Simulation of mono- and dual-wavelength airborne radar observations of precipitating systems at various frequency bands

We address the question of the most efficient couple (f, θ3dB) for airborne radar precipitating system observations, where f is the microwave frequency and θ3dB the beamwidth aperture at 3 dB. This problem is of importance. The meteorological hazard in civil aviation is mainly due to convective precipitating systems, and particularly hail and strong turbulence areas. A realistic and flexible model of precipitating systems is presented and simulations of airborne radar observations are performed at the six meteorological frequency bands (S, C, X, Ku, Ka, and W). In this work, the effect of f and θ3dB modification is shown through radar simulations of several precipitating systems. One is a numerical simulation composed of two successive rows of convective towers, another is inspired from NEXRAD data of a real mesoscale event of May 2nd 2003 in Alabama (USA), presenting hail-bearing convective towers, and the last one is a simulation of the mesoscale model RAMS. It is shown that some (f, θ3dB) couples are better than the one currently used by civil aviation. Notably C-band allows a better description than X-band of a meteorological radar scene, if the radar antenna size is increased. After that, we applied the dual-wavelength method to detect unambiguously hail in these precipitating systems. The question of the most efficient dual-wavelength couple is addressed by comparing several meteorological radar dual-bands. As hail is a non-Rayleigh scatterer at S, C, and X-bands, its reflectivity field is considerably higher as the frequency decreases. It is shown that even if S-X is the best couple, because the reflectivity difference is the highest, C-X is a dual-wavelength of interest. The S-C dual-wavelength can be interesting because of the negligible attenuating field, but the reflectivity difference is four times lower than the S-X one. It is also shown that, because of the non-Rayleigh scattering behavior of hailstones, the derivative of the dual-wavelength reflectivity ratio is a useful tool to unambiguously detect hail on the radar signal path. The model and methodology presented herein are adaptable to ground-based and satellite radars.