Determination of precipitable water and cloud liquid water over oceans from the NOAA 15 advanced microwave sounding unit

The advanced microwave sounding unit (AMSU) was finally launched in May 199 8 aboard the NOAA 15 satellite. Algorithms are provided for retrieving the total precipitable water (TPW) and cloud liquid water (CLW) over oceans usi ng the AMSU measurements at 23.8 and 31.4 GHz. Extensive comparisons are ma de between the AMSU retrievals of CLW and TPW and those obtained using othe r satellite instruments (Special Sensor Microwave Imager (SSM/I) and Tropic al Rainfall Measuring Mission (TRMM) Microwave Imager (TMI)) and ground-bas ed radiometers. The AMSU TPW is also compared against radiosonde data, wher e all of the results are in good agreement with rms differences less than 3 mm and biases less than 1 mm over the range between 5 and 60 mm. The CLW c omparisons show greater variability, although the time series of the AMSU a nd ground-based sensors follow each other and cover the same dynamic range of 0-0.5 mm. The AMSU CLW also compares well with the other satellite measu rements, although a bias exists between AMSU and TMI when the CLW exceeds 0 .5 mm.