Performance Evaluation of Blind Tropospheric Delay correction Models over Africa

Ludwig Combrinck,Joel Botai,Olalekan Adekunle Isioye

doi:10.4314/sajg.v4i4.10

Abstract

Tropospheric delay is a major error source in positioning by Global Navigation Satellite Systems (GNSS). Many techniques are available for tropospheric delay mitigation consisting of surface meteorological models and global empirical models. Surface meteorological models need surface meteorological data to give high accuracy mitigation while the global empirical models need not. However, most GNSS stations in the African region are not equipped with a meteorological sensor for the collection of surface meteorological data during the measurement. Zenith Tropospheric Delay (ZTD) is often calculated by the various high precision GNSS software packages by utilising standard atmosphere values. Lately, researchers in the University of New Brunswick and Vienna University of Technology have both developed global models (University of New Brunswick (UNB3M) and Global Pressure and Temperature 2 wet (GPT2w) models) for tropospheric delay correction, respectively. This report represents an appraisal of the performance of the GPT2w and UNB3M models with accurate International GNSS Service (IGS)- tropospheric estimations for fifteen IGS stations over a period of 1 year on the Africa continent. Both models perform significantly better at low latitudes than higher latitudes. There was better agreement between the GPT2w model and the IGS estimate than the UNB3m at all stations. Thus, the GPT2w model is recommended as a correction model of the tropospheric error for the GNSS positioning and navigation on the African Continent.Keywords: Global Navigation Satellite Systems (GNSS), Zenith Tropospheric Delay (ZTD), Zenith Wet Delay (ZWD), Zenith Hydrostatic Delay (ZHD), International GNSS Service (IGS), Blind Tropospheric models

Highlights

Introduction and backgroundTropospheric delay is one of the main error sources in the analysis of space geodetic techniques operating at microwave frequencies, such as Global Navigation Satellite Systems (GNSS), Very Long Baseline Interferometry (VLBI), or Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS).The tropospheric delay is usually separated into a hydrostatic delay that is modelled a priori, and a wet delay that is estimated from the space geodetic microwave observations
We have estimated the accuracies of the UNB3m and GPT2w tropospheric correction models over Africa by using the Zenith Tropospheric Delay (ZTD) time series from the global International GNSS Service (IGS) GNSS network in Africa, and Saastamoinen formula based on measured meteorological parameters
The UNB3m model utilises a lookup table with annual mean and amplitude of temperature, pressure, and water vapour pressure varying with regard to latitude and height

Summary

Introduction and background

Tropospheric delay is one of the main error sources in the analysis of space geodetic techniques operating at microwave frequencies, such as Global Navigation Satellite Systems (GNSS), Very Long Baseline Interferometry (VLBI), or Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS). GNSS geodetic software uses the Saastamoinen model with standard atmosphere models for a-poiri estimates In view of these shortcomings, it is of practical importance to construct a global model of average tropospheric delay correction with a certain accuracy to be used in the GNSS navigation and positioning in Africa, in which the zenith delay depends only on the latitude, elevation of observing station, and the date of observation. Saastamoinen (1972) gave the expression for the zenith wet delay model using the refractivity constant of Essen and Froome (1951) and for mid-latitudes and average conditions: ZWD 0.002277

UNB3m Hydrostatic Delay Model

Findings

Concluding Remarks