Determination of Tropospheric Parameters from ERA Surface Data for Space Geodetic Techniques

This study investigates methods of deriving meteorological parameters needed in space geodetic applications, from the surface data of the numerical weather model (NWM). It is more efficient than pressure level data in terms of storage and transmission. Based on more realistic assumptions for the structure of the troposphere, formulas for accurate vertical reduction of pressure (P) and precipitable water vapor (PWV) are deduced, and they are applied with the gridded lapse rate data provided by the GPT2w model. The new method achieves better accuracy especially when a large height difference between the grid point and station exists. Validation with global radiosonde observations shows that the RMS errors of P, temperature (T), and water vapor pressure (e) derived from 2.5° × 2.5° ERA surface data are 1.16 hPa, 1.95 K, and 1.76 hPa respectively; zenith tropospheric delays (ZTDs) calculated from derived P, T, and e values have a mean RMS error of 3.26 cm, comparable to that obtained from in situ measurements; adding PWV will increase ZTD estimation accuracy to 1.52 cm, comparable to that obtained from NWM pressure level data. Validations with Global Navigation Satellite System estimated ZTDs from global and regional station networks display similar results on the globe, as well as features for localized regions. Using higher spatial resolution NWM seems to have little effect on the accuracy of ZTDs calculated from P, T, and e, while it apparently improves the accuracy of ZTDs calculated from P, T, e, and PWV.