A Regional Stochastic Model for NOAA-Based Residual Tropospheric Delay

Hassan E. Ibrahim and Ahmed El-Rabbany

Abstract:	Recently, a number of regional and local monitoring networks have been established to generate tropospheric corrections. Among them is the NOAA tropospheric correction model, which incorporates GPS observations into numerical weather prediction (NWP) models. Although the NOAA model improved the precise point positioning (PPP) solution convergence compared with standard tropospheric models (e.g., Saastamoinen and Hopfield models), a residual tropospheric error component remains unmodelled. Such a residual error component is found to be temporally correlated, which may slow down the conversion of the PPP solution.. To overcome the limitations of the NOAA model, a stochastic modeling of the NOAA-based tropospheric delay residuals is proposed. Daily time series of NOAA zenith total tropospheric (ZTD) delays were generated for ten reference stations spanning North America for many days of 2006. The NOAA ZTD data series were then compared with the new IGS tropospheric product to obtain daily residuals data series at 5 minutes interval. The least-squares method was then used to find the bestfitting covariance function to the estimated autocovariance functions of the above daily residuals data series. Three models were tested for this purpose, namely the first-order Gauss-Markov, the second-order Gauss- Markov and the exponential cosine functions. Fitting results show that the exponential cosine gives the best fit most of the time, while the second-order Gauss-Markov model gives the worst fit. The results of the first-order Gauss-Markov model were comparable to those of the exponential cosine. Once developed, the selected empirical covariance function can be used to stochastically model the NOAA-based residual tropospheric delays through the modification of the PPP observation matrix.
Published in:	Proceedings of the 2008 National Technical Meeting of The Institute of Navigation January 28 - 30, 2008 The Catamaran Resort Hotel San Diego, CA
Pages:	877 - 883
Cite this article:	Ibrahim, Hassan E., El-Rabbany, Ahmed, "A Regional Stochastic Model for NOAA-Based Residual Tropospheric Delay," Proceedings of the 2008 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2008, pp. 877-883.
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