Abstract
Abstract. Opportunistic sensing of rainfall and water vapor using commercial microwave links operated within cellular networks was conceived more than a decade ago. It has since been further investigated in numerous studies, predominantly concentrating on the frequency region of 15–40 GHz. This article provides the first evaluation of rainfall and water vapor sensing with microwave links operating at E-band frequencies (specifically 71–76 and 81–86 GHz). These microwave links are increasingly being updated (and are frequently replacing) older communication infrastructure. Attenuation–rainfall relations are investigated theoretically on drop size distribution data. Furthermore, quantitative rainfall estimates from six microwave links, operated within cellular backhaul, are compared with observed rainfall intensities. Finally, the capability to detect water vapor is demonstrated on the longest microwave link measuring 4.86 km in path length. The results show that E-band microwave links are markedly more sensitive to rainfall than devices operating in the 15–40 GHz range and can observe even light rainfalls, a feat practically impossible to achieve previously. The E-band links are, however, substantially more affected by errors related to variable drop size distribution. Water vapor retrieval might be possible from long E-band microwave links; nevertheless, the efficient separation of gaseous attenuation from other signal losses will be challenging in practice.
Highlights
Electromagnetic (EM) waves in the microwave region are attenuated by water vapor, oxygen, fog, or raindrops
About 4 million Commercial microwave links (CMLs) were operated worldwide within cellular backhaul in 2016 (Ericsson, 2016) and about 5 million in 2018 (Ericsson, 2018). Most of these CMLs are operated at frequencies between 15 and 40 GHz (Ericsson, 2016, 2018), where raindrops and, to a lesser extent, water vapor represent a significant source of attenuation (Atlas and Ulbrich, 1977; Liebe et al, 1993)
The E-band evaluation concentrates on (i) the separation of gaseous attenuation from total observed loss, which is a prerequisite for CML water vapor retrieval; (ii) the relation between raindrop attenuation and rainfall intensity, including the effect of drop size distribution (DSD); and (iii) the influence of wet antenna attenuation (WAA) on CML quantitative precipitation estimates (QPEs)
Summary
Electromagnetic (EM) waves in the microwave region are attenuated by water vapor, oxygen, fog, or raindrops. Measurements of microwave attenuation at different frequency bands represent an invaluable source of information regarding the atmosphere. About 4 million CMLs were operated worldwide within cellular backhaul in 2016 (Ericsson, 2016) and about 5 million in 2018 (Ericsson, 2018) Most of these CMLs are operated at frequencies between 15 and 40 GHz (Ericsson, 2016, 2018), where raindrops and, to a lesser extent, water vapor represent a significant source of attenuation (Atlas and Ulbrich, 1977; Liebe et al, 1993). Information on the attenuation of any CML within countrywide networks is practically accessible in real time with a delay of several seconds from a remote location, typically a network operation center (Chwala et al, 2016) creating an appealing opportunistic sensing system capable of providing close-to-
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