Refinement of global gridded ray-traced Zenith tropospheric delay over Nigeria based on local GNSS network observations
Recent studies on the application of Zenith Tropospheric Delay (ZTD) in meteorology and geodesy have shown improved accuracy with the use of locally estimated ZTD compared to Global ZTD. This paper focuses on the refinement of global gridded ray-traced Vienna Mapping Functions 1 (VMF1) ZTD over Nige...
| Main Authors: | , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Elsevier
2023-02-01
|
| Series: | Geosystems and Geoenvironment |
| Subjects: | |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S2772883822001121 |
| _version_ | 1797959465422553088 |
|---|---|
| author | Ifechukwu Ugochukwu Nzelibe Timothy Oluwadare Idowu |
| author_facet | Ifechukwu Ugochukwu Nzelibe Timothy Oluwadare Idowu |
| author_sort | Ifechukwu Ugochukwu Nzelibe |
| collection | DOAJ |
| description | Recent studies on the application of Zenith Tropospheric Delay (ZTD) in meteorology and geodesy have shown improved accuracy with the use of locally estimated ZTD compared to Global ZTD. This paper focuses on the refinement of global gridded ray-traced Vienna Mapping Functions 1 (VMF1) ZTD over Nigeria, using ZTD estimates derived from local GNSS Continuously Operating Reference Stations (CORS) observations. Three (3) years of GNSS observations collected at 13 CORS located within the study area were post-processed using GNSS Analysis and Processing Software (GAPS) to derive the local GNSS-ZTD estimates. The global VMF1-ZTD were interpolated at the locations of the local GNSS-CORS. An optimal deep structured supervised Neural Network (NN) was derived by training feedforward networks using the Levenberg-Marquardt backpropagation algorithm, with spatiotemporal variables and VMF1-ZTD as inputs and the GNSS-ZTD as the target. The outputs from the NN model were assessed using internal and external data. Results from internal data evaluations indicated a robust and accurate model output with optimum network performances indicating MSE of ∼7.22 × 10−6 m and ∼4.56 × 10−4 m for hydrostatic and wet ZTD networks respectively. The external data evaluations performed using the International GNSS Services (IGS) Zenith Path Delay (ZPD), indicated an RMSE range of ∼0.041 m to 0.095 m for global-VMF1 and ∼0.030 m to 0.037 m for the Local Refine (LR)-VMF1. The results suggest that the application of ZTD estimates derived from local GNSS observations in the refinement of global gridded VMF1-ZTD yields an improved accuracy over Nigeria. Consequently, the LR-VMF1 ZTD estimates are recommended for improved accuracy, required for geodetic and meteorological applications in and around Nigeria |
| first_indexed | 2024-04-11T00:33:24Z |
| format | Article |
| id | doaj.art-0c7ee240823b4cd29f60982c2c9f79bd |
| institution | Directory Open Access Journal |
| issn | 2772-8838 |
| language | English |
| last_indexed | 2024-04-11T00:33:24Z |
| publishDate | 2023-02-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Geosystems and Geoenvironment |
| spelling | doaj.art-0c7ee240823b4cd29f60982c2c9f79bd2023-01-07T04:17:54ZengElsevierGeosystems and Geoenvironment2772-88382023-02-0121100137Refinement of global gridded ray-traced Zenith tropospheric delay over Nigeria based on local GNSS network observationsIfechukwu Ugochukwu Nzelibe0Timothy Oluwadare Idowu1Corresponding author.; Department of Surveying and Geoinformatics, Federal University of Technology Akure, Ondo State, NigeriaDepartment of Surveying and Geoinformatics, Federal University of Technology Akure, Ondo State, NigeriaRecent studies on the application of Zenith Tropospheric Delay (ZTD) in meteorology and geodesy have shown improved accuracy with the use of locally estimated ZTD compared to Global ZTD. This paper focuses on the refinement of global gridded ray-traced Vienna Mapping Functions 1 (VMF1) ZTD over Nigeria, using ZTD estimates derived from local GNSS Continuously Operating Reference Stations (CORS) observations. Three (3) years of GNSS observations collected at 13 CORS located within the study area were post-processed using GNSS Analysis and Processing Software (GAPS) to derive the local GNSS-ZTD estimates. The global VMF1-ZTD were interpolated at the locations of the local GNSS-CORS. An optimal deep structured supervised Neural Network (NN) was derived by training feedforward networks using the Levenberg-Marquardt backpropagation algorithm, with spatiotemporal variables and VMF1-ZTD as inputs and the GNSS-ZTD as the target. The outputs from the NN model were assessed using internal and external data. Results from internal data evaluations indicated a robust and accurate model output with optimum network performances indicating MSE of ∼7.22 × 10−6 m and ∼4.56 × 10−4 m for hydrostatic and wet ZTD networks respectively. The external data evaluations performed using the International GNSS Services (IGS) Zenith Path Delay (ZPD), indicated an RMSE range of ∼0.041 m to 0.095 m for global-VMF1 and ∼0.030 m to 0.037 m for the Local Refine (LR)-VMF1. The results suggest that the application of ZTD estimates derived from local GNSS observations in the refinement of global gridded VMF1-ZTD yields an improved accuracy over Nigeria. Consequently, the LR-VMF1 ZTD estimates are recommended for improved accuracy, required for geodetic and meteorological applications in and around Nigeriahttp://www.sciencedirect.com/science/article/pii/S2772883822001121Artificial Neural Network (ANN)Global Navigation Satellite Systems (GNSS)ModellingNigeria GNSS Network (NIGNET)RefinementZenith Tropospheric Delay (ZTD) |
| spellingShingle | Ifechukwu Ugochukwu Nzelibe Timothy Oluwadare Idowu Refinement of global gridded ray-traced Zenith tropospheric delay over Nigeria based on local GNSS network observations Geosystems and Geoenvironment Artificial Neural Network (ANN) Global Navigation Satellite Systems (GNSS) Modelling Nigeria GNSS Network (NIGNET) Refinement Zenith Tropospheric Delay (ZTD) |
| title | Refinement of global gridded ray-traced Zenith tropospheric delay over Nigeria based on local GNSS network observations |
| title_full | Refinement of global gridded ray-traced Zenith tropospheric delay over Nigeria based on local GNSS network observations |
| title_fullStr | Refinement of global gridded ray-traced Zenith tropospheric delay over Nigeria based on local GNSS network observations |
| title_full_unstemmed | Refinement of global gridded ray-traced Zenith tropospheric delay over Nigeria based on local GNSS network observations |
| title_short | Refinement of global gridded ray-traced Zenith tropospheric delay over Nigeria based on local GNSS network observations |
| title_sort | refinement of global gridded ray traced zenith tropospheric delay over nigeria based on local gnss network observations |
| topic | Artificial Neural Network (ANN) Global Navigation Satellite Systems (GNSS) Modelling Nigeria GNSS Network (NIGNET) Refinement Zenith Tropospheric Delay (ZTD) |
| url | http://www.sciencedirect.com/science/article/pii/S2772883822001121 |
| work_keys_str_mv | AT ifechukwuugochukwunzelibe refinementofglobalgriddedraytracedzenithtroposphericdelayovernigeriabasedonlocalgnssnetworkobservations AT timothyoluwadareidowu refinementofglobalgriddedraytracedzenithtroposphericdelayovernigeriabasedonlocalgnssnetworkobservations |