Simultaneous measurements with a 16.5 GHz polarisation diversity radar and the 28.56 GHz Comstar beacon are reported. Radar measurements of the differential propagation constant during a severe depolarisation event established that the depolarisation was due primarily to lossless scatterers above the melting layer, with little contribution from rain or the melting layer. Differential phase shifts as high as 1.7°/km at 16.5 GHz, corresponding to 2.9°/km at 28.56 GHz, were observed. Good agreement between radar derived and beacon measurements of differential phase shift was obtained.