On the Road to Operational Rainfall Monitoring with Commercial Microwave Links

Microwave links in cellular telecommunication networks can be employed for rainfall monitoring. Rainfall attenuates the electromagnetic signals transmitted from one telephone tower to another. By measuring the received power at one end of a microwave link as a function of time, the path-integrated attenuation due to rainfall can be calculated, which can be converted to path-averaged rainfall intensities. Microwave links from cellular communication networks have been proposed as a promising new rainfall measurement technique since one decade. They are particularly interesting for areas with few surface rainfall observations, such as developing countries and urban areas. Yet to date no operational (real-time) link-based rainfall products are available. To advance the process towards operational application and upscaling of this technique, long time series should be analyzed for different networks and climates.

Here the potential for long-term large-scale operational rainfall monitoring is demonstrated by utilizing a 2.5-year dataset from a cellular telecommunication network. The dataset consists of roughly 2,000 links covering the land surface of the Netherlands (35,500 km²). The quality of link rainfall maps is thoroughly quantified by an extensive validation against independent gauge-adjusted radar rainfall maps for. One of the goals is to quantify whether the cellular telecommunication network can yield rainfall maps of comparable or higher quality as those based on automatic rain gauge data (with a density of ~1 gauge per 1000 km²). Developing countries will usually have rain gauge networks with a lower density (and little or no weather radars). This helps to assess the added value of link-based rainfall estimates with respect to those from existing rain gauge networks, as well as the added value for adjustment of radar rainfall images.

The potential of these networks for rainfall monitoring is confirmed. Performance is less good in the winter, probably caused by dew formation on antennas and melting precipitation at the link path and on antennas. However, the good results found for the summer in a temperate climate, hold a promise for large-scale application in developing countries in (sub)tropical climates.