Microwave radiometer inter-calibration using the vicarious calibration method

The vicarious cold and warm calibration methods of Ruf, and Brown and Ruf, have been used to assess the calibration of the WindSat radiometer as well as the biases of the TMI, SSM/I F13 and SSM/I F14 radiometers relative to WindSat. WindSat biases computed as a function of scan position are consistent with a roll offset of the instrument of 0.2° and a pitch offset of 0.15°, and biases in the 6 GHz and 22 GHz channels of up to 8 Kelvins are consistent with an obstruction in the feed-horn edge of scan fields of view. Beam fractions and effective brightness temperatures of the obstructions are estimated for each affected channels using both the vicarious cold and warm calibration observations to produce an end-to-end WindSat calibration. Computed biases of TMI, SSM/I F13 and SSM/I F14 relative to WindSat agree well with independent estimates.