XRain is based on a dataset of historical precipitation measured using satellites. This dataset, known as GPM_3IMERGHH_06, is supplied by the Global Precipitation Measurement (GPM) mission, a joint project between NASA and JAXA.
GPM_3IMERGHH_06 (Huffman et al., 2019) is the GPM IMERG (Integrated Multi-satellitE Retrievals for GPM) Final Precipitation L3 Half Hourly 0.1 degree x 0.1 degree V06B.
The dataset provides a calibrated precipitation field (“precipitationCal”) in units of mm/hr. This data is derived from measurements made by passive microwave (PMW) sensors on a constellation of satellites orbiting the earth, and is calibrated against monthly precipitation totals taken from over 79,000 rain gauge stations across the world. Calibration rain gauge data is supplied by the Global Precipitation Climatology Centre (GPCC).
The dataset:
- Uses the WGS84 coordinate system with a spatial resolution of 0.1° by 0.1°; roughly 11 km by 11 km at the equator and 6 km by 11 km at ± 60° latitude
- Has a temporal resolution (i.e. time step) of 30 minutes, but is based on periodic near-instantaneous measurements as satellites orbit the earth
- Begins 1 June 2000, but for the XRain analysis only full years of data are used, from 1 Jan 2001 to 31 Dec 2020
- Has near-complete temporal coverage between 60° N and 60° S.
This resolution equates to 3600 cells (pixels) wide by 1200 cells high between 60° N and 60° S; a total of 4.32 million cells. The figure below plots mean annual depth between 60° N and 60° S (download the source GIS data here).
Remotely-sensed data such as this is not as accurate as rain gauge data which is measured directly, but satellite data is not limited to the locations where rain gauges are physically installed. We encourage you to carry out your own evaluation on the suitability of any information for your particular project, and to calibrate against known data where possible.