Furthermore, homogeneous regions are of great importance in the calibration activities of the SAR satellites in orbit, which are used to measure some radiometric indicators such as the radiometric resolution and the relative radiometric accuracy. In general, SAR radiometric calibration can be completed based on natural homogeneous regions, e.g., lawns, forests, seas, and rainforests, and it assumes that the selected region is uniform with a known average backscattering coefficient.7,8 In Ref. 8, these radiometric indicators are measured based on the Amazon rainforests. The flatness and isotropy of the Amazon rainforest allowed an approximate homogeneous characterization, which makes this region a reference site in the in-orbit radiometric calibration for a number of SAR satellites, e.g., RADARSAT-1 and RADARSAT-2. However, these natural targets usually appear as weak backscattering regions in SAR images. Under some conditions of high noise level, they may be obscured by noise and no longer be suitable for SAR radiometric calibration. In addition, due to their natural properties, the backscattering coefficients of these natural targets are uncontrollable, and the homogeneity is also influenced by environment factors, e.g., the homogeneity of the Amazon rainforest suffers from the moisture variation and temperature variation throughout the year. These may incur additional errors in SAR radiometric calibration.