Retrieving Water Vapor From an E‐Band Microwave Link With an Empirical Model Not Requiring In Situ Calibration

Abstract

Abstract An empirical model estimating water vapor density from the attenuation of electromagnetic waves at E‐band frequencies is proposed and tested on seven months of 5‐min attenuation observations from a 4.87‐km‐long full‐duplex E‐band commercial microwave link (CML) operating at 73.5 and 83.5 GHz. The model does not require in situ calibration. Estimated water vapor density is compared to the observations from two meteorological stations located nearby the CML end nodes. Best performance is achieved for the 83.5 GHz sublink (RMSE = 1.46 g m−3, R2 = 0.85) when the actual temperature is used as a model input, in addition to the attenuation data. Use of temperature averaged over the whole evaluation period resulted in significantly worse performance. The study demonstrates the potential of E‐band CMLs for measuring near‐surface air humidity and the need for careful quality control when upscaling the water vapor monitoring to the entire network of E‐band CMLs.

Keywords

• water vapor density
• opportunistic sensing
• commercial microwave link
• E‐band
• retrieval model