Analysis of Systematic Biases in Tropospheric Hydrostatic Delay Models and Construction of Correction Model

Abstract. In the fields of space geodetic techniques, such as Global Navigation Satellite System (GNSS), tropospheric zenith hydrostatic delay (ZHD) is chosen as the a priori value of tropospheric total delay. Therefore, the inaccuracy of ZHD will definitely infect parameters like the wet delay and the horizontal gradient of tropospheric delay, accompanied by an indirect influence on the accuracy of geodetic parameters, if not dealt with well at low elevation angles. In fact, however, the most widely used ZHD model currently seems to contain millimetre-level biases from the precise integral method. We explored the bias of traditional ZHD models and analysed the characteristics in different aspects on a global annual scale. It was found that biases differ significantly with season and geographical location, and the difference between the maximum and minimum values exceed 30 mm, which should be fully considered in the field of high-precision measurement. Then, we constructed a global grid correction model, which is named ZHD_crct, based on the meteorological data of year 2020 from ECMWF (European Centre for Medium-Range Weather Forecasts), and it turned out that the bias of traditional model in the current year could be reduced by ~50 % when the ZHD_crct was added. When we verified the effect of ZHD_crct on the biases in the next year, it worked almost the same as the former year. The mean absolute biases (MABs) of ZHD will be narrowed within ~0.5 mm for most regions, and the STD (standard deviation) will be within ~0.7 mm. This improvement will be helpful for researches on meteorological phenomena as well.