Evaluation and Improvement of the NPP CrIMSS Rain Flag

As part of the Suomi National Polar-orbiting Partnership (NPP), Crosstrack Infrared and Micrwoave Sounding Suite (CrIMSS), a joint system that utilizes the Crosstrack Infrared Sounder (CrIS) and the Advanced Technology Microwave Sounder (ATMS) in synergy, an ATMS only rain flag is utilized to edit out potentially rain contaminated scenes that will lead to degraded temperature and moisture profiles. The pre-launch CriMSS rain flag was based on a pre-launch AMSU-A heritage rain detection scheme that subsequently was replaced by a much more accurate and advanced scheme that utilizes both AMSU-A and AMSU-B/MHS channels, in particular, measurements at an above 89 GHz which is more sensitive to precipitation than those which use more traditional channels at or below 89 GHz. Analysis of the current CriMSS rain flag has shown several deficiencies when compared to the more accurate AMSU-B/MHS algorithms which are currently operational at NOAA/NESDIS for use on the POES satellites. This has been attributed to both the outdated nature of the AMSU-A algorithm that was used and the fact that the algorithm was not implemented properly. Thus, very little rain is detected in the Intratropical Convergence Zone (ITCZ), one of the rainiest regions on the globe. Additionally, the current algorithm detects very little precipitation over land since it is not utilizing the high frequency measurements above 89 GHz, as well as not taking advantage of the better spatial resolution at those frequencies.

In this paper, details on the evaluation of the current rain flag will be presented. Additionally, a proposed new rain flag, based on the current NOAA/NESDIS POES algorithm heritage, retrofitted to work with the ATMS sensor, will be presented.