Calibration of the fully polarimetric microwave imager (mwi) on the weather system follow-on - microwave (wsf-m) satellite

The MWI digitally correlates the v-pol and h-pol channels at 10.85, 18.85 and 36.75 GHz to generate the modified Stokes vector (v-pol, h-pol, 3(rd) Stokes and 4(th) Stokes). In addition to using the hot and cold views to obtain gain and offset, the coupling from each of the other polarizations needs to be removed to calibrate 3(rd) and 4(th) Stokes. The 1(st) Stokes coupling is easily computed using the hot and cold views, but the 2(nd) Stokes coupling cannot be computed with the on-board calibration scheme and must be determined pre-launch. Decoupling the 3(rd) and 4(th) Stokes channels requires knowledge of the receiver phase, which is obtained via on-board correlated noise sources. Additional coupling from the 2(nd) Stokes into the 3(rd) Stokes caused by misalignment of the antenna to the Earth is calibrated geometrically using the measured attitude. Faraday Rotation of the polarization is estimated and corrected from the total electron content in the atmosphere. Detailed antenna pattern measurements allow for the calibration of the beam squint via a modified Backus Gilbert approach.