GPS Meteorology Project in Japan

The nationwide GPS array established by GSI(Geographical Survey Institute), which cover the Japanese islands with 860 GPS stations, is one of the keys to promote this project. Although the primary purpose of the GPS system is put on geodetic applications, it also produces tropospheric zenith delay routinely as a byproduct. Since the spatial density of the GPS network is very high (mean distance between stations is about 25 km), we can map the troposphric zenith delay with high resolution in space and time. The other key is the fine grid model for weather forecast up to 10 km developed by JMA(Japan Meteorological Agency). Predicted value from the grid model can be used to estimate azimuthal anisotropy of tropospheric delay, as well as preferable zenith delay as a priori and the vertical profile of the troposphere for elevational correction applying GPS analysis. By combining those systems, improvement of the accuracy of space geodetic technique and weather forecast is expected.

In our project, we aim to build a water vapor information system which consists of three components; GSI's nationwide GPS array system, JMA's weather forecast system, and the water vapor information database. The GPS system and the weather forecast system form a feedback loop which helps to improve the accuracy of the both systems each other. The output from those systems are stored into the water vapor information database. The database are used for geodetic, meteorological and hydrological researches. It is expected that this project will throw a light on many kinds of research area; vertical crustal movements, sea level monitoring, meso-scale or local scale meteorological phenomena, regional water circulation, etc.