A comparison between terrestrial and satellite microwave links as opportunistic rainfall sensors

In the last decades, both the backhauling links of terrestrial wireless networks (Commercial Microwave Links, CMLs) and the downlink of satellite broadcasting/broadband services (Satellite Microwave Links, SML) operating in the Ku-band and above, say >10 GHz, revealed themselves as effective opportunistic systems for rainfall sensing. CMLs and SMLs exhibit, indeed, features that make them suitable to complement conventional measurements carried out by rain gauge networks, weather radars, and Earth observation satellites. Based on the experience achieved by several research Italian teams active since 2017, this paper compares CMLs and SMLs as opportunistic rainfall sensors from different perspectives. In detail, we will address technical aspects (complexity of data acquisition and processing), performance (spatio-temporal resolution, accuracy, sensitivity and benefits brought by AI techniques), data accessibility and ownership, and deployment and operational costs. Finally, the perspectives of such opportunistic sensors as operational tools are also assessed in accordance with the evolution of wireless networks: as for CMLs, fiber backhauling and the shift towards mmW bands, whereas for SMLs, the deployment of large and mega constellations of LEO satellites.