A Comparison of Near-Concurrent Measurements From the SSMIS and CoSMIR for Some Selected Channels Over the Frequency Range of 50-183 GHz.

Ten underflights of the Special Sensor Microwave Imager/Sounder (SSMIS) with Conical Scanning Millimeter-wave Imaging Radiometer (CoSMIR) onboard the NASA ER-2 aircraft were conducted over the coastal region of California between March 2004 and March 2005. The measured brightness temperature (T_b) values from both sensors are collocated and compared at frequencies of 50.3, 52.8, 53.6, 91.655, 150, 183.3 ± 1,183.3 ± 3, and 183.3 ± 6.6 GHz. The more transparent channels at 50.3, 91.655, and 150 GHz are strongly affected by the changes in surface emission and low-level liquid clouds. Thus, the average differences in T_b values (δT_b), measured by the two sensors, and their changes from flight to flight are difficult to assess. For the remaining opaque channels, using the CoSMIR measurements as reference, the lowest SSMIS T_b values occur when the SSMIS is completely under the Earth's shadow. As the satellite moves out of the Earth's shadow in the ascending passes, the SSMIS T_b values are found to gradually increase with more exposure to the sun. The magnitudes of these T_b changes are about 4-5 K for the three 183.3-GHz channels and about 2 K for the 52.8- and 53.6-GHz channels. [ABSTRACT FROM AUTHOR]