THE OPTICAL SPECTROPLUVIOMETER REVISITED

The optical spectropluviometer is a shadowgraph instrument able to mea sure independently the equivalent diameter and the fall speed of raind rops at ground level. Hardware and software modifications are proposed and tested. A modern digital signal processing system allows for the simultaneous sampling and analyzing of the signal delivered by the sen sor. The IR light transmission is pulsed to avoid interference with na tural radiation and the protection of the optics is improved. The vali dation procedure consists of comparing the rain rates derived from the measured drop size distributions with rain rates delivered by nearby rain gauges. The results obtained during 65 storm events show that the proposed improvements reduce th(: bias of the rain-rate estimation fr om 34% to 16%. Suggestions are given to further improve the performanc e of this instrument.