Comparison of 1-min rain rate derived from TRMM satellite data and raingauge data for microwave applications in Nigeria

Abstract

A comparative statistical study of derived 1-min rain rate using data obtained from Tropical Rainfall Measuring Mission (TRMM) satellite (3A12 V6 and 3B43V6) and raingauge measurements are presented. 30-years data of rainfall intensities obtained from the Nigerian Meteorological Agency rain-gauge network and 9-years rainfall data obtained from TRMM satellite are used. Cumulative distributions of rain rate were obtained using a combination of an improved version of the Moupfouma–Martin model for rain rate prediction in the tropical regions. Variations of rain rate of different integration time are compared for 28 stations across Nigeria. The Kriging interpolation method was used for spatial interpolation of rain accumulation values into a regular grid in order to obtain a highly consistent and predictable inter-gauge rainfall variation. Noticeable differences between rain rate estimated from rain-gauge and TRMM data were found to be a function of period and location. From quantitative comparison over each of the region, there are reasonably positive correlations between the two sets of data for different percentages of time with correlation coefficient varying from 0.84 to 0.99 at 99.99% availability of time. Comparison with ITU-R 837-5 shows that, ITU model underestimates rain rate as high as 51% from the mean value depending on the percentages of at which time rain rate is exceeded. The overall result shows that the gauge data perform better than TRMM data in most of the sites located in the SW, SE, SS, MB and NE regions, while TRMM data provided better results for sites in the NW region from the statistical perspective with the lower RMS values.