The theory and measurement of noncoherent microwave scattering parameters

The theories of observation and measurement of the average noncoherent scattering parameters for expansive scenes are developed and interpreted. The theory identifies all the scattering parameters and in this regard introduces three scattering coefficients not previously defined. The result is compared with the theory for coherent targets and a unique feature is identified. This feature, induced by spatial averaging, enables the theory to admit partially polarized returns. Intensity (power) and correlation techniques similar to that for coherent targets are proposed to measure all the scattering parameters. The sensitivity of the intensity technique to various practical realizations of the antenna polarization requirements is presented by means of computer simulated measurements. The simulations were conducted with a scattering characteristic similar to that of the sea. However, these results with the help of the theory axe easily extended to other characteristics. It is shown that careful adherence to the antenna polarization specifications is required to measure the weaker scattering parameters. In the case of the weaker parameters the complete antenna polarization property including the amplitude and relative phase of the orthogonal polarizations must be documented to validate the measurement. The results of this paper are useful for specifying radar scatterometer antennas, for designing meaningful noncoherent scattering experiments and for interpreting the character of scatterometer returns.