Geodetic Positioning Research Articles

GNSS-A Trajectory Optimization and Its Rose-Curve Solution Regarding Acoustic Delay Parameter Identification

Global Navigation Satellite System (GNSS)-Acoustic (GNSS-A) trajectory design is vitally important for precise seafloor geodetic positioning. However, GNSS-A trajectory optimization based on an ordinary GNSS-A observation model suffers a major setback due to a lack of consideration for the spatio-temporal variations of sound speed. We propose a GNSS-A trajectory optimization criterion based on a GNSS-A observation model appended with acoustic delay parameters characterizing the sound speed variations. In addition, we put the problem into a continuous function space to obtain a concise curve solution that is free from the sampling interval of observations. Particularly, a family of rose trajectory solutions is derived for developing unmanned GNSS-A systems. It shows that the optimal size of the rose trajectory is 2.8 times the water depth for the ordinary observation model, but the optimal size becomes at least 8.3 times the water depth for the observation model with the acoustic delay parameters. The more the parameters used to characterize the time-varying nature of the acoustic delay are adopted, the larger the trajectory size is needed. The proposed trade-off strategy between the cost increase and the precision benefit is recommended to shrink the trajectory size to reduce the ship-time cost and avoid the limitation of signal propagation. The proposed results are verified through the simulation tests and actual measurements. It shows that we should adopt the derived optimal trajectory to ensure the geometric precision of the acoustic delay parameters. The size of the GNSS-A trajectory adopted conventionally is far from the optimal size for inverting the sound speed field structure.

Local Gravity and Geoid Improvements around the Gavdos Satellite Altimetry Cal/Val Site

The isle of Gavdos, and its wider area, is one of the few places worldwide where the calibration and validation of altimetric satellites has been carried out during the last, more than, two decades using dedicated techniques at sea and on land. The sea-surface calibration employed for the determination of the bias in the satellite altimeter’s sea-surface height relies on the use of a gravimetric geoid in collocation with data from tide gauges, permanent global navigation satellite system (GNSS) receivers, as well as meteorological and oceanographic sensors. Hence, a high-accuracy and high-resolution gravimetric geoid model in the vicinity of Gavdos and its surrounding area is of vital importance. The existence of such a geoid model resides in the availability of reliable, in terms of accuracy, and dense, in terms of spatial resolution, gravity data. The isle of Gavdos presents varying topographic characteristics with heights larger than 400 m within small spatial distances of ~7 km. The small size of the island and the significant bathymetric variations in its surrounding marine regions make the determination of the gravity field and the geoid a challenging task. Given the above, the objective of the present work was two-fold. First, to collect new land gravity data over the isle of Gavdos in order to complete the existing database and cover parts of the island where voids existed. Relative gravity campaigns have been designed to cover as homogenously as possible the entire island of Gavdos and especially areas where the topographic gradient is large. The second focus was on the determination of a high-resolution, 1′×1′, and high-accuracy gravimetric geoid for the wider Gavdos area, which will support activities on the determination of the absolute altimetric bias. The relative gravity campaigns have been designed and carried out employing a CG5 relative gravity meter along with geodetic grade GNSS receivers to determine the geodetic position of the acquired observations. Geoid determination has been based on the newly acquired and historical gravity data, GNSS/Leveling observations, and topography and bathymetry databases for the region. The modeling was based on the well-known remove–compute–restore (RCR) method, employing least-squares collocation (LSC) and fast Fourier transform (FFT) methods for the evaluation of the Stokes’ integral. Modeling of the long wavelength contribution has been based on EIGEN6c4 and XGM2019e global geopotential models (GGMs), while for the contribution of the topography, the residual terrain model correction has been employed using both the classical, space domain, and spectral approaches. From the results achieved, the final geoid model accuracy reached the ±1–3 cm level, while in terms of the absolute differences to the GNSS/Leveling data per baseline length, 28.4% of the differences were below the 1cmSij [km] level and 55.2% below the 2cmSij [km]. The latter improved drastically to 52.8% and 81.1%, respectively, after deterministic fit to GNSS/Leveling data, while in terms of the relative differences, the final geoid reaches relative uncertainties of 11.58 ppm (±1.2 cm) for baselines as short as 0–10 km, which improves to 10.63 ppm (±1.1 cm) after the fit.

National Geospatial Policy: present status and a way forward towards unambiguous and consistent geodetic positioning in India

National Geospatial Policy: present status and a way forward towards unambiguous and consistent geodetic positioning in India

Centimeter-level-precision seafloor geodetic positioning model with self-structured empirical sound speed profile

In-field Sound Speed Profile (SSP) measurement is still indispensable for achieving centimeter-level-precision Global Navigation Satellite System (GNSS)-Acoustic (GNSS-A) positioning in current state of the art. However, in-field SSP measurement on the one hand causes a huge cost and on the other hand prevents GNSS-A from global seafloor geodesy especially for real-time applications. We propose an Empirical Sound Speed Profile (ESSP) model with three unknown temperature parameters jointly estimated with the seafloor geodetic station coordinates, which is called the 1st-level optimization. Furthermore, regarding the sound speed variations of ESSP we propose a so-called 2nd-level optimization to achieve the centimeter-level-precision positioning for monitoring the seafloor tectonic movement. Long-term seafloor geodetic data analysis shows that, the proposed two-level optimization approach can achieve almost the same positioning result with that based on the in-field SSP. The influence of substituting the in-field SSP with ESSP on the horizontal coordinates is less than 3 mm, while that on the vertical coordinate is only 2–3 cm in the standard deviation sense.

An ERA5 tropospheric parameters-augmented approach for improving GNSS precise point positioning

Precise Point Positioning (PPP) technology has developed into a potent instrument for geodetic positioning, ionospheric modeling, tropospheric atmospheric parameter detection, and seismic monitoring. As atmospheric reanalysis data products' accuracy and spatiotemporal resolution have improved recently, it has become important to apply these products to obtain high-accuracy tropospheric delay parameters, like zenith tropospheric delay (ZTD) and tropospheric horizontal gradient. These tropospheric delay parameters can be applied to PPP to reduce the convergence time and to increase the accuracy in the vertical direction of the position. The European Centre for Medium-Range Weather Forecasts Reanalysis 5 (ERA5) atmospheric reanalysis data is the latest product with a high spatiotemporal resolution released by the European Center for Medium-Range Weather Forecasts (ECMWF). Only a few researches have evaluated the application of ERA5 data to Global Navigation Satellite System (GNSS) PPP. Therefore, this study compared and validated the ZTD products derived from ERA5 data using ZTD values provided by 290 global International GNSS Service (IGS) stations for 2016–2017. The results indicated a stable performance for ZTD, with annual average bias and RMS values of 0.23 cm and 1.09 cm, respectively. Further, GNSS observations for one week in each of the four seasons (spring: DOY 92–98; summer: DOY 199–205; autumn: DOY 275–281; and winter: DOY 22–28) from 34 multi-GNSS experiments (MGEX) stations distributed globally in 2016 were considered to evaluate the performance of ERA5-derived tropospheric delay products in GNSS PPP. The performance of ERA5-enhanced PPP was compared with that of the two standard GNSS PPP schemes (without estimated tropospheric horizontal gradient and with estimated tropospheric horizontal gradient). The results demonstrated that ERA5-enhanced GNSS PPP showed no significant improvement in the convergence times in both the Eastern (E) and Northern (N) directions, while the average convergence time over four weeks in the vertical (U) direction improved by 53.3% and 52.7%, respectively (in the case of pngm station). The average convergence times for each week in the U direction of the northern and southern hemisphere stations indicated a decrease of 16.3%, 12.6%, 9.6%, and 9.1%, and 16.9%, 9.6%, 8.9%, and 14.5%, respectively. Regarding positioning accuracy, ERA5-enhanced PPP showed an improvement of 13.3% and 16.2% over the two standard PPP schemes in the U direction, respectively. No significant improvement in the positioning performance was observed in both the E and N directions. Thus, this study demonstrated the potential application of the ERA5 tropospheric parameters-augmented approach to Beidou navigation and positioning.

Rational methods of geodetic control of technogenic consequences of the development of oil and gas fields

The methods of controlling the consequences of the influence of manmade geomechanical processes caused by the extraction of hydrocarbons from the subsurface in the fields under development are considered. The possibilities of methods from the standpoint of separate determination of spatial and temporal quantitative parameters characterizing the deformed state of the skeletons of reservoirs and host rocks, the entire thickness of the rock mass above the deposit in an uneven field of compressive stresses and deformations of the earth’s surface are shown. The inconsistency of methods of classical repeated leveling, geodetic positioning and traditional radar interferometry in connection with the low level of representativeness of their results is noted. scientific novelty lies in the development of ways to improve the effectiveness of the method of radar satellite interferometry. As a result, the conditions for the effective use of radar satellite interferometry on the basis of a network of stationary points which coincide with the points of the leveling network method of spot geodetic sounding of deformation processes in the oil and gas fields under development have been determined and characterized.

A New Approach for Improving GNSS Geodetic Position by Reducing Residual Tropospheric Error (RTE) Based on Surface Meteorological Data

Positioning error components related to tropospheric and ionospheric delays are caused by the atmosphere in positioning determined by global navigation satellite systems (GNSS). Depending on the user’s requirements, the position error caused by tropospheric influences, which is commonly referred to as zenith tropospheric delay (ZTD), must be estimated during position determination or determined later by external tropospheric corrections. In this study, a new approach was adopted based on the reduction of residual tropospheric error (RTE), i.e., the unmodeled part of the tropospheric error that remains included in the total geodetic position error, along with other unmodeled systematic and random errors. The study was performed based on Global Navigation Satellite System (GLONASS) positioning solutions and accompanying meteorological parameters in a defined and harmonized temporal-spatial frame of three locations in the Republic of Croatia. A multidisciplinary approach-based analysis from a navigational science aspect was applied. The residual amount of satellite positioning signal tropospheric delay was quantitatively reduced by employing statistical analysis methods. The result of statistical regression is a model which correlates surface meteorological parameters with RTE. Considering the input data, the model has a regional character, and it is based on the Saastamoinen model of zenith tropospheric delay. The verification results show that the model reduces the RTE and thus increases the geodetic accuracy of the observed GNSS stations (with horizontal components of position accuracy of up to 3.8% and vertical components of position of up to 4.37%, respectively). To obtain these results, the Root Mean Square Error (RMSE) was used as the fundamental parameter for position accuracy evaluation. Although developed based on GLONASS data, the proposed model also shows a considerable degree of success in the verification of geodetic positions based on Global Positioning System (GPS). The purpose of the research, and one of its scientific contributions, is that the proposed method can be used to quantitatively monitor the dynamics of changes in deviations of X, Y, and Z coordinate values along coordinate axes. The results show that there is a distinct interdependence of the dynamics of Y and Z coordinate changes (with almost mirror symmetry), which has not been investigated and published so far. The resultant position of the coordinates is created by deviations of the coordinates along the Y and Z axes—in the vertical plane of space, the deviations of the coordinate X (horizontal plane) are mostly uniform and independent of deviations along the Y and Z axes. The proposed model shows the realized state of the statistical position equilibrium of the selected GNSS stations which were observed using RTE values. Although of regional character, the model is suitable for application in larger areas with similar climatological profiles and for users who do not require a maximum level of geodetic accuracy achieved by using Satellite-Based Augmentation Systems (SBAS) or other more advanced, time-consuming, and equipment-consuming positioning techniques.

Tree position estimation from TLS data using hough transform and robust least-squares circle fitting

Forest management and planning require information regarding the current state of the forest. Remote sensing techniques allow to obtain geospatial data, also for the forestry sector. As one of the remote-sensed technologies datasets, Terrestrial Laser Scanning data is widely used to derive detailed information about tree and forest stand parameters. This article presents the combination of circular Hough transform, denoising procedure, and robust least-square circle fitting method to extract stem positions from Terrestrial Laser Scanning data. In the proposed approach, initial tree stems position was detected with circular Hough transform. Then, obtained results were denoised to exclude most non-tree trunk points and analyze three-dimensional data from laser scanning to find exact circular tree stems with a robust least-square circle fitting method. The developed algorithm is effective in obtaining the trees’ geodetic positions from laser scanning data. The results generated in this study can be used as basics for further automatic determination of tree characteristics, such as tree species, height, or crown range. In this study, 94.8% tree stems delineation was generated with a mean accuracy of 87.2%, 1.64 cm of root mean square error for stem position, and 1.15 cm for tree radius measured at ground level. The process conducted in this research can be used to detect other circle-shaped objects, such as lamps or power towers, for which obtaining dense Terrestrial Laser Scanning data is available. The detected positions of these objects can power the geographic information systems or thematic industry systems, where it is necessary to determine the geodetic object position results from legal regulations.

Quality of the deflection of the vertical obtained from global geopotential models in horizontal geodetic positioning

Quality of the deflection of the vertical obtained from global geopotential models in horizontal geodetic positioning

Comparative accuracy assessment of the Bowring, Chord and Power series models for direct and indirect determination of geodetic coordinates

The computation of geodetic coordinates is the basis of geodetic surveying and foundation to modern techniques for geodetic network analyses and design of integrated survey schemes for monitoring and detecting structural deformations. The positional accuracy achievable by Direct and Indirect models of geodetic position determination depends on the varying lengths, azimuths and latitude of the first point of the network of stations. Existing knowledge gaps preclude a comprehensive understanding of the relative accuracies of these methods. Therefore, the aim of this study is to determine the achievable accuracies of three models (Bowring, Chord and Power Series) for direct and indirect position determination vis-a-vis the network configuration. The data comprised of 33 controls in the D-Chain geodetic network located in North-Central Nigeria, with a range of network of lines between 15.530km and 113.254km. Various attributes of the network such as azimuth, angle, distance, and coordinates were computed to a high accuracy and precision using a program written in the Matlab software environment. The results of the direct and indirect computation were summarised using descriptive statistics. Also, the accuracies of the computed coordinates were assessed by comparisons with the provisional (initial) coordinates of the controls. In the analysis of coordinate differences, the positional root mean square error (RMSE) for each of the three models in decreasing order of accuracies are: 4.572639341′′ (Chord), 4.601685022′′ (Power Series) and 4.601701034′′ (Bowring). The positional mean absolute deviation (MAD) for the three models in decreasing order of accuracies are 3.788841258′′ (Chord), 3.813184934′′ (Power Series) and 3.813198679′′ (Bowring) and this agrees with the RMSE trend for the network. This study has shown that the D-chain network configuration favours the use of Chord model for position determination based on the adopted configuration.

Ground Displacements Estimation through GNSS and Geometric Leveling: A Geological Interpretation of the 2016–2017 Seismic Sequence in Central Italy

Between August 2016 and January 2017, a very energetic seismic sequence induced substantial horizontal and vertical ground displacements in the Central Italian Apennines. After this event, the Italian Military Geographical Institute (IGM), owner and manager of the Italian geodetic networks, executed several topographic surveys in the earthquake area in order to update the coordinates of vertices belonging to the IGM95 geodetic network. The measurements began in the areas where the most significant deformation occurred: the localities of Amatrice and Accumoli, in the Rieti Province, and the area covering Norcia and Castelluccio, in the Province of Perugia, all the way to Visso (Province of Macerata). The activities described in this paper focused on the updated measurement of the IGM95 network points through GNSS and the restatement of extensive parts of the high precision geometric lines that were levelled until reaching stable zones. This unprecedented amount of data was used for a new geological interpretation of the seismic sequence, which confirms some of the previous hypotheses of the scientific community. In the analyzed territory, the latest estimate of the geodetic position points has allowed for an accurate determination of the east and the north and of the altitude components of the displacement induced by the earthquake through a comparison with the previous coordinates. The results confirm that the seismicity was induced by normal faults system activity. Still, they also indicate the possible influence of a significant regional thrust that conditioned the propagation of the seismicity in the area. The obtained maps of the displacement are coherent with other geodetic works and with a rupture propagation driven by the documented geotectonic structure.

A novel design concept of cost-effective permanent rail-track monitoring system

This paper presents a novel design concept of low-cost permanent monitoring system for rail-track problems. The introduced design is theoretically overcome the currant in-use designs in terms of providing permanent accurate observations for detecting rail-track irregularities for all railway network during service time using low-cost integrated sensors. The paper investigates the rail-track common irregularities by identifying the issues, presenting challenges, and highlighting the limitations of currently in-use rail-track monitoring techniques. Then, the potential of using cost-effective sensors and intelligent techniques for detecting the rail-track geometric parameters and rail irregularities is theoretically studied. This includes using low-cost GPS, MEMS-INS & high frequency single-point and multi-spot laser distance sensors for detecting rail surface cracks, fractures, cross-level, wrap, gauge and vertical & horizontal rail alignments. Different levels of GPS/MEMS-INS integration are covered, illustrating the advantages of each solution and the optimal utilization in the system. Vision-based monitoring using low-cost HD non-metric digital cameras is also investigated, showing the optimal specifications required for fulfill the system requirements. Data logging and GPS-time-based synchronization method is presented as a part of the design concept of the suggested system. The processing techniques and unit outputs are illustrated in details, showing how each unit works for detecting the rail-track irregularities, providing the geodetic positioning and the vision-based assessing. The main part of the system, which is Automatic Adjusted Wheeled Carrier Frame (AAWCF) is discussed in more details, showing simple and clear different views for all details and integrated sensors. It is recommended to carry out this idea, by building up and evaluating the performance of AAWCF in real railway environments, evaluating the design concept of each unit individually to know the weaknesses of each technique, and then evaluating the whole system in all expected railway cases to find out the advantages and limitations of this design concept.

Determination of the Minimum Safe Distance between a USV and a Hydro-Engineering Structure in a Restricted Water Region Sounding

Bathymetric surveys performed using small, unmanned vessels are increasingly used in coastal areas and regions difficult to access by hydrographic motorboats. Their geometric dimensions, manoeuvring parameters, low labour intensity, and costs of survey execution have allowed the unmanned survey vessel (USV) to be a commonly recognised surveying platform. It is equipped with a navigation system for positioning, maintaining a course or survey line, determining spatial orientation, and measuring depths. The operation zone of the global navigation satellite system (GNSS) in coastal water regions enables geodetic positioning in land-based surveys and of moving objects, also including, for example, a sounding vessel. Under difficult observational conditions, the positioning is limited by the obscuration of the upper hemisphere, i.e., the visibility of satellites and the reflection from high field buildings. This poses a threat to a small vessel operating at a very short distance from a hydro-engineering structure. Based on a study performed in a marina, the article presents the determination of the minimum safe distance of the planned survey line to the quay in terms of the USV’s dimensions under good sounding conditions. These include low and constant velocity and good observational conditions for a GNSS receiver. The analysis was conducted on survey lines perpendicular to the quay, which was approached twice at distances of 1–5 m, with a 0.5 m interval. A 1 m distance between the end of the survey line and the quay has been determined for the safety of USV’s navigation and continuity of geospatial data collection during bathymetric surveys.

Improved Seafloor Geodetic Positioning via Sound Velocity Correction Based on the Precise Round-Trip Acoustic Positioning Model

Seafloor geodetic positioning is crucial for evaluating the marine geodetic network and monitoring various marine activities. We propose a sound velocity correction method based on the precise round-trip acoustic positioning model to improve the accuracy of seafloor geodetic positioning. The proposed method models the sound velocity error related to sound velocity profile (SVP) deviation and time-varying error and reduces the propagation error of the acoustic rays in the ocean. The SVP deviation and seafloor position parameters are resolved simultaneously by the Bayesian estimation using the round-trip acoustic travel time. The time-varying errors of SVP are corrected through symbolic regression using multi-gene genetic programming (MGGP) even without any accurate pre-specified mathematical form of marine environmental variations. The results from sea trial conducted in the South China Sea at a depth of 3000 m demonstrate that the developed method compensates for the sound velocity errors and improves the positioning precision of the seafloor transponder, with the position difference between different data sets better than 46.12 cm, the standard deviation of acoustic time residuals better than 0.15 ms, and the square root of the variance of the position better than 0.41 cm.

Calculation Method to Determine the Zone of Underground Damage in Water Supply System Pipelines

The application of water conservation and leakage prevention at all stages of water delivery to the consumer can provide the rational and efficient use of water resources. The long length of heating and water supply networks, their high degree of wear and tear lead to the appearance of leaks. The paper describes research results on developing the calculating method for detecting underground damage zones in the water supply system pipeline. The basis for this study is the main difference between the regulated water intake for the needs of the water user and the uncontrolled loss of water from a damaged pipeline. The water user takes water from the water supply system in accordance with the designed parameters, and such a water intake will not cause unusual changes in the water pressure in the pipeline. The volume of water lost through pipeline damage will always be proportional to the sharp water pressure change in the pipeline. We developed the mathematical model to substantiate the detecting method of the pipeline damage zone. The model considers the operational characteristics of pipelines to the full extend: head and water flow, the degree of deterioration of water conduit, the geodetic position of water intake points. The mathematical model, confirmed earlier by dozens of independent experiments, made it possible to replace expensive hydraulic experiments and prove the possibility of using the developed method of detecting hidden damages of water conduits by extrapolating the measured piezometric heads. The proposed software system for calculating the underground pipeline damage zone in water supply systems makes it possible to determine the pipeline damage hidden zones based on solving the hydraulic problem for a linear pipeline and studying hydraulic processes. We can use the created optimization model as a proven analog of a physical hydraulic stand in hydraulic studies in the simulation mode.

Resilient observation models for seafloor geodetic positioning

Resilient observation models for seafloor geodetic positioning

Geodetic Seafloor Positioning Using an Unmanned Surface Vehicle—Contribution of Direction-of-Arrival Observations

Precise underwater geodetic positioning remains a challenge. Measurements combining surface positioning (GNSS) with underwater acoustic positioning are generally performed from research vessels. Here we tested an alternative approach using a small Unmanned Surface Vehicle (USV) with a compact GNSS/Acoustic experimental set-up, easier to deploy, and more cost-effective. The positioning system included a GNSS receiver directly mounted above an Ultra Short Baseline (USBL) module integrated with an inertial system (INS) to correct for the USV motions. Different acquisition protocols, including box-in circles around transponders and two static positions of the USV, were tested. The experiment conducted in the shallow waters (40 m) of the Bay of Brest, France, provided a data set to derive the coordinates of individual transponders from two-way-travel times, and direction of arrival (DOA) of acoustic rays from the transponders to the USV. Using a least-squares inversion, we show that DOAs improve single transponder positioning both in box-in and static acquisitions. From a series of short positioning sessions (20 min) over 2 days, we achieved a repeatability of ~5 cm in the locations of the transponders. Post-processing of the GNSS data also significantly improved the two-way-travel times residuals compared to the real-time solution.

THE INFLUENCE OF THE DEFLECTION OF THE VERTICAL ON GEODETIC SURVEYS IN BRAZIL

The densification of geodetic surveys using classical positioning techniques such as total stations may be necessary due to the quality of Global Navigation Satellite System (GNSS) positioning in urban canyons. However, the correction of distances and angles due to the deflection of the vertical (DV) is usually neglected in commercial softwares and internal software of total stations. Given that context, this research seeks to estimate the influence of DV on the horizontal geodetic positioning with total station in the Brazilian territory. Secondarily, it seeks to demonstrate the practical application of DV in the densification of geodetic networks. It is important to note that land surveys in Brazil must be connected to a geodetic network; therefore, the neglect of DV may degrade the positional quality of geodetic surveys. Results obtained indicate differences in horizontal geodetic positions of up to 45 ppm. Considering the desired positional quality of the geodetic network, such values demonstrate the importance of a proper correction for the DV.

ГЕОДЕЗІЯ, КАРТОГРАФІЯ І АЕРОФОТОЗНІМАННЯ

Aim. Determination of the elements of external spatial orientation of the surveying systems at the moment of image acquisition is the fundamental task in photogrammetry. Principally, this problem is solving in two ways. The first way is direct positioning and measuring of directions of camera optical axis in the geodetic space with the help of GNSS/INS equipment. The second way is the analytical solution of the problem using a set of reference information (often such information is a set of ground control points whose geodetic positions are known with sufficient accuracy and which are reliably recognised on aerial images of the photogrammetric block). The authors consider the task of providing reference and control information using the second approach, which has a number of advantages in terms of reliability and accuracy of determining the unknown image exterior orientation parameters. It is proposed to obtain additional images of ground control points by the method of their auxiliary aerial photography using an unmanned aerial vehicle (UAV) on a larger scale compared to the scale of the images of the photogrammetric block. The aim of the presented work is the implementation of the method of creating reference points and experimental confirmation of its effectiveness for photogrammetric processing. Methods and results. For the entire realization of the potential of the analytical way to determine the elements of external orientation of images, it is necessary to have a certain number of ground control points (GCP) and to keep the defined scheme of their location on the photogrammetric block. As the main source of input data authors use UAV aerial images of the terrain, which are obtained separately from the block of aerial survey, and have a better geometric resolution and which clearly depict the control reference points. Application of such auxiliary images gives the possibility of automated transferring of the position of ground control point into images of the main photogrammetric block. In our interpretation, these images of ground control points and their surroundings on the ground are called "control reference images". The basis of the work is to develop a method for obtaining the auxiliary control reference images and transferring of position of GCP depicted on them into aerial or space images of terrain by means of computer stereo matching. To achieve this goal, we have developed a processing method for the creation of control reference images of aerial image or a series of auxiliary multi-scale aerial images obtained by a drone from different heights above the reference point. The operator identifies and measures the GCP once on the auxiliary aerial image of the highest resolution. Then there is an automatic stereo matching of the control reference image in the whole series of auxiliary images in succession with a decrease in the resolution and, ultimately, directly with the aerial images of photogrammetric block. On this stage there are no recognition/cursor targeting by the human operator, and therefore there are no discrepancies, errors or mistakes related to it. In addition, if to apply fairly large size of control reference images, the proposed method can be used on a low-texture terrain, and therefore deal in many cases without the physical marking of points measured by GNSS method. And this is a way to simplify and reduce the cost of photogrammetric technology. The action of the developed method has been verified experimentally to provide the control reference information of the block of archival aerial images of the low-texture terrain. The results of the experimental approbation of the proposed method give grounds to assert that the method makes it possible to perform geodetic reference of photogrammetric projects more efficiently due to the refusal of the physical marking of the area before aerial survey. The proposed method can also be used to obtain the information for checking the quality of photogrammetric survey for provision of check points. The authors argue that the use of additional equipment - UAV of semi-professional class to obtain control reference images is economically feasible. Scientific novelty and practical relevance. The results of approbation of the "control reference image" method with obtaining stereo pairs of aerial images with vertical placement of the base are presented for the first time. There was implemented the study of the properties of such stereo pairs of aerial images to obtain images of reference points. The effectiveness of including reference images in the main block of the digital aerial triangulation network created on UAV’s images is shown.

English

Vertical and horizontal motion of the solid earth surface due to geological and geodynamical phenomena are generally consequences of terrain deformation. Variations as a result of the deformation affect structures, particularly large storage facilities that are steel and/or concrete in nature. The criticality of these phenomena underscores the need to carryout regular measurements and monitoring of its effect in all dimension. Over the years, methods and instrumentation for subsidence monitoring has evolved from the conventional to the recently high definition surveying approach with an increasing need to detect and analyse deformation changes with clarity at any given time. The aim of this work was to appraise the high definition surveying approaches in subsidence dynamics of crude oil storage facilities. Classical instrumentations and the terrestrial laser scanning equipment were deployed based on the principles of geodetic positioning and mapping for overlity, verticality and radial displacement parameters determination using the two approaches. This paper will provide spatial information in terms of point clouds, 2D and 3D models, vertical and radial displacement of the crude oil storage facility. The work will further demonstrate the optimal capability of high definition surveying approach in our quest to constantly manage the complexities associated with subsidence. Several crude oil storage facilities in addition to other private storage facilities all over the country, require a policy to ensure regular monitoring and analysis of these facilities especially with the trend of earth tremors being experienced in parts of the country.   Key words: Subsidence, high definition surveying, radial displacement, crude oil facility, geodetic positioning.