An initial ground validation of the Integrated Multisatellite Retrievals for GPM (IMERG) Day-1 product from March 2014 to August 2015 is presented for the tropical Andes. IMERG was evaluated along with the Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) against 302 quality-controlled rain gauges across Ecuador and Peru. Detection, quantitative estimation statistics, and probability distribution functions are calculated at different spatial (0.1°, 0.25°) and temporal (1 h, 3 h, daily) scales. Precipitation products are analyzed for hydrometeorologically distinct subregions. Results show that IMERG has a superior detection and quantitative rainfall intensity estimation ability than TMPA, particularly in the high Andes. Despite slightly weaker agreement of mean rainfall fields, IMERG shows better characterization of gauge observations when separating rainfall detection and rainfall rate estimation. At corresponding space-time scales, IMERG shows better estimation of gauge rainfall probability distributions than TMPA. However, IMERG shows no improvement in both rainfall detection and rainfall rate estimation along the dry Peruvian coastline, where major random and systematic errors persist. Further research is required to identify which rainfall intensities are missed or falsely detected and how errors can be attributed to specific satellite sensor retrievals. The satellite-gauge difference was associated with the point-area difference in spatial support between gauges and satellite precipitation products, particularly in areas with low and irregular gauge network coverage. Future satellite-gauge evaluations need to identify such locations and investigate more closely interpixel point-area differences before attributing uncertainties to satellite products.
Bibliographical noteFunding Information:
This research was funded by the British Council Peru Project ''Towards a high-resolution gridded precipitation product for the tropical Andes.'' W.B. also received funding from U.K. NERC (Grant NE-K010239-1,Mountain-EVO project). Authors S.P.B. and N.H. gratefully acknowledge the financial support provided by the Escuela Polit?cnica Nacional, for the development of the project PIJ-15-14: ''Evaluaci?n de la aplicaci?n potencial de la precipitaci?n satelital obtenida de la misi?n-Global Precipitation Measurement (GPM)-a la gesti?n integrada de los recursos h?dricos en el Ecuador.'' B.O.T.'s contribution was funded by NERC SSCP DTP (Grant NE/L002515/1). B.W.'s contribution was supported by USAID through the PEER Project ''Strengthening resilience of Andean river basin headwaters facing global change'' (PGA 084063). The authors thank INAMHI, EPMAPS, SENAMHI, CONDESAN, and all the iMHEA partners for access to gauge records. The IMERG and TMPA datasets were provided by the NASA Goddard Space Flight Center's PMM and PPS, which develop and compute IMERG and TMPA as a contribution to GPM and TRMM, respectively.
- Complex terrain
- Error analysis
- Satellite observations
- South America