Wirkung der Art und Quantität von Hydrometeoren auf polarimetrische Radargeräte unterschiedlicher Wellenlänge

Kurzfassung

By combining polarimetric radars of different frequencies, the possibility arises to investigate the behavior of backscatter and transmission of electromagnetic waves with changing frequency and to derive the microphysical cloud properties like LWC, R and N(D), using enhanced retrieval methods more precisely. A basis for this analysis is offered by the combined measurements of POLDIRAD (C-band) and the cloud radar MIRA36 (Ka-band) during the COPS campaign on July 8, 2007. Additionally, the vertical wind and the temperature profile of the considered vertical column above the supersite Achern was determined using a doppler sodar and several soundings. The aim of this thesis is to discuss the observed different behavior of Z of the two frequency bands and to confirm its dependency on the moments of N(D). Therefor, the process of scattering was analysed, executing a simulation program based on droplet number concentration, -size and aggregate state, and furthermore developing a retrieval method utilizing the shape of the Marshall-Palmer distribution. Using a vertical profile of LWC aligned with a case study, this approach allowed the calculation of the different profiles of ZHH of both frequency bands, as well as the w_D and sigma_D. Then, the simulated profile is compared with the complementary case study advanced with w, localized melting layer, as well as polarimetric and koherent hydrometeor classification that confirm the hypothesis of a correlation between frequency specific reflectivity differences and the N(D). In summary, the differences of the reflectivity factors are due to attenuation and backscatter effects. The former depends on size and number concentration of the hydrometeors in the volume, plus the wavelength of the radar, and induces an impact integrated over the radiation path. Considering the C-Band, this effect can be neclected for a the typical size of rain (D < 4mm), whereas an attenuating effect is established for D > 1mm, considering the Ka-Band. Additionally, the different behavior is increased, affected by resonance in the Mie region at D > 2.5mm. The similarity of retrieval output to the complementary measurements confirm the hypothesis, that the differences of Z can be explained and quantified by measured radar variables. Because of the implemented approximations Marshall-Palmer-distribution and Mie calculations in the retrieval method, deviations to the measurements are especially expected while simulating ice particles. As a result, the scatter calculations for simulating the microphysical properties using the retrieval method, should be advanced by the T-Matrix method and by using a more capable droplet size distribution.