TOPEX POSEIDON MICROWAVE RADIOMETER (TMR) .2. ANTENNA PATTERN CORRECTION AND BRIGHTNESS TEMPERATURE ALGORITHM/

The calibrated antenna temperatures measured by the TOPEX Microwave Ra diometer are used to derive radiometric brightness temperatures in the vicinity of the altimeter footprint, The basis for the procedure devi sed to do this-the antenna pattern correction and brightness temperatu re algorithm-is described in this paper, along with its associated unc ertainties, The algorithm is based on knowledge of the antenna pattern , the ground-based measurements of which are presented along with thei r analyses, Using the results of these measurements, we perform an err or analysis that yields the net uncertainties in the derived Th IR foo tprint brightness temperatures, The net brightness temperature uncerta inties range from 0.79 to 0.88 degrees K for the three TMR frequencies , and include the radiometer calibration uncertainties which range fro m 0.54 to 0.57 degrees K, We also derive an estimate of the uncertaint y incurred by using brightness temperatures measured in the similar to 40 km TMR footprint to estimate path delay in the similar to 3 km alt imeter footprint. The RR IS difference in path delay averaged over the largest TMR footprint relative to that in the altimeter footprint is estimated to be about 0.3 cm, Finally, we discuss the error associated with using unequal beams at the three TMR frequencies to derive path delays, and describe an approach using along-track averaging of the al gorithm brightness temperatures to reduce this error,