GNSS-based ZTD Application for Short term Rainfall Prediction in Mountainous Region
Hanggar G Mawandha(a*), M Kishimoto(a), Sulistiyani(b), Satoru Oishi(c)
a) Graduate School of Engineering, Kobe University, Japan
*mawandha[at]stu.kobe-u.ac.jp
b) Center for Volcanology and Geological Hazard Mitigation, Geological Agency, Indonesia
c) Research Center for Urban Safety and Security, Kobe University, Japan
Abstract
High-precision of rainfall prediction in a matter of rates and time is significant aspects for such issues in disaster mitigation, irrigation management, public services, and many others. 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 indirect measure of the integrated water vapor along the path and measured as Zenith Total Delay (ZTD). By studying the relationship between time-varying ZTD and rainfall, it can be found that the ZTD 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 ZTD is strongly correlated to rainfall occurrence based on the rain gauges measurement around Mt.Merapi region. The results show that the rate of true forecasted is about 65%, with the lead time recorded is two hours before the actual event.
Keywords: GNSS, ZTD, rainfall, prediction
Topic: Land and water resources engineering