. These are mainly divided into two categories, the variation in antenna and the variation in transmitter/receiver. Modified REV (Rotating Element Electric Field Vector) method, M. Seiji et al. (1982), is proposed for the calibration of antenna subsystem. By the compensation, the optimal antenna pattern can be maintained to keep high S/A and S/N of the SAR image, and the accurate antenna gain can be estimated For the calibration of transmitter/receiver, tone signal method and ERP (Effective Radiated Power) measurement method using REV antenna is proposed. By the compensation, the total gain variation of transmitter/receiver chains can be estimated. It is shown that the radiometric accuracy of 0.8 dB can be obtained by the above calibration methods together with the standard external calibration methods