32nd Conference on Broadcast Meteorology/31st Conference on Radar Meteorology/Fifth Conference on Coastal Atmospheric and Oceanic Prediction and Processes

Monday, 11 August 2003
X-port, a new X-band polarimetric system for hydrometeorological applications
Marielle gosset, LTHE / IRD, France, 38041 Grenoble cedex 9, Isere, France; and F. Cazenave
A new X-band radar system is being developped in our group : X port is a pulse magnetron radar (Pt 100 kW) with a choice of pulse lengths from .44 to 1 Ás and corresponding PRF ranging from 1 to 2.5 kHz. Polarisation diversity is obtained thanks to a 6 feet diameter, orthomode fed antenna. The radar is equipped with 2 receivers to allow simultaneous reception of both H and V polarization (better quality than for alternate). The acquisition system is PC based, on a linux system.: Coherent measurement is obtained thanks to reference on 'gate 0' (leak from TX). Digitalisation and extraction of the phase information (I,Q) is realized at the intermediate frequency level (60 MHz) thanks to a fast acquisition card ( 2 channels 14 bits). Radar signal processing is then done entirely on the receiving Linux-PC CPU, so that a high flexibility in the processing is achieved. The normal acquisition mode provides for each distance gate and each channel : the received power Ph and Pv, Doppler shift, calculated for any number of time samples. The computer also provides differential phase shift PHIdp, the correlation RHOhv, and a coherence indicator. The configuration also allows to acquire complete temporal series for FFT analysis of the Doppler spectrum. (At vertical elevation this mode is used for the study of the drop size distribution and its evolutionů. ) An experiment is currently setup to assess the quality of PHIdp based measurement of attenuation at X-band. The radar will be operating in a mountaneous area, where the ground echoes have been studied for many years, and the PHIdp estimate of attenuation will be compared to the surface reference techniques. The overall system performances and preliminary test results will be presented at the conference.

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