Practical accuracy of VRS RTK outside the Malaysian Real Time Kinematic Network (MyRTKnet)

Real Time Kinematic become a popular high precision technique in Malaysia. However, limitation of the distance for base station to rover station, this technique still difficult to implement. Virtual Reference Station (VRS) is a new concept developed by Trimble Terrasat is efficient method to overcome the limitation of classical RTK. The Malaysian Real-Time Kinematic Network (MyRTKnet) has been developed to facilitate RTK positioning in Malaysia. MyRTKnet consists 78 reference stations located at Peninsular Malaysia, Sabah and Sarawak. The most Northern reference station in Peninsular Malaysia located at Arau, Perlis. The gap distance from the Arau station to the Malaysia - Thailand border is around 35 km. This paper will discuss the practical accuracy of the RTK positioning using VRS generated by MyRTKnet outside the network. In this study, four points outside the MyRTKnet network were observed continuously in VRS RTK mode. Distances between rover station and the nearest physical reference station are 1 km, 10 km, 20 km and 30 km. It was found that the VRS generated using MyRTKnet can be achieved up to 6 cm in horizontal component and up to 8 m in vertical component even the positions of the rover stations are outside the MyRTKnet

Terrestrial laser scanners datum transformation: insignificant analysis of scale factor

Due to the measurement mechanism employed by terrestrial laser scanners (TLSs), the pre-processing procedure has become crucial procedure to orient all acquired data into global or ground coordinate system. Rather than utilising all seven-transformation parameters, most of TLS practitioners have neglected the scale factor. Taking into consideration the uncertainties in deriving range data, disregarding the scale factor in datum transformation computation could jeopardise the quality of pre-processed results. To rigorously examine this argument, two experiments have been designed by considering the element of multi distances and multi sensors. Utilising phase (i.e. Faro Focus 3D) and pulse-based (i.e. Leica ScanStation C10) scanners, both experiments were carried out with computation of seven (7) transformation parameters and scale factors were extracted for the assessment. With the aid of statistical analysis, the computed scale factors were mathematically differentiate to the ideal value (i.e. 1.000 or no scale effect). Under 95% confidence level, the null hypotheses for both experiments have indicate an agreement that scale factor can be neglected in datum transformation process for both types of terrestrial laser scanners

Kajian jaringan kawalan pugak bagi negeri Sarawak

The need for a proper levelling network has been the key requirement for modernizing the levelling infrastructure in the state of Sarawak. This thesis is aimed, firstly, to investigate and analyse the status of levelling data in Sarawak and to create a proper documentation of it. Secondly, the aim of the thesis is to study the potential use of GPS, combined with the newly establish precise geoid and the existing levelling network in Sarawak. Up to September 2002, DSMM Sarawak has already completed 19 lines of precise levelling and 55 lines of second-class levelling. Statistical test and pre-adjustment of the network are performed to analyse quality of the levelling data. The poor levelling network have caused difficulty in errors detection of levelling data. There are nine height differences in precise levelling data that still consist gross errors. GPS height transfer technique for 0.5-1.5 km baselines length were carried out for solving the problems of height transfer for river crossing. GPS measurements are performed for one and two hours using EGM96 and precise geoid model, WMG03A. Two hours observation using precise geoid gave consistent results and giving RMS differences of about ±1.4mm. Vertical datum biases are computed using GPS data on the second class benchmarks. Relative vertical datum biases are inconsistent for distances less than 10km. Bias that less than 15ppm is showed for distances 10 – 55km with geoid height differences 0.2 – 1.3m. The geoid height differences less than 0.2m represents bias below than 2ppm. This finding become as a guide for designing a network combine conventional and GPS levelling

The Malaysian seas: variation of sea level observed by tide gauges and satellite altimetry

Since a decade, satellite altimetry has demonstrated its capability in measuring temporal change of the global mean sea level with precision better than 1 mm/year. In altimetry data processing, the recently updated environmental and geophysical corrections were applied. The analysis of Topex data presented here is based on monthly averages using GOT00.2b ocean tide model. Sea level trends are estimated from 1.5 to 8.9 mm/year using two decades of tide gauges observations along coastal of Malaysia. Comparison of 1o x 1o areas at the tide gauge locations nearby Topex track clearly show good agreement in pattern and trend of sea level variations. Here, sea level variations for four areas in the Malaysian Seas have been investigated using ten years of Topex altimetry data. The time series of dynamic sea surface elevation clearly show El Nino effect on the end of 1997 and sea level rising in the Malaysian Seas. Linear terms of sea level variation for those areas are estimated at rates between 6.3-14.7 mm/year

Study of sea level variation of exclusive economic zone of Malaysia

Since a decade, satellite altimetry has demonstrated its capability in measuring temporal change of the global mean sea level with a precision better than 1 mm/year. Here, sea level variation for four areas in Exclusive Economic Zone (EEZ) of Malaysia have been investigated using eleven years of Topex altimetry data. The recently updated environmental and geophysical corrections were applied in altimetry data processing. The analysis of Topex data presented is based on cycle by cycle averages using GOT00.2b and FES2002 ocean tide model. The time series of dynamic sea surface elevation clearly show El Niño effect on the end of 1997 and sea level rising in EEZ of Malaysia. Linear term of sea level variation for those areas are estimated at a rate between 2.5 – 8.8 mm/year. Comparison results between two ocean tide present that GOT00.2b better than FES2002 for shallow water such as Malacca Strait

Monitoring of breakwater structure: GPS versus geodetic method

Until recently, we relied exclusively on traditional survey equipments such as EDM/total station/precise levels to determine the horizontal And horizontal movements that occur on large engineering structures such as long span bridges, dams and breakwaters. The GPS technology, however, allows us to measure horizontal and vertical motions much more effectively and conveniently, and it has increased dramatically in the past few years. With satellite information, a GPS receiver can very quickly determine its position to within a matter of meters. On breakwaters, however, an accuracy of a few centimeters is quite important for detecting the build up of stress and pressure caused by sea currents and wave rising toward the ground surface. Typically, we can measure the position of a breakwater benchmarks (monitoring stations) using GPS on a regular basis depending on the activity of the sea current movements especially during the monsoon seasons. GPS offers several advantages compared to breakwater surveys that use typical terrestrial survey instruments, for example, measurements can be made in almost any weather condition and at all time within the required accuracy. This paper therefore highlights the potential use of GPS and conventional geodetic survey methods in breakwater deformation survey. Data collection times were planned to minimize simultaneous logging intervals at redundant stations. The objective was to provide data that would enhance the baseline and network adjustments in the postprocessing of the data. In this paper, the first stage campaign of GPS and conventional geodetic survey method for the Kemaman Port Breakwater are presented

Quantifying deformation in North Borneo with GPS

The existence of intra-plate deformation of the Sundaland platelet along its eastern edge in North Borneo, South-East Asia, makes it an interesting area that still is relatively understudied. In addition, the motion of the coastal area of North-West Borneo is directed toward a frontal fold-and-thrust belt and has been fueling a long debate on the possible geophysical sources behind it. At present this fold-and-thrust belt is not generating significant seismic activity and may also not be entirely active due to a decreasing shelfal extension from south to north. Two sets of Global Positioning System (GPS) data have been used in this study; the first covering a time period from 1999 until 2004 (ending just before the Giant Sumatra–Andaman earthquake) to determine the continuous Sundaland tectonic plate motion, and the second from 2009 until 2011 to investigate the current deformations of North Borneo. Both absolute and relative positioning methods were carried out to investigate horizontal and vertical displacements. Analysis of the GPS results indicates a clear trend of extension along coastal regions of Sarawak and Brunei in North Borneo. On the contrary strain rate tensors in Sabah reveal that only insignificant and inconsistent extension and compression occurs throughout North-West Borneo. Moreover, station velocities and rotation rate tensors on the northern part of North Borneo suggest a clockwise (micro-block) rotation. The first analysis of vertical displacements recorded by GPS in North-West Borneo points to low subsidence rates along the western coastal regions of Sabah and inconsistent trends between the Crocker and Trusmadi mountain ranges. These results have not been able to either confirm or reject the hypothesis that gravity sliding is the main driving force behind the local motions in North Borneo. The ongoing Sundaland–Philippine Sea plate convergence may also still play an active role in the present-day deformation (crustal shortening) in North Borneo and the possible clockwise rotation of the northern part of North Borneo as a micro-block. However, more observations need to be collected to determine if the northern part of North Borneo indeed is (slowly) moving independently.Astrodynamics & Space Mission

Relative Sea Level Trends for the Coastal Areas of Peninsular and East Malaysia Based on Remote and In Situ Observations

Absolute sea-level rise has become an important topic globally due to climate change. In addition, relative sea-level rise due to the vertical land motion in coastal areas can have a big societal impact. Vertical land motion (VLM) in Southeast Asia includes a tectonically induced component: uplift and subsidence in plate boundary zones where both Peninsular and East Malaysia are located. In this paper, the relative sea-level trends and (seismic cycle-induced) temporal changes across Malaysia were investigated. To do so, the data (1984–2019) from 21 tide gauges were analyzed, along with a subset (1994–2021) of nearby Malaysian GNSS stations. Changes in absolute sea level (ASL) at these locations (1992–2021) were also estimated from satellite altimetry data. As a first for Peninsular and East Malaysia, the combination ASL minus VLM was robustly used to validate relative sea-level rise from tide-gauge data and provide relative sea-level trend estimates based on a common data period of 25+ years. A good match between both the remote and in situ sea-level rise estimations was observed, especially for Peninsular Malaysia (differences < 1 mm/year), when split trends were estimated from the tide gauges and GNSS time series to distinguish between the different VLM regimes that exist due to the 2004 Sumatra–Andaman megathrust earthquake. As in the south of Thailand, post-seismic-induced negative VLM has increased relative sea-level rise by 2–3 mm/year along the Andaman Sea and Malacca Strait coastlines since 2005. For East Malaysia, the validation shows higher differences (bias of 2–3 mm/year), but this poorer match is significantly improved by either not including data after 1 January 2014 or applying a generic jump to all East Malay tide gauges from that date onwards. Overall, the present relative sea-level trends range from 4 to 6 mm/year for Malaysia with a few regions showing up to 9 mm/year due to human-induced land subsidence

Quality assessment of terrestrial laser scanner surface deviation analysis in vegetation slope monitoring

Mechanised with ability to rapidly acquire three-dimensional (3D) data using non-contact measurement, terrestrial laser scanner (TLS) has become an option in landslide monitoring. Dense 3D point clouds provided from TLS has enable surface deviation analysis to rigidly examine the displacement that occurred on the monitored object. However, the existence of vegetation on land slope has become uncertainty in TLS measurement for landslide monitoring. To concretely measure the effect of vegetation, this study has performed two epoch landslide monitoring using tacheometry (for benchmarking) and TLS (Topcon GLS-2000) at Kulim Techno City, Kedah, Malaysia. Sixteen (16) artificial targets were well-distributed on the slope to determine the accuracy of the employed TLS, evaluate the capability of TLS to determine the stability of the slope and scrutinise the significant of vegetation uncertainties in TLS measurement. Results obtained revealed that Topcon GLS-2000 manage to obtained results that are statistically similar to tacheometry and provides 0.006m of accuracy. However, the presence of high incidence angles in TLS measurement has limited the capability to identify the significant displacement of the targets. With the aid of F-variance ratio test, the study has statistically proved that vegetation uncertainty is able to decrease the quality of TLS data.Landslide monitoring, Quality assessmen