Volume 17, Issue 1

Logistic processes of construction sites are transferred into virtual and full 3D environments to increase the interoperability for all project partners. These digital twins are emerging for the construction process of modern building processes and are already designed to be used for the operation of the building afterwards. In structural health monitoring (SHM) the sensor installations are also designed to monitor the structure over its whole lifespan. Therefore, the embedding process and the operation of the sensor systems and the Building Information Modelling (BIM) have overlapping long-term goals. Beside these 3D software advances in civil engineering, the working environments in the field of geodesy still follow more established approaches. In many cases using only 2D CAD plans and on-site visits at the existing structure are best practice for the design of geodetic monitoring installations. This paper describes the improvement of the concept creation of permanent monitoring systems with geodetic total stations in an interactive virtual 3D environment. The simulated instruments are behaving according to their specification data and are linked with a physics engine to automatically detect common problems in a network design like obstructed line of sights, disadvantageous incidence angles at the targets or automatic aiming issues due to multiple targets in the field of view. Furthermore, the Virtual Reality (VR) technology is introduced as a user interface for a virtual 3D planning environment. The functionality of the developed VR application is tested in a real-life use case for the feasibility study of the automatic monitoring of a railway tunnel.

The gravitational effects of ocean tide loading, which are one of the main factors affecting gravity measurements, consist of three components: (1) direct attraction from the tidal water masses, (2) radial displacement of the observing station due to the tidal load, and (3) internal redistribution of masses due to crustal deformation. In this study, software for gravitational effects of ocean tide loading was developed by evaluating a convolution integral between the ocean tide model and Green’s functions that describe the response of the Earth to tide loading. The effects of three-dimensional station coordinates, computational grid patterns, ocean tide models, Green’s functions, coastline, and local tide gauge were comprehensively considered in the programming process. Using a larger number of high-precision coastlines, ocean tide models, and Green’s functions, the reliability and applicability of the software were analyzed at coastal stations in the China Earthquake Gravity Network. The software can provide the amplitude and phase for ocean tide loading and produce a predicted gravity time series. The results can effectively reveal the variation characteristics of ocean tide loading in space and time. The computational gravitational effects of ocean tide loading were compared and analyzed for different ocean tide models and Green’s functions. The results show that different ocean tide models and Green’s functions have certain effects on the calculated values of loading gravity effects. Furthermore, a higher-precision local ocean tide model, digital elevation model, and local tidal gauge record can be further imported into our software to improve the accuracy of loading gravity effects in the global and local zones. The software is easy to operate and can provide a comprehensive platform for correcting the gravitational effects of ocean tide loading at stations in the China Earthquake Gravity Network.

Digital Elevation Models (DEMs) are real-world geographical databases that are important in studying many Earth related topics. Because the vertical accuracy of global DEMs differs across regions due to various reasons, acquiring reliable heights for a region using global height models is crucial. The objective of this study is to compare and assess the most reliable global height model for Sri Lanka. The official height system in Sri Lanka is the Mean Sea Level (MSL) based orthometric height system. In this study, the quality of ASTER, SRTM, NASADEM, MERIT, and DEMs compiled from digitized contour data of Sri Lanka was evaluated using the known heights of the Fundamental Benchmarks (FBMs) of Sri Lanka. In addition, recently published high-resolution Global Geopotential Models (GGMs) were used for the accuracy assessments of gravity related quantities computed using DEMs. The SGG-UGM-2 GGM, which showed the minimum STD and RMSE of geoid undulation difference was found as the best fit GGM over Sri Lanka. It was found that the NASADEM at its highest resolution, which gave the lowest RMSE of 2.954 m was the best global DEM for Sri Lanka.

The Department of Lands (DOL), Thailand, has adopted the Network-based Real-Time Kinematic (NRTK) Global Navigation Satellite System (GNSS) surveying technique using a Virtual Reference Station (VRS) to support cadastral surveys since 2011. Determining accurate coordinates of parcel boundary markers at building corners or near fences and walls is difficult because a GNSS range pole cannot be leveled with a circular bubble. This study aims to evaluate the performance of the receivers equipped with tilt sensors for horizontal and vertical positioning. Two types of tilt sensors used for evaluation were a magnetometer and micro-electro-mechanical system (MEMS) and an inertial measurement unit (IMU). Conducting the NRTK GNSS surveying tests was based on the pole tilt angles of 0°, 15°, 25°, 35°, and 45° from a plumb line in controlled and obstructed environments. The IMU-based tilt sensor had more advantage of accurately positioning over the MEMS sensor. The results showed that using the IMU, better than 4 cm horizontal positioning accuracy was achievable when the pole was tilted by 15° or less under non-multipath and open-sky conditions. The vertical accuracy was of a few centimeter levels and least sensitive to tilt angles using either type of sensor. However, none of the sensors precisely compensated for pole tilt in strong-multipath and complex environments, causing increased horizontal errors in decimeter levels.

The aim of this work is the determination of the parameters of the triaxial ellipsoid of the Moon, as derived from a quasi-selenoid model. After a detailed description of various quasi-selenoid models of the lunar gravity field, which were proposed in the last twenty years, we prepare suitable data sets of three-dimensional Cartesian coordinates. The mathematical model adopted is the general (polynomial) equation of an ellipsoid functionally related to the nine unknowns: the coordinates of the ellipsoid center, the three rotation angles and the three ellipsoid semiaxes. Furthermore, we adopt mathematical models for one special and two degenerate cases of the triaxial ellipsoid. We implement the least-squares method of indirect observations and we derive results for eighteen data sets of quasi-selenoidal points. From the results, we report the values of the semiaxes of the triaxial ellipsoid of fitting with three unknowns, for the model GL0660B, to be 1,738,256.3 ± 0.2 m, 1,738,023.1 ± 0.2 m and 1,737,603.2 ± 0.2 m, while the other unknowns remain insignificant. This triaxial ellipsoid leads to the improvement in the RMS value of the height anomaly at about 12 per cent in comparison to the oblate spheroid.

Real-time positioning in suburban and urban environments has been a challenging task for many Intelligent Transportation Systems (ITS) applications. In these environments, positioning using Global Navigation Satellite Systems (GNSS) cannot provide continuous solutions due to the blockage of signals in harsh scenarios. Consequently, it is intrinsic to have an independent positioning system capable of providing accurate and reliable positional solutions over GNSS outages. This study exploits the integration of Light Detection and Ranging (LiDAR), gyroscope, and odometer sensors, and a novel real-time algorithm is proposed for this integration. Real field data, collected by a moving land vehicle, is used to test the presented algorithm. Three simulated GNSS outages are introduced in the trajectory such that each outage lasts for five minutes. The results show that using the proposed algorithm can achieve a promising navigation performance in urban environments. In addition, it is shown that the denser environments, that existed over the second and third outages, can provide better positioning accuracies as more features are extracted. The horizontal errors over the first outage, with less density of surroundings, reached 7.74 m (0.43%) error with a mean value of 3.15 m. Moreover, the horizontal errors in the denser environments over the second and third outages reached 4.97 m (0.28%) and 3.99 m (0.23%), with mean values of 2.25 m and 1.89 m, respectively.

Ionospheric scintillations due to plasma irregularities can severely affect the modern dynamic and technological systems whose operations rely on satellite-based navigation systems. We investigate the occurrence of ionospheric scintillation in the equatorial and low latitude region over Malaysia after the 2011 Valentine’s Day solar flare. A network of three Global Ionospheric Scintillation and Total Electron Content Monitor (GISTM) GSV4004B receivers with increasing latitudes from the magnetic equator were used to monitor ionospheric TEC, rate of change of TEC index (ROTI), and amplitude (S4) as well as phase ( σ φ ) scintillation indices. The results show a simultaneous sudden rise in S4 and σ φ along with a significant depletion of TEC at all three locations. However, the largest enhancement of scintillation indices accompanying a substantial TEC depletion is observed at the farthest low latitude station (UNIMAS) from the equator with values around 0.5, 0.3 rad, and 1 TECU, respectively. The corresponding values at the near-equatorial station (Langkawi; 0.4, 0.2 rad, and 3 TECU) and intermediate station (UKM; 0.45, 0.3 rad, and 5 TECU) are examined along with ROTI variations, confirming the simultaneous occurrence of kilometer-scale and sub kilometer scale irregularities during 17 and 18 February 2011. The radiation effects of the solar flare on the ionosphere were prominently recognized at the local nighttime hours (around 14:00 to 17:00 UT) coinciding with the equatorial prereversal enhancement (PRE) time to seed the equatorial plasma bubbles (EPBs) enhancement that resulted in ionospheric irregularities over the low latitudes. The significant TEC depletion seen in the signals from selected GPS satellites (PRNs 11, 19, 23, and 32) suggests plausible degradation in the performance of GPS-based services over the Malaysian region. The study provides an effective understanding of the post-flare ionospheric irregularities during an episode of minor geomagnetic storm period and aligns with the efforts for mitigating the scintillation effects in space-based radio services over low latitudes.