The design, analysis, and demonstration of a digital-correlation microwave
polarimeter for use in Earth remote sensing is presented. We begin with an
analysis of a three-level digital correlator and develop the correlator tra
nsfer function and radiometric sensitivity. A fifth-order polynomial regres
sion is derived for inverting the digital correlation coefficient into the
analog statistic. In addition, the effects of quantizer threshold asymmetry
and hysteresis are discussed. A two-look unpolarized calibration scheme is
developed for identifying correlation offsets. The developed theory and ca
libration method are verified using a 10.7 GHz and a 37.0 GHz polarimeter.
The polarimeters are based upon 1-GS/s three-level digital correlators and
measure the first three Stokes parameters. Through experiment, the radiomet
ric sensitivity is shown to approach the theoretical as derived earlier in
the paper and the two-look unpolarized calibration method is successfully c
ompared with results using a polarimetric scheme. Finally, sample data from
an aircraft experiment demonstrates that the polarimeter is highly useful
for ocean wind-vector measurement.