A Review of Technical Aspects and Challenges in Opportunistic Rainfall Estimation Using Satellite and Terrestrial Microwave Links: How wireless infrastructure can be used for rainfall monitoring

The idea of using terrestrial or satellite microwave links (SMLs) 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 fronthauling and backhauling 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 Internet of Things (IoT) satellite-based service subscribers, namely SMLs. CMLs and SMLs have different characteristics from those of 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 completely missing. Unlike previous reviews on the topic, this work aims to survey 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 we then 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.