Marine geoid modeling from multi-mission satellite altimetry data using least squares stokes modification approach with additive corrections

• Main Author: Mohammad Yazid, Nornajihah
• Format: Thesis
• Language: English
• Published: 2018
• Subjects: NA Architecture
• Online Access: http://eprints.utm.my/id/eprint/81729/1/NornajihahMohammadYazidMFABU2018.pdf; http://eprints.utm.my/id/eprint/81729/; http://dms.library.utm.my:8080/vital/access/manager/Repository/vital:126893

Marine geoid is crucial for orthometric height determination. The airborne and shipborne surveys have been used for geoid and gravity surveys in marine areas, but they could only cover a limited coverage area due to the high cost and time constraints. Over the last 30 years, satellite altimeter has become an important tool for global geoid and gravity field recovery, with nearly 60% of the Earth’s surface in relation to the height of the ocean could be covered. This enables researchers to replace the conventional marine geoid models, and surveys can be conducted faster with a larger coverage area at a reduced cost. This study presents an attempt to model marine geoid from multi-mission satellite altimetry data using Least Squares Stokes Modification Approach with Additive Corrections. Six altimetry data were used to derive the mean sea surface which was processed in the Radar Altimeter Database System. The gravity anomaly was computed using Gravity Software, and planar Fast Fourier Transformation method was applied. The evaluation, selection, blunder detection, combination and re-gridding of the altimetry-derived gravity anomalies and Global Geopotential Model data were demonstrated. The cross validation approach was employed in the cleaning and quality control of the data with the combination of the Kriging interpolation method. Marine geoid was computed based on the Least Squares Stokes Modification Approach with Additive Corrections. The optimal condition modification parameters of 4° spherical cap, 0.4 mGal terrestrial gravity data error and 0.1° correlation length were applied. Then, the additive corrections based on Downward Continuation, Atmospheric Effects and Ellipsoidal Corrections were combined with the estimated geoid to provide a precise marine geoid over the Malaysian seas. Three selected levelling observations at tide gauge stations at Geting, Cendering and Pelabuhan Klang were used to verify the accuracy of the computed marine geoid model. The derived mean sea surface represents -0.4945m mean error and 2.2592m root mean square error values after being evaluated with the mean sea surface of Denmark Technical University 13. The gravity anomaly data from tapering window width with block 300 from hhawtimr4 assessments denotes the optimum gravity anomaly results with root mean square error value, 17.8329mGal. The accuracy of marine geoid model corresponds to the standard deviation, 0.098m and the root mean squared error value, 0.177m. The findings suggest that the marine geoid model can be utilized for the orthometric height determination in marine areas. The by-product of this research, the Malaysian Marine Geoid Calculator (MyMG) could assist users in extracting marine geoid in Malaysian seas.