Academic literature on the topic 'Space geodetic surveys'

The technology of the schemes development automation for areal coverage with aerial and space photography materials is proposed. Within its framework, a method for automatic coordinate referencing of images on the Earth’s ellipsoid surface with the subsequent determination of nomenclature sheets of topographic maps on a composite table was substantiated and implemented. The proposed method is based on the algorithms for calculating the azimuths and lengths of lines connecting the projections of the photographing points (inverse geodetic problem) and the coordinates of the images corner points’ projections (direct geodetic problem). The formulas for solving the geodetic tasks of the images coordinate referencing over long distances are obtained as a result of transforming and integrating the equations of geodetic lines described by the Claireau equation though F. Bessel’s method. It can be used when planning and performing aerial and space surveys, as well as to determine the cartographic base in order to select the starting points for photogrammetric condensation of the geodetic network. The technology is focused on the automation of phototriangulation technical design procedures and is good for linking images to the corresponding sections of electronic and digital maps.

The article deals with studying the historic design development of the eckers as landseparating tools, depending on the theoretical and practical matters of peasant land tenure, surveying forest areas, and those adjacent to the waters. The authors show that dividing lands of different practical use and establishing their boundaries is an important and necessary part of the land Fund state accounting, and its success depends on the qualified geodetic support possibilities. It is considered that the need to divide the land space can be traced in the laws of the knowledge development, performing geodetic works and improving the instruments’ design. As a result of the study, it was revealed that eckers make the only group of “earth-separating” tools; they are currently conventionally referred to as angle-measuring ones. Their main function is to divide space at fixed angles. The absence of a scale makes us think about their “non-measuring” purpose. The authors show that the features of the first “earth-separating” technical devices are basic for more complex designs of geodetic instruments, enabling to conduct diverse geodetic surveys in a certain historical era, depending on the application purpose and the tools using method.

Modeling trajectories of radio components ejected by the nucleus of 4C31.61 (2201+315) and observed by very long baseline interferometry (VLBI) in the frame of the MOJAVE survey suggests that they are ejected from three different origins that possibly host three different supermassive black holes. These origins correspond to three stationary components, one of which one is the VLBI core. Most of the mass of the nucleus is associated with a supermassive binary black hole system whose separation is ≈0.3 milliarc second, that is, a distance of ≈1.3 parsec and the mass ratio is ≈2. In contrast, the mass ratio with respect to the third black hole is ≈1/100. The three origins lie within 0.6 milliarc second, or a distance of ≈2.6 parsec. Based in this structure of the nucleus, we explain the variations observed in the astrometric coordinate time series obtained from VLBI geodetic surveys. This study shows that it is possible to exploit large MOJAVE-like VLBI databases to propose more insights into the structure of the extragalactic radio sources that are targeted by VLBI in geodetic and astrometry programs.

Extraction of underground minerals causes subsidence of the ground surface due to gravitational forces. The subsidence rate depends on the type of extracted ore, as well as its shape, thickness, and depth. Additionally, the embedding and overburden rock properties influence the time needed for the deformations to reach the surface. Using the results of geodetic deformation monitoring, which supply the information on pattern and magnitude of surface deformation, the performance of the mine may be evaluated. The monitoring can supply information on the actual rock mass behaviour during the operation and in many cases during the years after the mining operations have ceased. Geodetic methods of deformation monitoring supply information on the absolute and relative displacements (changes in position in a selected coordinate system) from which displacement and strain fields for the monitored object may be derived. Thus, geodetic measurements provide global information on absolute and relative displacements over large areas, either at discrete points or continuous in the space domain. The geodetic methods are affected by errors caused by atmospheric refraction and delay of electromagnetic signal. Since geodetic measurements allow for redundancy and statistical evaluation of the quality of the data, they generally provide reliable results. Usually, the designed accuracy of deformation measurements should allow for the detection of at least one third of the expected maximum deformations over the desired time span at the 95% probability level. In ground subsidence studies in mining areas, 10 mm accuracy at 95% level in both vertical and horizontal displacements is typically required. In the case of salt mines, the process of ground subsidence in viscous rock is slow; therefore, subsidence monitoring surveys may be performed once a year. In subsidence determination, two techniques are commonly used: leveling and satellite positioning. The satellite positioning technique is used to determine the 3D (horizontal coordinates and height) or 2D position of monitored points (only horizontal coordinates). When comparing the heights determined from satellite and leveling surveys, it has to be noted that the leveling heights are referred with respect to the geoid (orthometric heights), while heights determined from satellite surveys are referred with respect to the ellipsoid (ellipsoidal height). In the case of satellite surveys, the accuracy of horizontal position is typically 2–3 times better than vertical. The analysis of the optimal session duration lead to the conclusion that in order to achieve the sub-cm accuracy of horizontal coordinates at 95% confidence level, the satellite positioning session length using Global Positioning System (GPS) should be at least three hours long. In order to achieve the sub-cm accuracy of height coordinate at 95% confidence level in a single observation session, the GPS session length should be at least twelve hours long.

Abstract Precise knowledge of the oceanic Mean Dynamic Topography (MDT) is crucial for a number of geodetic applications, such as vertical datum unification and marine geoid modelling. The lack of gravity surveys over many regions of the Greek seas and the incapacity of the space borne gradiometry/gravity missions to resolve the small and medium wavelengths of the geoid led to the investigation of the oceanographic approach for computing the MDT. We compute two new regional MDT surfaces after averaging, for given epochs, the periodic gridded solutions of the Dynamic Ocean Topography (DOT) provided by two ocean circulation models. These newly developed regional MDT surfaces are compared to three state-of-theart models, which represent the oceanographic, the geodetic and the mixed oceanographic/geodetic approaches in the implementation of the MDT, respectively. Based on these comparisons, we discuss the differences between the three approaches for the case study area and we present some valuable findings regarding the computation of the regional MDT. Furthermore, in order to have an estimate of the precision of the oceanographic approach, we apply extensive evaluation tests on the ability of the two regional ocean circulation models to track the sea level variations by comparing their solutions to tide gauge records and satellite altimetry Sea Level Anomalies (SLA) data. The overall findings support the claim that, for the computation of the MDT surface due to the lack of geodetic data and to limitations of the Global Geopotential Models (GGMs) in the case study area, the oceanographic approach is preferable over the geodetic or the mixed oceano-graphic/geodetic approaches.

AbstractWe report the results of a successful 12-hour 22-GHz VLBI experiment using a heterogeneous network that includes radio telescopes of the Long Baseline Array (LBA) in Australia and several VLBI stations that regularly observe in geodetic VLBI campaigns. We have determined positions of three VLBI stations, atca-104, ceduna and mopra, with an accuracy of 4–30 mm using a novel technique of data analysis. These stations have never before participated in geodetic experiments. We observed 105 radio sources, and amongst them 5 objects which have not previously been observed with VLBI. We have determined positions of these new sources with the accuracy of 2–5 mas. We make the conclusion that the LBA network is capable of conducting absolute astrometry VLBI surveys with an accuracy better than 5 mas.

The development of a seamless vertical reference surface is accompanied by a number of challenges pertinent to the availability, volume and uncertainty of bathymetric and topographic data. Data uncertainty, which is by far the most difficult to deal with, is attributed to various sources of errors including those of geodetic and hydrographic origin. The uncertainties in the geodetic measurements originate mainly from the limitations in the geodetic technique employed, i.e. terrestrial or space. Old nautical charts and topographic maps were based on terrestrial techniques, which are far less accurate than modern space techniques. In addition, the distribution of the positioning uncertainty is not expected to follow a consistent pattern across the chart (map). This is mainly due to the inconsistent datum distortion as well as the discrepancies in the measuring techniques in the subsequent chart (map) versions. The existing paper (and digitized) charts in many areas of the world were also based on old hydrographic surveying methods, for example the lead-line, which are far less accurate than modern techniques such as multibeam echo-sounding surveys. This creates inconsistent depth uncertainty across the chart. As uncertainties are propagated into the estimated transformation parameters, estimated positions and their covariance matrix, it is of utmost importance that they are properly modelled. This paper addresses the issue of uncertainty in hydrographic data and suggests ways to account for it.

Abstract. Global Navigation Satellite Systems (GNSS) are space based positioning techniques and widely used in geodetic applications. Geodetic networking accomplished by engineering surveys constitutes one of these tasks. Geodetic networks are used as the base of all kinds of geodetic implementations, Co from the cadastral plans to the relevant surveying processes during the realization of engineering applications. Geodetic networks consist of control points positioned in a defined reference frame. In fact, such positional information could be useful for other studies as well. One of such fields is geodynamic studies that use the changes of positions of control stations within a network in a certain time period to understand the characteristics of tectonic movements. In Turkey, which is located in tectonically active zones and struck by major earthquakes quite frequently, the positional information obtained in engineering surveys could be very useful for earthquake related studies. For this purpose, a GPS (Global Positioning System) network of 650 stations distributed over Istanbul (Istanbul GPS Triangulation Network; abbreviated IGNA) covering the northern part of the North Anatolian Fault Zone (NAFZ) was established in 1997 and measured in 1999. From 1998 to 2004, the IGNA network was extended to 1888 stations covering an area of about 6000 km2, the whole administration area of Istanbul. All 1888 stations within the IGNA network were remeasured in 2005. In these two campaigns there existed 452 common points, and between these two campaigns two major earthquakes took place, on 17 August and 12 November 1999 with a Richter scale magnitude of 7.4 and 7.2, respectively. Several studies conducted for estimating the horizontal and vertical displacements as a result of these earthquakes on NAFZ are discussed in this paper. In geodynamic projects carried out before the earthquakes in 1999, an annual average velocity of 2–2.5 cm for the stations along the NAFZ were estimated. Studies carried out using GPS observations in the same area after these earthquakes indicated that point displacements vary depending on their distance to the epicentres of the earthquakes. But the directions of point displacements are similar. The results obtained through the analysis of the IGNA network also show that there is a common trend in the directions of point displacements in the study area. In this paper, the past studies about the tectonics of Marmara region are summarised and the results of the displacement analysis on the IGNA network are discussed.

The 2011 Tohoku-oki earthquake generated large displacements in and around the Japanese islands that were detected by the nationwide GPS network, sea-floor geodetic surveys, and space-borne radars. The east-west extension exerted on the Japanese islands by this event induced inland events of Mw6 or larger earthquakes. Coseismic subsidence of up to 1 m was observed along the coast where subsidence was found during the interseismic period. This observation contradicts expectations based on the concept of the recurrence of inter-plate earthquakes. Therefore, postseismic motions or other large events are expected to resolve this paradox.

The authors analyze the methods of engineering-geodetic and design of Railways in remote and sparsely populated areas. It is shown that one of the ways to improve the efficiency of design work significantly, especially for the design of roads in sparsely populated regions is the use of remote sensing materials and geoinformation technologies that enable you to apply the methods of geospatial and geological analysis, modeling and forecasting with the use of software and hardware systems of information support in design of Railways on the basis of computer geological interpretation of space survey materials. The problems of integrating geoinformation technologies in the system of computer-aided design of Railways are considered. The tasks of improving modern methods of engineering researches are set. This will significantly reduce the time and financial costs in the design, and rise the efficiency of engineering surveys.

Rapid regional climate warming in the Antarctic Peninsula (AP) has led to several major ice shelves retreating, and eventually collapsing, since the 1970s. In response, feeding glaciers have exhibited rapid acceleration and thinning, contributing to sea-level rise. This ice mass unloading induces a solid Earth response, which can be measured by geodetic observations. Observed rates of three-dimensional solid Earth deformations contain contributions due to both present and past ice mass variations (i.e. since Last Glacial Maximum, LGM) and horizontal plate tectonics. The solid Earth viscoelastic adjustments due to ice-ocean loading changes are known as Glacial Isostatic Adjustment (GIA). Accurate knowledge of GIA is essential for correcting gravity-based estimates of present-day ice-mass change. Observing solid Earth deformation caused by present-day ice mass change can be used to constrain the GIA response by inferring the Earth's viscoelastic properties. A few studies based on seismic or geodetic datasets have inferred Earth's rheological properties in the AP but the results are not yet conclusive. This thesis seeks to improve understanding of the solid Earth rheology in the AP by using spatiotemporally extended, three-dimensional geodetic observations and viscoelastic modeling. GPS observations up to 2018 are used to constrain the Earth rheology in the region around the former Larsen A and B ice shelves. I make use of interferometric synthetic aperture radar (InSAR) observations to further understand the ice mass change and solid Earth rheology in the northern Antarctic Peninsula (NAP), the first such application of InSAR in Antarctica. Finally, I extend the study region further south, to the northern Marguerite Bay (NMB) region, to determine ice mass change over 2002-2018 and explain non-linear deformation observed in GPS records using viscoelastic modeling. Previous work has shown that GPS measurements of bedrock uplift in the NAP can only be explained by a viscoelastic response to post-2002 ice surface unloading, with upper-mantle viscosities of ~ <2×10\(^{18}\) Pa s and a wide range of elastic lithosphere thicknesses. This thesis shows that since around 2011, the GPS uplift rates have reduced which is in accord with recent estimates of much-reduced ice mass loss in this region. The extended GPS uplift analysis and viscoelastic modeling confirms earlier estimates of low upper-mantle viscosities in this region but shows little sensitivity to variations in modeled lithospheric thickness. Along with GPS-derived bedrock uplift time series, the horizontal GPS components are also investigated for the first time. The horizontal GPS displacements are directed towards the south-west, in accord with the known and ongoing ice mass loss in the eastern Peninsula. The east coordinate component is shown to be sensitive to ice mass change, and modeling of it confirms that this region is underlain by the upper mantle viscosities suggested by the GPS uplift rates. In order to consider the horizontal components, uncertain plate motion must be removed from the time series, and so four test scenarios of plate motion were tested. The results from this experiment indicate that the ITRF2014 plate motion model accurately describes the Palmer (PALM) station motion and suggests that any potential plate model error or post-LGM GIA signal has a magnitude of ~ ± 0.5 mm/year for this region. I expanded the GPS datasets from a small number of stations to include spatially-extensive InSAR observations by the Sentinel-1A C-band dataset, consisting of nearly 85 and 84 acquisitions during the 2014.9-2017.8 period over the Larsen A and B regions, respectively. In the region of Larsen-B, large relative line-of-sight (LOS) displacements are observed at outlet glaciers of low elevation where ice unloading is high. InSAR also indicates that mass loss around the southern part of the Larsen-A region is higher relative to the northern part. Comparing these InSAR data and far-field GPS-based results to updated viscoelastic modeling for the Larsen-B region refines the understanding of lithospheric thickness, demonstrating a poor fit to a thin lithosphere. InSAR shows a good agreement for lithospheric thicknesses in the range of ~85-130 km with the upper-mantle viscosities preferred from comparison with the GPS time series. This is an early and potential application of InSAR to Antarctic deformation and can be further improved with better knowledge of tropospheric water vapour in this region. This thesis also investigates the ice mass changes from ~2002 around the NMB region, about ~350 km south of the Larsen-B, and subsequent solid Earth deformation. The mass balance estimation over this region suggests that the ice mass loss reduced around the Rothera research station since ~2012 and the Muller Ice Shelf since ~2009 compared to 2004-2012 and 2002- 2009, respectively. GPS measurements of bedrock uplift in NMB show time-varying rates of uplift varying between ~2.2 and 7.0 mm/year over 2002-2018. A comparison between GPS and modeled viscoelastic deformation up to 2015 suggests an upper mantle viscosity of ~0.1- 80×10\(^{18}\) Pa s but allows a wide range of effective elastic lithosphere thickness for NMB. The precise solid Earth properties of the AP remain to be conclusively determined, but our investigation sets an approximate range for the effective lithospheric thickness and upper mantle viscosity, which will help to understand more complex features of the solid Earth in this region in the future.

AbstractIn a joint effort, experts from measurement science and space-geodesy develop instrumentation and methods to further strengthen traceability to the SI definition of the metre for geodetic reference frames (GRF). GRFs are based on space-geodetic observations. Local-tie surveys at co-location sites play an important role for their computation. Novel tools are hence developed for reference point monitoring, but also for local tie vector determination and ground truth provision. This contribution reports on the instrumental approaches and achievements after 24 months project duration and discusses the remaining work in the project.

AbstractThe objective of this paper is to introduce CyCLOPS, a novel strategic research infrastructure unit, and present its current progress of implementation, and integration in the National geodetic, geophysical and geotechnical infrastructure of the government-controlled areas of the Republic of Cyprus. CyCLOPS is co-funded by the European Regional Development Fund and the Republic of Cyprus through the Research and Innovation Foundation under the grant agreement RIF/INFRASTRUCTURES/1216/0050. CyCLOPS is developed via the collaboration of the Cyprus University of Technology (CUT) and the German Aerospace Center (DLR), and supported by the Cyprus Geological Survey Department and the Department of Lands and Surveys. The main objective of CyCLOPS is to establish an integrated infrastructure for space-based monitoring of geohazards using the most prominent earth observation technologies (EO), such as GNSS and InSAR. Furthermore, the infrastructure will densify and form the backbone for the definition of the next generation national datum of the Republic of Cyprus. Eleven Tier-1/2 state-of-the-art GNSS CORS, precise weather stations, tiltmeters and specifically designed InSAR triangular trihedral corner reflectors will be deployed, in a collocated fashion, at selected locations throughout the government-controlled areas of Cyprus. The collocated configuration will be established and installed to be compliant with the most stringent CORS monumentation specifications, support all current GNSS constellations and SAR missions. Finally, one of CyCLOPS’ fundamental aims is to actively contribute to the on-going efforts and growing demand for more precise positioning services and high-quality modern reference frames, in conformity with the recommendations of the UN-GGIM (and its Subcommittee of Geodesy) to establish and enhance national geodetic infrastructures to support the sustainable management of geospatial information on the changing Earth.

AbstractLocal tie vectors are a crucial component within the combination of several space geodetic techniques. The vectors define the geometric relations between the space geodetic techniques, referring to the invariant reference points of such techniques. The Global Geodetic Observing System aims for an accuracy of 1 mm in the position on a global scale. In ITRF2014, about 50 % of the used local ties show discrepancies of more than 5 mm w.r.t. the global solution. In the framework of the IAG/IERS Working Group on Site Survey and Co-location or joint research projects like the international GeoMetre project strategies to improve the reference point determination and the local ties are developed. Strategies mainly comprise the development or the recommendation for surveying instruments, developing approaches for transforming local measurements to the global frame, and deriving innovative analysis procedures to derive the reference point of space geodetic techniques.In this contribution, we focus on the reference point determination. At the Geodetic Observatory Wettzell, a measurement campaign was carried out in September 2020 to evaluate the benefit of close range photogrammetry in the framework of reference point determination. For this purpose, the invariant reference point of a Satellite Laser Ranging telescope was derived several times using various configurations. The estimated reference point and the axis offset vary in a range of ±0.1 mm and ±0.02 mm, respectively. The resulting standard deviations of the coordinate components of the combined solution are less than 0.1 mm and impressively demonstrate the potential of the presented method.

AbstractThe Japan Coast Guard (JCG) operates Satellite Laser Ranging (SLR) and Global Navigation Satellite System (GNSS) instruments at the Shimosato Hydrographic Observatory (SHO) in Wakayama Prefecture located at the southernmost area of the main island of Japan. SHO is a co-location site where SLR and GNSS can be linked by precisely measuring the local tie vector (relative position) between these two space geodetic techniques. In November 2020, JCG collaborated with the Geospatial Information Authority of Japan (GSI) and performed a local tie survey to precisely determine the local tie vector between the stone marker of the GNSS station and the invariant point (IVP) of the SLR telescope. The IVP of the SLR telescope was determined by an indirect method, in which the reflector targets mounted on the SLR telescope were precisely observed from the surrounding temporary marks. The SLR telescope was rotated at a constant interval during the survey so that the observed target positions form arcs, from which we determined the azimuth and elevation axes; the orthogonal projection of the elevation axis onto the azimuth axis was determined as the IVP. The resulting local tie vector and its variance-covariance information were submitted for the development of the upcoming International Terrestrial Reference Frame 2020 (ITRF2020).

As a reflection upon the entire text, the Afterword returns to the trope of imagined geographies. This it does under three rubrics, namely “alternative realms,” “The rise and fall of the Thirteenth-Century World System,” and “borderless histories.“ As explained, the book offered multiple examples where both cartographic and chorographic representations reflected the world as seen through the prism of civilizations. In an age before imperialism and imperial geography, geographic space was a far more fluid concept in line with civilizational and religious verities. No one owned the borderlands - often badlands - and no one but pirates owned the seas. But in the age of imperialism, matched by the science of trigonometric measurement, geodesic survey and the setting down of fixed coordinates and boundaries, geography appeared as its handmaiden. As suggested, if there is a serious takeaway from the discussion, then we should acknowledge that the weight of the past sets the context for the present. Moreover, as this book has dared to suggest, from a classical age civilizations have indulged in imagining their worlds in highly creative ways.