Assessment of Empirical Troposphere Model GPT3 Based on NGL's Global Troposphere Products.

Junsheng Ding,Junping Chen

doi:10.3390/s20133631

Abstract

Tropospheric delay is one of the major error sources in GNSS (Global Navigation Satellite Systems) positioning. Over the years, many approaches have been devised which aim at accurately modeling tropospheric delays, so-called troposphere models. Using the troposphere data of over 16,000 global stations in the last 10 years, as calculated by the Nevada Geodetic Laboratory (NGL), this paper evaluates the performance of the empirical troposphere model GPT3, which is the latest version of the GPT (Global Pressure and Temperature) series model. Owing to the large station number, long time-span and diverse station distribution, the spatiotemporal properties of the empirical model were analyzed using the average deviation (BIAS) and root mean square (RMS) error as indicators. The experimental results demonstrate that: (1) the troposphere products of NGL have the same accuracy as the IGS (International GNSS Service) products and can be used as a reference for evaluating general troposphere models. (2) The global average BIAS of the ZTD (zenith total delay) estimated by GPT3 is −0.99 cm and the global average RMS is 4.41 cm. The accuracy of the model is strongly correlated with latitude and ellipsoidal height, showing obviously seasonal variations. (3) The global average RMS of the north gradient and east gradient estimated by GPT3 is 0.77 mm and 0.73 mm, respectively, which are strongly correlated with each other, with values increasing from the equator to lower latitudes and decreasing from lower to higher latitudes.

Highlights

(3) The global average root mean square (RMS) of the north gradient and east gradient estimated by GPT3 is 0.77 mm and 0.73 mm, respectively, which are strongly correlated with each other, with values increasing from the equator to lower latitudes and decreasing from lower to higher latitudes
The Global Navigation Satellite Systems (GNSS) signals are delayed and bent as they pass through the atmosphere, and the positioning error due to this is defined as atmospheric delay
We describe the development of Global Pressure and Temperature (GPT) series models and the Nevada Geodetic Laboratory (NGL) troposphere products with more than 10,000 stations worldwide over a 20-year span and, the NGL troposphere products are evaluated using IGS troposphere products as true values, and the results show that

Summary

Introduction

The Global Navigation Satellite Systems (GNSS) signals are delayed and bent as they pass through the atmosphere, and the positioning error due to this is defined as atmospheric delay. The portion of the atmospheric delay caused by the ionosphere is called the ionospheric delay, while the portion caused by the unionized neutral atmosphere is called the tropospheric delay. The tropospheric delay can be divided into hydrostatic delay (HD) and wet delay (WD) [1,2]. The hydrostatic delay accounts for 90% of the total tropospheric delay and can be accurately estimated by the model with a calculation accuracy of up to millimeters [3]. The wet delay is the main limiting factor of the tropospheric delay modeling accuracy, which is often involved in calculations as unknown parameters in precision positioning

Methods

Results

Conclusion