Evaluation of GPM DPR products after orbit boost using disdrometers over Italy

Precipitation monitoring plays a key role in understanding Earth's climate system and its effects on sectors such as hydrology, water resource management, and agriculture. Satellite-based measurements, particularly through missions like the Global Precipitation Measurement (GPM), have significantly enhanced our ability to observe precipitation patterns globally. Onboard the GPM Core Observatory, the Dual-frequency Precipitation Radar (DPR), consisting of the Ku-band Precipitation Radar (KuPR), which operates at 13.6 GHz, and the Ka-band precipitation radar (KaPR) at 35.5 GHz. The DPR has proven to be an indispensable instrument for characterizing water cycle study applications. To extend the life of a satellite, in order to guarantee the continuity of observations, a common strategy is to increase the orbit altitude. For this reason, on November 7 and 8, 2023, the GPM Core Observatory performed two orbit boost maneuvers that raised its altitude from 407 km to 442 km. As a result of this orbital elevation, the observing parameters of the GPM DPR instruments underwent some changes, such as the increase of spatial resolution and of the minimum detectable rain rate, which has had an impact on some geophysical products. To ensure the accuracy and reliability of satellite data over time, the GPM mission supported a Ground Validation program, which aims to verify and improve precipitation retrieval algorithms over time using multiple ground based instruments. This study focuses on GPM DPR Level 2 Version 7, which is the first to incorporate a modified scan pattern for the KaPR, introduced on May 21, 2018. This adjustment enables the dual-frequency radar to operate across the full observation swath. This study compares the GPM DPR Version 7 products, specifically the earlier Version 7A (before the orbit boost) with Version 7C (after the orbit boost), over Italy, using data from a network of ground-based laser disdrometers networked by the GID (Gruppo Italiano Disdrometria, in Italian). The dual-frequency-based 2ADPR-FS, as well as the single-frequency-based 2AKa-FS and 2AKu-FS Version 7 Level 2 DPR products are used. GPM data from May 22, 2018, to November 30, 2024, were analyzed. The following variables have been investigated: reflectivity factors at the Ku and Ka bands corrected for attenuation, rainfall rate, and DSD parameters D_m and N_w. Statistical indices are used to assess the agreement between satellite observations and disdrometer data. After the orbit boost, dual frequency still presents a slightly better agreement with disdrometers with respect to single frequency products. Discrepancies, however, were noted in the performance of rainfall and microphysical parameters, especially in areas with complex terrain and disdrometers located at high altitudes. In general, the comparison of Version 7A and Version 7C products with disdrometers helped reveal the limited influence of the orbit boost on the quality of DPR products. The results suggest that an orbital adjustment, similar to those implemented for the GPM mission, can be effectively adopted by other missions aimed at reconstructing the 3D structure of clouds and precipitation, since extending the satellite's operational life results in only a negligible impact on the quality of the data products.