A Review of Technical Aspects and Challenges in Opportunistic Rainfall Estimation Using Satellite and Terrestrial Microwave Links

The idea of using terrestrial or satellite microwave links as opportunistic sensors (OSs) of rainfall is more than 15 years old and the literature on the topic is vast. Many studies focused on rain detection and quantification from the data collected by the front- and back-hauling links of mobile networks, namely, commercial microwave links (CMLs). More recently, several researchers have also investigated the signals received by the ground terminals of TV-SAT or of IoT satellite-based service subscribers, namely satellite microwave links (SMLs). CMLs and SMLs have different characteristics than conventional sensors (CSs) of rainfall, hence they have the potential to complement measurements collected by rain gauges (RGs) or weather radars (WRs), as well as to provide unique data in the several areas of the globe where rainfall monitoring systems are scarce or missing at all. Unlike previous reviews on the topic, this work aims at surveying the technical challenges involved by the usage of devices and data not designed for rainfall monitoring. In particular, we draw a state-of-the-art flowchart of OS data processing, we analyze the disturbances that affect the raw data, and, finally, we present a comparative analysis of the major studies on the validation of OS rainfall estimates, based on a set of Key Performance Indicators (KPIs). The similarities and differences of satellite and terrestrial links as rainfall sensors are highlighted. To conclude, we propose an author’s view on the future of rainfall measurements by CMLs and SMLs, which is closely tied to the evolution of wireless communication networks.