Extended Abstract

check of echo intensity data is also conducted.Fig. 1 Accumulation of radarintensity data.(Left) one hour averagedecho(Right) same as the leftexcept for consideration ofmovements of echoes.3.2 CALIBRATION OF RADAR DATAIn this section, we describe the procedures for calibrating one hour accumulated echointensities with raingauge measurements to estimate precipitation.3.2.1 CALIBRATION OVER ALL RADAR OBSERVATIONAL RANGEOne hour accumulated echo int ensities at the grids of rai ngauges are generallydifferent from those raingauge values. Because raingauge measurement is morereliable, we calibrate the echo intensities of a radar with raingauge observations withinthe observational range of the radar under the following two conditions.(1) an average of calibrated echo intensities of a radar over a domain should be equalto those of other radars observing the same domain.(2) an average of the calibrated echo intensit ies at the grids of raingauges should beequal to the average of the raingauge values.3.2.2 CALIBRATION OVER LANDThe calibrated echo intensities as abov e are further calibrated to be equal t oraingauge data at local scales ( Makihara, 2000). For example, the calibrated echointensities at a grid g derived in 3.2.1 is calibrated again with raingauges within about40km from the grid g. A calibration factor at the grid g is calculated with weightedinterpolation of the calibra tion factors of the grids of above raingauges. Here, acalibration factor of a raingauge grid is defined as a ratio of a rai ngauge value to thecalibrated echo intensity at the grid of ra ingauge derived in 3.2.1. The weight for theinterpolation takes into account following items.(1) distances between the grid g and raingauges(2) differences between the ec ho intensity at the gri d g and those at the grids ofraingauges(3) beam attenuation rate by precipitation(4) uniformity of raingauge distribution-108-