Sea level change in the Malaysian seas from multi-satellite altimeter data

Seas from satellite altimetry data of the Topex, Jason-1, ERS-1, ERS-2 and Envisat missions. During the past two decades, satellite altimeter has provided its capability in measuring the global mean of sea level with precision better than 1 mm/year. Sea level data retrieval and reduction were carried out using Radar Altimeter Database System (RADS). In RADS data processing, the recently updated environmental and geophysical corrections were applied. Sixth 1° × 1° areas were chosen for the altimeter data comparison and to find the best ocean tide model for Malaysian Seas, where the altimeter tracks are nearby to tide gauge locations. Similarity in the pattern of sea level variations indicated good agreements between tide gauge data and altimeter data using FES2004 ocean tide model. It also showed that the altimeter data can be used to investigate sea level rise for Malaysian Seas. Here, sea level variations for four areas in the Malaysian Seas have been investigated using 15 years of altimeter data. The altimeter sea level time series revealed that since 1993, the mean sea level in Malaysian Seas has been rising at a rate of between 1.42 – 4.08 mm/year. This information is important to study alternative energy extraction and environmental issues related to flood investigations and global warming

Sea level rise estimation and interpretation in Malaysian region using multi-sensor techniques

Rise in sea level is one of the disastrous effects of climate change. A relatively small increase in sea level could affect the natural coastal system. This study presents an approach to estimate before interpreting the precise sea level trend based on a combination of multi-sensor techniques in the Malaysian region over a period of 19 years. In the study, six altimeter missions were used to derive the absolute sea levels which were processed in the Radar Altimeter Database System. Next, 21 tide gauge stations along the coastlines of Malaysia were utilised to derive the rate of relative sea levels that took into account sea level changes and vertical land motions. To obtain absolute sea level at tide gauge, vertical land motions at these stations were removed by employing three techniques, namely GPS, Persistent Scatterers Interferometric Synthetic Aperture Radar and altimeter minus tide gauge. Bernese software with double difference strategy was employed to process data from 87 local and 30 international GPS stations. Using Persistent Scatterers Interferometric Synthetic Aperture Radar, the Stanford Method for Persistent Scatterer software processed 111 images. Besides that, the satellite altimeter and tide gauges were used to retrieve the differential rates estimated by altimetry and tidal data to obtain the rate of vertical land motion. Following that, absolute sea level rates from the tide gauge stations and multi-satellite altimeter missions were combined. This combination produced the regional sea level trend of the Malaysian seas. The findings from the multi-sensor techniques showed that the regional sea level trend has been rising at a rate of 2.65 ± 0.86 mm/yr to 6.03 ± 0.79 mm/yr for the chosen sub-areas, with an overall mean of 4.47 ± 0.71 mm/yr. Upon completion of the study, a Sea Level Information System for the Malaysian seas was developed to facilitate users in analysing, manipulating and interpreting sea level and vertical land motion data. This system is expected to be valuable for a wide variety of climatic applications to study environmental issues related to flood and global warming in Malaysia

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

A review of current development of altimetry technique for tidal and water level measurement practices and its relevance to energy industry applications

With massive geospatial coverage and adequate time series of sea surface height, spatio-temporal multi-mission satellite altimetry tidal modelling emerges as a profound potential solution for increasing accuracy and minimising variation across multiple offshore applications. Therefore, this article attempts to review the current implementation of satellite altimetry in the applicable area of studies relevant to conventional oil and gas applications toward sustainable energy applications. The implication of current spatio-temporal enhancement of tidal measurement by satellite altimetry at the coastal area and the offshore zone is discussed mainly to elaborate on current achievement as well as to gauge potential future optimisation for offshore applications in the energy industry. Spatio-temporal enhancement in conventional oil and gas field applications improves the integration of various offshore construction applications. The impact of this application is more significant as engineering construction adopts stringent and higher vertical data accuracy acceptance criteria. More comprehensive spatial information coverage of tidal regime, co-tidal range, the offshore co-tidal pattern should be more accessible by more intensive spatio-temporal enhancement attempts in various studies and implementations. This leads to higher reliability and integrity of offshore vertical references derivation

The development of continuous hydrographic datum using geodetic based approaches: A review

The development of a continuous hydrographic datum along the coastal region for a precise datum determination for any hydrographic survey works is very important. The development started in 2005 by France that developed the first phase of Bathymetry with reference to the Ellipsoid (BATHYELLI) and its second phase in 2011. Then in 2009, the United Kingdom with collaboration with Ireland developed the Vertical Offshore Reference Frame (VORF), followed by the Continuous Chart Datum for Canadian Water (CCDCW) in 2010 by the Canadian Hydrographic Services (CHS) and Canadian Geodetic Survey (CGS). Then in 2018, Netherlands and Belgium collaborate to develop Vertical Reference Frame for the Netherlands (NEVREF) that consist of two elements which are Netherlands Quasi-Geoid 2018 (NLGEO2018) model and also Netherlands Lowest Astronomical Tide 2018 (NLLAT2018) model. Finally, the latest development of continuous hydrographic datum was conducted by the Kingdom of Saudi Arabia (KSA) in 2019, a system known as Saudi Continuous Chart Datum (SCCD). Therefore, this paper provides a review of the approaches in creating a continuous hydrographic datum which encompasses the usage of tide gauge station, satellite altimetry, and interpolation algorithm, Global Navigation Satellite System (GNSS), Digital Elevation Model (DEM), Geoid Model and Hydrodynamic Ocean Tide Models. The findings show that the integration of tidal station, satellite altimetry, GNSS levelling and geoid model is the most appropriate solution for a continuous and accurate hydrographic datum along the coastal line. Finally, the future research direction is also discussed in this review paper

Estimation of surface elevation changes at bare earth riverbank using differential DEM technique of UAV imagery data

Estimating surface elevation changes at bare earth riverbank is challenging because of the non-visibility effect of this phenomenon, especially for short observation periods. Hence, the spatio-temporal detection at a short-term period determines the geomorphological changes by comparing the same area at different observation epochs. This study attempts to assess surface elevation changes components which include erosion and accretion, using the geomorphological changes detection (GCD) technique based on multi-temporal unmanned aerial vehicle (UAV) imagery. Using a multi-rotor UAV and high accuracy Global Navigation Satellite System instrument, the data acquisition process was conducted in Kilim River in the December 2016 and December 2017 to complete a one-year interval. To generate a very high accuracy of orthomosaics and digital elevation model (DEM), the structured from motion and multi-view stereo techniques were used. Then, GCD method, which involves a difference of DEM (DoD) was performed to evaluate the surface elevation changes that comprising erosion and accretion using GCD analysis tool. This study discovered that surface raising was more dominant than surface lowering, at 31.70% (raw) and 31.67% (thresholded), the per cent elevation raising at 68.30% (raw) and 68.33% (thresholded), the per cent imbalance (departure from equilibrium) at 18.30% (raw) and 18.33% (thresholded) and the net to total volume ratio at 36.60% (raw) and 36.67% (thresholded). The results showed how the UAV platform provides a way to evaluate surface elevation changes in bare earth areas with decent accuracy and enables further study on river geomorphological-related issues in the future

Least square modification of stokes formulae with additive corrections estimator for Klang Valley geoid modeling

Klang Valley is a fast-growing area and its development shall be equivalent with precise measurements for a precise vertical reference. Thus, existing vertical reference with 3 centimetres (cm) is inadequate and processed with complicated remove-compute-restore (RCR) procedure. Apart from this, areas such as Klang Valley should better than one (1) centimetre level vertical reference. Meanwhile processing method for vertical reference should be simplified and easy tasking. Because of that, methodology for this study is by employing the least squares modification of Stokes formula with additive corrections (KTH). This approach fully uses anomalies rather than residuals which it is more complicated. At the same time, the additive corrections estimator introduced combining the direct and indirect computations method. Datasets used in this study were refined rigorously prior to the gridding scheme in cross validation, free air anomalies, as well as anomaly correction. The KTHKVGM2020 gravimetric and geometric geoid models are evaluated from the reference position using GNSS levelling. It found that KTHKVGM2020 Geoid model is better than one (1) centimetre for Klang Valley area with efficiency processing method. Therefore, the study is an essential in future to develop high-precision geoid model with efficient methods particular for urban and rapidly developing areas

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

A short review on causes of sea level rise for climate monitoring

Sea level rise has currently become a major issue for climate change. It has globally drawn attention because as time passes, global sea levels will continue to rise at an accelerating rate in the 21st century. It will cause a serious impact on environmental problems such as coastal inundation, salt intrusion, coastal erosion, and other phenomena. These scenarios lead to earth problems in which land and oceans continue shifting due to climate change, posing a threat to the very existence of all living beings in the coming years. As a result, climate monitoring is critical for tracking the change. Therefore, this paper reviews the physical factors that contribute to sea level rise. The main contributors for sea level rises, such as ice melting from land into the ocean, thermal expansion, a slowing of the Gulf Stream, and land sinkage, are being discussed. This paper also emphasises the studies of regional sea level, and sea level rate changes. Finally, this review will be discussed in order to clarify the causes of sea level rise issues for human society

Euler pole parameter estimation of sunda plate from present-day GPS site velocities in Malaysia

Malaysia is situated at Sunda plate that experience highly dynamic of earth's crust with frequent earthquake and volcano activities. The effect of plate motion causing the static-based geodetic reference frame in Malaysia is no longer relevant to support the centimeter level of Global Positioning System (GPS) application. Therefore, an updated Sundaland plate motion model is necessary to cater to the effect thus preserving the reliability of the geodetic reference frame. This study aimed at determining regional plate motion of Sundaland in support of dynamic reference frame. The work involved in generating precise Position Errors Time Series (PETS) from GPS Continuous Operating Reference System (CORS) data in Malaysia and neighbouring country. The Coordinates Time Series (CTS) were then used to estimate velocity vector and the precision form the results depicted at -8.0429±3.0215mm, 3.873±3.288mm, and 0.913±7.775mm for component northing, easting and up, respectively. From the velocity vector, location of Euler pole of Sunda plate was found at latitude 5.8482 ° N and longitude -95.1017 ° E with estimated angular momentum of 0.201O/Myr± 0.0389. It can be expected that the result will be useful for maintaining the reliability of the reference frame in South East Malaysia