Non‐systematic errors of monthly oceanic rainfall derived from Passive Microwave Radiometry

Abstract

We compute the non‐systematic errors of monthly oceanic rainfall over 5° latitude by 5° longitude boxes derived from data taken by the Special Sensor Microwave Imager (SSM/I) on board the Defense Meteorological Satellite Program (DMSP) satellites and TRMM Microwave Imager (TMI). The mean rain rates between 1998 and 1999 are calculated to be 3.0, 2.85, 2.89 mm day−1 and the non‐systematic errors 22.2%, 22.4% and 19.7% for SSM/I onboard the DMSP F13, F14 and TMI, respectively. The non‐systematic error for the TMI is smaller than that for one SSM/I at the low rain rates but is comparable at rain rates higher than about 5mm day−1. The TRMM objective of 1mm day−1 for non‐systematic error is met by TMI for rain rates up to 5–6mm day−1. Improved space‐borne sampling strategy, such as that proposed for the Global Precipitation Mission (GPM), is needed to achieve errors better than 10% at the higher rain rates.