Ami Hassan Md Din

Sea Surface Circulation in the Straits of Malacca and the Andaman Sea Using Twenty-Three Years Satellite Altimetry Data

The ocean circulation in the Straits of Malacca is derived using the satellite altimeter data from January 1993 until 2015. The satellite altimeters are TOPEX, Jason-1, Jason-2, ERS-1, ERS-2, Envisat, SARAL, and Cryosat. The sea surface height derived from the satellite altimeter has been very useful in the study of the ocean circulation but still is not appropriate for the oceanographic application. This is because it is a superposition of geophysical effect such as the tidal effect. The tidal models are more suitable to be used in the open sea like the South China Sea. The tidal effect is rather complex to be determined, especially in a shallow water area like the area in the Strait of Malacca. In order to remove the tidal effect, the best ocean tide model needs to be examined to determine the ocean circulation in the Straits of Malacca. To verify the result, the sea level anomaly (SLA) data were compared to the tide gauge data and the pattern obtained are regularly the same. In order to check the ocean circulation using the altimetric data, the result was compared with the trajectories drifter from Marine Environmental Data Station (MEDS) of Canada. The trajectories of the drifter have confirmed that the current pattern around studied region during June 9, 1999 until July 9, 1999.

Accuracy Assessment of TanDEM-X DEM and Global Geopotential Models for Geoid Modeling in the Southern Region of Peninsular Malaysia

In modeling of geoid model, global digital elevation models (GDEMs) and global geopotential models (GGMs) involve in most part of the geoid computation process. Any errors in GDEMs and GGMs will introduce errors directly in geoid computation. Therefore, this study aims to evaluate the six recent GGMs and new digital elevation model from TanDEM-X, as well as the previously available GDEMs, SRTM GDEMs, over the southern region of Peninsular Malaysia. The evaluation of GDEMs has been performed with the use of high-precision Global Navigation Satellite System (GNSS) and EGM96 as vertical reference consisting of 277 stations. Meanwhile, the evaluation of GGMs is carried out using sixty-two (62) collocated GPS/leveling benchmarks (BMs). Based on the statistical analysis, it is shown that the improvement of DEM from TanDEM-X data is compared to the previously available DEMs, SRTM GDEMs. DEM from TanDEM-X of 30-m arc resolution is much better than TanDEM-X of 12-m arc resolution, as well as SRTM 30m and 90m. Comparison of GGMs with GNSS leveling shows that geoid height from GOCO05c fits well with the local geoid model.

Significant wave height assessment using multi mission satellite altimeter over Malaysian seas

Satellite altimeter is one of the useful technique to study the variation of ocean parameters with a good temporal and spatial measurements. In situ measurements such as buoy has own disadvantages in terms of spatial observations. Thus, with the combination of satellite altimeter and buoy can improve the significant wave height measurements for both spatial and temporal over the seas. Generally, the measurement of significant wave height from altimeter using the Ku-band signal, while SARAL is borne with Ka-band altimeter (AltiKa). The aim of this research is to study the reliability of wave height data from the satellite altimeter to support marine renewable energy development. This Significant wave height (Hs) is retrieved from multi mission satellite altimeter by Radar Altimeter Database System (RADS) and evaluated using in-situ measurement over the Malaysian seas (0°N - 14°N and 95°E - 126°E). A validation with selected buoys located at Sabah Sea (5.83 N, 114.39 E) and Sarawak Sea (5.15 N, 111.82 E) is performed by statistical approach and presenting good correlation of 0.92 and 0.18 for RMSE. A climatology assessment is performed by analyzing the condition of significant wave height during monsoons. This paper highlighted, collocation between altimeter and buoy are well-correlated and reliable to use for a marine analysis for renewable energy development.

Gravimetric geoid modeling in the northern region of Peninsular Malaysia (NGM17) using KTH method

In this study, a new geoid model for the northern region of Peninsular Malaysia (NGM17) was computed using an alternative method known as the Least Squares Modification of Stokes formula (LSMS) with Additive Corrections (AC) or commonly called the KTH method. The NGM17 geoid was derived from the recent terrestrial gravity data provided by Department of Surveying and Mapping Malaysia (DSMM), the most recent global digital elevation model ALOS World 3D (AW3D-30) GDEM, global geopotential model (GGM) derived from three satellite gravity missions, marine gravity anomalies extracted from DTU 10 Global Gravity Field and WGM2012 Earths gravity anomalies. The gravimetric geoid model derived in this study (NGM17) as well as the geoid obtained from DSMM were then evaluated against the GNSS-levelling data. The statistical analysis obtained shows that NGM17 gives slightly better accuracy with the mean error of NGM17 and DSMM geoid model were 0.2568m and 1.1648m respectively, and the RMSE of ?0.2686m and ?1.1656m respectively.

A review of advancement of hydrographic surveying towards ellipsoidal referenced surveying technique

Hydrographic surveying is one of the most seasoned types of marine research and includes a procedure of gathering bathymetry information that can be utilized as a part of creating and maintaining nautical chart. Establishment of modern nautical chart is very crucial to marine safety, coastal zone management and fish and mineral industries. This paper is an attempt to review the advancement of hydrographic surveying technique from the past decade towards Ellipsoidal Referenced Survey technique. An overview of hydrographic surveying, basic principle of development techniques and considering the merits and hindrances of the techniques will be summarized to support future application. Discussion of future directions will also be outlined.

Mean dynamic topography over Peninsular Malaysian seas using multimission satellite altimetry

Abstract. The development of satellite altimeters (SALTs) has brought huge benefits, among which is the ability to more adequately sense ocean-surface topography. The radar altimeter database system was used to capture and process ENVISAT, CRYOSAT-2, SARAL, JASON-1, and JASON-2 SALT data of 5 years between 2011 and 2015. The time series of monthly multimission SALT data showed an estimated sea level trend of 1.0, 2.4, 2.4, 3.6, and 12.0  mm/year at Gelang, Port Kelang, Kukup, Cendering, and Keling. The correlation analysis for the selected tide gauge stations produced satisfying results of R-squared with 0.86, 0.89, 0.91, and 0.97 for Cendering, Sedili, Gelang, and Geting, respectively. The ITG-Grace2010s geoid model was used to compute the mean dynamic topography (MDT) and plot to a grid of 0.25 deg for the Malacca Strait and South China Sea of Peninsular Malaysia, with Keling, Port Kelang, Geting, Sedili, and Johor Bahru tide gauge stations having values determined by interpolation to be 1.14, 1.19, 1.26, 1.88, and 2.91 m, respectively. MDT is computed from the SALT with respect to Port Kelang, the north–south sea slope ranges between −0.64 and 0.29  m/50  km and −0.01 and 0.52  m/50  km along the east and west coasts of Peninsular Malaysia, respectively.

Assessing the Reliability and Validity of Satellite Altimetry-Derived Wet Delay in Peninsular Malaysia

Water vapor is known as a gas state of water. The nature of the water vapor is invisible, which means it cannot be seen but can be sensed by the humidity in the air. As the climate is warming due to the increase of carbon dioxide and other anthropogenic greenhouse gases, water vapor is expected to increase rapidly as models broadly conserve relative humidity. Water vapor consists of two components, namely, dry and wet delay. Only wet delay will be highlighted in this study due to which the dry delay can be modeled easily. The wet delay in the atmosphere needs to be monitored as to detect and predict changes in earth’s climate particularly for weather forecasting. There are many methods that can be used to measure the wet delay such radiosonde and Global Positioning System (GPS). But both of them had their limitations; for example, they were point-based solutions means that the wet delay can be derived at a certain area. Radiosonde method needs to be launched twice daily, and for a single launch, cost a lot. This study presents an effort to extract the wet delay measurement from radiometer system using satellite altimeter. The advantage of using satellite altimeter is that the wet delay parameter can be retrieved on land and marine areas. Thus, it can improve the spatial resolution for wet delay retrieval. This study employs the altimetry-derived wet delay trend based on multi-mission satellite altimeter in the Peninsular Malaysia for 1-year data, in 2014. Two altimeter missions were used, namely, Jason-2 and Saral. Radar Altimeter Database System (RADS) was used to extract the water vapor data. Altimetry-derived water vapor was verified with GPS-derived Zenith Wet Delay (ZWD) at six GPS Continuously Operating Reference System (CORS) stations. The verification results showed that the RMSE between the altimetry-derived wet delay and GPS-derived wet delay was about 3–12 cm. Furthermore, the data from the satellite altimeter is in a good shape with the seasonal variation of precipitation according to the climatic classification of the region. Besides that, the observed data also give reasonable values when considered for the wet and dry seasons because the value from the CORS and satellite altimeter only had a slight difference. In conclusion, altimetry-derived wet delay is promising to be used in climate and weather research in the future.

Wave Height Climatology Assessment from Multi-mission Satellite Altimeter for Renewable Energy

The fact that we will lose the source of fossil fuel in the future is undeniable. Hence, it is crucial to find the replacement of this resource. In present day, wave energy is found to be one of the sources of renewable energy. This chapter is proposing to assess the wave height climatology over the Malaysian seas in order to support renewable energy. The key step in the assessment of wave height climatology over Malaysian seas, South China Sea, Malacca Straits, Sulu Sea and Celebes Sea, is by acquiring an accurate and reliable wave height data. The Radar Altimeter Database System (RADS) was used to extract the 24 years of significant wave height data from January 1993 to December 2016. Altimetry-derived wave height data were validated with ground truth observation from wave buoy and Acoustic Doppler Current Profiler (ADCP). The wave height magnitude and pattern were then analysed particularly to see its characteristic during monsoon season. The monthly average of altimetry significant wave height from January 1993 to December 2016 was mapped in this study. The findings clearly show that the Northeast monsoon has the most significant effect of wave height variation over Malaysian seas, while the Southwest monsoon has minimal effect. The reliability of satellite altimetry also proved based on the RMSE and correlation results, which are 0.2515 m and 0.9396, respectively. This study offers useful wave height information especially related to renewable energy in the Malaysian seas for future studies.

Sea Level Impact Due to El Nino and La Nina Phenomena from Multi-mission Satellite Altimetry Data over Malaysian Seas

The El Nino and La Nina phenomena indirectly provide dramatic changes to the sea level that can be caused by floods and drought, and affect various marine activities. For the past centuries, the main approach to measure sea level changes is by using coastal tide gauges. However, there is inconsistency in observing sea level variations using tide gauge data for the Malaysian country. The inconsistency is due to irregular geographical distributions of tide gauge stations established at coastal areas and there are no long-term tide records for the deep sea. An alternative method in order to solve this issue is by measuring the absolute sea level from space, i.e., satellite altimeter technique. Satellite altimeter implements excellent potential as an integral mechanism to the conventional coastal tide gauge instruments for monitoring sea level variation of Malaysian seas, especially for the deep sea. The aim of this research is to study the sea level pattern due to the effects of El Nino and La Nina phenomena using a combination of multi-mission satellite altimeters in the Malaysian seas. Radar Altimeter Database System (RADS) is used for retrieval and reduction of sea level data from satellite altimeter. Then, sea level data from tide gauge was used to verify satellite altimeter derive the sea level data. The result of this research shows that satellite altimetry is reliable in other to monitor changes in sea level. It also shows that El Nino and La Nina phenomena can also contribute as one of the factors to sea level changes around Malaysian seas. Hence, this research will specifically help in the determination of sea level in Malaysia and to the professionals who have authority in governmental, environmental planning, agriculture, marine engineering, and economics.

Real-Time Precise Point Positioning (RT-PPP) for Positioning and Mapping

Real-Time Precise Point Positioning (RT-PPP) has started to develop among Global Positioning System (GPS) community due to some reasons, such as reference stations are required, very economical and easy to operate from everywhere. By using a dual-frequency receiver with the support from GPS precise products, RT-PPP has proven to give centimetre to decimeter positioning accuracy. Recently, the position can be obtained in real time using the real-time GPS precise products provided by many national geodetic agencies. Current real-time GPS positioning systems also allow accurate positioning by carrier phase-based double differencing approach. However, the limitation of using the differential approach is the process needs simultaneous data collection from common satellites at the reference station and the rover. Directly, the data acquisition process will become more difficult and this will decrease the suitability of this technique in other potential applications. The aim of this research is to analyse the current performance of RT-PPP technique using Hemisphere Atlas for positioning and mapping. This research also assessed the positioning accuracy between RT-PPP and static GPS techniques. Then, the reliability of RT-PPP for cadastral purposes is also evaluated. Methodologically, RT-PPP used Hemisphere Atlas, which is a dual-frequency receiver for position determination by processing raw pseudorange and carrier phase observations with the support from precise GPS orbit and clock information. The results of this research show that the coordinate for both positioning and mapping purposes using Hemisphere Atlas are within centimetre-level accuracy, i.e. below 10 cm for positioning and below 30 cm for cadastral purposes. Therefore, this study anticipates that RT-PPP has the potential to offer better operational flexibility that will guide for the full implementation of this technology particularly in surveying and mapping in the future.