Degree of Polarization at Simultaneous Transmit. Theoretical Aspects

We consider weather radar measurements at simultaneous transmission and simultaneous reception of horizontal and vertical polarizations, and show that the degree of polarization at simultaneous transmit (p_s) is related to differential reflectivity and copolar correlation coefficient at simultaneous transmit (namely, Z_DR^hy and ρ_hv^hy). We evaluate the potential of degree of polarization at simultaneous transmit for weather radar applications, in particular, we note that, contrary to the copolar correlation coefficient, the degree of poalarization is not biased in presence of cross-polarizing scatterers (positive LDR). Ultimately, we explore the consequences of adjusting the transmit polarization state of dual-pol weather radars: slant linear polarization leads to smaller biases in polarimetric variables, whereas circular polarization leads to intresting theoretical developments for the degree of polarization. Data from KOUN, the polarimetric prototype of the WSR-88D, will be used to evaluate the degree of polarization and compare it with the copolar correlation coefficient. The RHIs are most often very similar, with differences emerging only in presence of scatterers with low pho_hv and large ZDR.