The validation of satellite precipitation estimates with ground observations plays a vital role in the search for sources of errors. Additionally, satellite estimates and their performance change with precipitation types, intensities, and geographical conditions. An international team of scientists led by Rajani Kumar Pradhan of the Czech University of Life Sciences recently published an article reviewing the Integrated Multi-Satellite Retrievals for GPM (IMERG) validation studies around the globe characterized by various locations, topography, and climatic regions. Their results show that the distribution of IMERG validation studies worldwide is not uniform. For instance, countries like China, USA and India dominate with the highest number of studies while research over much of Africa is lagging behind (Figure 1).
Fig. 1. Geographical distribution of IMERG validation studies across the globe. The points do not represent the extent of the study domain but rather the mean latitude and longitude of the domain.
The spatial distribution of POD, FAR, and correlation values reported among the reviewed studies are shown in Figure.2. These values are based on a comparison of IMERG daily precipitation with the corresponding gauge observation on a daily scale. In terms of continents, IMERG has good detection skills over Africa with POD ranging from 0.73 to 0.84, and FAR up to 0.35, but moderate correlation ranging from 0.42 to 0.54. Similarly, North America (POD = 0.73–0.8, FAR = 0.17) and South America (POD = 0.51–0.89, FAR = 0.12–0.37) revealed a good detection skill, except Bolivia which reports the highest FAR of 0.56. In addition, both the continents reported a reasonable correlation (0.54–0.65) of IMERG with the reference data sets. High spatial variation in both POD and correlation is observed in Asia, varying from the poor results over Myanmar to high values over India. In addition, the East Asian countries such as Thailand, the Philippines, Nepal, and Malaysia have correlation values ranging from 0.5 to 0.69, whereas Japan, India, and China have COR > 0.7. In western Asian countries, Iran and Pakistan present a medium correlation (0.47 and 0.67, respectively). In terms of false detection, Iran reported a FAR of 0.51, which could be attributed to the prevailing arid condition, and evaporation of light precipitation before reaching the ground’s surface. Moreover, based on the POD, FAR, and COR values among the studies, it can be concluded that IMERG shows its good detection skills throughout various climatic and topographic conditions and has better agreement with the reference observations in overall precipitation estimation.
Read the whole article by Pradhan et al. at https://doi.org/10.1016/j.rse.2021.112754