[G06-1] Troposphere monitoring I

[G06-1-03] Impact of advanced ZTD estimate method – Separation from site coordinates estimation –

^○Seiichi Shimada^{1, 2}, Shingo Shimizu³, Kazuhisa Tsuboki⁴, Yusuke Morimoto⁴ (1.The University of Tokyo, Tokyo, Japan, 2.Nippo Co. Ltd., Kawasaki, Japan, 3.The National Research Institute for Earth Science and Disaster Prevention (NIED), Tsukuba, Japan, 4.Nagoya University)

We introduce the new procedure to estimate zenith total delay (ZTD) to obtain GPS precipitable water (PWV) for the assimilation of the numerical weather models (NWM). In general, the major systematic error source of the ZTD estimation is the trade-off between the ZTD and the coordinate solutions usually simultaneously estimated in the GNSS analysis. In the analysis of the ZTD estimation, we fix the accurate site coordinates and exclude the trade-off systematic errors.
In the first step of the procedure, we estimate site coordinates as well as hourly ZTD, every four-hourly atmospheric gradient, and independent ambiguities of all of the GEONET network sites as well as the IGS fiducial sites applying the GAMIT program. In the second step, we estimate the accurate present-day site coordinates of the GEONET sites, estimating from the recent 30-days' time series of the site coordinates solutions applying the Kalman filtering of the GLOBK program, constraining the IGS fiducial site coordinates. Then in the final step of the procedure, we estimate every hourly ZTD and every four-hourly gradients of the GEONET sites fixing the site coordinates obtained in the second step.
To evaluate the advanced ZTD estimation, we compare the PWV values calculated from the three kind of ZTDs obtained by three different analysis procedures. We assimilate the PWVs to the CReSS NWM, and examine the impact of the PWVs in the heavy rain in the Southern Gifu Prefecture, Central Japan, on July 15 2010. Examining the wide area distribution of water vapor in the objective analysis, only the ZTDs obtained applying the procedure mentioned above (advanced ZTDs) shows the sharp contrast of the mixing ratio. coincides significantly The heavy rain phenomena calculated using the advanced ZTDs only significantly coincides with the observation.