The Global Precipitation Measurement (GPM) satellite, launched by NASA and JAXA in 2014, is designed to measure rainfall from space. Scientists often compare GPM data to ground-based rain gauges to check its accuracy. However, these comparisons show mixed results—sometimes the satellite matches well with ground data, and sometimes it doesn’t.

In 2023, Lehman College (CUNY) installed a NASA-built rain gauge station with two tipping buckets to help validate GPM data. Analysis of rainfall events in 2024 showed a wide range of correlation values (R² from 0 to 0.9), indicating inconsistent agreement between satellite and ground measurements.

To improve the analysis, researchers added data from a nearby weight-based MESONET gauge that helped to verify the accuracy of the NASA gauge. MESONET is a network of 127 weather stations across New York State. Additional MRMS radar data provided high-resolution rainfall estimates and helped explore how rainfall varied within the GPM satellite’s field of view.

The study found that when rainfall was clustered and uniform, the satellite data matched better with ground measurements. In contrast, scattered rainfall led to weaker correlations. Seasonal patterns also played a role: spring showed the highest median correlation, while autumn had the lowest.