Precise Geodetic Measurements Research Articles

The contributions of space geodesy to the construction of sustainable cities in Africa and around the world

The accelerate urbanisation African cities caused by the massive rural exodus contributed to the demographic boom of these cities. Our cities barely breathe. The swamps of yesterday have become the habitats of today, the marine areas become a refuge by excellence for families newly arrived in the city. This is the birth of precarious neighborhoods with growing land insecurity. The disappearance of marine and coastal biodiversity, the increase in pollution in all its forms; this is where space geodesy comes in. Recognized as one of the great revolutions of Navigation. Space geodesy has made available to territories and continents including the oceans a set of techniques that in their applications participate in the construction and management of sustainable cities in Africa and in the world; it participates through its fields of application in atmospheric monitoring, marine environment monitoring, territorial, climatological to ensure a better life on land, underground, in water and under water. These techniques and application are an urban decision support for the construction and management of sustainable cities; precise geodetic measurements make it possible to assess topography, identify flood zones, with facilitates the installation of resilient infrastructure.

METHOD FOR BUILDING A WORKING GEODETIC NETWORK OF REFLECTIVE MARKS FOR CONSTRUCTION NEEDS

The work in the implementation of construction works for large production buildings, residential complexes, airports, sports complexes, examination of deformations and many other activities that require precise geodetic measurements can be optimized during and quality through the creation and use of geodetic reflective marks. The article discusses how to stabilize and measure the working base and part of the processing theory.

The Influence of Pillar Displacements on Geodetic Measurements

This paper deals with the effects that displacements of the measuring pillar have on precise geodetic measurements. The changes in the position of the control points on the object or its surroundings can only be determined with well stabilized and stable reference points. These points are usually stabilized with measuring pillars which are not always constructed in an optimal manner. If they are placed in a dark tube with a high absorption factor, solar heating on one side of the pillar can cause the pillar to deflect considerably due to the temperature difference on the two sides of the pillar. This paper presents the influence of such a displacement, if the pillar is a survey point, orientation point, or control point. We show that even small displacement of the survey point can have important influence on all measurements and that the error in some cases significantly increases, e.g., if the standard deviations of the coordinates of the survey point are 1 mm and their covariance is assumed to be zero, the standard deviation of the distance between measured and exact position of the control point exceeds the value of 2.2 mm.

Preliminary Estimation and Validation of Polar Motion Excitation from Different Types of the GRACE and GRACE Follow-On Missions Data

The Gravity Recovery and Climate Experiment (GRACE) mission has provided global observations of temporal variations in the gravity field resulting from mass redistribution at the surface and within the Earth for the period 2002–2017. Although GRACE satellites are not able to realistically detect the second zonal parameter (ΔC20) of geopotential associated with the flattening of the Earth, they can accurately determine variations in degree-2 order-1 (ΔC21, ΔS21) coefficients that are proportional to variations in polar motion. Therefore, GRACE measurements are commonly exploited to interpret polar motion changes due to variations in the global mass redistribution, especially in the continental hydrosphere and cryosphere. Such impacts are usually examined by computing the so-called hydrological polar motion excitation (HAM) and cryospheric polar motion excitation (CAM), often analyzed together as HAM/CAM. The great success of the GRACE mission and the scientific robustness of its data contributed to the launch of its successor, GRACE Follow-On (GRACE-FO), which began in May 2018 and continues to the present. This study presents the first estimates of HAM/CAM computed from GRACE-FO data provided by three data centers: Center for Space Research (CSR), Jet Propulsion Laboratory (JPL), and GeoForschungsZentrum (GFZ). In this paper, the data series is computed using different types of GRACE/GRACE-FO data: ΔC21, ΔS21 coefficients of geopotential, gridded terrestrial water storage anomalies, and mascon solutions. We compare and evaluate different methods of HAM/CAM estimation and examine the compatibility between CSR, JPL, and GFZ data. We also validate different HAM/CAM estimations using precise geodetic measurements and geophysical models. Analysis of data from the first 19 months of GRACE-FO shows that the consistency between GRACE-FO-based HAM/CAM and observed hydrological/cryospheric signals in polar motion is similar to the consistency obtained for the initial period of the GRACE mission, worse than the consistency received for the best GRACE period, and higher than the consistency obtained for the terminal phase of the GRACE mission. In general, the current quality of HAM/CAM from GRACE Follow-On meets expectations. In the following months, after full calibration of the instruments, this accuracy is expected to increase.

Optimization-based Attitude Determination in Geodetic Applications

AbstractA new approach to determining the attitude of a rigid body is suggested, which does not rely on the use of magnetometers. In the framework of this approach, the problem of determining the attitude reduces to solving a minimization problem for a function of three variables (angles characterizing the initial attitude of the body). The proposed method can be employed in precise geodetic measurements carried out with the use of a geodetic pole with a satellite antenna and an IMU installed on its top when, for some reasons, the surveyor cannot position the pole vertically (e.g., near walls or buildings). The use of the traditional approach, which relies on a compass and accelerometers, in this case does not ensure the desired accuracy of the attitude determination due to magnetic disturbances (both external ones and those induced by the receiver) affecting badly compass readings. The discussion is illustrated by results of field experiments.

A functional-precision analysis of the Vertical Comparator for the Calibration of geodetic Levelling Systems

Abstract Precise geodetic levelling measurements use a measuring set consisting of a precise digital level and digital (bar coded) levelling staffs. Such a measuring set enables automation of height measurement records and obtaining the accuracy of double-run levelling at the level of ±0.2 mm/1 km. Under the existing legislation (international and domestic) levels and levelling staffs should be subject to periodic tests followed by the issuing of calibration certificates. Such tests are carried out with the use of comparators and specialized measuring stations. The paper presents the development and construction of such an instrument, namely the Vertical Comparator for the Calibration of Levelling Systems (hereinafter referred to as VCCLS) in the Laboratory of Geodetic Technologies (LGT) of the Wroclaw University of Environmental and Life Sciences (Pol. Uniwersytet Przyrodniczy we Wroclawiu; hereinafter: UPWr). Presented and discussed in the paper are experimental and research works concerning the construction and functionality of the comparator as well as the environment conditions in the LGT. An analysis of the results of testing of two levelling systems: of Leica and Trimble companies allowed for defining the extended uncertainty of the comparator (at the confidence level of 95%), which amounted to ±2.1 μm. The paper demonstrates the advantages of the original Vertical Comparator for the Calibration of geodetic Levelling Systems as compared to design solutions known from the professional literature. Designed and constructed at UPWr, the novel VCCLS is characterized by uncomplicated construction, simple adjustment of its interferometric measuring system and versatility as it can be used to test digital geodetic levelling systems which apply both digital and analog levelling staffs of different manufacturers (including Leica, Trimble, Topcon, Sokkia, Zeiss).

Prograde and Retrograde Terms of Gravimetric Polar Motion Excitation Estimates from the GRACE Monthly Gravity Field Models

From 2002 to 2017, the Gravity Recovery and Climate Experiment (GRACE) mission’s twin satellites measured variations in the mass redistribution of Earth’s superficial fluids, which disturb polar motion (PM). In this study, the PM excitation estimates were computed from two recent releases of GRACE monthly gravity field models, RL05 and RL06, and converted into prograde and retrograde circular terms by applying the complex Fourier transform. This is the first such analysis of circular parts in GRACE-based excitations. The obtained series were validated by comparison with the residuals of observed polar motion excitation (geodetic angular momentum (GAM)–atmospheric angular momentum (AAM)–oceanic angular momentum (OAM) (GAO)) determined from precise geodetic measurements of the pole coordinates. We examined temporal variations of hydrological excitation function series (or hydrological angular momentum, HAM) in four spectral bands: seasonal, non-seasonal, non-seasonal short-term, and non-seasonal long-term. The general conclusions arising from the conducted analyses of prograde and retrograde terms were consistent with the findings from the equatorial components of PM excitation studies drawn in previous research. In particular, we showed that the new GRACE RL06 data increased the consistency between different solutions and improved the agreement between GRACE-based excitation series and reference data. The level of agreement between HAM and GAO was dependent on the oscillation considered and was higher for long-term than short-term variations. For most of the oscillations considered, the highest agreement with GAO was obtained for CSR RL06 and ITSG-Grace2018 solutions. This study revealed that both prograde and retrograde circular terms of PM excitation can be determined by GRACE with similar levels of accuracy. The findings from this study may help in choosing the most appropriate GRACE solution for PM investigations and can be useful in future improvements to GRACE data processing.

Determining and Evaluating the Hydrological Signal in Polar Motion Excitation from Gravity Field Models Obtained from Kinematic Orbits of LEO Satellites

This study evaluates the gravity field solutions based on high-low satellite-to-satellite tracking (hl-SST) of low-Earth-orbit (LEO) satellites: GRACE, Swarm, TerraSAR-X, TanDEM-X, MetOp-A, MetOp-B, and Jason 2, by converting them into hydrological polar motion excitation functions (or hydrological angular momentum (HAM)). The resulting HAM series are compared with the residuals of observed polar motion excitation (geodetic residuals, GAO) derived from precise geodetic measurements, and the HAM obtained from the GRACE ITSG 2018 solution. The findings indicate a large impact of orbital altitude and inclination on the accuracy of derived HAM. The HAM series obtained from Swarm data are found to be the most consistent with GAO. Visible differences are found in HAM obtained from GRACE and Swarm orbits and provided by different processing centres. The main reasons for such differences are likely to be different processing approaches and background models. The findings of this study provide important information on alternative data sets that may be used to provide continuous polar motion excitation observations, of which the Swarm solution provided by the Astronomical Institute, Czech Academy of Sciences, is the most accurate. However, further analysis is needed to determine which processing algorithms are most appropriate to obtain the best correspondence with GAO.

Months‐Long Subduction Slow Slip Events Avoid the Stress Shadows of Seismic Asperities

AbstractWith precise geodetic measurements, slow transient fault slip events with durations from days to years have been documented at subduction zones for two decades. Long‐lasting transient events with durations longer than 100 days occur at the downdip edge of seismogenic zones. With such long durations, only a few events have been documented so far. Takagi et al. (2019, https://doi.org/10.1029/2018JB016738) propose a new methodology to detect these events and successfully apply it to the Nankai subduction zone in which they characterize 24 events, including 11 new detections. Combined with other observations from around the Pacific rim, they suggest that the lateral segmentation of long‐lasting slow slip events is controlled by the location of seismic asperities associated with their stress shadows.

Surface strain rate colour map of the Tatra Mountains region (Slovakia) based on GNSS data

AbstractThe surface deformation of the Tatra Mountains region in Western Carpathians can nowadays be studied directly thanks to precise geodetic measurements using the GNSS. The strain or stress tensor field is, however, a rather complex “data structure” difficult to present legibly and with sufficient resolution in the form of a classical map. A novel and promising approach to the solution of this problem is coding the three principal strain or stress values into the three colour channels (red, green, blue) of an RGB colour. In our previous study, the colour depended on the stress tensor shape descriptors. In the current study, the adapted colouring scheme uses a subset of shape descriptors common to stress and strain, which differ only in the scaling factor. In this manner, we generate the colour map of the surface strain rate field, where the colour of each grid point carries the information about the shape of the strain rate tensor at that point. The resulting strain rate colour map can be displayed simultaneously with the map of the faults or elevations and be easily checked for the data or interpolation method errors and incompatibility with the geophysical and geological expectations.

From geophysics to geodetic datum: updating the NZGD2000 deformation model

ABSTRACTThe deformation model is a critical component of New Zealand Geodetic Datum 2000 (NZGD2000), the official reference frame for New Zealand. The model is used to manage the relationship between the NZGD2000 and the global International Terrestrial Reference Frame (ITRF), in which precise geodetic measurements are made. Consequently, the deformation model has a direct impact on NZGD2000 coordinates. With improved knowledge of the secular deformation field and models of significant earthquakes to have affected New Zealand since 2000 now being available, the decision was made to update the deformation model. At the same time, the 14-parameter transformation between ITRFs to be used in New Zealand was officially defined.

Modern trends of geodetic measurements in the underground mine 'Sasa' of lead and zinc ore

This paper gives an overview of development the modern trends of geodetic measurements in the underground mine of lead and zinc ore 'Sasa' in Makedonska Kamenica. The precise geodetic measurements are of crucial importance, especially in the mines with underground exploitation. The precise geodetic data have a very big impact on safety in preparation the underground mine facilities, as well as in every working process in the mine exploitation.

Investigation of snow-firn thickness and ground in the East Antarctica by means of geophysical radar

Results of field investigations of snow-and-firn thickness and ground structures performed with the use of geophysical radar GPR (Ground-Penetrating Radar) are discussed in the paper. Industrial radar GSSI SIR10B (Geophysical Survey Systems, Inc., USA) with «5106» antenna (pulses frequency of 200 MHz) was used. Its mean wavelength is 1.57±0.18 km. The main purpose of this work was to test this new technique for solution of glaciological and geological problems. The works were done during the austral summer season of 2012 – 2013 (58 th Russian Antarctic Expedition) in the Eastern Antarctica and mainly concentrated in the vicinity of the Lake Vostok, between the Russian stations Vostok and Progress (the Larsemann Hills). The GPR sounding was carried out together with precise geodetic measurements. The electromagnetic wave propagation in the snow-firn layer was analyzed using the data on density obtained from the 5G borehole at the Vostok Station. Investigations near the Vostok Station focused on a huge snow ridge or so-called “megadune” located eastward from the station at a distance of 30 km. About 80 km of the GPR cross-sections were collected there. Eight internal layers were traced. They demonstrated wavy forms with amplitudes of about 10 m high which corresponded to the megadunes. Main result of GPR investigations in the Larsemann Hills was our understanding of the snow-firn and ground structures in this region. The GPR data collected on structures of crevasses near Progress-1, shallow glacier near the Progress-3, and ground not far from Progress-2 are also discussed. Methodological recommendations on using the GPR under conditions of the Eastern Antarctica were developed.

Field tests of L1 phase centre variation models of surveying-grade GPS antennas

GNSS antenna electrical phase center variability is a source of errors in precise geodetic measurements, particularly in reference frame maintenance, satellite precise levelling, deformation monitoring, the establishment of geodetic control networks, geodynamic research, etc. It has a considerable influence on the precision and accuracy of the resulting coordinates. Previous research shows that changing the antenna on the monitored point often results in a considerable bias in the derived height coordinate component. In theory, if electrical phase center is sufficiently modeled, antenna changes should have negligible effect on coordinates. We present the analysis of the influence of the GPS antenna models on the resulting marker position. Numerical tests are based on field measurements. The GPS data collected at the test baseline were processed using Bernese GPS Software Version 5.0. The research shows that the IGS and NGS phase center variation models for some types of the surveying (rover) antennas are still imperfect and are contaminated by constant errors, which may exceed even ± 5 mm for horizontal coordinates components and ± 25 mm for vertical ones.

Deformation Measurements of Gabion Walls Using Image Based Modeling

The image based modeling finds use in applications where it is necessary to reconstruct the 3D surface of the observed object with a high level of detail. Previous experiments show relatively high variability of the results depending on the camera type used, the processing software, or the process evaluation. The authors tested the method of SFM (Structure from Motion) to determine the stability of gabion walls. The results of photogrammetric measurements were compared to precise geodetic point measurements.

Estimates of Minor Ocean Tide Loading Displacement and Its Impact on Continuous GPS Coordinate Time Series

The site displacement due to ocean tidal loading is regarded as one of the largest uncertainties in precise geodetic positioning measurements, among which the effect of minor ocean tides (MOT), except for the 11 main tidal constituents, are sometimes neglected in routine precise global positioning system (GPS) data processing. We find that MOT can cause large vertical loading displacements with peak-to-peak variations reaching more than 8 mm at coastal/island stations. The impact of MOT on the 24-hour GPS solution is slightly larger than the magnitude of MOT loading itself, with peak-to-peak displacement variation at about 10 mm for the horizontal and 30 mm for the vertical components. We also find that the vertical velocity of all the selected stations in the Southwest Pacific was reduced by more than 10% after considering the MOT effect, while stations with weighted root mean square reduced data account for 62%, 59%, and 36% for the up, east, and north components respectively, in particular for most coastal/island stations. Furthermore, MOT correction could significantly reduce the annual signal of the global stacked east component, the near fortnightly and the long-term periodic signals in the up component. The power of some anomalous harmonics of 1.04 cycle per year is also decreased to some extent. These results further proved the benefits of MOT correction in precise GPS data processing.

Evaluation of Symmetric Neutral-Atmosphere Mapping Functions Using Ray-Tracing Through Radiosonde Observations

Abstract The aim of this paper is to compare the validity of six recent symmetric mapping functions. The mapping function models the elevation angle dependence of the tropospheric delay. Niell Mapping Function (NMF), Vienna Mapping Function (VMF1), University of New Brunswick- VMF1 (UNB-VMF1) mapping functions, Global Mapping Function (GMF) and Global Pressure and Temperature (GPT2)/GMF are evaluated by using ray tracing through 25 radiosonde stations covering different climatic regions in one year. The ray-traced measurements are regarded as “ground truth”. The ray-tracing approach is performed for diverse elevation angle starting at 5° to 15°. The results for both hydrostatic and non-hydrostatic components of mapping functions support the efficiency of online-mapping functions. The latitudinal dependence of standard deviation for 5° is also demonstrated. Although all the tested mapping functions can provide satisfactory results when used for elevation angles above 15°, for high precision geodetic measurements, it is highly recommended that the online-mapping functions (UNBs and VMF1) be used.The results suggest that UNB models, like VMF have strengths and weaknesses and do not stand out as being consistently better or worse than the VMF1. The GPT2/GMF provided better accuracy than GMF and NMF. Since all of them do not require site specific data; therefore GPT2/GMF can be useful as regards its ease of use.

Great earthquakes on Canada’s west coast: a review This article is one of a series of papers published in this Special Issue on the themeLithoprobe — parameters, processes, and the evolution of a continent. Geological Survey of Canada Contribution 20090196.

The first Lithoprobe transect in 1984 across Vancouver Island had primary objectives to define the structure associated with subduction and constraints on the potential for great thrust earthquakes. The Lithoprobe results and the comprehensive multidisciplinary data collection and analyses that followed provide compelling evidence for past great earthquakes along the Cascadia subduction zone from Vancouver Island to northernmost California, and for present elastic strain build up toward future great events. There is evidence of sudden coastal subsidence up to 2 m and of deep-sea turbidite deposits indicating strong shaking from huge earthquakes at irregular intervals averaging about 500 years, the last in 1700. Precision geodetic measurements define the present buckling of the coastal region, diagnostic of elastic strain accumulation on a locked thrust fault. The landward extent of rupture and, therefore, shaking at coastal cities is constrained by (i) the pattern of elastic strain buildup, (ii) the estimated temperatures on the fault, (iii) the updip limit of episodic tremor and slip (ETS), (iv) the downdip change in reflection character of the thrust, and (v) the magnitude of coastal subsidence in the most recent, 1700, and previous great events. The major earthquakes are very large, M9, rupturing most of the Cascadia margin, but mainly offshore, limiting somewhat the shaking at inland cities but producing large tsunamis. The ETS that occurs at intervals of just over a year appears to involve slow slip on the subduction thrust downdip of the rupture zone that increases stress on the locked zone and may indicate time varying potential for great events.

A review of the GGP network and scientific challenges

The Global Geodynamics Project (GGP) started on July 1, 1997 and is now in its 11th year of operation. It has a relatively small number of stations (24), compared to seismic (GSN) or geodetic (GPS) networks, but it is the only database that is accumulating relative gravity measurements worldwide. As any scientific organization matures, there is a change in the culture of the project and the people involved. To remain viable, it is necessary not only to maintain the original goals, but also to incorporate new ideas and applications on the science involved. The main challenges within GGP are to ensure: (a) that the instruments are properly calibrated, (b) that data is being recorded with the highest accuracy, and with appropriate hydrological instrumentation, and (c) that the flow of data from all recording stations to the ICET database continues as agreed in within the GGP framework. These practical matters are the basis for providing high quality recordings that will extend the usefulness of the network into the future to meet new challenges in geosciences. Several new stations have been brought into operation in the past few years, but the data availability from some of these stations still leaves room for improvement. Nevertheless, the core group of stations established more than 10 years ago has been able to maintain the high standards of the original concept, and much research has been published using network data in areas as diverse as hydrology, polar motion, and Earth’s normal modes. GGP will also participate in some of the scientific tasks of the Global Geodetic Observing System program, at least initially by providing relative gravity measurements for collocation with other high precision geodetic measurements.

Ocean tidal loading displacement around Korean Peninsula

Accuracy of various space geodetic techniques such as GPS and VLBI has been recently improved and the periodic deformation of the Earth due to lunar and solar tides, and the tide induced tidal loading on various parts of the Earth must be corrected. This problem becomes more serious in the areas where the tidal loading becomes enhanced due to coastal and topographic amplifications. Bay of Fundy (Canada) and Kyunggi Bay (Korea) are two such areas. In order to minmize the contamination of high precision geodetic measurements by tide related deformation, numerical representation of tides and tide induced deformation, are investigated and estimated in selected areas around the Korean peninsula. The radial component of displacements caused by the main (M2) semidiurnal tidal constituent was computed using a grid cell of 5 arc minute. The maximum radial displacement due to M2 semidiurnal tide in the Kyunggi Bay, Korea, reaches up to 1.8 cm.