Optimization of GPS water vapor tomography technique with radiosonde andCOSMIC historical data

摘要

The near-real-time high spatial resolution of atmospheric water vapordistribution is vital in numerical weather prediction. GPS tomographytechnique has been proved effectively for three-dimensional water vaporreconstruction. In this study, the tomography processing is optimized in afew aspects by the aid of radiosonde and COSMIC historical data. Firstly,regional tropospheric zenith hydrostatic delay (ZHD) models are improved andthus the zenith wet delay (ZWD) can be obtained at a higher accuracy.Secondly, the regional conversion factor of converting the ZWD to theprecipitable water vapor (PWV) is refined. Next, we develop a new method fordividing the tomography grid with an uneven voxel height and a varied watervapor layer top. Finally, we propose a Gaussian exponential verticalinterpolation method which can better reflect the vertical variationcharacteristic of water vapor. GPS datasets collected in Hong Kong inFebruary 2014 are employed to evaluate the optimized tomographic method bycontrast with the conventional method. The radiosonde-derived andCOSMIC-derived water vapor densities are utilized as references to evaluatethe tomographic results. Using radiosonde products as references, the testresults obtained from our optimized method indicate that the water vapordensity accuracy is improved by 15 and 12 % compared to those derived from theconventional method below the height of 3.75 km and above the height of3.75 km, respectively. Using the COSMIC products as references, the resultsindicate that the water vapor density accuracy is improved by 15 and 19 %below 3.75 km and above 3.75 km, respectively.