sensors-logo

Journal Browser

Journal Browser

Monitoring and Understanding the Earth’s Change by Geodetic Methods

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Remote Sensors".

Deadline for manuscript submissions: closed (15 June 2022) | Viewed by 27192

Special Issue Editors

Departamento de Matemática Aplicada, University of Alicante, 03690 Alicante, Spain
Interests: space geodesy; satellite dynamics; earth rotation theory and models; space sciences; Earth sciences; astrometry; numerical methods; celestial mechanics
Special Issues, Collections and Topics in MDPI journals
Departamento de Matemática Aplicada, University of Alicante, 03690 Alicante, Spain
Interests: space geodesy; earth observation; sea level, ocean geostrophy; satellite altimetry; satellite gravimetry
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Contemporary geodetic observations allow measurement of positions, shape, and gravity in the Earth’s system and their time variations with unprecedented accuracy. Besides, all the Earth’s observations are referred to a terrestrial reference frame, which is conventionally realized with data from four main space geodesy techniques: Global Navigation Satellite Systems (GNSS), Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), and Doppler Orbitography and Radio Positioning Integrated by Satellite (DORIS). The same data, coming from sensing quasars to satellites, are used for the consistent realization of the celestial reference frame and determination of the time-varying Earth’s rotation and main dynamical parameters, i.e., center of mass and inertia tensor. Satellite altimetry is crucial for monitoring sea level variations since 1993, whilst the Gravity Recovery and Climate Experiment (GRACE) satellite mission opened a new era in inferring the Earth’s mass redistributions and understanding the water cycle better.

The range of applications is extended when space-based data are analysed jointly with those provided by in situ techniques, leading also to more accurate results. Geodetic methods allow monitoring, getting deeper insight, and developing models of a wide class of processes of the Earth system that interact with the so-called three pillars of modern geodesy, namely geometry, kinematics, and gravity. They provide information of scientific and societal value on various smooth or sudden changes or natural hazards, like ocean and continental water, ice sheets, soil moisture, droughts, denudation, earthquakes, tsunamis, etc.

This Special Issue welcomes contributions addressing:

  • Monitoring of Earth system components from geodetic techniques: VLBI, GNSS, SLR, DORIS, LLR (lunar laser ranging), etc.
  • Monitoring of Earth system components from geodetic satellite observations: Altimetry, gravity field (GRACE and GRACE Follow-On), magnetic field (CHAMP, SWARM), etc.
  • Determination of global Earth parameters and features at non-global scales
  • Current findings, monitoring capabilities, and prospects of geodetic methods for getting further insight into the Earth’s change
  • Impact of reference frames realization, station motion modelling and mathematical procedures of analysis
  • State-of-the-art of well-established geodetic techniques and emerging instruments: laser rings, in situ or onboard geopotential-sensing optical atomic clocks, etc.
  • Related geophysical models

Prof. Dr. José M. Ferrándiz

Dr. Isabel Vigo
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Remote sensing
  • Earth system monitoring
  • geodetic VLBI and GNSS
  • SLR
  • gravity field variations
  • near-surface geophysics
  • geocenter motion
  • reference frames
  • Earth rotation

Published Papers (13 papers)

Order results
Result details
Select all
Export citation of selected articles as:

Research

17 pages, 1737 KiB  
Article
The Short-Term Prediction of Length of Day Using 1D Convolutional Neural Networks (1D CNN)
by Sonia Guessoum, Santiago Belda, Jose M. Ferrandiz, Sadegh Modiri, Shrishail Raut, Sujata Dhar, Robert Heinkelmann and Harald Schuh
Sensors 2022, 22(23), 9517; https://0-doi-org.brum.beds.ac.uk/10.3390/s22239517 - 06 Dec 2022
Cited by 7 | Viewed by 2618
Abstract
Accurate Earth orientation parameter (EOP) predictions are needed for many applications, e.g., for the tracking and navigation of interplanetary spacecraft missions. One of the most difficult parameters to forecast is the length of day (LOD), which represents the variation in the Earth’s rotation [...] Read more.
Accurate Earth orientation parameter (EOP) predictions are needed for many applications, e.g., for the tracking and navigation of interplanetary spacecraft missions. One of the most difficult parameters to forecast is the length of day (LOD), which represents the variation in the Earth’s rotation rate since it is primarily affected by the torques associated with changes in atmospheric circulation. In this study, a new-generation time-series prediction algorithm is developed. The one-dimensional convolutional neural network (1D CNN), which is one of the deep learning methods, is introduced to model and predict the LOD using the IERS EOP 14 C04 and axial Z component of the atmospheric angular momentum (AAM), which was taken from the German Research Centre for Geosciences (GFZ) since it is strongly correlated with the LOD changes. The prediction procedure operates as follows: first, we detrend the LOD and Z-component series using the LS method, then, we obtain the residual series of each one to be used in the 1D CNN prediction algorithm. Finally, we analyze the results before and after introducing the AAM function. The results prove the potential of the proposed method as an optimal algorithm to successfully reconstruct and predict the LOD for up to 7 days. Full article
(This article belongs to the Special Issue Monitoring and Understanding the Earth’s Change by Geodetic Methods)
Show Figures

Figure 1

10 pages, 4541 KiB  
Communication
Detection of a New Large Free Core Nutation Phase Jump
by Zinovy Malkin , Santiago Belda and Sadegh Modiri 
Sensors 2022, 22(16), 5960; https://0-doi-org.brum.beds.ac.uk/10.3390/s22165960 - 09 Aug 2022
Cited by 1 | Viewed by 1221
Abstract
We announce the detection of a new large jump in the phase of the free core nutation (FCN). This is only the second such large FCN phase jump in more than thirty years of FCN monitoring by means of a very long baseline [...] Read more.
We announce the detection of a new large jump in the phase of the free core nutation (FCN). This is only the second such large FCN phase jump in more than thirty years of FCN monitoring by means of a very long baseline interferometry (VLBI) technique. The new event was revealed and confirmed by analyzing two FCN models derived from a long-time series of VLBI observations. The jump started in 2021 and is expected to last until the late fall of 2022. The amplitude of the phase jump is expected to be approximately 3 rad, which is as much as 1.5 times larger than the first phase jump in 1999–2000. A connection of the new FCN phase jump with the recent geomagnetic jerk started in 2020 is suggested. Full article
(This article belongs to the Special Issue Monitoring and Understanding the Earth’s Change by Geodetic Methods)
Show Figures

Figure 1

9 pages, 286 KiB  
Article
The Accuracy Assessment of the PREM and AK135-F Radial Density Models
by Robert Tenzer, Yuting Ji and Wenjin Chen
Sensors 2022, 22(11), 4180; https://0-doi-org.brum.beds.ac.uk/10.3390/s22114180 - 31 May 2022
Viewed by 1453
Abstract
The Earth’s synthetic density and gravitational models can be used to validate numerical methods for global (or large-scale) gravimetric forward and inverse modelling formulated either in the spatial or spectral domains. The Preliminary Reference Earth Model (PREM) density parameters can be adopted as [...] Read more.
The Earth’s synthetic density and gravitational models can be used to validate numerical methods for global (or large-scale) gravimetric forward and inverse modelling formulated either in the spatial or spectral domains. The Preliminary Reference Earth Model (PREM) density parameters can be adopted as a 1-D reference density model and further refined using more detailed 2-D or 3-D crust and mantle density models. Alternatively, the AK135-F density parameters can be used for this purpose. In this study, we investigate options for a refinement of the Earth’s synthetic density model by assessing the accuracy of available 1-D density models, specifically the PREM and AK135-F radial density parameters. First, we use density parameters from both models to estimate the Earth’s total mass and compare these estimates with published results. We then estimate the Earth’s gravity field parameters, particularly the geoidal geopotential number W0 and the mean gravitational attraction and compare them with published values. According to our results, the Earth’s total mass from the two models (the PREM and the AK135-F) differ less than 0.02% and 0.01%, respectively, when compared with the value adopted by the International Astronomical Union (IAU). The geoidal geopotential values of the two models differ from the value adopted by the IAU by less than 0.1% and 0.04%, respectively. The values of the mean gravitational attraction of the two models differ less than 0.02% and 0.08%, respectively, when compared with the value obtained from the geocentric gravitational constant and the Earth’s mean radius. These numerical findings ascertain that the PREM and AK135-F density parameters are suitable for defining a 1-D reference density model. Full article
(This article belongs to the Special Issue Monitoring and Understanding the Earth’s Change by Geodetic Methods)
16 pages, 1426 KiB  
Article
Inter-Comparison of UT1-UTC from 24-Hour, Intensives, and VGOS Sessions during CONT17
by Shrishail Raut, Robert Heinkelmann, Sadegh Modiri, Santiago Belda, Kyriakos Balidakis and Harald Schuh
Sensors 2022, 22(7), 2740; https://0-doi-org.brum.beds.ac.uk/10.3390/s22072740 - 02 Apr 2022
Cited by 2 | Viewed by 1305
Abstract
This work focuses on the assessment of UT1-UTC estimates from various types of sessions during the CONT17 campaign. We chose the CONT17 campaign as it provides 15 days of continuous, high-quality VLBI data from two legacy networks (S/X band), i.e., Legacy-1 (IVS) and [...] Read more.
This work focuses on the assessment of UT1-UTC estimates from various types of sessions during the CONT17 campaign. We chose the CONT17 campaign as it provides 15 days of continuous, high-quality VLBI data from two legacy networks (S/X band), i.e., Legacy-1 (IVS) and Legacy-2 (VLBA) (having different network geometry and are non-overlapping), two types of Intensive sessions, i.e., IVS and Russian Intensives, and five days of new-generation, broadband VGOS sessions. This work also investigates different approaches to optimally compare dUT1 from Intensives with respect to the 24 h sessions given the different parameterization adopted for analyzing Intensives and different session lengths. One approach includes the estimation of dUT1 from pseudo Intensives, which are created from the 24 h sessions having their epochs synchronized with respect to the Intensive sessions. Besides, we assessed the quality of the dUT1 estimated from VGOS sessions at daily and sub-daily resolution. The study suggests that a different approach should be adopted when comparing the dUT1 from the Intensives, i.e., comparison of dUT1 value at the mean epoch of an Intensive session. The initial results regarding the VGOS sessions show that the dUT1 estimated from VGOS shows good agreement with the legacy network despite featuring fewer observations and stations. In the case of sub-daily dUT1 from VGOS sessions, we found that estimating dUT1 with 6 h resolution is superior to other sub-daily resolutions. Moreover, we introduced a new concept of sub-daily dUT1-tie to improve the estimation of dUT1 from the Intensive sessions. We observed an improvement of up to 20% with respect to the dUT1 from the 24 h sessions. Full article
(This article belongs to the Special Issue Monitoring and Understanding the Earth’s Change by Geodetic Methods)
Show Figures

Figure 1

19 pages, 5941 KiB  
Article
New Cable Delay Measurement System for VGOS Stations
by Pablo García-Carreño, Javier González-García, María Patino-Esteban, Francisco J. Beltrán-Martínez, Marta Bautista-Durán, Pablo Luis López-Espí and José A. López-Pérez
Sensors 2022, 22(6), 2308; https://0-doi-org.brum.beds.ac.uk/10.3390/s22062308 - 16 Mar 2022
Viewed by 2267
Abstract
This paper presents the new cable delay measurement system (CDMS) designed at Yebes Observatory (IGN, Spain), which is required for the VLBI Global Observing System (VGOS) stations. This system measures the phase difference between the 5 MHz reference signal from the hydrogen maser [...] Read more.
This paper presents the new cable delay measurement system (CDMS) designed at Yebes Observatory (IGN, Spain), which is required for the VLBI Global Observing System (VGOS) stations. This system measures the phase difference between the 5 MHz reference signal from the hydrogen maser and the 5 MHz signal that reaches the broadband receiver through a coaxial cable, for the generation of calibration tones. As a result, the system detects the changes in the length of that coaxial cable due to temperature variations along the cable run and flexures caused by VGOS radio telescope movements. This CDMS outperforms the previous versions: firstly, it does not require a frequency counter for phase/delay measurements; secondly, it largely reduces the use of digital circuits; hence, reducing digital noise; and thirdly, it has a remotely controlled automatic calibration subsystem. The system was tested in the laboratory and in the radio telescope, and the measurements of both set-ups are shown. These measurements include the total noise, accuracy, hysteresis, and stability. The results in the radio telescope can be correlated with the different factors that affect the cable, such as temperature and flexures. The system allows to achieve an RMS noise of less than 0.5 ps, significantly improving the requirements established in VGOS. The system is currently installed in the Red Atlántica de Estaciones Geodinámicas y Espaciales (RAEGE)Yebes VGOS 13.2 m radio telescope, and will be installed in the Norwegian Mapping Authority (NMA) twin VGOS radio telescopes, in the Finnish Geospatial Research Institute (FGI) VGOS station and in the RAEGE Santa María VGOS radio telescope (Açores, Portugal). Full article
(This article belongs to the Special Issue Monitoring and Understanding the Earth’s Change by Geodetic Methods)
Show Figures

Figure 1

18 pages, 4740 KiB  
Article
Analysis of the Results of the Borowiec SLR Station (7811) for the Period 1993–2019 as an Example of the Quality Assessment of Satellite Laser Ranging Stations
by Stanisław Schillak, Paweł Lejba, Piotr Michałek, Tomasz Suchodolski, Adrian Smagło and Stanisław Zapaśnik
Sensors 2022, 22(2), 616; https://0-doi-org.brum.beds.ac.uk/10.3390/s22020616 - 13 Jan 2022
Cited by 3 | Viewed by 1359
Abstract
This paper presents the results of an orbital analysis of satellite laser ranging data performed by the Borowiec SLR station (7811) in the period from July 1993 to December 2019, including the determination of the station positions and velocity. The analysis was performed [...] Read more.
This paper presents the results of an orbital analysis of satellite laser ranging data performed by the Borowiec SLR station (7811) in the period from July 1993 to December 2019, including the determination of the station positions and velocity. The analysis was performed using the GEODYN-II orbital program for the independent monthly orbital arcs from the results of the LAGEOS-1 and LAGEOS-2 satellites. Each arc was created from the results of the laser observations of a dozen or so selected stations, which were characterized by a large number of normal points and a good quality of observations. The geocentric and topocentric coordinates of the station were analyzed. Factors influencing the uncertainty of the measurements were determined: the number of the normal points, the dispersion of the normal points in relation to the orbits, and the long-term stability of the systematic deviations. The position leap at the end of 2002 and its interpretation in ITRF2014 were analyzed. The 3D stability of the determined positions throughout the period of study was equal to 12.7 mm, with the uncertainty of determination being at the level of 4.3 mm. A very high compliance of the computed velocity of the Borowiec SLR station (24.9 mm/year) with ITRF2014 (25.0 mm/year) was found. Full article
(This article belongs to the Special Issue Monitoring and Understanding the Earth’s Change by Geodetic Methods)
Show Figures

Figure 1

26 pages, 8555 KiB  
Article
Robust Estimation of Deformation from Observation Differences Using Some Evolutionary Optimisation Algorithms
by Mehmed Batilović, Radovan Đurović, Zoran Sušić, Željko Kanović and Zoran Cekić
Sensors 2022, 22(1), 159; https://0-doi-org.brum.beds.ac.uk/10.3390/s22010159 - 27 Dec 2021
Cited by 2 | Viewed by 2593
Abstract
In this paper, an original modification of the generalised robust estimation of deformation from observation differences (GREDOD) method is presented with the application of two evolutionary optimisation algorithms, the genetic algorithm (GA) and generalised particle swarm optimisation (GPSO), in the procedure of robust [...] Read more.
In this paper, an original modification of the generalised robust estimation of deformation from observation differences (GREDOD) method is presented with the application of two evolutionary optimisation algorithms, the genetic algorithm (GA) and generalised particle swarm optimisation (GPSO), in the procedure of robust estimation of the displacement vector. The iterative reweighted least-squares (IRLS) method is traditionally used to perform robust estimation of the displacement vector, i.e., to determine the optimal datum solution of the displacement vector. In order to overcome the main flaw of the IRLS method, namely, the inability to determine the global optimal datum solution of the displacement vector if displaced points appear in the set of datum network points, the application of the GA and GPSO algorithms, which are powerful global optimisation techniques, is proposed for the robust estimation of the displacement vector. A thorough and comprehensive experimental analysis of the proposed modification of the GREDOD method was conducted based on Monte Carlo simulations with the application of the mean success rate (MSR). A comparative analysis of the traditional approach using IRLS, the proposed modification based on the GA and GPSO algorithms and one recent modification of the iterative weighted similarity transformation (IWST) method based on evolutionary optimisation techniques is also presented. The obtained results confirmed the quality and practical usefulness of the presented modification of the GREDOD method, since it increased the overall efficiency by about 18% and can provide more reliable results for projects dealing with the deformation analysis of engineering facilities and parts of the Earth’s crust surface. Full article
(This article belongs to the Special Issue Monitoring and Understanding the Earth’s Change by Geodetic Methods)
Show Figures

Figure 1

9 pages, 1626 KiB  
Article
The Celestial Frame and the Weighting of the Celestial Pole Offsets in the Computation of VLBI-Based Corrections for the Main Lunisolar Nutation Terms
by Víctor Puente and Marta Folgueira
Sensors 2021, 21(24), 8276; https://0-doi-org.brum.beds.ac.uk/10.3390/s21248276 - 10 Dec 2021
Viewed by 1723
Abstract
Very long baseline interferometry (VLBI) is the only technique in space geodesy that can determine directly the celestial pole offsets (CPO). In this paper, we make use of the CPO derived from global VLBI solutions to estimate empirical corrections to the main lunisolar [...] Read more.
Very long baseline interferometry (VLBI) is the only technique in space geodesy that can determine directly the celestial pole offsets (CPO). In this paper, we make use of the CPO derived from global VLBI solutions to estimate empirical corrections to the main lunisolar nutation terms included in the IAU 2006/2000A precession–nutation model. In particular, we pay attention to two factors that affect the estimation of such corrections: the celestial reference frame used in the production of the global VLBI solutions and the stochastic model employed in the least-squares adjustment of the corrections. In both cases, we have found that the choice of these aspects has an effect of a few μas in the estimated corrections. Full article
(This article belongs to the Special Issue Monitoring and Understanding the Earth’s Change by Geodetic Methods)
Show Figures

Figure 1

15 pages, 5089 KiB  
Article
Towards Understanding the Interconnection between Celestial Pole Motion and Earth’s Magnetic Field Using Space Geodetic Techniques
by Sadegh Modiri, Robert Heinkelmann, Santiago Belda, Zinovy Malkin, Mostafa Hoseini, Monika Korte, José M. Ferrándiz and Harald Schuh
Sensors 2021, 21(22), 7555; https://0-doi-org.brum.beds.ac.uk/10.3390/s21227555 - 13 Nov 2021
Cited by 2 | Viewed by 1881
Abstract
The understanding of forced temporal variations in celestial pole motion (CPM) could bring us significantly closer to meeting the accuracy goals pursued by the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG), i.e., 1 mm accuracy and 0.1 mm/year [...] Read more.
The understanding of forced temporal variations in celestial pole motion (CPM) could bring us significantly closer to meeting the accuracy goals pursued by the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG), i.e., 1 mm accuracy and 0.1 mm/year stability on global scales in terms of the Earth orientation parameters. Besides astronomical forcing, CPM excitation depends on the processes in the fluid core and the core–mantle boundary. The same processes are responsible for the variations in the geomagnetic field (GMF). Several investigations were conducted during the last decade to find a possible interconnection of GMF changes with the length of day (LOD) variations. However, less attention was paid to the interdependence of the GMF changes and the CPM variations. This study uses the celestial pole offsets (CPO) time series obtained from very long baseline interferometry (VLBI) observations and data such as spherical harmonic coefficients, geomagnetic jerk, and magnetic field dipole moment from a state-of-the-art geomagnetic field model to explore the correlation between them. In this study, we use wavelet coherence analysis to compute the correspondence between the two non-stationary time series in the time–frequency domain. Our preliminary results reveal interesting common features in the CPM and GMF variations, which show the potential to improve the understanding of the GMF’s contribution to the Earth’s rotation. Special attention is given to the corresponding signal between FCN and GMF and potential time lags between geomagnetic jerks and rotational variations. Full article
(This article belongs to the Special Issue Monitoring and Understanding the Earth’s Change by Geodetic Methods)
Show Figures

Figure 1

14 pages, 7414 KiB  
Communication
A Tri-Band Cooled Receiver for Geodetic VLBI
by José A. López-Pérez, Félix Tercero-Martínez, José M. Serna-Puente, Beatriz Vaquero-Jiménez, María Patino-Esteban, Pablo García-Carreño, Javier González-García, Óscar García-Pérez, Francisco J. Beltrán-Martínez, Carlos Albo-Castaño, Juan D. Gallego-Puyol, Isaac López-Fernández, Carmen Díez-González, Inmaculada Malo-Gómez, Laura Barbas-Calvo, Pablo de Vicente-Abad and José A. López-Fernández
Sensors 2021, 21(8), 2662; https://0-doi-org.brum.beds.ac.uk/10.3390/s21082662 - 10 Apr 2021
Cited by 1 | Viewed by 2525
Abstract
This paper shows a simultaneous tri-band (S: 2.2–2.7 GHz, X: 7.5–9 GHz and Ka: 28–33 GHz) low-noise cryogenic receiver for geodetic Very Long Baseline Interferometry (geo-VLBI) which has been developed at Yebes Observatory laboratories in Spain. A special feature is that the whole [...] Read more.
This paper shows a simultaneous tri-band (S: 2.2–2.7 GHz, X: 7.5–9 GHz and Ka: 28–33 GHz) low-noise cryogenic receiver for geodetic Very Long Baseline Interferometry (geo-VLBI) which has been developed at Yebes Observatory laboratories in Spain. A special feature is that the whole receiver front-end is fully coolable down to cryogenic temperatures to minimize receiver noise. It was installed in the first radio telescope of the Red Atlántica de Estaciones Geodinámicas y Espaciales (RAEGE) project, which is located in Yebes Observatory, in the frame of the VLBI Global Observing System (VGOS). After this, the receiver was borrowed by the Norwegian Mapping Autorithy (NMA) for the commissioning of two VGOS radiotelescopes in Svalbard (Norway). A second identical receiver was built for the Ishioka VGOS station of the Geospatial Information Authority (GSI) of Japan, and a third one for the second RAEGE VGOS station, located in Santa María (Açores Archipelago, Portugal). The average receiver noise temperatures are 21, 23, and 25 Kelvin and the measured antenna efficiencies are 70%, 75%, and 60% in S-band, X-band, and Ka-band, respectively. Full article
(This article belongs to the Special Issue Monitoring and Understanding the Earth’s Change by Geodetic Methods)
Show Figures

Figure 1

22 pages, 3404 KiB  
Article
Application of Optimization Algorithms for Identification of Reference Points in a Monitoring Network
by Waldemar Odziemczyk
Sensors 2021, 21(5), 1739; https://0-doi-org.brum.beds.ac.uk/10.3390/s21051739 - 03 Mar 2021
Cited by 5 | Viewed by 1824
Abstract
Geodetic measurements are commonly used in displacement analysis to determine the absolute values of displacements of points of interest. In order to properly determine the displacement values, it is necessary to correctly identify a subgroup of mutually stable points constituting a reference system. [...] Read more.
Geodetic measurements are commonly used in displacement analysis to determine the absolute values of displacements of points of interest. In order to properly determine the displacement values, it is necessary to correctly identify a subgroup of mutually stable points constituting a reference system. The complexity of this task depends on the spatial size of the network, the timespan of measurements and geological conditions affecting the type of changes in the location of points. As a consequence of the abovementioned factors, the task of stable identification in a longer timespan for a subgroup of points may produce equivocal results. In particular, it is likely that alternative subgroups of reference points meeting the mutual stability criteria will be selected, sometimes without common reference points. The proposed method of reference system identification utilises optimisation algorithms. Two such algorithms were tested, i.e., simulated annealing (SA) and Hooke-Jeeves (HJ) method. Two numerical examples were used to test the proposed method. Although in the first example both methods delivered a positive result, the second example showed the superiority of the SA method over the HJ. The proposed method can be considered a tool supporting the person analysing and making calculations in reaching the ultimate decision on reference points. Full article
(This article belongs to the Special Issue Monitoring and Understanding the Earth’s Change by Geodetic Methods)
Show Figures

Figure 1

14 pages, 6431 KiB  
Article
Multi-Channel Singular Spectrum Analysis on Geocenter Motion and Its Precise Prediction
by Xin Jin, Xin Liu, Jinyun Guo and Yi Shen
Sensors 2021, 21(4), 1403; https://0-doi-org.brum.beds.ac.uk/10.3390/s21041403 - 17 Feb 2021
Cited by 2 | Viewed by 1977
Abstract
Geocenter is the center of the mass of the Earth system including the solid Earth, ocean, and atmosphere. The time-varying characteristics of geocenter motion (GCM) reflect the redistribution of the Earth’s mass and the interaction between solid Earth and mass loading. Multi-channel singular [...] Read more.
Geocenter is the center of the mass of the Earth system including the solid Earth, ocean, and atmosphere. The time-varying characteristics of geocenter motion (GCM) reflect the redistribution of the Earth’s mass and the interaction between solid Earth and mass loading. Multi-channel singular spectrum analysis (MSSA) was introduced to analyze the GCM products determined from satellite laser ranging data released by the Center for Space Research through January 1993 to February 2017 for extracting the periods and the long-term trend of GCM. The results show that the GCM has obvious seasonal characteristics of the annual, semiannual, quasi-0.6-year, and quasi-1.5-year in the X, Y, and Z directions, the annual characteristics make great domination, and its amplitudes are 1.7, 2.8, and 4.4 mm, respectively. It also shows long-period terms of 6.09 years as well as the non-linear trends of 0.05, 0.04, and –0.10 mm/yr in the three directions, respectively. To obtain real-time GCM parameters, the MSSA method combining a linear model (LM) and autoregressive moving average model (ARMA) was applied to predict GCM for 2 years into the future. The precision of predictions made using the proposed model was evaluated by the root mean squared error (RMSE). The results show that the proposed method can effectively predict GCM parameters, and the prediction precision in the three directions is 1.53, 1.08, and 3.46 mm, respectively. Full article
(This article belongs to the Special Issue Monitoring and Understanding the Earth’s Change by Geodetic Methods)
Show Figures

Figure 1

15 pages, 4035 KiB  
Article
Analysis of the Quality of SLR Station Coordinates Determined from Laser Ranging to the LARES Satellite
by Stanisław Schillak, Paweł Lejba and Piotr Michałek
Sensors 2021, 21(3), 737; https://0-doi-org.brum.beds.ac.uk/10.3390/s21030737 - 23 Jan 2021
Cited by 8 | Viewed by 2434
Abstract
The LARES (LAser RElativity Satellite) was built by the Italian Space Agency (ASI) and launched on 13 February 2012 by the European Space Agency. It is intended for studying the Lense–Thirring effect resulting from general relativity as well as for geodynamic studies and [...] Read more.
The LARES (LAser RElativity Satellite) was built by the Italian Space Agency (ASI) and launched on 13 February 2012 by the European Space Agency. It is intended for studying the Lense–Thirring effect resulting from general relativity as well as for geodynamic studies and satellite geodesy. The satellite is observed by most ground laser stations. The task of this work is to determine the station coordinates and to assess the quality of their determination by comparison with the results from the LAGEOS-1 and LAGEOS-2 satellites. Observation results in the form of normal points (396,105 normal points in total) were downloaded from the EUROLAS Data Center for the period from 29 February 2012 to 31 December 2015. Seven-day orbital arcs were computed by the NASA GSFC GEODYN-II software, determining the coordinates of seventeen selected measuring stations. The average Root Mean Square (RMS) (15.1 mm) of the determined orbits is nearly the same as for LAGEOS (15.2 mm). The stability of the coordinates of each station (3DRMS) is from 9 mm to 46 mm (for LAGEOS, from 5 mm to 15 mm) with the uncertainty of determining the coordinates of 3–11 mm (LAGEOS 2–7 mm). The combined positioning for the LARES + LAGEOS-1 + LAGEOS-2 satellites allows for the stability of 5–18 mm with an uncertainty of 2–6 mm. For most stations, this solution is slightly better than the LAGEOS-only one. Full article
(This article belongs to the Special Issue Monitoring and Understanding the Earth’s Change by Geodetic Methods)
Show Figures

Figure 1

Back to TopTop