Atmospheric radar wind profilers operating at several different frequencies are now used routinely as research tools to profile the atmosphere during field campaigns. The ability of these relatively small moveable profilers to measure the reflectivity and motion of hydrometeors in precipitating clouds has been utilized in many campaigns, including the Hawaiian Rainband Project (HARP) and the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE), and most recently in the Tropical Rainfall Measuring Missions (TRMM) Ground Validation Field Campaigns.

Quantified precipitation measurements such as rain rate and drop size distribution are obtained from the observed Doppler spectral moments of reflectivity and radial velocity. In addition, utilizing the observed Doppler spectral width and the observed vertical structure, it is also possible to classify observations into categories such as stratiform, convective, or mixed.

Of course it is necessary to absolutely calibrate the profiler reflectivities in order to quantify the reflectivity dependent precipitation parameters. To this end a Joss-Waldvogel disdrometer was collocated with the profilers used in each of the TRMM Ground Validation Field Campaigns. The addition of this instrument as a reference standard has proven a powerful addition to the sites, enabling semi-continuous monitoring of the profiler absolute calibration. In addition, having this ongoing reference has been extremely useful in the early detection and identification of occasional hardware malfunctions.

This paper focuses on several issues that arise in the calibration of profilers using impact disdrometers. We show results of inter-comparisons of profiler reflectivities with disdrometer reflectivities calculated from surface drop-size distributions and direct attention to sampling issues inherent in the small sample size of the disdrometer and other issues that can cause disdrometer and profiler reflectivities to disagree.