Dynamic determination of the baseline level in microwave links for rain monitoring from minimum attenuation values

In recent years, the use of commercial microwave links (CMLs) as tools for remote sensing of the environment has attracted special interest. However, in order to use attenuation measurements taken by microwave links for estimating the rain, one needs to determine the baseline attenuation level. Existing methods frequently use the low attenuation values that are observed during the periods prior to the onset of the rain that have been identified as dry for determining the baseline attenuation level during rainy periods. In this paper, we present a theoretical analysis that justifies the use of the lower attenuation values and propose a systematic method for estimating the baseline attenuation level on the fly that does not need a dry/wet classification. Thus, the proposed method produces a dynamic baseline, which is continuously updated. This method can be implemented on measurements taken from a single CML, in real time, without using either historic or side information. We implemented this method on actual CMLs based measurements and demonstrated its capability to estimate monthly, daily, and hourly rainfall. The resultant estimates were validated by measurements from dedicated weather sensor and rain gauges and are shown to produce accurate estimates of the hourly, daily, and monthly cumulative rain depths.