An approach to calibrate the polarimetric variables is proposed. It consists of measurements in which the plane of the array is horizontal (i.e., broadside is pointing up) and electronic scans are made at high elevations in multiple directions. The plan is to make the proposed measurements on a recently developed PAR that has the capability to position the array in the horizontal plane. Physical considerations indicate that in directions that are axially symmetric with respect to broadside the differential reflectivity should be the same if the geometrically induced bias dominates the other influences. This can be quickly checked to assess the initial biases of the PPAR because at high elevation angles the intrinsic differential reflectivity is zero. Some bounds on the auxiliary effects that can add to the bias will be quantified. Similarly pairs of the correlation coefficient values between the intended horizontally and vertically polarized fields should exhibit same bias. Thus, the proposed measurements on weather signal can indicate poor calibration and/or significant cross coupling. The approach can be useful for first order corrections in directions not too far off the principal planes.
To complement the experimental phase, numerical prediction of the biases is being developed. We hope that the degree of agreement between the predicted and measured biases will establish if the numerical solver can provide satisfactory calibration. This is a long term effort of upmost importance for future PPARs because these will unlikely have the option to horizontally position their array antennas.