Simulation-based error analysis on the comparison between rainfall rates measured by a spaceborne radar and by ground-based instruments

The Tropical Rainfall Measuring Mission (TRMM) is a United States-Japan joint project for rain measurement from space. The first spaceborne rain radar has been installed aboard the TRMM satellite. The performance of the TRMM radar should always be validated against reference data. Use of the rainfall rate measured by ground-based instruments such as rain radar, rain gauges, or a radio link is a possible way to validate the TRMM radar. We have analyzed errors in the comparison of rainfall rates measured with the TRMM radar and with the ground-based instruments by means of a computer simulation that uses actual ground-based rain radar data. Results show that if the rainfall rate measured by the TRMM is compared with that measured by the ground-based radar at a higher correlation, the time difference between the TRMM and the ground-based radar measurements should be less than 5 minutes. Results also show that if the rainfall rate measured by the TRMM is compared with that measured by rain gauges and a radio link within a typical error on the radar measurement, nine rain gauges with 1 minute integration time or 16 rain gauges with 10 minutes integration time will be required in a pixel of the TRMM, and propagation path longer than 7 km of a radio link will be required.