COMPARISON OF COHERENT AND NONCOHERENT POLARIMETRIC RADAR MEASUREMENTTECHNIQUES AT 95 GHZ

Polarimetric radar measurements can be made either coherently, by meas uring covariances of the various elements of the complex scattering ma trix, or noncoherently, by measuring a series of scattered Stokes vect ors associated with a set of transmit polarizations. The coherent appr oach can be difficult to apply at millimeter wavelengths, where rapid decorrelation of the scattered signal can cause errors in the measured covariance terms. The noncoherent method is not adversely affected by rapid decorrelation but requires a more complex transmitter to genera te multiple polarizations. To compare these two techniques, a 95-GHz p olarimetric radar was recently modified to simultaneously measure the Mueller matrix using the coherent and noncoherent approaches. Backscat ter measurements of foliage are presented showing the conditions under which the coherent measurements are in error. Finally, we show how to reduce motion-induced errors associated with the coherent technique w hen sampling a rapidly decorrelating scene.