Enhanced quantitative precipitation estimation through the opportunistic use of Ku TV-SAT links via a dual-channel procedure

Abstract

Earth-satellite microwave links such as TV-SAT can help for rainfall monitoring and could be a complement or an alternative to ground-based weather radars, rain gauges or Earth observation satellites. Rain-induced attenuation which is harmful for telecommunication is exploited here as an opportunistic way to estimate rain rate along the link path. This technique provides rain measurements at a fine temporal resolution (a few tens of seconds) and with a spatial resolution of a few kilometres, which is a good compromise for human activities such as civil security (watershed monitoring, flash flood), agriculture or transport. The advantages of this technique include the low cost of the equipment used, as well as the cost of on-site maintenance. However, the measured attenuation does not directly provide rain intensity, requiring the estimation of additional parameters. These include the contribution of natural radiation from the atmosphere. In this paper, we detail a theoretical framework allowing us to estimate rainfall from the measurements of a low-cost sensor operating simultaneously over two parts of the Ku frequency band. This framework is assessed in a densely instrumented area in the south of France, where very good results are obtained when compared to rain gauge measurements, in terms of both overall rain accumulation and rainfall rate distribution. Then we apply this dual-channel method in Côte d'Ivoire, in the metropolitan area of Abidjan, where such an approach is very promising. It is shown that this technique when compared to rain gauge measurements gives far better results than a naive single-channel approach neglecting the natural radiation of atmosphere but that significant errors remain in rainfall assessment, leading to a persistent underestimation of rain accumulation. Finally we discuss various effects that could lead to this remaining underestimation, opening the door for further studies.