Investigation of Rainfall Forecasting Using the Difference of GNSS Zenith Total Delay with Elevation Cut-off Angles

The Global Navigation Satellite System (GNSS) is able to use for not only global positioning, but also meteorological observation. The zenith total delay (ZTD) is one of influential parameter both in these applications [1]-[7]. Since the ZTD relates the amount of water vapor in troposphere, rainfall forecasting is basically based on the ZTD [7]. However, false alarm sometimes occurs because the ZTD indicates implicit rainfall. And precision of estimated ZTD in GNSS analysis operation depends on the elevation angle of arrival at GNSS receiver. Thus, the difference of ZTD time series is newly introduced for improving forecasting precision in this paper. Observed result of ZTD variation before rainfall occurrence is compared to non-rainy state with different elevation cut-off angle.