Tajul Ariffin Musa

The Geocentric Datum of Malaysia: Preliminary Assessment and Implications

The reliability of the national geocentric datum must be assessed regularly to maintain high geospatial accuracy in terms of consistency with respect to the global datum, i.e. International Terrestrial Reference Frame (ITRF). This can be accomplished by considering the spatial and temporal variations caused by plate tectonic movements. This study aims to assess the reliability of Geocentric Datum of Malaysia (GDM2000) by analysing the datum shifts via the displacements of the Malaysian Real Time Kinematic Network (MyRTKnet) stations caused by tectonic movements as well as the displacements induced by reference frame effects. A significant land displacement up to 17 and 30 cm in north and east components were found respectively, due to local active fault and the cumulative plate tectonic motion. The implications of a non-geocentric datum are also discussed.

Atmospheric remote sensing using GNSS in the Australasian region: From temperate climates to the tropics

It is known that the zenith path delay (ZPD) is a valuable meteorological parameter. In this paper, ZPD values from Australian and Malaysian Global Positioning System (GPS) reference stations are derived and compared in order to show the climatic contrast between the two regions. Based on the analysis of the two data sets, a higher and shorter-term variability of the estimated ZPD is observed in Malaysia. The quality of the estimated ZPD is examined by benchmarking against International GNSS Service (IGS) troposphere products. The differences range from 4–12mm RMS.

Application of moderate resolution imaging spectroradiometer snow cover maps in modeling snowmelt runoff process in the central Zab basin, Iran

Abstract Snow, as one form of precipitation, plays a very significant role in the water cycle and in water resource management. However, the spatial and temporal variations in snow cover complicate the monitoring of this role. Field measurements, especially in mountainous areas, are often impossible without the use of new technologies. In this study, moderate resolution imaging spectroradiometer (MODIS) at 500-m resolution has been used to provide a map of snow cover area (SCA) using the normalized difference snow index in the central Zab basin in West Azerbaijan, Iran. Eight-day composite data are used to minimize the effect of cloud cover and maximize the amount of useable SCA images. The importance of snow in this basin was simulated using a snowmelt runoff model (SRM) as one of the major applications of daily MODIS-8 images based on various algorithms. The location of snow gauge stations on digital elevation model (DEM) of central Zab basin extracted from advanced space borne thermal emission and reflection radiometer images by using bilinear interpolation method. The SCA index, along with spectral threshold on bands 2 and 4, provided a stable relationship for extraction of the snow cover map in the study area. The simulated flow in the water year 2010 to 2011 had a coefficient of determination ( R 2 ) of 0.8953 and a volume difference ( D v ) of 0.1498%, which shows a good correlation between the measured and computed runoff by using the SRM in the central Zab basin. The first results of the modeling process show that MODIS snow covered area product can be used for simulation and measuring value of snowmelt runoff in central Zab basin. The studies found that the SCA results were more reliable in the study area.

Performance analysis of ISKANDARnet: a research-based network RTK positioning system

GNSS positioning within the equatorial region suffers from distance-dependent errors due to severe atmospheric delays, which results in difficulty for the network ambiguity resolution process. Hence, it is a challenge to maintain the capability of centimetre-level positioning in this region. Subsequently, a network of Continuously Operating Reference Stations (CORS) situated in the developing region of Iskandar Malaysia, known as ISKANDARnet, has been developed by Universiti Teknologi Malaysia (UTM) as a research platform to support academic activities and high-precision positioning applications. The ISKANDARnet with its Network-based Real-Time Kinematic (N-RTK) technique provides a means to meet the challenge. In this study, the performance of ISKANDARnet N-RTK has been analysed in terms of positional accuracy, performance of ambiguity resolution, and effectiveness of network corrections by conducting real-world-scenario tests: (i) at different user locations, (ii) in varied observation sessions, and (iii) by external assessment with the national commercial N-RTK system, i.e., the Malaysia Real-Time Kinematic GNSS Network (MyRTKnet). The results indicated that significant changes in ambiguity resolution occur at different user locations and observation sessions, providing insight into the varying distance-dependent errors. Moreover, the positioning accuracy agrees to within centimetre-level of the national commercial N-RTK system.

Application of low-cost tools and techniques for landslide monitoring

This paper proposes a low-cost landslide monitoring system using the Reverse Real-Time Kinematic (RRTK) technique. The server-based processing technique, which utilizes the two-way communication channel for the computation and transmission of the user’s accurate position, is discussed. The basic infrastructure requirements for RRTK in lowcost landslide monitoring application are described. In order to implement the proposed RRTK algorithm, real-time data streaming of raw Global Positioning System (GPS) data of both the reference and rover station(s) to the control centre, are performed. A high pass filtering technique was employed to detect outliers in the observations. Finally, the autocorrelation of GPS time series was investigated to validate the presence of white and coloured noises in the GPS observations.

Reverse RTK data streaming for low-cost landslide monitoring

This chapter describes the preliminary study of real-time data streaming in support of the proposed low-cost landslide monitoring system using the Reverse Real-Time Kinematic (RRTK) technique. The RRTK algorithm was implemented by streaming raw Global Positioning System (GPS) data of both the reference and roving station(s) to the control centre for processing, and transmission of the position solution to the roving station. The main purpose of the data streaming was to investigate the quality of the measurements, for utilization in landslide modelling and analysis in near real-time. A novel methodology using a high pass filtering technique was implemented, to detect outliers in the observations. Also, the autocorrelation of GPS time series was investigated.

The estimation of receiver code bias for MyRTKnet stations

This paper presents the estimation of receiver code bias of Global Positioning System (GPS) continuously operating reference stations (CORS) over Malaysian region, MyRTKnet stations. In this study, we used the Bernese software and adopted the algorithm from IONOLAB method to estimate the receiver code bias (RCB). It has been found that the RCB from Bernese and IONOLAB show a good correlation with RCB from the International GNSS Service (IGS) analysis centre with R2 values are within 0.3 ns to 0.7 ns and 0.6 ns to 0.9 ns, respectively. The estimation of RCB for MyRTKnet shows that there are no latitudinal dependencies of the RCB values. It has been found that 99% of the receivers have standard deviation below than 1 ns for both methods. It also found that both methods can provide reliable RCBs value as the mean vertical total electron content (VTEC) computed using RCBs from both methods shows a similar trend and fluctuation from IGS global ionospheric maps (GIM). Hence, it is suggested that further studies can be carried out using both methods to study the variations of RCB for a longer period to improve total electron content (TEC) estimation.

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.

In search of the Malaysian extended continental shelf

Over the years, the sovereignty proclamation of Coastal States for their extended continental shelf has been a crucial matter. The declaration and extension of a continental shelf under the United Nations Convention on the Law of the Sea provide significant potential for many developing nations in economics, trades, resource exploitation, communication and security. Hence, the application of satellite altimeter, as one of the solutions for collecting bathymetry data to define the approximate limits of the continental shelf, is reviewed. This paper also discusses the possible significance or contribution of space-derived bathymetry, i.e. the seafloor topography, either independently or harmoniously with different datasets, to meet the element of the Article 76 of UNCLOS.

Spatial and Seasonal Ionospheric Error Growth in DGPS Measurement: A Case Study in Malaysia

This paper tackles the Equatorial ionosphere and its effects on Differential Global Positioning System (DGPS) error growth over Malaysia by using a network of GPS Continuously Operating Reference Stations (CORS). Seasonal variation of ionospheric delay has been examined and findings show that the effect of spatial variation of ionospheric errors in DGPS is very significant during the equinoctial seasons. Furthermore, a DGPS regression model was developed and tested during the solar maximum year in 2013 by using internet-based DGPS. The results show that the model is capable of estimating DGPS positional errors for distances of user to reference station less than 680 km.