Application of the 2D-video-distrometer for weather radar data inversion

Conversion of radar reflectivity Z to precipitation rate R is the basic tas k in weather radar data processing. The relationship Z = a * R-b depends on precipitation fine structure, like material type, shape and size distribut ion. In order to apply the right constants for Z-R conversion, ancillary pr ecipitation characteristics are required. The 2D-Video Distrometer (2DVD) o ffers the capability of measuring particle shapes and sizes (front and side views) with precision in the order of 0.2 mm, as well as the particle's fa ll speed, with an error typically less than 5%, over an active catchment ar ea of approx. 100 cm(2). Over the last eight years an extensive data base h as been collected with such distrometers, in different climates and seasons . Significant samples have been extracted from this data base, in order to check the validity of so far used Z-R relationships and their extreme cases . It is found, that tropical rain contains more smaller, showery or convect ive events in moderate climate more bigger drops than expected by present p arameter limits. The overall result of this study is that traditional liter ature models and parameter limits may be exceeded in nature, and in particu lar that higher Z,, values may be observed than expected, caused by an exce ss of large drops. (C) 2000 Elsevier Science Ltd. Ail rights reserved.