Opportunistic Rainfall Measurements from Dual Channel KU-Band Receiver

Abstract

We focus in this paper on the use of satellite attenuation in Ku-frequency band for measuring rainfall, using low-cost sensors allowing to measure only the total received power. This implies that the measured powers are not only composed of the satellite signal, but also include a radiometric contribution, which is the atmospheric radiation and the receiving system noise. In case of heavy rainfall, while the satellite signal weakens, the atmospheric radiation becomes more important and neglecting it can lead to a significant underestimation of rainfall. In this paper, we introduce the theoretical framework of these measurements, and derive a simple method for correcting this underestimation, based on the measurements of the received power on two channels (different frequencies and / or polarizations), one with strong satellite signal and the other one with no or weak satellite signal. Then we do a preliminary assessment of this method in Abidjan, Ivory Coast, where such a sensor has been deployed during 9 months close to a rain gauge. These preliminary results show that this method seems to lead to rainfall assessments better than using a single-channel approach, but only after a calibration phase to assess the difference in the gain of the system between the two channels we use.