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A variety of systems and platforms have been used over the past three decades to acquire radar backscatter data of terrain. The variability in the reported data was evaluated for agricultural crops under "similar" phenological conditions and for approximately the same sensor parameters (frequency, polarization, and angle of incidence). The evaluation reveals wide variations in the magnitude of the scattering coefficient among different measurement programs. While it is difficult to determine the exact causes of these variations it is quite evident that extreme care must be employed in 1) monitoring the measurement system transfer function, 2) calibrating the system on an absolute basis, and 3) acquiring and reporting detailed target parameter information.
Bush et al. (Mon,) studied this question.