Improved Precipitation Rates and Data Quality by Using Polarimetric Measurements

Abstract

The additional information provided by polarisation-diversity radar has the potential to remove many of the ambiguities and uncertainties present when only the conventional reflectivity (Z) and Doppler information are available. In this chapter we emphasise the application in an operational environment with a typical one-degree beam-width radar and a dwell time of about one-sixth of a second, so that it completes a PPI every minute and provides rainfall estimates with a spatial resolution of 2 km or better. An excellent and very comprehensive book on polarimetric Doppler weather radar has recently appeared by Bringi and Chandrasekar (2001), and we refer the reader to this book for detailed derivations and analysis which we will simply quote. Essentially, polarimetric radar provides information on the shape and orientation of the radar targets. In Sect. 5.2, we define the polarisation parameters, summarise their applications and discuss the theoretical and practical limits to the accuracy with which they can be estimated. The variation of raindrop shape with size and the typical raindrop size spectra are reviewed in Sect. 5.3. The following sections consider how to exploit the shape and orientation information from a polarimetric radar which can transmit and receive horizontally and vertically polarised radiation, as described by Gekat et al. (2003), this book.