Application of antenna with controllable polarization for hail and icing areas detection

Abstract

Discussed here is the possibility of finding the areas of hail and icing in clouds that are dangerous for aircraft to fly in. The method is based on the polarization effects appearing due to returning of 10 GHz radar signals from various hydrometeorological particles.

The preceding theoretical study has made it possible to obtain mathematical patterns showing dependence of the polarization parameters (differential reflectivity and depolarizatioirvalue AP) on the shape, phase structure, orientation angle, and form-factor of diffusing particles. The results have shown that simultaneous determining of Z_dr and AP allows to find the shape and the orientation angle of elliptical scatterers, and by this to exclude the apriory assumptions about the orientation of particles. These parameters in their own turn are connected to the microphysical characteristics of reflecting objects. This opens the way for creation means for the localizing areas of hail and icing. Realization of dualpolarization sounding is possible if there is an opportunity of automatic control of the radiated signal polarization. The reception of the signal with the same polarization as radiated and the signal with orthogonal polarization is necessary. Unfortunately the known airborne weather radars do not provide such opportunity. Here we point out to the technical and economic advantages and shortcomings of single-channel approaches to the design of radar polarimeters. For the experimental investigation, a parabolic-reflector antenna of the airborne weather radar «Groza-M» (wavelength 3.2 cm) has been modernized, and a polarization-control block was introduced. The technical advantage of proposed simple and cheap antenna with controllable polarization is the opportunity of reception, and then re-sending to the input of a single-channel receiver, of the main component of the signal reflected from the target as well as the cross-polarized component (at any polarization of radiated signal). This permits to receive various combinations of polarization parameters of signals at transmission and reception, and thus, to improve the functional performance of antenna. The results of antenna testing and analysis of experimental data received with the aid of polarimetric radar are given in the paper. These results agree with theoretical considerations. The results of sounding of natural clouds were used for the synthesis of algorithms of the hail areas detection and zones of probable aircraft’s icing finding. Here the differential reflectivity Z depolarization AP and radar reflectivity dBZ were used in common. The results of the work show the possibility and usefulness of the design of airborne and ground-based equipment for effective detection of the dangerous-to-flight hail and icing areas in clouds.