Establishment of New Fitted Geoid Model in Universiti Teknologi Malaysia

Ismail, M. F.; Din, Ami Hassan Md; Uti, Mat Nizam; Omar, Abdullah Hisam

doi:10.5194/isprs-archives-xlii-4-w9-27-2018

Cited by 6 publications

(6 citation statements)

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“…The RTM effects on the gravity anomaly and the height anomaly were computed using the GRAVSOFT TC program, with a radius of 20 km for the detailed DTM and 200 km for the coarse grid. Thus, we need three models to calculate the RTM effects with TC program; these are the detailed (SRTM3arc), coarse, and reference DTMs in Ismail et al (2018) which the reference height grid was estimated by lowpass filtering the detailed DTM in order to represent the topographic signal above the maximum degree of the GGM used (Forsberg 1984). The coarse and reference DTM models were created as follows:…”

Section: Quasigeoid Determination Methodologymentioning

confidence: 99%

A high-resolution gravimetric quasigeoid model for Vietnam

Vũ

Bruinsma

Bonvalot

2019

Earth Planets Space

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A high-resolution gravimetric quasigeoid model for Vietnam and its surrounding areas was determined based on new gravity data. A set of 29,121 land gravity measurements was used in combination with fill-in data where no gravity data existed. Global Gravity field Models plus Residual Terrain Model effects and gravity field derived from altimetry satellites were used to provide the fill-in information over land and marine areas. A mixed model up to degree/order 719 was used for the removal of the long and medium wavelengths and the calculation of the quasigeoid restore effects. The residual height anomalies have been determined employing the Stokes integral using the Fast Fourier Transform approach and deterministic kernel modification proposed by Wong-Gore, as well as by means of Least-Squares Collocation. The accuracy of the resulting quasigeoid models was evaluated by comparing with height anomalies derived from 812 co-located GNSS/levelling points. Results are very similar; both local quasigeoid models have a standard deviation of 9.7 cm and 50 cm in mean bias when compared to the GNSS/levelling points. This new local quasigeoid model for Vietnam represents a significant improvement over the global models EIGEN-6C4 and EGM2008, which have standard deviations of 19.2 and 29.1 cm, respectively, for this region.

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Section: Quasigeoid Determination Methodologymentioning

confidence: 99%

A high-resolution gravimetric quasigeoid model for Vietnam

Vũ

Bruinsma

Bonvalot

2019

Earth Planets Space

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“…Once the geoid height is known, the orthometric height (H) can be measured based on the MyGeoid model, i.e., the Malaysian geoid model (Equation (1)). The geoid determination of Malaysia is based on gravimetry (airborne, surface, and satellite altimetry), which is located downward relative to the surface of the topography, after removal of a spherical harmonic reference field expansion [48,49]. The orthometric height is simplified as the difference between the geoid height and ellipsoidal height, as shown in Equation (1): H = h − N, where H = orthometric height;h = ellipsoidal height;N = geoid height.…”

Section: Methodsmentioning

confidence: 99%

Evaluating Water Level Changes at Different Tidal Phases Using UAV Photogrammetry and GNSS Vertical Data

Mohamad

Khanan

Ahmad

et al. 2019

Sensors

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Evaluating water level changes at intertidal zones is complicated because of dynamic tidal inundation. However, water level changes during different tidal phases could be evaluated using a digital surface model (DSM) captured by unmanned aerial vehicle (UAV) with higher vertical accuracy provided by a Global Navigation Satellite System (GNSS). Image acquisition using a multirotor UAV and vertical data collection from GNSS survey were conducted at Kilim River, Langkawi Island, Kedah, Malaysia during two different tidal phases, at high and low tides. Using the Structure from Motion (SFM) algorithm, a DSM and orthomosaics were produced as the main sources of data analysis. GNSS provided horizontal and vertical geo-referencing for both the DSM and orthomosaics during post-processing after field observation at the study area. The DSM vertical accuracy against the tidal data from a tide gauge was about 12.6 cm (0.126 m) for high tide and 34.5 cm (0.345 m) for low tide. Hence, the vertical accuracy of the DSM height is still within a tolerance of ±0.5 m (with GNSS positioning data). These results open new opportunities to explore more validation methods for water level changes using various aerial platforms besides Light Detection and Ranging (LiDAR) and tidal data in the future.

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“…Computation of bias. Observed Geoid heights, 𝑁 𝑔𝑛𝑠𝑠 may be computed from spirit-levelled orthometric heights, 𝐻 and GNSS-measured ellipsoidal heights, ℎ using the famous equation [27]: -…”

Section: Comparison With Gnss-levelled Heightsmentioning

confidence: 99%

“…Equation (2) was used to determine the model-derived geoid undulations implied by the GGMs. The differences or bias for each GGM was computed for statistical analysis using the following equation [27]: -…”

Section: Comparison With Gnss-levelled Heightsmentioning

confidence: 99%

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A combined regional Geopotential Model using optimized global Gravity Field Solutions

Nyoka

Din²,

Pa’suya³

et al. 2022

IOP Conf. Ser.: Earth Environ. Sci.

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To develop a gravimetric geoid, a Global Geopotential Model (GGM) is required to minimise the truncation error arising from using the Stokes integral with a limited number of gravity data points. The choice of a best-fitting GGM determines the accuracy of a gravimetric geoid solution. Selecting a suitable GGM is a rigorous process, requiring both internal and external evaluation of all GGMs available at the International Center for Globa Earth Models (ICGEM). Moreover, GGMs perform differently depending on the wavelength, and it is difficult to obtain a GGM that performs best across the full harmonic spectrum. In this study, a combined GGM is developed from a selection of the most recent and high-resolution GGMs covering Peninsular Malaysia. The selected models are first synthesized harmonically to obtain geoid undulations at collocated GNSS-levelled points, and free air anomalies at randomly sampled points across the study area. These quantities are compared with the observed geoid undulations and point gravity anomalies interpolated from a grid of free air anomalies. The best performing GGMs are then used to produce a combined GGM, by selecting the spherical harmonic coefficients with the best characteristics for every degree. The signal and error spectra of the new GGM are compared with the selected geopotential models. The combined GGM produced a higher cumulative signal to noise ratio (SNR) of 4402.669 compared to all the selected GGMs, with XGM2016 and Eigen-6C following suit with SNR of 4139.561 and 4092.462, respectively. Besides, the new combined GGM performed better across the whole harmonic spectrum than all selected GGMs. The use of combined GGMs in geoid modelling, instead of a single GGM may be more desirable because they can improve the quality of results.

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Establishment of New Fitted Geoid Model in Universiti Teknologi Malaysia

Cited by 6 publications

References 0 publications

A high-resolution gravimetric quasigeoid model for Vietnam

A high-resolution gravimetric quasigeoid model for Vietnam

Evaluating Water Level Changes at Different Tidal Phases Using UAV Photogrammetry and GNSS Vertical Data

A combined regional Geopotential Model using optimized global Gravity Field Solutions

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