| Summary: | The use of orthometric height for various application is very significant. Ideally, orthometric height refers to geoid field. In practice, reference is often used is mean sea level (MSL) which is measured at one or several tidal stations. inter-tidal stations are not connected to each other, and the MSL difference of each tidal station can reach 2 m. It can lead to problems in the height system that very influential on the work that needs data of height, especially for the work that cover the region area. To overcome this problem, height system unification effort is needed. The purpose of this research is to unify the height system through the determination of sea surface topography (SST) which is produced by using a combination of tidal data, Envisat altimetry satellite, and hybrid geoid model of Java Island.
The main data that used in this research are tidal and Envisat altimetry satellite data in the period January 2010 to December 2010, with research sites in three tidal stations namely Cilacap, Sadeng and Prigi tide station. Evaluation is done by testing several weighting techniques to interpolate the value of the correction process. Spatial interpolation method used is Inverse Distance Weighted (IDW) with weighting technique which is a technique I (equation (II.41)), the second technique (equation (II.42)), and the third technique (equation (II.46)). The best determination of weighting technique is based on the results of cross validation test. Testing is done by calculating a difference (deviation) between the value of SST modeling results and values of SST that serve as a reference accuracy (SST fix), which is the value of SST on Sadeng tidal station. The next best weighting technique used for SST modeling in Java. Finally, the unification of height system is controlled and analyzed by using the 3D data position of the tidal station from measurement of GPS and SST data, so that the unification of height system can be done absolutely.
The results of this research concluded that the MSL that are obtained from tide data in each tidal stations namely: Cilacap (22,752 m), Sadeng (22,529 m), and Prigi (27,545 m). The MSL from Envisat altimetry satellite data approximately between -10 to 40 m with an average value of 20,821 m. The evaluation result of weighting technique indicated that technique II is the best, with a deviation value of 0.019 m (1.9 cm). The evaluation result of SST model show that SST values in the southern coastal areas of Java Island ranged from 0.2 to 7.6 m. There are areas that have a SST values are quite extreme, which is in the position 108o E to 108.5o E with SST values above 6 m.
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