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 manuscript provides the first evaluation of rainfall and water vapor sensing with microwave links operating at an E band (specifically, 71–76 GHz and 81–86 GHz), which are increasingly updating, and 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 by one order of magnitude more sensitive to rainfall than devices operating in the 15–40 GHz range and are thus able to 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.
Atmospheric observations with E-band microwave links – challenges and opportunities
