Improved Algorithms for the Measurement of Total Precipitable Water and Cloud Liquid Water from SARAL Microwave Radiometer Observations

Abstract

SARAL carried onboard a radar altimeter that provides very precise measurements of the sea surface height (SSH). Like other altimetric missions, SARAL carries a passive microwave radiometer (PMR) for wet tropospheric correction to SSH. In the present study, new algorithms are developed for the retrieval of cloud liquid water (CLW) and total precipitable water vapor (TPW) over the global oceans from PMR measurements of the brightness temperatures. A radiative transfer and genetic algorithm based retrieval scheme is proposed for the estimation of CLW and TPW from SARAL PMR. The comparisons of CLW from PMR with independent measurements from GPM-GMI and SSMIS within and outside ±40° latitudes show correlation (R) of 0.86 and 0.83, bias of 0.7 and −3.61 mg/cm², and root mean square error (RMSE) of 8.42 and 8.07 mg/cm², respectively. Similarly, TPW from PMR with GPM-GMI and SSMIS show R of 0.99 and 0.98, bias of −0.04 and −0.03 g/cm² and RMSE of 0.17 and 0.17 g/cm², respectively. The retrieval accuracy of CLW and TPW from the new algorithms is compared with these parameters provided in the SARAL geophysical data records as finished products, which showed substantial improvement in the quality of the parameters from the new algorithm.

Keywords:

• Cloud liquid water
• microwave radiometer
• radar altimeter
• sea surface height
• significant wave height
• water vapor

Acknowledgments

Authors are thankful to NASA (USA) for providing TRMM 3B42 data, NCEP/NOAA for model derived environmental fields, RSS (Remote Sensing Systems) for GMI and SSMIS geophysical products, and ISRO & CNES for SARAL data.