Towards a Redefinition of the National Geodetic Vertical Datum by the Integrated Geodesy Adjustment- A Viewpoint

Determination of Mean Sea Level (MSL) as a vertical datum for orthometric heights is a vital requirement for the readjustment of the National Geodetic Levelling Network. The vertical datum is defined to be the geoid whereby it's practical realization was brought by tide gauge obervations at very few selected points e.g. ports. Geodetic levelling observation could use these tide gauges as fixed points. Unfortunately, the so-called determined MSL differs significantly from the geoid due to local phenomena, such as sea surface topography, ocean currents, tides, etc. The solution leads to distortion in the levelling network or other height information. Using integration approach of the Global Positioning System (GPS) data connected between tide gauges, satellite altimetry data on sea near the tide gauges, derived potential differences (from levelling nets and gravity observations), gravity anomalies and the deflection of the vertical surrounding the tide gauges, the required reference surface could be precisely determined. From geodetic point of view, these data contribute to the vertical datum problem and is briefly presented in this paper by the expression of the associated parameters of the Integrated Geodesy Adjusment's Concept

A preliminary determination of a gravimetric geoid in Peninsular Malaysia

It is considered that precise gravimetric geoid determination is one of the main geodetic problems in Peninsular Malaysia for the near future, since the Global Positioning System (GPS) defined ellipsoidal coordinates require geoidal heights in practice. Geoidal heights can be determined by either a geopotential model alone, or in combination with local gravity and height data. The reference gravity field contributed by the geopotential model can be improved by a tailoring method. This is the main objective of the study; a tailored model called OSU89B-MM (Malaysian Model) complete to degree and order 360 was developed by fitting the pre-existing geopotential model OSU89B to the updated mean free-air anomalies of half degree blocks in the peninsular region. Numerical analyses indicate that the tailoring technique has improved the reference gravity field by about 50% for point anomalies (from 23 mgals to 11 mgals). Tests on absolute geoid heights in selected areas where GPS and levelling data were available have demonstrated about 10% improvement (1 cm to 2 cm) of the tailored model over OSU89B, whereby the long wavelength errors have been partly diminished. The gravimetric geoid height has been computed in three test areas (which were characterised by different types of topography, gravity density and coverage) by Least Squares Collocation (LSC) and Fast Fourier Transforms (FFT). The local height data were also utilised in a remove-restore procedure in order to study the gravitational influence of the topography, especially in test areas of rough terrain. Results show that the standard deviation of the absolute differences between the control GPS/levelling derived geoid heights and predicted gravimetric geoid heights have improved by 5 cm (from 11 cm to 6 cm) compared to the corresponding differences implied by OSU89B- MM. Work carried out in areas of high topographic relief (for which no GPS data were available) has nevertheless shown the terrain contribution to the geoid height to be as much as 0.5 m to 1.5 m

The GPS data processing strategies for the engineering structure monitoring scheme

Monitoring and detecting deformations within an engineered structure can be determined using a number of geodetic (precise) methods, e.g. geotechnical approach, terrestrial observations and spacebased methods. Nowadays, the GPS technology has become the most important tool for estimating the large structural engineering deformation such as buildings, dams, long span bridges, etc. In order to ensure that the engineering structures are exhibiting a safe deformation behavior, a repeated and/or continuous GPS measurements can be employed. The GPS technology provides a quick and precise method of determining 3D movements of a structure over time. Application of GPS technique of deformation detection on a high-rise building is one example of this approach. The appropriate processing strategies of GPS observable to estimate the geodetic parameters of interest is usually carried out in post processing mode, but one may ask ‘how does one really tell the quality of GPS solutions?’ Two types of adjustments can be used in GPS processing, e.g. minimal constraint and constraint adjustment.. This paper therefore highlights the processing strategies of the GPS data from two epoch observations for monitoring surveys - Case study: KOMTAR building, in Penang, Malaysia. The results of the adjustment in deformation surveys are presented and discussed

Astronomi lanjutan

Buku ini mengandungi beberapa bab iaitu kandungan, bab 1: pengenalan, kegunaan, permukaan rujukan dan definisi-definisi utama dalam astronomi geodesi, peristilahan tahun, tahun tropika, bab 2: sistem koordinat jumantara dan transformasi, jenis-jenis sistem koordinat jumantara, koordinat transformasi, kaedah transformasi matriks, bab 3: sistem waktu dan penetapan waktu, waktu universal, sistem waktu utc, duti, saat lompat, bab 4: perubahan sistem koordinat jumantara, gerakan dinamik yang berujukan kepada bintang, pusingan kutub, perubahan kedudukan objek jumantara disebabkan oleh kesan fizikal, gerakan relatif di antara bintang-bintang, bab 5: katalog bintang dan efermeris, jenis-jenis efemeris, katalog utama bintang, mengemaskini kedudukan bintang daripada katalog apfs, hitungan kedudukan koordinat ketara katalog bintang fk4, bab 6: peralatan optikal, peralatan kelas pertama, jenama teodolit jenis universal, tentukur alat teodolit wild t4 dan dkm-3a, peralatan balai cerap, bab 7: penentuan azimut (geodesi dan astronomi), prinsip kaedah black, spesifikasi penentuan, cerapan di lapangan, kaedah hitungan, bab 8: penentuan latitud, kaedah penentuan, pembetulan pada perbezaan jarak zenit cerapan, spesifikasi penentuan, program bintang, bab 9: penentuan longitud, persamaan longitud, kaedah penentuan, spesifikasi penentuan,, aturcara di lapangan, bab 10: penentuan serentak latitud dan longitud, persamaan latitud-longitud, spesifikasi penentuan, cerapan di lapangan, hitungan, rujukan, indeks

The Use of FFT Method in Geoid Modelling

The paper presents the spectral method known as Fast Fourier Transform (FFT) to compute discrete convolution integrals. Geoid heights are computed by reformulating the Stokes' equation in convolution form and using gridded residual gravity anomalies as input data. Discrete spectra of the kernel functions are used for the geoid heights appending simultaneously zero-padding around the input gravity matrix in order to avoid circular convolution effects. This procedure provides identical results to those from the rigorous numerical integration. The computed quantities are compared to a set of geoid heights derived from a contribution of GPS traverse with levelled orthometric heights

Evaluation of the EGM96 model of the geopotential in Peninsular Malaysia

A set of higher degree and order of spherical harmonic potential coefficients ( Cnm, Snm ) plays an important part in gravity field modelling , e.g. reference model for the gravimetric solution. The satellite and terrestrial data used in the development of the global geopotential model have improves with time. For example, the most recent EGM96 model incorporate new 30’ X 30’ surface gravity anomalies, normal equations from direct altimetry data (TOPEX/POSEIDON, GEOSAT & ERS-1). This paper presents the accuracy of the anomalous gravity field determined from the potential coefficients of the EGM96 model over the Malaysia region. Dividing the region into 0.5 x 0.5 block and testing the mean fit for each block, it shows how well the residual gravity anomalies is modelled by EGM96 model compared to geopotential model OSU91A. To assess the quality of the estimated geoid height from EGM96(NEGM) and OSU91A (NOSU) , comparison are made with the corresponding height derived from 136 GPS control poinst (NGPS/Lev). The overall results of absolute and relativen geoid height differences showed that the EGM96 is definitely the best high-order geopotential model to be used as reference gravity field modelling for the Peninsular Malaysia

Slope gradient analysis at different resolution using terrestrial laser scanner

Slope instability in landslide prone area is a costly problem, which can lead to travel disruption, property damages, and injury or loss of life. For many years, slope monitoring activities are largely carried out by conventional survey instruments such as Total Station, levelling and Global Positioning System (GPS). However, these techniques is a time consuming, hazardous, and costly process, and it can be difficult to ensure that problems are recorded and handled in a consistent manner. Terrestrial laser scanners (TLS) find rapidly growing interest in remote sensing and photogrammetry field as efficient tools for fast and reliable threedimensional (3D) point cloud data acquisition. The TLS technology is based on the reflectorless and contactless acquisition of a point cloud of the topography using the time-of-flight distance measurement of an infrared laser pulse. This paper describes the capabilities of TLS in slope mapping studies. The main objective of this study is to evaluate the slope mapping pattern at different resolution. This study has been conducted at Cameron Highland, Malaysia, which approximately located at latitude 4d2636 and longitude 101d234. Several data acquisitions on selected cut slopes were performed using the Topcon GLS1500 laser scanner. Ground control points were established using Real Time Kinematic GPS to provide a local coordinate system on laser scanning data. Resolution of a laser scanner determines a density of point cloud during data acquisition. In this experiment, there is a different number of resolution has been set during data acquisition in order to evaluate the result of slope mapping pattern. It was found that, resolution gives an effect in slope mapping pattern

Gravity Anomaly And Topography Induced By Repeated Fault Motions

The Accumulation Hypothesis deals with the origin of the gravity anomaly and topography around an active fault. This hypothesis was postulated that the gravity anomaly around active faults is the product of repeated fault motions; higher gravity anomaly will occured in compressed areas while lower anomaly in dilated areas. If it is the case, the topography around an active fault can also be interpreted in terms of repeated coseismic elevation change. This paper therefore presents the characters of gravity changes and topography caused by strike-slip faulting at fujimi Valley, Nagano Prefecture, Japan. In order to compute theoretical gravity changes and elevation (h), we use analytical expressions of and 8h caused by faulting on a finite rectangular plane buried in a homogeneoous half-space. The expected gravity anomaly and topography for this test area are compared with the observed data. The analyses have shown that the simple fault model yields gravity anomaly which agrees well with the observations. Similarly, the same model also generates the elevation changes that is consistent with the actual topography of the test area

The time series analysis in GPS structural monitoring schemes

https://sale.aliexpress.com/__pc/brand_shopping_week_clothing.htmNowadays, the Global Positioning System (GPS) has evolved as an important tool for estimating structural deformation in large engineering structures for examples bridges, dams and high rise buildings. Continuous GPS measurement can be employed in order to ensure that the engineering structures is exhibiting safe deformation behaviour for the purpose of safety assessment as well as preventing any disaster in the future. Today, GPS receivers for positioning and timing are capable to output range observations at high rates, typically once per second or even higher, for instance at 5 or 10 Hz. One is easily provided with dense and extensive time series of code and phase observations to all GPS satellites in view, on both the L1 and L2 frequency. Here, continuous solution enables time series of increased temporal resolution, from which deformation motion can be estimated from a shorter data time span and with more confidence of the episodic sampling of deformation signals. Furthermore, it offers the ability to mitigate systematic biases that results from multipath, atmospheric delays and other temporal considerations. In this study, we examined the GPS results collected from the instrument installed on top of the tower, in order to evaluate the existence of low and high frequency noises embedded in the observed data. The low pass filter, also known as least squares smoothing has been used to extract the high frequency noise and finally, the time series analysis was used to detect structural movement

Experimental detection of the Penang bridge vibration with real time kinematic gps

Vibration and dynamic deflection of bridge is an important aspect for bridge security evaluation. With the advance in sensor systems, data acquisition, data communication and computational methodologies, instrumentation-based monitoring has been a widely accepted technology to monitor and diagnose structural health and conditions for civil engineering structures such as bridges. For the health monitoring of bridges, sensors, which are reliable and robust, portable, non-destructive and automated such as Global Positioning System (GPS), are well suited. In addition, GPS also offer an opportunity for real or near real-time monitoring. This paper reports on the first experimental realization of the bridge evaluation using real time kinematic (RTK) GPS technique through a series of tests conducted on the Penang Bridge. It gives details of the methodology and a strategy for detecting vibration of the bridge. This paper also focuses on applying frequency domain method to bridge vibration. Finally conclusions are drawn with regard to the feasibility of the GPS in a bridge vibration measurement