Determination of Indonesia Marine Deflection of Vertical from Multi-Mission Altimetry Satellite Data Ahmad Fauzan(a*), Dudy Darmawan Wijaya(a), Ivonne Milichristi Radjawane(b), Hansan Park(c)
a)Geodesy Research Group, Institut Teknologi Bandung
Jalan Ganesha 10, Bandung 40132, Indonesia
*Corresponding Author^s email: ahmdfauznn[at]gmail.com
b)Oceanography Research Group, Institut Teknologi Bandung
Jalan Ganesha 10, Bandung 40132, Indonesia
c)Marine Technology Cooperation Research Center
Abstract
The geoid is a closed surface that can represent the geometry of the earth and an equipotential surface of gravity that coincides with the mean sea level. Based on data collection, the geoid is divided into land geoid and marine geoid. This research will focus on marine geoid. Marine geoid with high accuracy can be obtained from measurements of shipborne and airborne, but both have limitations in terms of global coverage that is not dense, requires a long time, low temporal resolution, and the data is difficult to access for political reasons thus that it is not possible to use it for modeling marine geoid with a large area. Currently, satellite altimetry is the most important technology for constructing marine geoids because of its uniform global distribution, closer measurement points, consistent level of precision, requires less time, high temporal resolution, and can be used in all weather. Based on the Regulation of the Head of the Geospatial Information Agency (BIG) Number 13 of 2021 concerning the Indonesian Geospatial Reference System (SRGI), it is stated that the vertical reference system used in Indonesia is INAGEOID. The marine geoid component in INAGEOID was obtained from DTU17 which uses data from many altimetry satellite missions, namely CryoSat-2, Jason-1, and SARAL/AltiKa with accuracy in the range of 10 to 20 cm. This accuracy value is still not sufficient as a reference in the large-scale mapping of 1:1,000, namely 5 cm. To improve the accuracy of the geoid, it is necessary to select the right altimetry satellite data and processing methods. The sea geoid is obtained from sea surface height (SSH) measured by altimetry satellites. In order to reduce long wavelength errors in SSH measurements such as satellite orbit errors, signal propagation errors, and topographical errors, SSH gradient calculation is carried out by subtracting between two adjacent SSH points and then dividing by the sphere distance between them. For short distances, the gradient SHH equals the deflection of vertical (DOV). Furthermore, used the inverse Vening Meinesz (IVM) method to convert it into a geoid. This research will carry out high-accuracy DOV determinations from multi-missions altimetry satellite data, namely SARAL/AltiKa, CryoSat-2, Jason-1/2/3, Topex/Poseidon, Sentinel-3A, Sentinel-3B, and Envisat. DOV filtering is done to remove noise that collides with the signal on the shortwave. The DOV that has been filtered is then converted into sea gravity and validated with sea gravity data as a result of shipborne measurements. With this research, it is expected that the accuracy of marine geoid in Indonesia will be less than 5 cm.
Keywords: Marine deflection of vertical- satellite altimetry- Indonesia
