Assessing TROPICS SmallSat Precipitation for IMERG

Abstract

NASA's Time‐Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission provides rapid‐refresh microwave measurements through a low‐cost smallsat constellation, each equipped with the TROPICS Millimeter‐wave Sounder (TMS). To assess TROPICS‐derived precipitation for potential integration into the Global Precipitation Measurement (GPM) mission's Integrated Multi‐satellite Retrievals for GPM (IMERG), this study evaluates precipitation retrievals from four of the TROPICS satellites using Precipitation Retrieval and Profiling Scheme (PRPS), relative to the GPM radar‐radiometer combined product (2BCMB) over ocean and land, as well as five sensors in the GPM radiometer constellation, including two cross‐track scanning sensors [Advanced Technology Microwave Sounder (ATMS) and Microwave Humidity Sounder (MHS)], and three conical‐scanning sensors [Special Sensor Microwave Imager/Sounder (SSMIS), GPM Microwave Imager (GMI), and Advanced Microwave Scanning Radiometer 2 (AMSR2)]. Over ocean, the PRPS‐TMS precipitation intensity estimates correlate better (0.52–0.56) with 2BCMB than ATMS (0.39) and MHS (0.38), which exhibit unrealistic multi‐peak intensity distributions. However, TMS performs worse than conically scanning sensors, with greater bias, most likely due to the lack of low‐frequency channels and the availability of vertical and horizontal polarizations. Over land, TMS underestimates heavy precipitation to a greater extent than all sensors in the GPM constellation except SSMIS, with similar coarser spatial resolution. Furthermore, TMS retrievals show a clear scan‐position dependence, with performance degrading toward the swath edge. Among the four TMS sensors, precipitation detection performance and precipitation intensity estimation are generally consistent, with precipitation occurrence, correlation, and bias statistics all indicating stable retrieval performance throughout the TROPICS mission duration.