Developing Malaysia continuous hydrographic datum (MyCHD) by assimilating tide gauge, satellite altimeter, and global hydrodynamic model
Mohd Faizuddin Abd Rahman, Mohammad Hanif Hamden, Ami Hassan Md Din, Mohd Razali MahmudAbstract
The advancement of multi-mission satellite altimeters has greatly enhanced the conventional approach of using a tide gauge station to establish a localised hydrographic datum. However, there are still several limitations in continually depending on a small number of sparsely distributed tide gauge stations and wide satellite altimeter track missions, even with its continuous monitoring of ocean data at local and worldwide coverage. Such limitation has left a region farther away from the satellite altimeter track and tide gauge stations without any hydrographic data. Hence, this study aims to develop Malaysia’s Continuous Hydrographic Datum (MyCHD) by combining the satellite altimeter, tide gauge station, and global hydrodynamic model (GHM). In addition, the reliability of MyCHD was also assessed to determine the rate of improvement by incorporating GHM as additional hydrographic data. The research methodology involves collecting data from the Department of Survey and Mapping Malaysia (DSMM) tide gauge stations along Malaysia’s coastline, as well as satellite altimetry data from TOPEX, Jason-1, Jason-2, and GEOSAT Follow-On (GFO) via the Radar Altimeter Database System (RADS). Additionally, Indian Ocean GHM data from Oregon State University (OSU) was also utilised. The tide gauge, satellite altimetry, and GHM datasets encompass 26 years of tidal observations, spanning from 1993 to 2018. All hydrographic data were processed using harmonic analysis in Unified Tidal Analysis and Prediction (UTide) within MATLAB to establish the hydrographic datum. The derived Lowest and Highest Astronomical Tide (LAT and HAT) from tide gauge, satellite altimetry, and GHM data were referred to the Mean Sea Level (MSL) for compatibility in data integration; these were designated as LATMSL and HATMSL, respectively. Then, using ArcGIS software, the LATMSL and HATMSL were interpolated using Inverse Distance Weighting (IDW). In contrast to the integration of tide gauge and satellite altimeter, the statistical assessment showed that the integration of tide gauge, satellite altimeter, and GHM has a better agreement with the DSMM tide gauges, with a Root Mean Square Error (RMSE) of ± 0.671 m for LATMSL and ± 0.370 m for HATMSL. In percentage terms, incorporating GHM data with tide gauge and satellite altimeter in establishing MyCHD has significantly improved its reliability by 17 % for LATMSL and 30 % for HATMSL respectively. In conclusion, the hydrographic datum is now available at any coordinate along Malaysia’s coast with the establishment of MyCHD (LATMSLand HATMSL).