Estimation Models of Geoid in Nigeria Using Doppler Satellite Observations

Ezeigbo, C. U.

doi:10.1007/978-1-4612-3104-2_28

Cited by 2 publications

(3 citation statements)

References 3 publications

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“…The problem has resulted from the failure to reduce the astronomical observations to the agreed Conventional International Origin, C. I. O. Hence, the result was a geoid tilted from the north-western side to the northeast as reported in Ezeigbo (1991). III.…”

Section: The Defects In the Nigerian Geodetic Networkmentioning

confidence: 99%

“…As a result, a geoidal profile along the 12 th parallel Traverse (CFL series) indicates geoidal height discrepancies of up to 12 m (Adaminda and Field, 1985). Also, investigations by Ezeigbo (1991) and Agajelu (1990) identified scale distortions between 1-3 ppm in the network due to the absence of a geoid height model in the North-Eastern part. Apart from that, the so-called development method adopted for the computation has cast a great deal of doubt on the credibility of our geodetic data, particularly now that the result from measurement obtained using precise modern instruments reveals a lot of biases on such data.…”

Section: The Defects In the Nigerian Geodetic Networkmentioning

confidence: 99%

“…What remains is to carry out a rigorous (least squares) adjustment of the observations and then (if L40 was included in the survey) determine n. If these are done, approximately correct orthometric heights, Ho will be obtained for all stations (Uzodinma, 2005) Ho = Hs+ n where Ho is the required approximate orthometric height Hs is the spirit levelling height n is the least square adjustment values This approach should be able to remove the wider discrepancies (up to 12 m) noticed in the models determined by different authors Ezeigbo (1991) and Agajelu (1990). Furthermore, all the existing benchmarks should be identified; horizontal and vertical observation should be carried out on the benchmarks, and then the approximate orthometric height determined.…”

Section: Way Forwardmentioning

confidence: 99%

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The Review and Development of the Nigerian Geodetic Control Network

Aleem

Abubakar

2022

J. Geospat. Surv.

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The Nigeria Geodetic Networks were established using primarily triangulation, traversing, trilateration, doppler and levelling networks for numerous control requirements in both surveying and national spatial reference networks. These networks have a number of inherent negative failings that affect its reliability of usage. Various investigations have identified many weaknesses in the network, starting with the origin and other subsequent observational and adjustment defects. Thus, the need to obtain accurate and consistent sets of coordinates with the available space technology and equipment to update and strengthen the network has now become necessary. This work reviews the status of the existing Nigeria Geodetic Networks, and possible ways to improve them are highlighted. The work further proposes a strategy to obtain the most accurate and consistent set of coordinates to serve Geodesy and Geodynamics research, spatial referencing and other mapping activities in the country. The proposed programme of action for improving these networks includes: reobserving the existing network, new set of computations and adjustment of the entire network of controls, and the selection of a suitably chosen system to meet the present and future geodetic needs of positioning.

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Section: The Defects In the Nigerian Geodetic Networkmentioning

confidence: 99%

Section: The Defects In the Nigerian Geodetic Networkmentioning

confidence: 99%

Section: Way Forwardmentioning

confidence: 99%

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The Review and Development of the Nigerian Geodetic Control Network

Aleem

Abubakar

2022

J. Geospat. Surv.

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Evaluation of GOCE/GRACE and combined global geopotential models using GNSS/levelling data over Nigeria

Bako,

Elsaka,

Kusche

et al. 2024

Stud Geophys Geod

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Global Geopotential Models (GGMs) provide valuable information about Earth’s gravity field functionals, such as geoid heights and gravity anomalies. However, ground-based datasets are required to validate these GGMs at the regional and local scales. In this study, we validated the accuracy of GGMs by comparing them with ground-based Global Navigation Satellite System (GNSS)/levelling data for the first time in Nigeria. We employed two validation scenarios: with and without considering spectral consistency using the spectral enhancement method (SEM) to incorporate high and very high frequencies of the gravity field spectrum from the combined global gravity field model (XGM2019e_2159) and the residual terrain model (RTM) derived from the Shuttle Radar Topography Mission (SRTM) data, respectively. The results of this evaluation confirmed that the application of SEM improved the assessment of the GGM solutions in an unbiased manner. Integrating XGM2019e_2159 and SRTM data to constrain the high-frequency component of geoid heights in Gravity Field and Steady-State Ocean Circulation Explorer (GOCE)-based GGMs led to an improvement of approximately 10% in reducing the standard deviation (STD) relative to when SEM was not applied. GO_CONS_GCF_2_TIM_R6 at spherical harmonics (SH) of up to degree and order 260 demonstrated the lowest STD when compared to GO_CONS_GCF_2_DIR_R6 and GO_CONS_GCF_2_SPW_R5, with a reduction from 0.380 m without SEM application to 0.342 m with SEM implementation. In addition, four transformation models, namely, linear, four-parameter, five-parameter, and seven-parameter models, were evaluated. The objective is to mitigate the reference system offsets between the GNSS/levelling data and the GGMs and to identify the particular parametric model with the smallest STD across all GGMs. This effort reduced the GGMs misfits to GNSS/levelling to 0.30 m, representing a 15.3% decrease in STD. Notably, the XGM2019e_2159 model provides this improvement.

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Estimation Models of Geoid in Nigeria Using Doppler Satellite Observations

Cited by 2 publications

References 3 publications

The Review and Development of the Nigerian Geodetic Control Network

The Review and Development of the Nigerian Geodetic Control Network

Evaluation of GOCE/GRACE and combined global geopotential models using GNSS/levelling data over Nigeria

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