scholarly journals SHAtropE—A Regional Gridded ZTD Model for China and the Surrounding Areas

2020 ◽  
Vol 12 (1) ◽  
pp. 165 ◽  
Author(s):  
Junping Chen ◽  
Jungang Wang ◽  
Ahao Wang ◽  
Junsheng Ding ◽  
Yize Zhang
Keyword(s):  
Meteorological Data ◽  
Grid Point ◽  
Mainland China ◽  
Propagation Delay ◽  
Convergence Time ◽  
Tropospheric Delay ◽  
Delay Model ◽  
Observation Network ◽  
Surrounding Areas ◽  
Improved Accuracy

A regional zenith tropospheric delay (ZTD) empirical model, referred to as SHAtropE (SHanghai Astronomical observatory tropospheric delay model—Extended), is developed and provides tropospheric propagation delay corrections for users in China and the surrounding areas with improved accuracy. The SHAtropE model was developed based on the ZTD time series of the continuous GNSS sites from the Crustal Movement Observation Network of China (CMONOC) and GNSS sites of surrounding areas. It combines the exponential and periodical functions and is provided as regional grids with a resolution of 2.5° × 2.0° in longitude and latitude. At each grid point, the exponential function converts the ZTD from the site height to the ellipsoid, and the periodical terms, including both annual and semi-annual periods, describe ZTD’s temporal variation. Moreover, SHAtropE also provides the predicted ZTD uncertainty, which is valuable in Precise Point Positioning (PPP) with ZTD being constrained for faster convergence. The data of 310 GNSS sites over 7 years were used to validate the new model. Results show that the SHAtropE ZTD has an accuracy of 3.5 cm in root mean square (RMS) quantity, which has a mean improvement of 35.2% and 5.4% over the UNB3m (5.4 cm) and GPT3 (3.7 cm) models, respectively. The predicted uncertainty of SHAtropE ZTD shows seasonal variations, where the values are larger in summer than in winter. By applying the SHAtropE model in the static PPP, the convergence time of GPS-only and BDS-only solutions are reduced by 8.1% and 14.5% respectively compared to the UNB3m model, and the reductions are 6.9% and 11.2% respectively for the GPT3 model. As no meteorological data are required for the implementation of the model, the SHAtropE could thus be a refined tropospheric model for GNSS users in mainland China and the surrounding areas. The method of modeling the ZTD uncertainty can also be used in further global tropospheric delay modeling.

scholarly journals Empirical Orthogonal Function Analysis and Modeling of Global Tropospheric Delay Spherical Harmonic Coefficients

2021 ◽  
Vol 13 (21) ◽  
pp. 4385
Author(s):  
Yongchao Ma ◽  
Hang Liu ◽  
Guochang Xu ◽  
Zhiping Lu
Keyword(s):  
Empirical Orthogonal Function ◽  
Spherical Harmonic ◽  
Function Analysis ◽  
Meteorological Data ◽  
Regional Scale ◽  
Global Scale ◽  
Tropospheric Delay ◽  
Delay Model ◽  
Product Model ◽  
Orthogonal Function

Based on the ERA-5 meteorological data from 2015 to 2019, we establish the global tropospheric delay spherical harmonic (SH) coefficients set called the SH_set and develop the global tropospheric delay SH coefficients empirical model called EGtrop using the empirical orthogonal function (EOF) method and periodic functions. We apply tropospheric delay derived from IGS stations not involved in modeling as reference data for validating the dataset, and statistical results indicate that the global mean Bias of the SH_set is 0.08 cm, while the average global root mean square error (RMSE) is 2.61 cm, which meets the requirements of the tropospheric delay model applied in the wide-area augmentation system (WAAS), indicating the feasibility of the product strategy. The tropospheric delay calculated with global sounding station and tropospheric delay products of IGS stations in 2020 are employed to validate the new product model. It is verified that the EGtrop model has high accuracy with Bias and RMSE of −0.25 cm and 3.79 cm, respectively, with respect to the sounding station, and with Bias and RMSE of 0.42 cm and 3.65 cm, respectively, with respect to IGS products. The EGtrop model is applicable not only at the global scale but also at the regional scale and exhibits the advantage of local enhancement.

scholarly journals Establishment of a Real-Time Local Tropospheric Fusion Model

2019 ◽  
Vol 11 (11) ◽  
pp. 1321 ◽  
Author(s):  
Yibin Yao ◽  
Xingyu Xu ◽  
Chaoqian Xu ◽  
Wenjie Peng ◽  
Yangyang Wan
Keyword(s):  
Real Time ◽  
Meteorological Data ◽  
Rapid Development ◽  
Water Vapor Pressure ◽  
Auxiliary Information ◽  
Satellite System ◽  
Tropospheric Delay ◽  
Navigation Systems ◽  
Delay Model ◽  
Fusion Model

The tropospheric delay is one major error source affecting the precise positioning provided by the global navigation satellite system (GNSS). This error occurs because the GNSS signals are refracted while travelling through the troposphere layer. Nowadays, various types of model can produce the tropospheric delay. Among them, the globally distributed GNSS permanent stations can resolve the tropospheric delay with the highest accuracy and the best continuity. Meteorological models, such as the Saastamoinen model, provide formulae to calculate temperature, pressure, water vapor pressure and subsequently the tropospheric delay. Some grid-based empirical tropospheric delay models directly provide tropospheric parameters at a global scale and in real time without any auxiliary information. However, the spatial resolution of the GNSS tropospheric delay is not sufficient, and the accuracy of the meteorological and empirical models is relatively poor. With the rapid development of satellite navigation systems around the globe, the demand for real-time high-precision GNSS positioning services has been growing dramatically, requiring real-time and high-accuracy troposphere models as a critical prerequisite. Therefore, this paper proposes a multi-source real-time local tropospheric delay model that uses polynomial fitting of ground-based GNSS observations, meteorological data, and empirical GPT2w models. The results show that the accuracy in the zenith tropospheric delay (ZTD) of the proposed tropospheric delay model has been verified with a RMS (root mean square) of 1.48 cm in active troposphere conditions, and 1.45 cm in stable troposphere conditions, which is significantly better than the conventional tropospheric GPT2w and Saastamoinen models.

scholarly journals A comprehensive comparison of atmospheric mapping functions for GPS measurements in Egypt

2012 ◽  
Vol 2 (3) ◽  
pp. 216-223 ◽  
Author(s):  
S. A. Younes ◽  
A. G. Elmezayen
Keyword(s):  
Meteorological Data ◽  
Mapping Function ◽  
Propagation Delay ◽  
Tropospheric Delay ◽  
Radio Waves ◽  
Dual Frequency ◽  
Mapping Functions ◽  
Limiting Error ◽  
Comprehensive Comparison ◽  
Delay Prediction

AbstractThe principal limiting error source in the Global Positioning System (GPS) is the mismodeling of the delay experienced by radio waves in propagating through the atmosphere. The atmosphere causing the delay in GPS signals consists of two main layers: the ionosphere and the troposphere. The ionospheric delay can be mitigated using dual frequency receivers, but the tropospheric delay is often corrected using a standard tropospheric model. The tropospheric delay can be described as a product of the delay at the zenith and a mapping function, which models the elevation dependence of the propagation delay. A large number of mapping functions have been developed for use in the analysis of space geodetic data. An assessment of most of these mapping functions including those developed by Niell (NMF), Herring (MTT), Davis (CfA-2.2), Ifadis, Chao, Black & Eisner (B & E), Yang & Ping, Moffett, Vienna (VMF), and Isobaric (IMF) have been performed. The behavior of these mapping functions was assessed by comparing their results with highly accurate Numerical Integration based Models (NIM) for three different stations in Egypt (Aswan, Helwan, and Mersa Matrouh) at different times throughout the year. The meteorological data used in this study was taken from the Egyptian Meteorological Authority (EMA) as average values between 1990 and 2005. It can be concluded that the Black & Eisner mapping function is recommended for dry tropospheric delay prediction for low zenith angles, whereas VMF will be the choice for elevation angles up to 10°.

scholarly journals Investigation on the Impact of Tropospheric Delay on GPS Height Variation near the Equator

2009 ◽  
Vol 4 (3) ◽  
Author(s):  
Joseph D Dodo ◽  
Mohd Hafiz Yahya ◽  
Nor Bin Kamarudin
Keyword(s):  
Meteorological Data ◽  
Simulated Data ◽  
Signal Propagation ◽  
Equatorial Region ◽  
Tropospheric Delay ◽  
Delay Model ◽  
Height Variation ◽  
Maximum Delay ◽  
Height Component ◽  
The Impact

One of the major problems currently facing satellite-based positioning is the atmospheric refraction of the GPS signal caused by the troposphere. The tropospheric effect is much more pronounced at the equatorial region due to its hot and wet conditions. This affects the GPS signal due to the variability of the refractive index, which in turn affects the positional accuracy, especially in the height components. This paper presents a study conducted in the Southern Peninsular Malaysia located at the equatorial region, to investigate the impact of tropospheric delay on GPS height variation. Four campaigns were launched with each campaign lasting for three days. The Malaysian real-time kinematic GPS network (MyRTKnet) reference stations in Johor Bahru were used. GPS RINEX data from these stations were integrated with ground meteorological data observed concurrently from a GPS station located at the Universiti Teknologi Malaysia (UTM), at varying antenna heights for each session of observation. A developed computer program called TROPO.exe based on the Saastamoinen tropospheric delay model was used in estimating the amount of tropospheric delay. The result reveals that, there is inconsistency in the delay variation, reaching maximum delay of 18 m in pseudo-range measurement. The height component shows variations with a maximum value of 119.100 cm and a minimum value of 37.990 cm. The result of the simulated data shows 5.00 m of differences in height gives an effect or improvement of 1.3 mm in signal propagation. This indicates that, tropospheric delay decreases with increase in antenna height.

scholarly journals Evaluation of Wet Mapping Functions Used in Modeling Tropospheric Propagation Delay Effect on GPS Measurements

2017 ◽  
Vol 11 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Sobhy Abdel-Monam Younes
Keyword(s):  
A Priori ◽  
Mapping Function ◽  
Propagation Delay ◽  
Radiosonde Data ◽  
Tropospheric Delay ◽  
Delay Effect ◽  
Gps Measurements ◽  
Mapping Functions ◽  
Significant Bias ◽  
Mapping Techniques

Background:The author compares several methods to map the a priori wet tropospheric delay of GNSS signals in Egypt from the zenith direction to lower elevations.Methods and Materials:The author compared the following mapping techniques against ray-traced delays computed for radiosonde profiles under the assumption of spherical symmetry: Saastamoinen, Hopfield, Black, Chao, Ifadis, Herring, Niell, Moffett, Black and Eisner and UNBabc mapping functions. Radiosonde data were computed from radiosonde stations at the Egyptian stations; in the south of Egypt, near the Mediterranean Sea, and near the Red Sea over a period of 5 years (2000-2005), most of the stations launched radiosonde twice daily, every day of the year. Moreover, data is received from the Egyptian Meteorology Authority.Results and Conclusion:The results indicate that currently, the saastamoinen mapping function should be used for all geodetic applications in Egypt, and if necessary, the Chao and Moffett mapping functions can serve as an acceptable replacement without introducing a significant bias into the station position.

scholarly journals An improved global zenith tropospheric delay model GZTD2 considering diurnal variations

2016 ◽  
Author(s):  
YiBin Yao ◽  
YuFeng Hu ◽  
Chen Yu ◽  
Bao Zhang ◽  
JianJian Guo
Keyword(s):  
Diurnal Variations ◽  
Atmospheric Parameter ◽  
Tropospheric Delay ◽  
Delay Model ◽  
Grid Data ◽  
International Gnss Service ◽  
Data Set ◽  
Average Bias ◽  
Global Average ◽  
Zenith Tropospheric Delay

Abstract. The zenith tropospheric delay (ZTD) is an important atmospheric parameter in the wide application of GNSS technology in geoscience. Given that the temporal resolution of the current Global Zenith Tropospheric Delay model (GZTD) is only 24 h, an improved model GZTD2 has been developed by taking the diurnal variations into consideration and modifying the model expansion function. The data set used to establish this model is the global ZTD grid data provided by Global Geodetic Observing System (GGOS) Atmosphere spanning from 2002 to 2009. We validated the proposed model with respect to ZTD grid data from GGOS Atmosphere, which was not involved in modeling, as well as International GNSS Service (IGS) tropospheric product. The obtained results of ZTD grid data show that the global average Bias and RMS for GZTD2 model are 0.2 cm and 3.8 cm respectively. The global average Bias is comparable to that of GZTD model, but the global average RMS is improved by 3 mm. The Bias and RMS are far better than EGNOS model and the UNB series models. The testing results from global IGS tropospheric product show the Bias and RMS (−0.3 cm and 3.9 cm) of GZTD2 model are superior to that of GZTD (−0.3 cm and 4.2 cm), suggesting higher accuracy and reliability compared to the EGNOS model, as well as the UNB series models.

scholarly journals Areal melt and discharge modelling of Storglaciären, Sweden

1997 ◽  
Vol 24 ◽  
pp. 211-216 ◽  
Author(s):  
Regine Hock ◽  
Christian Noetzli
Keyword(s):  
Meteorological Data ◽  
Grid Point ◽  
Digital Terrain Model ◽  
Turbulent Fluxes ◽  
Heat Fluxes ◽  
Balance Model ◽  
Turbulent Heat ◽  
Terrain Model ◽  
Digital Terrain ◽  
One Year

A grid-based glacier melt-and-discharge model was applied to Storglaciären, a small valley glacier (3 km2) in northern Sweden, for the melt seasons of 1993 and 1994. The energy available for melt was estimated from a surface energy-balance model using meteorological data collected by automatic weather stations on the glacier. Net radiation and the turbulent heat fluxes were calculated hourly for every grid point of a 30 m resolution digital terrain model, using the measurements of temperature, humidity, wind speed and radiative fluxes on the glacier. Two different bulk approaches were used to calculate the turbulent fluxes and compared with respect to their impact on discharge simulations. Discharge of Storglaciären was simulated from calculated meltwater production and precipitation by three parallel linear reservoirs corresponding to the different storage properties of firn, snow and ice. The performance of the model was validated by comparing simulated discharge to measured discharge at the glacier snout. Depending on which parameterization of the turbulent fluxes was used, the timing and magnitude of simulated discharge was in good agreement with observed discharge, or simulated discharge was considerably underestimated in one year.

Exact Subthreshold Integration with Continuous Spike Times in Discrete-Time Neural Network Simulations

2007 ◽  
Vol 19 (1) ◽  
pp. 47-79 ◽  
Author(s):  
Abigail Morrison ◽  
Sirko Straube ◽  
Hans Ekkehard Plesser ◽  
Markus Diesmann
Keyword(s):  
Grid Point ◽  
Propagation Delay ◽  
Integration Scheme ◽  
The Novel ◽  
Neuron Models ◽  
Exact Integration ◽  
Wide Range ◽  
Network Simulations ◽  
Adequate Representation ◽  
Grid Points

Very large networks of spiking neurons can be simulated efficiently in parallel under the constraint that spike times are bound to an equidistant time grid. Within this scheme, the subthreshold dynamics of a wide class of integrate-and-fire-type neuron models can be integrated exactly from one grid point to the next. However, the loss in accuracy caused by restricting spike times to the grid can have undesirable consequences, which has led to interest in interpolating spike times between the grid points to retrieve an adequate representation of network dynamics. We demonstrate that the exact integration scheme can be combined naturally with off-grid spike events found by interpolation. We show that by exploiting the existence of a minimal synaptic propagation delay, the need for a central event queue is removed, so that the precision of event-driven simulation on the level of single neurons is combined with the efficiency of time-driven global scheduling. Further, for neuron models with linear subthreshold dynamics, even local event queuing can be avoided, resulting in much greater efficiency on the single-neuron level. These ideas are exemplified by two implementations of a widely used neuron model. We present a measure for the efficiency of network simulations in terms of their integration error and show that for a wide range of input spike rates, the novel techniques we present are both more accurate and faster than standard techniques.

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