Measuring rainfall with microwave links: the influence of temporal sampling strategies

Single-frequency microwave links can be used to monitor path-averaged precipitation by determining the rain-induced attenuation along the link path, as for example is done with commercial microwave links (CMLs) from cellular telecommunication networks. However, using these networks to estimate precipitation, the temporal resolution of these estimates is bound to the temporal sampling strategy employed by the network operator, which solely uses the information on the link signal to assure the functioning of the network. Moreover, not all operators store the same variables describing the link signal. Most commonly, a temporal resolution of 15 minutes with a recording of the minimum and maximum values during this interval is applied. For research purposes, often higher temporal resolutions in combination with averaged values are preferred. Yet, it is uncertain how these sampling strategies affect the computed amount and intensity of rainfall. To address this uncertainty, we investigate the influence of various temporal sampling strategies regarding the link signal on the estimated amounts and intensities of rainfall events from a single microwave link. For the analysis, we resample microwave link data to multiple intervals and variables characterizing the measured signal. The original data consist of three collocated microwave links sampled at 20 Hz, all operational for more than a year, and covering a 2.2 km path over the city Wageningen in the Netherlands. Additionally, the resulting rainfall estimates for the intervals and variables are compared to measurements of five disdrometers deployed along the link path. Overall, the results of this study can help to quantify the uncertainties associated with rainfall estimates from microwave links.