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A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Satellite Missions for Earth and Planetary Exploration".

Deadline for manuscript submissions: closed (15 December 2023) | Viewed by 20136

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Special Issue Editors

Dr. Xiaogong Hu

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Guest Editor

Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai, China
Interests: astronomy; orbit determination; spacecraft
Special Issues, Collections and Topics in MDPI journals

Dr. Mladen Zrinjski

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Guest Editor

Faculty of Geodesy, University of Zagreb, Zagreb, Croatia
Interests: geodesy; global navigation satellite systems (GNSS); remote sensing; metrology; optical geodetic instruments; electronic geodetic instruments; automation of procedures of geodetic measurements; precise geodetic measurements

Dr. Walyeldeen Godah

E-Mail Website
Guest Editor

Institute of Geodesy and Cartography, 27 Modzelewski St., 02-679 Warsaw, Poland
Interests: GNSS data for geodynamics process; satellite gravity modelling; terrestrial (relative/absolute) gravity measurements; reference system/frame; height system
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Thank you all for the efforts and support devoted to our previous Special Issue on ‘Space-Geodetic Techniques’. The first volume was a smashing success, with multiple papers published and extensive attention in the scientific community. As such, we are pleased to announce the release of this second volume of the Special Issue, which aims to continue following the latest improvements in the space-geodetic field.

Space-geodetic techniques such as very long baseline interferometry (VLBI), global navigation satellite systems (GNSS), satellite laser ranging (SLR), interferometric synthetic aperture radar (InSAR), Doppler orbitography and radio-positioning integrated by satellite (DORIS), satellite altimetry and gravimetry, etc., have played an increasingly significant role in Earth exploration and geodetic research. Benefiting from the rapid development of satellite techniques and the creation of ground-/space-based observing systems, the establishment and maintenance of the Earth’s reference frame, the Earth’s rotation and geodynamics, navigation and positioning in high precision, gravity fields, geodetic observation, and the remote sensing and modeling of the Earth’s atmosphere and ionosphere, as well as deep space exploration, are facilitated with more accurate and dense data and are attracting more and more attention for solving challenging scientific problems.

This second Special Issue welcomes all studies related to applications of different space-geodetic techniques in space and ground observations in Earth sciences. The topics may cover anything from the classical estimation of Earth observation at high precision to more comprehensive aims and scales. Articles may address but are not limited to the following topics:

Global and regional gravity field modeling;
Satellite gravimetry and applications in global change;
Satellite altimetry and oceanography;
Geodetic remote sensing;
Applications of remote sensing in the global water cycle;
Next-generation positioning;
Techniques and applications in high-precision GNSS;
Atmosphere modeling and monitoring;
Space weather research;
GNSS reflectometry;
Geodetic observations and geodynamics;
Crust deformation and natural hazard monitoring;
Earth rotation;
Planetary geodesy.

Dr. Xiaogong Hu
Dr. Mladen Zrinjski
Dr. Walyeldeen Godah
Guest Editors

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. Remote Sensing 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 2700 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

ground and satellite gravimetry
satellite altimetry
positioning
orbit determination
atmosphere
space weather
global climate change
geodynamics
natural hazard monitoring
earth rotation
planetary geodesy
GNSS-R

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Space-Geodetic Techniques in Remote Sensing (24 articles)
Space-Geodetic Techniques (Third Edition) in Remote Sensing (2 articles)

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20 pages, 1599 KiB

Open AccessArticle

Impact of Pseudo-Stochastic Pulse and Phase Center Variation on Precision Orbit Determination of Haiyang-2A from Experimental HY2 Receiver GPS Data

by Youyuan Wang, Jinyun Guo, Shaoshuai Ya, Yongjun Jia, Hengyang Guo, Xiaotao Chang and Xin Liu

Remote Sens. 2024, 16(8), 1336; https://doi.org/10.3390/rs16081336 - 10 Apr 2024

Viewed by 945

Abstract

Haiyang-2A (HY-2A) is the first marine dynamic environment satellite established by China, which has made significant contributions to the marine scientific research field. It carries the satellite-based GPS receiver named HY2, which was independently developed by China. It is an experimental satellite-borne GPS receiver for low earth orbit satellites, and during its operational period in orbit, the satellite-borne GPS data are not made accessible to the public. Therefore, this paper assesses the quality of HY-2A satellite-borne GPS data based on indicators such as satellite visibility, multipath effect, and ionospheric delay. The results indicate that the data acquired by the HY2 receiver are of high quality. The precise orbit determination (POD) uses the reduced-dynamic (RD) method. The adjustment effects of the pseudo-stochastic pulse time interval and a priori sigma on POD are analyzed, and the antenna phase center variation (PCV) is estimated using the direct method and residual method. Furthermore, this paper investigates the impact of PCV models with different resolutions (10° × 10° and 5° × 5°) on satellite orbit determination. To evaluate the orbit precision, three methods are used for validation, including carrier phase residual analysis, external precise science orbit (PSO) validation, and SLR three-dimensional (3D) validation, respectively. The results indicate that the highest orbit precision is achieved when the pseudo-stochastic pulse time interval is configured to 15 min, with the a priori sigma of 1 × 10⁻⁸ m/s². The orbit carrier phase residuals reach the millimeter level. The 10° × 10°PCV model was estimated using the direct method and residual method, respectively; the root mean square of the external orbit validation for both methods show a millimeter-level improvement. The results obtained from the direct method and residual method are comparable. The resolution is increased from 10° to 5°, and the improvement in orbital precision is relatively small. The results obtained from the SLR 3D validation are consistent with those from the external PSO validation. The experimental results contribute valuable information for the POD of the HY2 series satellites. Full article

(This article belongs to the Special Issue Space-Geodetic Techniques II)

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19 pages, 1811 KiB

Open AccessArticle

An Updated Estimate of Geocenter Variation from Analysis of SLR Data

by Minkang Cheng

Remote Sens. 2024, 16(7), 1189; https://doi.org/10.3390/rs16071189 - 28 Mar 2024

Cited by 1 | Viewed by 1056

Abstract

The Earth’s center of mass (CM) is defined in satellite orbit dynamics as the center of mass of the entire Earth system, including the solid Earth, oceans, cryosphere, and atmosphere. The CM can be realized using the vector from the origin of the International Terrestrial Reference Frame (ITRF) to the CM, and directly estimated from satellite laser ranging (SLR) data. In previous studies and ITRF translations, SLR observations were assumed to contain only a constant, systematic, station-dependent bias. This treatment leads to a difference of a few mm between the SLR results and other estimates, such as GPS-based global inversions. We show that the difference cannot be attributed to the deficiency of the distribution of SLR tracking stations but is due to the impact of a significant surface-loading-induced seasonal signal captured in the laser range measurement (appearing in station range bias) during the traveling of the laser light pulse. The errors in the modeling of the troposphere zenith delay considerably impact the determination of geocenter motion from SLR data. The SLR-data-derived geocenter motion becomes comparable to the global inversion results when the range biases and thermosphere delay for SLR tracking stations in the SLR network are adjusted as part of the monthly solution. Full article

(This article belongs to the Special Issue Space-Geodetic Techniques II)

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20 pages, 4355 KiB

Open AccessArticle

Estimation of Earth Rotation Parameters Based on BDS-3 and Discontinuous VLBI Observations

by Chenxiang Wang, Jizhang Sang, Xingxing Li and Pengfei Zhang

Remote Sens. 2024, 16(2), 333; https://doi.org/10.3390/rs16020333 - 14 Jan 2024

Cited by 1 | Viewed by 1126

Abstract

Earth rotation parameters (ERPs) are fundamental to geodetic and astronomical studies. With its high measurement accuracy and stability, the Very Long Baseline Interferometry (VLBI) plays an irreplaceable role in estimating the ERPs and maintaining the earth reference frame. However, the imperfect global station distribution, observation discontinuity, and vast cost of the VLBI make the GNSS a more attractive technique. In 2020, the third generation of the BeiDou Navigation System (BDS), namely BDS-3, was constructed completely. In this study, we conducted a series of experiments to estimate Earth’s rotation parameters based on the continuous BDS-3 observation data, the discontinuous VLBI observation data, and the combined BDS-3 and discontinuous VLBI observation data. We used two methods, namely the weighted averaging method and the normal equation combination method, to obtain ERP combination solutions. The results are compared with the International Earth Rotation and Reference Systems Service (IERS) EOP 20C04 at 00:00:00 UTC. Final results show that (a) the estimation accuracy becomes stable when the number of BDS-3 tracking stations is more than 40. At the same time, both the number of stations and the volume of polyhedrons formed by the observing stations affect the accuracy of the ERPs estimated by the BDS-3 or VLBI. (b) Results have also shown that the inclusion of the BDS-3 IGSO and GEO satellites contributes little to the ERP estimation. (c) For the BDS-3-only MEO satellites solution, the root mean square (RMS) was 113.2 µas, 102.8 µas, and 13.1 µs/day for X-pole coordinate, Y-pole coordinate, and length of day (LOD), respectively. For the VLBI solution, the RMSs of the X-pole, Y-pole, and LOD were 100.4 µas for the X-pole, 94.2 µas for the Y-pole, and 14.1 µs/day. The RMS was 82.6 µas, 70.3 µas, and 10.5 µs/day for the combined X-pole, Y-pole, and LOD using the weighted averaging method. It was 78.2 µas, 62.6 µas, and 8.6 µs/day when the normal equation combination method was applied. This demonstrates that by taking advantage of the BDS-3 and VLBI technique combinations, accuracy in estimating the ERPs can be improved over that using either of them, in addition to enhanced stability and reliability. Full article

(This article belongs to the Special Issue Space-Geodetic Techniques II)

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15 pages, 5571 KiB

Open AccessArticle

A NavCom Signal Authentication Scheme Based on Twice Two-Way Satellite Time Transfer

by Xiaomei Tang, Sixin Wang, Jiyang Liu and Feixue Wang

Remote Sens. 2024, 16(1), 10; https://doi.org/10.3390/rs16010010 - 19 Dec 2023

Viewed by 836

Abstract

Low Earth Orbit (LEO) satellite communication systems typically achieve identity authentication through the encryption and decryption of two-way information, which requires complex key management systems. In contrast, the integration of navigation and communication (NavCom) signals provides novel opportunities for physical observation and authentication solutions due to its measurement functions. This paper introduces a novel signal authentication scheme based on twice two-way satellite time transfer (TWSTT) for LEO satellite systems. It leverages the non-mutated nature of the clock difference to ascertain the legitimacy of the signal by measuring the clock difference of signals at different instances. Unlike traditional authentication methods, this approach directly exploits the temporal and spatial characteristics of the signal, negating the necessity for intricate authorization key systems. Additionally, it adeptly tackles the challenges posed by spoofing interference. The performance analysis indicates that this scheme can achieve a high detection probability for the repeater spoofing signal in the low carrier-to-noise ratio conditions. Full article

(This article belongs to the Special Issue Space-Geodetic Techniques II)

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19 pages, 5398 KiB

Open AccessArticle

Preliminary Estimations of Mars Atmospheric and Ionospheric Profiles from Tianwen-1 Radio Occultation One-Way, Two-Way, and Three-Way Observations

by Min Liu, Lue Chen, Nianchuan Jian, Peng Guo, Jing Kong, Mei Wang, Qianqian Han, Jinsong Ping and Mengjie Wu

Remote Sens. 2023, 15(23), 5506; https://doi.org/10.3390/rs15235506 - 26 Nov 2023

Cited by 3 | Viewed by 1313

Abstract

The radio occultation method, one of the methods used to provide planetary atmospheric profiles with high vertical resolution, was applied to China’s first Mars mission, Tianwen-1. We carried out observations based on the Chinese Deep Space Network, and one-way, two-way, and three-way modes were used for Doppler observations from the Tianwen-1 spacecraft. We successfully obtained effective observations from Tianwen-1 on 22 and 25 March 2022. An inversion system developed for Tianwen-1 radio occultation observations enabled the derivation of neutral atmospheric density, pressure, temperature, and electron density profiles of Mars. Utilizing one-way tracking data, Martian ionospheric electron density profiles were retrieved at latitudes between 68.7 and 70.7 degrees (N). However, the presence of strong random walk noise in one-way tracking data led to poor inversion results. Meanwhile, Martian ionospheric electron density and neutral atmosphere profiles were extracted from two-way and three-way tracking data at latitudes between 55.1 and 57.0 degrees (S) on 22 March and at latitudes between 62.8 and 63.4 degrees (S) on 25 March. Importantly, our inversion results from Tianwen-1 maintained consistency with results from the Mars Express and the Chapman theory (mainly in the M2 layer). Through two days’ observation experiments, we established and verified the occultation solution system and prepared for the follow-up occultation plans. Full article

(This article belongs to the Special Issue Space-Geodetic Techniques II)

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29 pages, 64326 KiB

Open AccessArticle

A Comparison of Gravimetric, Isostatic, and Spectral Decomposition Methods for a Possible Enhancement of the Mantle Signature in the Long-Wavelength Geoidal Geometry

by Robert Tenzer and Wenjin Chen

Remote Sens. 2023, 15(19), 4845; https://doi.org/10.3390/rs15194845 - 6 Oct 2023

Cited by 1 | Viewed by 1216

Abstract

A long-wavelength geoidal geometry characterizes the most pronounced features of the Indian Ocean geoid low and the West Pacific and North Atlantic geoid highs. These large geoid undulations (globally roughly within ±100 m) are mainly attributed to a deep mantle structure and large lithospheric density and geometry variations (such as the African superswell), while maximum geoid modifications by a topographic relief of Himalaya and Tibet are up to ~30 m. To enhance the mantle signature in a long-wavelength geoidal geometry, gravimetric, isostatic, and spectral decomposition methods can be applied. In this study, we demonstrate that isostatic schemes yield isostatic geoid models that closely resemble a long-wavelength geoidal geometry. The gravimetric method, on the other hand, modifies the mantle geoid significantly. Further modifications of the mantle geoid by removing gravitational contributions of lithospheric mantle density and lithospheric thickness variations should (optimally) enhance the signature of the deep mantle in the sub-lithospheric mantle geoid. Our results confirm this assumption by revealing (large-scale) positive anomalies in the Central Pacific and along the Atlantic Ocean that are coupled by two negative anomalies in the East Pacific and South Eurasia. A gravimetric method thus better enhances the mantle signature in the geoidal geometry than isostatic and spatial decomposition methods. Nonetheless, our results also indicate the presence of possibly large errors in geoid modelling results that limit their full implementation in gravimetric studies of the Earth’s mantle density structure without using tomographic images of the mantle and additional geophysical, geothermal, and geochemical constraints. Full article

(This article belongs to the Special Issue Space-Geodetic Techniques II)

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21 pages, 9016 KiB

Open AccessArticle

GNSS Receiver Antenna Absolute Field Calibration System Development: Testing and Preliminary Results

by Antonio Tupek, Mladen Zrinjski, Marko Švaco and Đuro Barković

Remote Sens. 2023, 15(18), 4622; https://doi.org/10.3390/rs15184622 - 20 Sep 2023

Cited by 3 | Viewed by 1980

Abstract

For high-precision Global Navigation Satellite Systems (GNSS) positioning based on carrier-phase measurements, knowledge of the GNSS receiver antenna electrical signal reception characteristics, i.e., phase center, is crucial. Numerous studies have led to the understanding of the influence of GNSS receiver antenna phase center corrections (PCCs) on GNSS positioning accuracy and other estimated parameters (e.g., receiver clock estimates, ambiguities, etc.). With the goal of determining the PCC model of GNSS receiver antennas, only a few antenna calibration systems/facilities are in operation or under development worldwide. The International GNSS Service (IGS) publishes type-mean PCC models for almost all geodetic-grade GNSS antennas. However, the type-mean models are not perfect and do not fully reflect the signal reception properties of individual GNSS receiver antennas. Relevant published scientific research has shown that the application of individual PCC models significantly improves the accuracy of GNSS positioning and other estimated parameters. In this article, the new automated GNSS antenna calibration system, recently developed at the Laboratory for Measurements and Measuring Technique (LMMT) of the Faculty of Geodesy of the University of Zagreb in Croatia, is presented. The developed system is an absolute field calibration system based on the utilization of a Mitsubishi MELFA 6-axis industrial robot. During calibration, the robot tilts and rotates the GNSS antenna under test (AUT) around a fixed point within the antenna. The antenna PCC modelling is based on time-differenced double-difference carrier-phase observations. Our preliminary results for the Global Positioning System (GPS) L1 (G01) frequency show a submillimeter repeatability of the estimated PCC model and a submillimeter agreement with the Geo++ GmbH calibration results. Full article

(This article belongs to the Special Issue Space-Geodetic Techniques II)

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23 pages, 2180 KiB

Open AccessArticle

Analysis of the Results Determining the Positions and Velocities of Satellite Laser Ranging Stations during Earthquakes in 2010–2011

by Stanisław Schillak, Agnieszka Satarowska, Dominik Sankowski and Piotr Michałek

Remote Sens. 2023, 15(14), 3659; https://doi.org/10.3390/rs15143659 - 22 Jul 2023

Cited by 2 | Viewed by 1363

Abstract

This paper presents an analysis of the results determining the positions and the velocities of the 21 selected satellite laser ranging stations which performed observations from January 2008 to December 2012. This particularly interesting period of five years was selected, during which two strong earthquakes occurred near the stations. The focus was directed on the stations where the effects of the earthquakes were observed, i.e., Koganei (7308), Simosato (7838), and Changchun (7237) as a result of the tsunami in Japan on 11 February 2011, as well as Concepcion (7405IR) and San Juan (7406) as a result of the earthquake in Chile on 27 February 2010. The station positions were computed using the GSFC NASA GEODYN-II orbital software from the observations results of the satellites LAGEOS-1 and LAGEOS-2. The geocentric coordinates of the stations were determined from the normal equations of both satellites. The station velocities were computed from the positions determined for the observation epoch using the linear regression method. For each station, the following parameters were determined: mean total coordinates stability, standard deviation of determined positions and mean deviation from ITRF for topocentric components. For the best stations, the stability ranged from 4.0 mm to 6.5 mm, with the standard deviation of determined positions ranging from 0.9 mm to 1.7 mm. For two stations, a quadratic change in the station position was detected instead of a normal linear one after strong earthquakes. Full article

(This article belongs to the Special Issue Space-Geodetic Techniques II)

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19 pages, 17142 KiB

Open AccessArticle

Augmented Gravity Field Modelling by Combining EIGEN_6C4 and Topographic Potential Models

by Panpan Zhang, Lifeng Bao, Yange Ma and Xinyu Liu

Remote Sens. 2023, 15(13), 3418; https://doi.org/10.3390/rs15133418 - 6 Jul 2023

Cited by 1 | Viewed by 1238

Abstract

One of the key goals of geodesy is to study the fine structure of the Earth’s gravity field and construct a high-resolution gravity field model (GFM). Aiming at the current insufficient resolution problem of the EIGEN_6C4 model, the refined ultra-high degree models EIGEN_3660 and EIGEN_5480 are determined with a spectral expansion approach in this study, which is to augment EIGEN_6C4 model using topographic potential models (TPMs). A comparative spectral evaluation for EIGEN_6C4, EIGEN_3660, and EIGEN_5480 models indicates that the gravity field spectral powers of EIGEN_3660 and EIGEN_5480 models outperform the EIGEN_6C4 model after degree 2000. The augmented models EIGEN_3660 and EIGEN_5480 are verified using the deflection of the vertical (DOV) of China and Colorado, gravity data from Australia and mainland America, and GNSS/leveling in China. The validation results indicate that the accuracy of EIGEN_3660 and EIGEN_5480 models in determining height anomaly, DOV, and gravity anomaly outperform the EIGEN_6C4 model, and the EIGEN_5480 model has optimal accuracy. The accuracy of EIGEN_5480 model in determining south–north component and east–west component of the DOV in China has been improved by about 21.1% and 23.1% compared to the EIGEN_6C4 model, respectively. In the mountainous Colorado, the accuracy of EIGEN_5480 model in determining south–north component and east–west component of the DOV has been improved by about 28.2% and 35.2% compared to EIGEN_6C4 model, respectively. In addition, gravity value comparison results in Australia and mainland America indicate that the accuracy of the EIGEN_5480 model for deriving gravity anomalies is improved by 16.5% and 11.3% compared to the EIGEN_6C4 model, respectively. Full article

(This article belongs to the Special Issue Space-Geodetic Techniques II)

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15 pages, 6877 KiB

Open AccessArticle

Centimeter-Level Orbit Determination of GRACE-C Using IGS-RTS Data

by Duoduo Li, Xuhua Zhou and Kai Li

Remote Sens. 2023, 15(7), 1832; https://doi.org/10.3390/rs15071832 - 29 Mar 2023

Cited by 1 | Viewed by 1699

Abstract

GNSS real-time applications greatly benefit from the International GNSS Service’s (IGS) real-time service (RTS). This service does more than provide for terrestrial precise point positioning (PPP); it also brings more possibilities for space-borne technology. With this service, the State-Space Representation (SSR) product, which includes orbit corrections and clock corrections, is finally available to users. In this paper, the GPS real-time orbit and clock corrections provided by 11 analysis centers (ACs) from the day of the year (DOY) 144 to 153 of 2022 are discussed from 3 perspectives: integrity, continuity, and accuracy. Moreover, actual observation data from the GRACE-C satellite are processed, along with SSR corrections from different ACs. The following can be concluded: (1) In terms of integrity and continuity, the products provided by CNE, ESA, and GMV perform better. (2) CNE, ESA, and WHU are the most accurate, with values of about 5 cm for the satellite orbit and 20 ps for the satellite clock. Additionally, the clock accuracy is related to the Block. Block IIR and Block IIR-M are slightly worse than Block IIF and Block IIIA. (3) The accuracy of post-processing reduced-dynamic precise orbit determination (POD) and kinematic POD are at the centimeter level in radius, and the reduced-dynamic POD is more accurate and robust than the kinematic POD. Full article

(This article belongs to the Special Issue Space-Geodetic Techniques II)

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19 pages, 6773 KiB

Open AccessArticle

Bathymetry Refinement over Seamount Regions from SAR Altimetric Gravity Data through a Kalman Fusion Method

by Yihao Wu, Junjie Wang, Yueqian Shen, Dongzhen Jia and Yu Li

Remote Sens. 2023, 15(5), 1288; https://doi.org/10.3390/rs15051288 - 26 Feb 2023

Cited by 1 | Viewed by 1874

Abstract

Seafloor topography over seamount areas is crucial for studying plate motions, seafloor seismicity, and seamount ecosystems. However, seamount bathymetry modeling is difficult due to the complex hydrodynamic environment, biodiversity, and scarcity of shipborne echo sounding data. The use of satellite altimeter-derived gravity data is a complementary way of bathymetry computation; in particular, the incorporation of synthetic aperture radar (SAR) altimeter data may be useful for seamount bathymetry modeling. Moreover, the widely used filtering method may have difficulty in combing different bathymetry data sets and may affect the quality of the computed bathymetry. To mitigate this issue, we introduce a Kalman fusion method for weighting and combining gravity-derived bathymetry data and the reference bathymetry model. Numerical experiments in the seamount regions over the Molloy Ridge show that the use of SAR-based altimetric gravity data improves the local bathymetry model, by a magnitude of 14.27 m, compared to the result without SAR data. In addition, the developed Kalman fusion method outperforms the traditionally used filtering method, and the bathymetry computed from the Kalman fusion method is improved by a magnitude of 9.34 m. Further comparison shows that our solution has improved quality compared to a recently released global bathymetry model, namely, GEBCO 2022 (GEBCO: General Bathymetric Chart of the Oceans), by a magnitude of 34.34 m. The bathymetry model in this study may be substituted for existing global bathymetry models for geophysical investigations over the target area. Full article

(This article belongs to the Special Issue Space-Geodetic Techniques II)

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18 pages, 4113 KiB

Open AccessArticle

Clock Ensemble Algorithm Test in the Establishment of Space-Based Time Reference

by Guangyao Chen, Nan Xing, Chengpan Tang and Zhiqiao Chang

Remote Sens. 2023, 15(5), 1227; https://doi.org/10.3390/rs15051227 - 23 Feb 2023

Cited by 1 | Viewed by 1949

Abstract

A new concept of a space-based synchronized reference network is proposed with the development of an optical frequency reference and laser inter-satellite link. To build such time reference, three clock ensemble algorithms, namely the natural Kalman timescale (NKT) algorithm, the reduced Kalman timescale (RKT) algorithm, and the two-stage Kalman timescale (TKT) algorithm are considered. This study analyzes and compares the performance of these algorithms using BDS, GPS, and Galileo satellite clock data from the GFZ GNSS clock corrections, which will be used in constructing future space-based time references. The study shows that the NKT algorithm improves frequency stability by 0.1–0.2 orders of magnitude in the short and medium term. When the satellite clock is mostly a hydrogen clock, the RKT and NKT are close, and the short and medium-term frequency stability slightly increases. In contrast, the TKT algorithm produces a timescale that improves frequency stability by 1–3 orders of magnitude. A quadratic polynomial model predicts the three timescales, with the results indicating that the short-term prediction accuracy of the satellite clock is within 1ns, and the TKT algorithm’s prediction accuracy is 1–2 orders of magnitude higher than that of the NKT and RKT algorithms. With the deployment of next-generation Low Earth Orbit (LEO) satellites equipped with higher-precision clocks, the space-based time reference system will achieve improved accuracy and greater potential for practical applications. Full article

(This article belongs to the Special Issue Space-Geodetic Techniques II)

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13 pages, 3568 KiB

Open AccessTechnical Note

Analysis of the Ranging Capability of a Space Debris Laser Ranging System Based on the Maximum Detection Distance Model

by Mingliang Zhang, Guanyu Wen, Cunbo Fan, Bowen Guan, Qingli Song, Chengzhi Liu and Shuang Wang

Remote Sens. 2024, 16(4), 727; https://doi.org/10.3390/rs16040727 - 19 Feb 2024

Cited by 2 | Viewed by 1593

Abstract

Based on the radar equation and system noise characteristics, the maximum detection range model of a space debris laser ranging system at a 1064 nm wavelength is established, taking into account the factors of atmospheric transmission and sky background radiance. Through theoretical analysis and simulation experiments, the influencing factors of atmospheric transmission and sky background radiance are studied, and the influencing factors are normalized into the maximum detection range model by polynomial fitting. The results indicate that a high atmospheric transmission comes from a high altitude and low target zenith angle; a low sky background radiance comes from a small target zenith angle and low solar altitude angle, while the angular distance has no obvious influence on the sky background radiance. The experimental results indicate that the comprehensive accuracy of the maximum detection range model of the system is 86%, and the effectiveness of the model is verified by using a 1064 nm wavelength laser ranging for the debris target with a distance of 700–1100 km and a cross section area of 4–10 m². The model can be used to evaluate the ability of the space debris laser ranging system at a 1064 nm wavelength. Full article

(This article belongs to the Special Issue Space-Geodetic Techniques II)

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