Comparison of a Precipitable Water Vapor with GNSS and Compact Microwave Radiometer

Introduction

Localized severe weather causes serious damage on our life. To prevent dangerous disasters such as typhoons, heavy rains, fog and hail, real-time observation of Precipitable Water Vapor (PWV) efficiently detects the precursor phenomenon. Especially microwave radiometer gives us a very effective solution. Based on this background, FURUNO research department developed a prototype of compact and light-weight microwave Radiometer. This report shows results of evaluation of the prototype.

Case study

This study shows a comparison of PWV observation from 27 September 2018 to 14 January 2019. Three meteorological observation systems, microwave Radiometer (prototyped by FURUNO), Radiosonde (by Japan Meteorological Agency and DPRI) and GNSS (RTNet by Hitz) were installed at Shionomisaki, Japan. Since the distance between the systems is only approximately 400m, it could be considered that the instruments observe same sky and same PWV.

Results

High correlation factor for PWV values between the Radiometer, RTNet and Radiosonde (RAOB) was obtained as shown on Fig.1. This result indicates the Radiometer prototyped by FURUNO was able to observe PWV fluctuation. Observation difficulty during precipitation period (colored blue on the Fig.1) with radiometers is widely known. The Radiometer show overwhelmed values during precipitation period. But we have concluded that the Radiometer has provided adequate figures excluding the precipitation period as shown on Fig.2. The correlation coefficient between Radiometer and Radiosonde is 0.98 including times of rain, and RMSE is 3.1mm. On the other hand, when it is sunny, the correlation coefficient is 0.98 and RMSE is 2.6mm.

Conclusions

This study shows the comparison of PWV observation from 27 September 2018 to 14 January 2019. Fluctuation of Precipitable Water Vapor is observed by three meteorological instruments, microwave Radiometer (prototyped by FURUNO), Radiosonde and GNSS. The result shows the measurement accuracy of PWV fluctuation between 10mm and 70mm at autumn and winter time was equivalent to Radiosonde and RTNet. The observation using a compact and light-weight microwave radiometer prototyped by FURUNO indicates the possibility for understanding the atmospheric fluctuation. It helps local weather observation and prediction, and we expect the Radiometer contributes to effective disaster prevention.

KEYWORDS: Microwave Radiometer, Precipitable Water Vapor, GNSS, Radiosonde