Rain rates, drop size information, and precipitation type, obtained from one-way differential propagation phase and attenuation along a microwave link

We report measurements of total path differential phase along a 23 km microwave link in northwest England, in addition to measurements of total path attenuation at 17.6 GHz and 12.8 GHz, with the latter at both horizontal and vertical polarizations. Since the differential phase measurements are one-way, they do not contain backscatter differential phase (unlike radar measurements of differential phase). We show that differential phase is sensitive to atmospheric effects, but that it can help identify both snow and sleet (a mixture of melting particles and rain) near the ground. Additionally, we found that it gave unexpectedly accurate path-averaged rain rates. We also report measurements from a second, 15 km, link operating at 22.9 GHz and 14.1 GHz. There is evidence from this link, which had no topographic constraints on its beam width, that differential phase can be affected by interference possibly caused by scattering from the terrain. The measurements give some information about the path-average drop size distribution being experienced by the link.