Estimation of Local-Scale Precipitable Water Vapor Distribution Around Each GNSS Station Using Slant Path Delay: Evaluation of a Severe Tornado Case Using High-Resolution NHM

Abstract

Precipitable water vapor (PWV) derived from a ground-based global navigation satellite system (GNSS) can be regarded as a representative value of the PWV above each GNSS station. It is inherently difficult to capture local-scale water vapor distribution using GNSS-derived PWV.
Shoji et al. (2014) proposed a new method that utilizes GNSS slant path delays (SPDs) to estimate the PWV distribution around each GNSS station.
To evaluate this new method, we simulated GNSS SPDs using a high-resolution numerical weather prediction model result, emulated GNSS analysis, retrieved PWVs, and compared their accuracy with the conventional method for a severe tornado that occurred in Japan on 6 May, 2012.
Comparison results demonstrate the validity of the new method for this case. The conventional procedure introduces a 0.3 to 0.7 mm root mean square error (RMSE) at the GNSS site. Errors made by simple extrapolation increased with distance and reached 1.5 mm at about 1 to 3 km. The distance dependency of PWV errors in the new procedure varied with SPD elevation angle. Using SPD with an elevation angle exceeding 15°, we were able to estimate PWV with 1.5mm or better RMSE within 6km from a GNSS station.