Range dependent errors in radar rainfall estimation

Abstract

Effect of the Earth’s curvature and increasing of radar beam as a function of range from a radar site cause the observation altitude and measurement volume to increase with range from the radar. This leads to error in radar rainfall estimates as a function of range. The objective of this paper was to study error characteristic of initial radar rainfall estimates of the Pimai radar as a function of range by considering the errors in term of differences between logarithmic of rain gauge and the corresponding radar rainfall data which were calculated by using the climatological Z-R relationship of the study area (logR_G-logR_R). Thirty-nine rainfall events recorded from the Pimai radar and 50 automatic rain gauges data during 2003-2004 were used in this study. The results of this study showed that error in initial radar rainfall estimates of the Pimai radar increase as a function of range at the range greater or equal to 70 km from the radar site. This range dependent error can be further used to adjust initial radar rainfall estimates for the Pimai radar to be equivalent to ground rainfall using rain gauge data.