Journal of Surveying Engineering

Precise orbit determination (POD) is the procedure for determining the orbit of a satellite with high accuracy. Compared with global navigation satellite systems (GNSS), the low Earth orbit (LEO) satellites have some different features in space, mainly due to perturbations caused by dynamic forces related to their altitudes. Methods for POD of LEO satellites have been developed over the last decades. Nowadays, postprocessed precise orbits are used in different space applications such as radio occultation, satellite altimetry, and interferometric synthetic-aperture radar missions. The advancements in technology decrease the size of LEO satellites and developments in theory increase their orbital accuracy. In recent years, onboard POD has become a hot topic in the navigation and positioning field, which is crucial for, e.g., formation flying of small satellites and GNSS-aided LEO megaconstellations for positioning purposes. This contribution reviews LEO POD methods based on undifferenced GNSS observations in both postmission and real-time data processing. It comprises the quality control step, the models used and their limitations, processing algorithms, and different validation methods. To have a clear insight into the current and the future state of the LEO POD, the most recent developments and important achievements are also discussed.

Terrestrial laser scanning (TLS) and drone-based structure-from-motion (SfM) photogrammetry allowed the study of soil deformations due to blast-induced liquefaction during an experiment carried out on 4 June 2018. The research aimed at both evaluating the measurement quality and estimating the rammed aggregate piers (RAPs) effectiveness in mitigating the effects of soil liquefaction. These effects mainly consist of subsidence and deposits of ejected and extruded materials. The comparison between multitemporal 3D models provided surface variation maps and volume changes. In addition, classical topographical leveling allowed the measurement of subsurface vertical displacement along a specific cross section. The results pointed out a significant reduction, higher than 50% of soil deformation in areas improved by RAPs installation; moreover, the corresponding volume variations were no more than about 37% of those occurred in the not improved area. Finally, a critical comparison between remote sensing and leveling suggested that surface variation maps could underestimate the area lowering up to 15% in this kind of terrain.

A unique local tsunami had a very large impact on the coastal stations near Dålk Glacier; this kind of tsunami is related to iceberg activity. To provide a reference for tsunami warning and disaster prevention at these coastal research stations, a total of 41 abnormal water-surface oscillations caused by iceberg-induced tsunamis have been recorded and analyzed since February 2010. The seasonal and interannual variations in the tsunamis were determined by analyzing meteorological data and Landsat imagery. Based on these variation characteristics, double exponential smoothing was employed to fit the historical records and predict the next occurrence of an iceberg-induced tsunami, including the time and maximum absolute value of elevation of water-surface oscillation. The results showed that the date prediction error could be within a week, and the mean relative error of prediction for the elevation of water-surface oscillation was approximately 36.8%. Despite instability of prediction accuracies, this study provides an important clue to iceberg-induced tsunami warning and disaster prevention at coastal stations near calving glaciers, as well as for safe berthing and unloading of research vessels near these stations.

Technological advancements in virtual reality have opened the door for widespread dissemination and application in engineering education. In surveying engineering, outdoor labs are essential, because they offer great means for experiential learning and preparation for real applications. However, challenges related to weather, inaccessibility to sites, transportation costs, and liability reduce time spent with instruments, and limit comprehension of surveying procedures and preparedness for the job market. Through virtual reality, we can create realistic surveying scenarios that are difficult to implement in practice, such as surveying in cities, at construction sites, and in different terrain scenarios. In addition, virtual reality can be used to support remote and online learning. This paper presents the thorough implementation of virtual reality labs in a surveying engineering first-year class. Technical feedback showed that surveying labs were recreated with a high level of fidelity, which is important to transfer skills learned in virtual reality to the real environment. Students stated that virtual reality gave them more incentives to learn, added to the fun of learning, and improved their overall learning experience. Furthermore, students indicated that virtual reality labs helped them understand surveying procedures and the operation of instruments, and they considered virtual labs to be a useful tool for preparation for physical labs. Pedagogical assessments using grades from previous years showed that the virtual reality labs enhanced student learning. Barriers of virtual reality, such as nausea and motion sickness, limit their extensive use. Despite a few negatives, virtual reality offers viable solutions to challenges in surveying engineering education, with the potential for further development and integration in other surveying courses.

The upcoming State Plane Coordinate System of 2022 has spurred considerable interest in design, development, and implementation of large-scale conformal map projections designed at Earth’s surface instead of the reference ellipsoid surface. Such projections address overall linear distortion, which accounts for the combination of scale distortion and ellipsoid height distortion. A method for minimizing root-mean-square (RMS) linear distortion in map projection design is presented. It is based upon least-squares “best fits” of map projection surfaces to Earth’s surface, represented by sets of height data points. Linear distortions, across three common conformal map projections (Lambert conformal conic, transverse Mercator, and Hotine oblique Mercator), are controlled by sets of “critical” parameters that have nonlinear functional relationships with position. These functional relationships are linearized and used in iterative least-squares solutions to find estimates for the parameters that minimize the sum of the squares of linear distortions for the entire input height data point set. The methodology can include weighting for priorities such as population and transportation corridors. Examples are presented and comparisons with existing map projections are made, for both unweighted and population-weighted data sets. It is recognized that there can be design considerations, involving linear distortion, other than or in addition to minimizing its root-mean square.

Linear trends, or site velocities, derived from global navigation satellite system (GNSS) positional time series have been commonly applied to site stability assessments, structural health monitoring, sea-level rise, and coastal submergence studies. The uncertainty of the velocity has become a big concern for stringent users targeting structural or ground deformation at a few millimeters per year. GNSS-derived positional time series are autocorrelated. Consequently, conventional methods for calculating the standard errors of the linear trends result in unrealistically small uncertainties. This article presents an approach to accounting for the autocorrelation with an effective sample size ($N_{eff}$). A robust methodology has been developed to determine the 95% confidence interval (95%CI) for the site velocities. It is found that the 95%CI fits an inverse power-law relationship over the time span of the time series (vertical direction: $95\%\mathrm{CI}=5.2T^{-1.25}$; east–west or north–south directions: $95\%\mathrm{CI}=1.8T^{-1.0}$). For static GNSS monitoring projects, continuous observations longer than 2.5 and 4 years are recommended to achieve a 95%CI below $1\mathrm{mm}/\mathrm{year}$ for the horizontal and vertical site velocities, respectively; continuous observations longer than 7 years are recommended to achieve a 95%CI below $0.5\mathrm{mm}/\mathrm{year}$ for the vertical land movement rate (subsidence or uplift). The 95%CI from 7-year GNSS time series is equivalent to the 95%CI of the sea-level trend derived from 60-year tide gauge observations. The method and the empirical formulas developed through this study have the potential for broad applications in geosciences, sea-level and coastal studies, and civil and surveying engineering.

The Hong Kong–Zhuhai–Macao Bridge (HZMB) is the longest sea-crossing bridge in the world. The primary Global Navigation Satellite System (GNSS) control network of the HZMB has the outstanding characteristics and difficulties of long distance across the sea (nearly 32 km) in an approximate east–west direction, poor satellite positioning environment, high precision requirement of construction positioning, long construction period, and complicated transformations of the coordinate systems of China, Hong Kong, Zhuhai, Macao, and the HZMB project. Taking the primary GNSS control network of the HZMB as an example, this paper studied the key technical issues in establishment and repetition survey of the primary GNSS control network of a large-scale and high-precision sea-crossing bridge. Firstly, the three-dimensional engineering coordinate system based on International Terrestrial Reference Frame (ITRF) and the two-dimensional plane coordinate system with projection length deformation less than $5\mathrm{mm}/\mathrm{km}$ were designed and established according to the engineering characteristics and requirements. Secondly, the control point selection, networking, and observation schemes were designed. Thirdly, the data processing technologies of high-precision GNSS control network of sea-crossing bridge and tunnel engineering project, including International GNSS Service (IGS) reference station technology, satellite orbit fixing technology, various error correction techniques, and engineering datum network technology, were studied and put forward. Fourthly, the accuracy analysis of baseline solution and network adjustment was carried out by using the fifth repetition survey data of the primary GNSS control network of the HZMB. Finally, the repetition survey results of the network were compared and analyzed.