Regional mean sea surface and mean dynamic topography models around Malaysian seas developed from 27 years of along-track multi-mission satellite altimetry data

Contemporary Universiti Teknologi Malaysia 2020 Mean Sea Surface (UTM20 MSS) and Mean Dynamic Topography (UTM20 MDT) models around Malaysian seas are introduced in this study. These regional models are computed via scrutinizing along-track sea surface height (SSH) points and specific interpolation methods. A 1.5-min resolution of UTM20 MSS is established by integrating 27 years of along-track multi-mission satellite altimetry covering 1993–2019 and considering the 19-year moving average technique. The Exact Repeat Mission (ERM) collinear analysis, reduction of sea level variability of geodetic mission (GM) data, crossover adjustment, and data gridding are presented as part of the MSS computation. The UTM20 MDT is derived using a pointwise approach from the differences between UTM20 MSS and the local gravimetric geoid. UTM20 MSS and MDT reliability are validated with the latest Technical University of Denmark (DTU) and Collecte Localisation Services (CLS) models along with coastal tide gauges. The findings presented that the UTM20, CLS15, and DTU18 MSS models exhibit good agreement. Besides, UTM20 MDT is also in good agreement with CLS18 and DTU15 MDT models with an accuracy of 5.1 and 5.5 cm, respectively. The results also indicate that UTM20 MDT statistically achieves better accuracy than global models compared to tide gauges. Meanwhile, the UTM20 MSS accuracy is within 7.5 cm. These outcomes prove that UTM20 MSS and MDT models yield significant improvement compared to the previous regional models developed by UTM, denoted as MSS1 and MSS2 in this study

Ellipsoidally Referenced Surveying Technique: A Review of the Current Status and Development of Ellipsoidally Referenced Surveying Technique in the Coastal and Offshore Zones for Hydrographic Survey Practice

Technologies sophistication in addition to the Industry 4.0 trend has contributed to the high-accuracy ellipsoidal height from the Global Navigation Satellite System (GNSS) to be used in hydrography for vertical positioning. The method known as Ellipsoidally Referenced Surveying (ERS) provides direct measurement of sea floor to the ellipsoid and a translation of the reference from the ellipsoid to the precise geoid or chart datum. This article is an attempt to review the nations which have adopted ERS technique for hydrographic survey practice. A few case studies on practicing ERS technique are summarised to determine the ability of this technique. Future outlooks are also discussed on realising the ERS technique in Malaysia and the role of agencies in supporting the ERS realisation. In conclusion, adopting this technique will modernise and indirectly challenge the new norm in hydrographic surveying practice in Malaysia.La sofisticación de las tecnologías*, además de la tendencia de la Industria 4.0, han contribuido a que la altura elipsoidal de alta precisión del Sistema Mundial de Navegación por Satélite (GNSS) sea utilizada en la hidrografía para el posicionamiento vertical. El método conocido como Levantamientos referenciados elipsoidalmente (ERS) proporciona una medición directa del fondo marino al elipsoide y una traducción de la referencia a partir del elipsoide al geoide preciso o al datum de cartas. Este artículo es un intento de revisar las naciones que han adoptado la técnica ERS para la práctica de los levantamientos hidrográficos. Se resumen algunos estudios de casos sobre la práctica de la técnica ERS para determinar la capacidad de esta técnica. También se examinan las perspectivas futuras de la realización de la técnica ERS en Malasia y el rol de las agencias en el apoyo a la realización de la ERS. En conclusión, la adopción de esta técnica modernizará y desafiará indirectamente a la nueva norma en la práctica de los levantamientos hidrográficos en Malasia.La sophistication des technologies, en plus de la tendance Industry 4.0, a contribué à ce que la hauteur ellipsoïdale de haute précision issue du système mondial de navigation par satellite (GNSS) soit utilisée en hydrographie pour le positionnement vertical. La méthode connue sous le nom de levés référencés à l’ellipsoïde (ERS) fournit des mesures directes du fond marin à l’ellipsoïde et\ une translation précise de la référence de l’ellipsoïde par rapport au géoïde ou au zéro des cartes. Le présent article décrit une tentative de passer en revue les nations qui ont adopté la technique ERS pour la pratique des levés hydrographiques. Quelques cas d’étude sur la pratique des levés ERS sont résumés afin de déterminer les capacités de cette technique. De futures perspectives font également l’objet de discussions quant à la réalisation de la technique ERS en Malaisie, ainsi qu’au rôle des agences à l’appui de la réalisation de l’ERS. En conclusion, l’adoption de cette technique modernisera et défiera indirectement la nouvelle norme en matière de pratique hydrographique en Malaisie

Sea level anomaly assessment of SARAL/AltiKa mission using high and low resolution data

Peninsular Malaysia is located at the focal point of Sunda Shelf, encompassed by the South China Sea to the East and by Andaman Sea at Indian Ocean in the west that causes various phenomena relevant to sea level along Malaysian coast. When the monsoons strike, the effect of wind and other factors will change the variability of Sea Level Anomaly (SLA) along coastal Malaysia. Traditionally, sea level change is observed using tide gauge installed along Malaysian coastal area. However, the data obtained is limited to the tide gauge station area, the sea level data for the deep sea cannot be obtained and there is no long-term record of observation. Therefore, satellite altimeter is used as a new alternative which enables sea level data to be obtained from space observation and to monitor SLA via SARAL/AltiKa which available since 2013, thus complementing the tide gauge. The aim of this study is to derive SLA parameter from high and low resolution of satellite altimetry data. This study involved the acquisition of SLA data by using RADS and PEACHI (AVISO) database system from satellite mission SARAL/AltiKa. Sequentially, SLA data has been analysed and evaluated based on tide gauge data provided by using UHSLC system. Comparison between the high resolution (PEACHI) and low resolution (RADS) data has been made to evaluate the density of altimetry data in term of distance to coast. As a result, high resolution (PEACHI) data are more accurate for coastal application with root mean square error (RMSE) of ±0.14 metre level. The analysis shows that the footprint of high resolution altimetry data is denser than the low resolution altimetry data. Data from distance to coast for PEACHI achieved a satisfactory standard deviation of residual, which is ranged between 0 cm to 1.04 cm as compared to altimetry RADS which is ranged 0.34 cm to 12.57 cm. The results can be used by various agencies in planning and developing Malaysian coastal areas as well as in assisting the development of community economies such as fishery and tourism activities

Assessment of the accuracy and precision of MyRTKnet real-time services

From a network of ninety-six (96) Continuously Operating Reference Stations (CORS), the Department of Survey and Mapping Malaysia (DSMM) has developed a reliable real-time data streaming service known as the Malaysia Real-Time Kinematic GNSS Network (MyRTKnet). MyRTKnet is now operating on Leica SpiderNet system that is configured to provide coordinate to users in Geocentric Datum of Malaysia 2000 (GDM2000). As the name implied, GDM2000 is a geocentric datum for Malaysia, developed based upon the International Terrestrial Reference Frame (ITRF) 2000 or ITRF2000. One could argue that the quality of coordinates provided by MyRTKnet are less optimal as the latest realisation of ITRF at present is ITRF2014. This study aims to investigate the accuracy and precision of the resultant coordinates from MyRTKnet real-time services through a comparison with the control-quality coordinates from a network of post-processed data at some independent points for positioning purpose. Meanwhile for mapping purpose, the coordinates from Network Real-Time Kinematic (NRTK) at selected Cadastral Reference Marks (CRM) points were compared with their known values. The results show that the observed points in ITRF2000 move approximately 37 cm away from the points in ITRF2014 due to the constant movement of Sundaland Block. Meanwhile for the assessment of NRTK technique, there is no significant displacement for coordinates in ITRF2000 but ITRF2014 with the values of 4.4 and 39.8 cm at KDOJ point, respectively. The discrepancy in ITRF2014 could be due to the improper datum transformation procedure. For mapping, NRTK technique is still not reliable to be adopted for determination of boundaries based on the results derived as the vector displacements for two (5.5 cm and 8.1 cm) out of three CRM exceed the allowable limit (5 cm). In conclusion, it is worth noting that, NRTK technique adopted for positioning should addressed a proper datum transformation process (ITRF2014 to ITRF2000) to improve quality of data meanwhile for mapping works, the NRTK technique is still unreliable to be implemented

Assessment of coastal altimetry data in the South China Sea using multiple frequency approaches

With a coastline length extending over 13, 000 km, including the Malaysia region, the South China Sea presents a challenge to retrieve high quality data along the coastal area especially the sea level anomaly and significant wave height. Currently, coastal altimetry is still facing some issues especially when using the low frequency data such as data lacking near the coast, questionable data accuracy since the altimeter footprint contaminated with the land and less coverage of data from the installed ground truth data. This study aims to assess the coastal altimetry data of sea level and significant wave height in the South China Sea using low and high frequency approaches. This study involved deriving data from sea level anomaly (SLA) and significant wave height (SWH) through the use of Prototype for Expertise on AltiKa for Coastal, Hydrology and Ice (PEACHI) for high frequency and Radar Altimeter Database System (RADS) for low frequency of altimetry and ground truth station which is from tide gauge and Acoustic Wave and Current Profiler (AWAC). Comparison between altimetry and ground truth data has been made in order to validate the significant agreement between them. The validation of the data is to evaluate both types of frequencies with respect to the coastal distance. Consequently, the high frequency results for coastal results with a root mean square reliable ±0.14 metre level for the sea level anomaly (SLA) and ±0.18 metre level for significant wave height (SWH) are more reliable. PEACHI distance-to-coast data obtained a sufficient standard residual deviation ranging from 0 cm to 2.87 cm compared to RADS altimetry ranging from 0.08 cm to 14.20 cm. The findings of this study indicate that the coastal altimetry data benefit coastal development, coastal defence, monitoring and tourism by various related agencies

Accuracy assessment of quasi-seamless hydrographic separation models in Malaysian waters

The hydrographic survey reduction using ellipsoid has been available since the advent of the global navigation satellite system (GNSS), with a potential to streamline operation and enhance bathymetric output. Spatially continuous separation surfaces connecting a chart datum (CD) to a geodetic ellipsoid is required for this technique. Universiti Teknologi Malaysia (UTM) has invented a new quasi-seamless separation model for Malaysian waters, known as the Malaysian Vertical Separation (MyVSEP) model, through semi-empirical models to capture the spatial variability of a tidal datum between coastal and offshore areas. A continuous vertical datum is established to develop MyVSEP models by combining the coastal and offshore datasets. The coastal datasets referred to the vertical reference point computed from coastal tide gauges, while the offshore datasets referred to the vertical reference surfaces derived from satellite altimetry. Mean sea level (MSL) or mean sea surface (MSS), mean dynamic topography (MDT), lowest astronomical tide (LAT), and highest astronomical tide (HAT) are the vertical datums involved in developing the continuous MyVSEP model. However, the integration of the vertical datum has only been conducted over the Peninsular Malaysia region. For Sabah and Sarawak, datum integration cannot be implemented due to the limitation of coastal datasets. The assessment of the integrated vertical datum with coastal tide gauges is discussed in this study. The finding shows that the root mean square error (RMSE) agreement between the integrated Universiti Teknologi Malaysia 2020 (iUTM20) model and coastal tide gauges yields below 2.0 cm. The iUTM20 lowest astronomical tide and highest astronomical tide models also show significant improvement compared to the altimetric-derived tidal models, which recorded the root mean square error agreement with coastal tide gauges of 1.8 cm and 2.0 cm, respectively. The development of a continuous vertical separation model for the Ellipsoidally Referenced Surveying technique indirectly optimizes marine geospatial information resources, especially for the National Hydrographic Centre in Malaysia

Ellipsoidally referenced surveying technique

Technologies sophistication in addition to the Industry 4.0 trend has contributed to the high-accuracy ellipsoidal height from the Global Navigation Satellite System (GNSS) to be used in hydrography for vertical positioning. The method known as Ellipsoidally Referenced Surveying (ERS) provides direct measurement of sea floor to the ellipsoid and a translation of the reference from the ellipsoid to the precise geoid or chart datum. This article is an attempt to review the nations which have adopted ERS technique for hydrographic survey practice. A few case studies on practicing ERS technique are summarised to determine the ability of this technique. Future outlooks are also discussed on realising the ERS technique in Malaysia and the role of agencies in supporting the ERS realisation. In conclusion, adopting this technique will modernise and indirectly challenge the new norm in hydrographic surveying practice in Malaysia

Sea level trend over Malaysian seas from multi-mission satellite altimetry and vertical land motion corrected tidal data

Rise in sea levels is one of the disastrous effects of climate change. A relatively small increase in sea level could affect natural coastal systems. In a study of long-term changes in sea level and measurements of postglacial rebound, monitoring vertical land motion (VLM) is of crucial interest. This study presents an approach to estimate precise sea level trends based on a combination of multi-sensor techniques in the Malaysian region over 19 years. In this study, satellite altimeters (SALT) were used to derive absolute sea levels (ASLs). Tide gauge (TG) stations along the coast of Malaysia were utilised to derive the rate of relative sea levels using sea level changes and VLMs. To obtain ASL at TGs, VLM at these stations were computed using Global Positioning System (GPS), Persistent Scatterer Interferometric Synthetic Aperture Radar (PS InSAR), and SALT minus TG. The computed VLMs mostly show similarities in signs rather than magnitude. The findings from the multi-sensor techniques showed that regional sea level trends ranged from 2.65 ± 0.86 mm/yr to 6.03 ± 0.79 mm/yr for chosen sub-areas, with an overall mean of 4.47 ± 0.71 mm/yr and overall subsidence. This information is expected to be valuable for a wide variety of climatic applications and for studying environmental issues related to flooding and global warming in Malaysia

Refinement of gravimetric geoid model by incorporating terrestrial, marine, and airborne gravity using KTH method

We compute a new gravimetric geoid model for Peninsular Malaysia (PMGG2020) based on the Royal Institute of Technology (KTH) method. The PMGG2020 was computed from 8474 terrestrial gravity points, satellite altimetry-derived gravity anomaly (DTU17), 24,855 airborne gravity data, and the TanDEM-X Digital Elevation Model. All the gravity datasets were combined and gridded onto a 1-min resolution using the 3D Least Square Collocation (LSC) method with EIGEN-6C4 as the reference field. GO_CONS_GCF_2_SPW_R4 was used to provide long wavelengths of gravity field up to 130 maximum degrees and order in the geoid computation. Based on an evaluation using 173 Global Navigation Satellite System (GNSS)-levelling points distributed over Peninsular Malaysia, the precision of the PMGG2020 was 0.058 m. It is almost identical to the accuracy of the official Peninsular Malaysia gravimetric geoid, WMG03A. Using airborne gravity, the precision of PMGG2020 showed a significant improvement of ~4 cm over the existing KTH-derived geoid model, PMSGM2014. These results highlight the significant effect of airborne gravity data on the accuracy of the geoid model

DataSheet1_Accuracy assessment of quasi-seamless hydrographic separation models in Malaysian waters.pdf

The hydrographic survey reduction using ellipsoid has been available since the advent of the global navigation satellite system (GNSS), with a potential to streamline operation and enhance bathymetric output. Spatially continuous separation surfaces connecting a chart datum (CD) to a geodetic ellipsoid is required for this technique. Universiti Teknologi Malaysia (UTM) has invented a new quasi-seamless separation model for Malaysian waters, known as the Malaysian Vertical Separation (MyVSEP) model, through semi-empirical models to capture the spatial variability of a tidal datum between coastal and offshore areas. A continuous vertical datum is established to develop MyVSEP models by combining the coastal and offshore datasets. The coastal datasets referred to the vertical reference point computed from coastal tide gauges, while the offshore datasets referred to the vertical reference surfaces derived from satellite altimetry. Mean sea level (MSL) or mean sea surface (MSS), mean dynamic topography (MDT), lowest astronomical tide (LAT), and highest astronomical tide (HAT) are the vertical datums involved in developing the continuous MyVSEP model. However, the integration of the vertical datum has only been conducted over the Peninsular Malaysia region. For Sabah and Sarawak, datum integration cannot be implemented due to the limitation of coastal datasets. The assessment of the integrated vertical datum with coastal tide gauges is discussed in this study. The finding shows that the root mean square error (RMSE) agreement between the integrated Universiti Teknologi Malaysia 2020 (iUTM20) model and coastal tide gauges yields below 2.0 cm. The iUTM20 lowest astronomical tide and highest astronomical tide models also show significant improvement compared to the altimetric-derived tidal models, which recorded the root mean square error agreement with coastal tide gauges of 1.8 cm and 2.0 cm, respectively. The development of a continuous vertical separation model for the Ellipsoidally Referenced Surveying technique indirectly optimizes marine geospatial information resources, especially for the National Hydrographic Centre in Malaysia.</p