# Earth-to-Earth Microwave Rain Attenuation Measurements: A Survey On the Recent Literature
## 4 Rainfall Measurements Through Backhaul Cellular Infrastructure
To obtain the attenuation caused by rain, a baseline is set during the wet season by interpolating the total attenuation within a window between 1 h before and 6 h after the rain period, to eliminate wet antenna attenuation (WAA). The baseline on dry seasons was simply the transmitter-receiver power difference. In contrast to conventional rain gauges, the microwave links performance is relatively more stable across all topologies layouts even during heavy rainfall events that they highly variate in both time and space. [PERSON] et al. addressed the restrictions on access and data acquisition (DAQ) by commercial microwave links [47]. In their work, they developed an open-source DAQ system written in Python to acquire real-time data from homogeneous and heterogeneous networks with high temporal resolution time. Data from 450 Ericsson MINI-LINK TN CMLs were acquired every min with only several seconds' of delay. [PERSON] et al. used data from a vast number of 2044 path links in a population of about 35,000 km\({}^{2}\) in the Netherlands [48]. Received signal levels from Nokia and NEC microwave links were sampled every ten Hz while the maximum and minimum values of the received power were saved every 15 min. Additional information, such as geographic coordinates were also logged. The power resolution was 0.1 dB for NEC microwave links and 1 dB for Nokia. The total number of usable data was 894 days, while the operating frequency for the majority of the links was between 37 and 40 GHz. Two rain gauge networks validated the data. In the automated network, with a density of about 1 in 1000 km\({}^{2}\), automatic precipitation was measured every hour and daily. In the second manual network, the data obtained daily, and the density was about one gauge per 100 km\({}^{2}\). Additional radar rainfall data were obtained from two ground-based C-band weather radars. In Italy, they used attenuation from microwave links in the K-band to create 2-D maps of accumulated rainfall [49]. The microwave links operated at 25 GHz with a medium path link of 6 km in the Treviso area. The impregnated power was recorded with a sampling rate of 15 times per 2 min and the power resolution was equal to 3 dB. The measurements took place in September 2015. As far as the data from the nine rain gauges, they had rainfall accumulation per 24 h. Despite the small number of links, the reconstructed rain map was satisfactorily useful due to how it was by a collocated rain gauge network. Relevant to the progress of rainfall monitoring due to cellular power measurements [50], the use of the measurements being acquired from commercial cellular networks is discussed. Each channel is supposed to be the microwave link between two base stations. Consequently, this set-up was used as a rain sensor based on the fact of signal attenuation, which was directly associated to the rain rate. Specifically, the OSN (opportunistic sensors networks) technology is used with the drawback of lower quality sensing which is compensated by the whole network's measurement efficiency. In turn, the utilized OSN had the characteristics of a large number of sensors, proper spatial distribution (entire country) and built-in diversity (links with different lengths and frequencies). This technique is better compared to that of a radar, thus the it can provide correlation up to 0.9647 and a measurement rate every 10 s. Nevertheless, a common protocol provides measurements every 15 min, and the technique based on OSNs is not proposed for rain mapping over oceans. Certainly, high quality maps can be produced with the use of OSNs [51]. In particular, the authors in [50] have studied the way that links' spatial geometry can lead to a well-derived rainfall map. They mention that they accomplished a dynamic rainfall map over an area of 15 km\({}^{2}\) with a spatial resolution of 1 km, while the temporal resolution had been set to 1 min.