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You searched for subject:(Zenith wet delay). Showing records 1 – 3 of 3 total matches.

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Curtin University of Technology

1. Lo, Johnny Su Hau. Estimation of tropospheric wet delay from GNSS measurements .

Degree: 2011, Curtin University of Technology

The determination of the zenith wet delay (ZWD) component can be a difficult task due to the dynamic nature of atmospheric water vapour. However, precise estimation of the ZWD is essential for high-precision Global Navigation Satellite System (GNSS) applications such as real-time positioning and Numerical Weather Prediction (NWP) modelling.The functional and stochastic models that can be used for the estimation of the tropospheric parameters from GNSS measurements are presented and discussed in this study. The focus is to determine the ZWD in an efficient manner in static mode. In GNSS, the estimation of the ZWD is directly impacted by the choice of stochastic model used in the estimation process. In this thesis, the rigorous Minimum Norm Quadratic Unbiased Estimation (MINQUE) method was investigated and compared with traditional models such as the equal-weighting model (EWM) and the elevationangle dependent model (EADM). A variation of the MINQUE method was also introduced. A simulation study of these models resulted in MINQUE outperforming the other stochastic models by at least 36% in resolving the height component. However, this superiority did not lead to better ZWD estimates. In fact, the EADM provided the most accurate set of ZWD estimates among all the models tested. The EADM also yielded the best ZWD estimates in the real data analyses for two independent baselines in Australia and in Europe, respectively.The study also assessed the validity of a baseline approach, with a reduced processing window size, to provide good ZWD estimates at Continuously Operating Reference Stations (CORS) in an efficient manner. Results show that if the a-priori station coordinates are accurately known, the baseline approach, along with a 2-hour processing window, can produce ZWD estimates that are statistically in good agreement with the estimates from external sources such as the radiosonde (RS), water vapour radiometer (WVR) and International GNSS Service (IGS) solutions. Resolving the ZWD from GNSS measurements in such a timely manner can aid NWP model in providing near real-time weather forecasts in the data assimilation process.In the real-time kinematic modelling of GNSS measurements, the first-order Gauss- Markov (GM) autocorrelation model is commonly used for the dynamic model in Kalman filtering. However, for the purpose of ZWD estimation, it was found that the GM model consistently underestimates the temporal correlations that exist among the ZWD measurements. Therefore, a new autocorrelation dynamic model is proposed in a form similar to that of a hyperbolic function. The proposed model initially requires a small number of autocorrelation estimates using the standard autocorrelation formulations. With these autocorrelation estimates, the least-squares method is then implemented to solve for the model’s parameter coefficients. Once solved, the model is then fully defined. The proposed model was shown to be able to follow the autocorrelation trend better than the GM model. Additionally, analysis of real data at an…

Subjects/Keywords: zenith wet delay (ZWD); real-time positioning and Numerical Weather Prediction (NWP) modelling; tropospheric wet delay; GNSS measurements

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Lo, J. S. H. (2011). Estimation of tropospheric wet delay from GNSS measurements . (Thesis). Curtin University of Technology. Retrieved from http://hdl.handle.net/20.500.11937/2289

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Lo, Johnny Su Hau. “Estimation of tropospheric wet delay from GNSS measurements .” 2011. Thesis, Curtin University of Technology. Accessed April 23, 2021. http://hdl.handle.net/20.500.11937/2289.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Lo, Johnny Su Hau. “Estimation of tropospheric wet delay from GNSS measurements .” 2011. Web. 23 Apr 2021.

Vancouver:

Lo JSH. Estimation of tropospheric wet delay from GNSS measurements . [Internet] [Thesis]. Curtin University of Technology; 2011. [cited 2021 Apr 23]. Available from: http://hdl.handle.net/20.500.11937/2289.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Lo JSH. Estimation of tropospheric wet delay from GNSS measurements . [Thesis]. Curtin University of Technology; 2011. Available from: http://hdl.handle.net/20.500.11937/2289

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation


The Ohio State University

2. alojaiman, shahad N M A A. Tropospheric Delay Modeling using GNSS Observations from Continuously Operating Reference Stations (CORS).

Degree: MS, Civil Engineering, 2019, The Ohio State University

PPP exhibits through many previous studies the possibility to achieve high accuracy estimation of tropospheric paraments. Either Zenith wet delay (ZWD) or Precipitable Water Vapor (PWV) can be estimated by PPP processing of GNSS data in either real time or post processing mode. PWV is further utilized as a tool from which rainfall forecasting models are established especially in sites where such data may not be available. In this study PPP processing of GNSS data leads to the estimation of ZTD as well as ZWD values. A test is first conducted in which MGEX sites are processed on July 22nd, 2019 and January 11th, 2019 to estimate ZTD values and establish PPP’s accuracy based on IGS final solutions and tropospheric products as reference data. An approach in which the site coordinates are fixed instead of estimated by PPP is then tested on the same MGEX sites to examine its contribution to the accuracy of ZTD estimates. 37 CORS sites around the United States are then processed for three day between August 7th 2019 and August 9th 2019 with PPP and site coordinates fixing to create ZTD, ZWD, and PWV maps of the area from which patterns and models can be generated. The created maps were analyzed alongside NASA’s Goddard Earth Sciences Data and Information Services Center’s precipitation maps of near real time and TRMM Multi-Satellite Precipitation Analysis TMPA products. Finally, PWV reference data was obtained from UCAR’s COSMIC program and daily averaged to be compared with the PWV values extracted from the previously estimated ZWD. The PPP processing of MGEX sites with GPS and GLONASS data resulted in mm level differences between estimated and referenced ZTD data with RMS values as low as 1.55 mm. Site coordinates fixing enhanced ZTD estimates slightly based on the same referenced ZTD data. The examination of maps showed clear consistency between the estimated ZWD as well as PWV maps of the area and the reference precipitation maps of the same day especially as precipitation and weather patterns changed daily. The estimated PWV maps reflected that change from day to day specifically the prominent changes observed around the NESC, NEST, and DSRC sites. PWV validation resulted in PWV errors mostly less than 2 mm and as low as 0.18 mm. The approach has the potential of further CORS network expansion for a more accurate model with location correlated parameters to estimates PWV considered. Future work could also include real time PPP processing with ambiguity fixing to enhance ZWD estimation. Advisors/Committee Members: Wang, Lei (Advisor).

Subjects/Keywords: Civil Engineering; PPP; CORS; Tropospheric delay; Continuously Operating Reference Stations; GNSS; IGS; GPS; MGEX; Zenith total delay; Zenith wet delay; PWV; ZTD; ZWD; Precipitable Water Vapor

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

alojaiman, s. N. M. A. A. (2019). Tropospheric Delay Modeling using GNSS Observations from Continuously Operating Reference Stations (CORS). (Masters Thesis). The Ohio State University. Retrieved from http://rave.ohiolink.edu/etdc/view?acc_num=osu1574536144031026

Chicago Manual of Style (16th Edition):

alojaiman, shahad N M A A. “Tropospheric Delay Modeling using GNSS Observations from Continuously Operating Reference Stations (CORS).” 2019. Masters Thesis, The Ohio State University. Accessed April 23, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1574536144031026.

MLA Handbook (7th Edition):

alojaiman, shahad N M A A. “Tropospheric Delay Modeling using GNSS Observations from Continuously Operating Reference Stations (CORS).” 2019. Web. 23 Apr 2021.

Vancouver:

alojaiman sNMAA. Tropospheric Delay Modeling using GNSS Observations from Continuously Operating Reference Stations (CORS). [Internet] [Masters thesis]. The Ohio State University; 2019. [cited 2021 Apr 23]. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=osu1574536144031026.

Council of Science Editors:

alojaiman sNMAA. Tropospheric Delay Modeling using GNSS Observations from Continuously Operating Reference Stations (CORS). [Masters Thesis]. The Ohio State University; 2019. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=osu1574536144031026


RMIT University

3. Yuan, Y. Real-time retrieval of precipitable water vapour from GNSS precise point positioning.

Degree: 2015, RMIT University

Global Positioning System (GPS) meteorology (GPS-MET) as a novel approach for precipitable water vapour (PWV) sounding using ground-based GPS receivers has been conducted since earlier 1990s. Further research to date is based on post-processing or near-real-time processing using differenced GPS observations. It still remains a challenging task at high temporal resolutions and in real time. In addition, new Global Navigation Satellite Systems (GNSS) are under development quickly. This has the potential to improve the retrieval of PWV, leading GPS-MET research to a new stage of GNSS-MET. This study aims to take these aspects into account and investigates the retrieval of zenith total delay (ZTD) and PWV using real-time precise point positioning (PPP) approach. The PPP processing in this study is conducted using the BKG (the Federal Agency for Cartography and Geodesy) NTRIP Client (BNC) software platform which is substantially modified. The modifications include the modelling of tropospheric delay in which GPT2 is implemented and the corrections of error sources such as solid Earth tides, ocean tide loading and the antenna-related. The retrieved ZTD is then converted into PWV by multiplying a dimensionless proportionality which is derived from the Forecast Vienna Mapping Functions 1 (VMF1-FC) model. The retrievals of ZTD and PWV are validated using GPS observations in a one-month period at 20 globally distributed stations. The derived real-time ZTDs at most stations agree well with the tropospheric products from the International GNSS Service (IGS) and the root mean square (RMS) errors are <12 mm. The RMS errors of the PWVs in comparison with the radiosonde data are ≤3 mm. Note that 15 mm accuracy is the threshold if ZTDs are input to Numerical Weather Prediction (NWP) models and 3 mm accuracy is the threshold if PWVs are inputs to weather nowcasting according to the document by World Meteorological Organization (WMO). Furthermore, the theoretical accuracy of PWVs in various conditions is analysed. The RMS error of PWV is proved to be a strictly increasing function of zenith wet delay (ZWD) and weighted mean temperature. Hence the retrieval of PWV is more challenging in higher temperature and humidity conditions. This research proves that even in poor retrieval conditions, i.e., high humidity and temperature, an accuracy of PWV at 3 mm level is still achievable using the real-time ZTD from PPP and the empirical models for the determination of weighted mean temperature. A preliminary study of the ZTD retrieval using multi-GNSS data is also conducted in this study. The addition of GLONASS (GLObal NAvigation Satellite System) observations will significantly increase the number of visible satellites and improve the Dilution of Precision (DOP) indices like Positional DOP (PDOP) and Geometric DOP (GDOP). However, a test of ZTD retrieval at 12 global IGS stations shows that adding GLONASS data degrades the accuracy of ZTD. A further analysis implies that the multi-GNSS processing can be improved by the…

Subjects/Keywords: Fields of Research; GPS meteorology; GNSS meteorology; Zenith total delay; Precipitable water vapour; Precise point positioning; Multiple GNSS; Tropospheric delay; Zenith wet delay; NTRIP; Numerical weather prediction; Weather nowcasting; Global Navigation Satellite System

Record DetailsSimilar RecordsGoogle PlusoneFacebookTwitterCiteULikeMendeleyreddit

APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Yuan, Y. (2015). Real-time retrieval of precipitable water vapour from GNSS precise point positioning. (Thesis). RMIT University. Retrieved from http://researchbank.rmit.edu.au/view/rmit:161611

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Yuan, Y. “Real-time retrieval of precipitable water vapour from GNSS precise point positioning.” 2015. Thesis, RMIT University. Accessed April 23, 2021. http://researchbank.rmit.edu.au/view/rmit:161611.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Yuan, Y. “Real-time retrieval of precipitable water vapour from GNSS precise point positioning.” 2015. Web. 23 Apr 2021.

Vancouver:

Yuan Y. Real-time retrieval of precipitable water vapour from GNSS precise point positioning. [Internet] [Thesis]. RMIT University; 2015. [cited 2021 Apr 23]. Available from: http://researchbank.rmit.edu.au/view/rmit:161611.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Yuan Y. Real-time retrieval of precipitable water vapour from GNSS precise point positioning. [Thesis]. RMIT University; 2015. Available from: http://researchbank.rmit.edu.au/view/rmit:161611

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

.