GNSS-based PWV Application for Short Term Rainfall Prediction in Mountainous Region

Abstract

Rainfall in the mountainous region has unique characteristics related to time-varying and spatial distribution. In Mt. Merapi region, located at the border of Special Region of Yogyakarta Province and Central Java Province, Indonesia, rainfalls are typically classified as the deep-convective type, which occurs in a short period with high intensity. Therefore, short term rainfall predictions in a proper way remain challenging tasks. The use of remote monitoring instruments such as the GNSS (Global Navigation Satellite System) is believed to provide a better measurement accuracy through the identification of water vapor variation in the process of deep convection weather. GNSS observes the geodetic position of the GNSS antenna or receiver while it broadcasts microwave signals continuously through the atmosphere to the ground-based receivers. As they travel through the atmosphere, the microwave signals are mostly influenced by ionospheric and neutral atmospheric effects, which cause some delays. By using a sufficiently dense network of GNSS receivers, the impact of the neutral atmosphere delay can be estimated as a by-product of the geodetic processing. These delays can be regarded as an integrated water vapor along the path, namely Precipitable Water Vapor (PWV), which can be indirectly measured by Zenith Total Delay (ZTD). By studying the relationship between time-varying PWV and rainfall, it can be found that the PWV level increases sharply before raining. Through the deployment of GNSS receivers, the spatial feature of rainfall characteristics is also depicted. The initial results showed that the increase of PWV is strongly correlated to rainfall occurrence based on the rain gauge measurement around Mt. Merapi region. The results show that the correct forecasted rate is about 47%-62% with the PWV increment time is three hours.