Digital correlation microwave polarimetry: Analysis and demonstration

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.