It is becoming increasingly clear that improvements are needed in the methodology for measuring precipitation in order to make progress in properly representing the hydrological cycle in numerical models. While this is a global problem, it is necessary to have reliable local measurements of precipitation to validate satellite retrievals and model predictions, This paper presents a novel low-powered S-band precipitation profiler that has been developed and utilized by the NOAA Aeronomy Laboratory for calibration and validation for the Tropical Rainfall Measuring Mission (TRMM). The precipitation profiler can be calibrated by a collocated disdrometer and used as a calibration tool for scanning radars. More importantly, it has been demonstrated that drop-size distributions can be retrieved from the profiler making it possible to determine precipitation parameters directly without using empirical Z-R relations. This suggests that the profiler has an important role to play in integrated hydrological observing systems of the future.

The NOAA Aeronomy Laboratory has used profilers at 915 MHz and S-band for precipitation research in several tropical field campaigns during the past decade. S-band is a convenient frequency to use for this purpose since it is not attenuated even in heavy precipitation. It also coincides with the frequency of the WSR-88D. The low-powered S-band system uses a dish antenna and only points vertically. It is relatively insensitive to Bragg scatter. The low-powered S-band profiler has been extensively utilized in TRMM ground validation field campaigns over the past few years. In each campaign the profiler was collocated with a 915 MHz profiler. The two profilers operating side by side obtained independent measures of reflectivity that have been used to cross-validate the two profilers.

In this paper we show sample observations of precipitating clouds seen during the TRMM field campaigns and show how the profiler can be used as a transfer standard for calibration of scanning radars.