Determining gravity potential difference via VLBI time comparisons

2021 ◽  
Author(s):  
Yifan Wu ◽  
Wen-Bin Shen
Keyword(s):  
High Reliability ◽  
Space Station ◽  
Potential Difference ◽  
Gravity Potential ◽  
Atomic Clocks ◽  
Height System ◽  
Celestial Bodies ◽  
Excellent Work ◽  
Present Simulation ◽  
Comparison Technique

<p>VLBI technique plays important role in both astronomy and geodesy due its fantastic ability to determine the position of celestial bodies and the length of baseline on Earth. Moreover it also presents excellent work on time comparisons between atomic clocks located in remote positions where optical fiber links are not accessible. Due to its high reliability and stability, the information of Earth’s gravity field can be extracted from VLBI time comparisons in the framework of general relativity. In this study, we provide a formulation to determine the gravity potential difference by VLBI time comparisons. In fact the precision of the estimated gravity potential depends on the performance of participated clocks and the accuracy of time comparison technique. Thus we present simulation experiments using clocks with 10<sup>-16</sup>@1d stability and broadband VLBI observation and determine gravity potential difference within a VLBI network around world with 10 m<sup>2</sup>/s<sup>2 </sup>precision which is equivalent to 1 m in height. The results could be greatly improved using optical atomic clocks with much higher stabilities. Furthermore it can be applied to height transfer across oceans and unifying the height system. This study is supported by the National Natural Science Foundations of China (NSFC) under Grants 42030105, 41721003, 41804012, 41631072, 41874023, and Space Station Project (2020)228.</p>

scholarly journals The peril of adjusting for baseline when using change as a predictor

2019 ◽  
Author(s):  
Kimmo Sorjonen ◽  
Daniel Falkstedt ◽  
Bo Melin ◽  
Michael Ingre
Keyword(s):  
High Risk ◽  
Sample Size ◽  
Simulation Study ◽  
Strong Correlation ◽  
High Reliability ◽  
Large Sample Size ◽  
Present Simulation ◽  
Very High ◽  
Time Point

Some studies have analyzed the effect of a predictor measured at a later time point (X1), or of the X1-X0 difference, while adjusting for the predictor measured at baseline (X0), on some outcome Y of interest. The present simulation study shows that, if used to analyze the effect of change in X on Y, there is a high risk for this analysis to produce type 1-errors, especially with a strong correlation between true X and Y, when X0 and X1 are not measured with very high reliability, and with a large sample size. These problems are not encountered if analyzing the unadjusted effect of the X1-X0 difference on Y instead, and as this effect exhibits power on par with the adjusted effect it seems as the preferable method when using change between two measurement points as a predictor.

An Approach for Determining the Geopotential Difference between The Atomic Clocks Ensemble in Space (ACES) and a ground station

2020 ◽  
Author(s):  
Mostafa Ashry ◽  
Wenbin Shen ◽  
Xiao Sun
Keyword(s):  
Simulation Experiment ◽  
Current Status ◽  
Atomic Clocks ◽  
Theory Of Relativity ◽  
General Theory Of Relativity ◽  
Ground Station ◽  
Wide Range ◽  
Height System ◽  
Key Aspects ◽  
Near Future

<p>According to the general theory of relativity, two clocks placed at two different positions with different geopotential run at different rates. Thus one can determine the geopotential difference between these two points by comparing the running rates of the two clocks. In this paper, we propose, design and describe in detail an approach for determining the geopotential difference between The Atomic Clocks Ensemble in Space (ACES/PHARAO mission) and a ground station based upon a simulation experiment. The correction due to Ionosphere, troposphere and Sagnac effect will be taken into account. Our team is working on a wide range of problems that need to be solved in order to achieve high accuracy in (almost) real-time. In this paper, we will present some key aspects of the measurement, as well as the current status of the software's development. the proposed approach may have prospective applications in geoscience, and especially, based on this approach a unified world height system could be realized with one-centimetre level accuracy in the near future.</p>

scholarly journals DEVELOPMENT OF DECISION TOOL FOR A PROBLEM-SOLVING ACTIVITY USING PAIRWISE COMPARISON TECHNIQUE TO SUPPORT AN INTUITIVE DECISION

2020 ◽  
Vol 1 ◽  
pp. 423-430
Author(s):  
N. Tanaiutchawoot ◽  
N. Bursac ◽  
J. Gross ◽  
S. Rapp ◽  
A. Albers
Keyword(s):  
Product Development ◽  
High Reliability ◽  
Pairwise Comparison ◽  
New Product ◽  
Decision Tool ◽  
Interactive Interface ◽  
Processing Information ◽  
User Friendly ◽  
Comparison Technique ◽  
Decision Errors

AbstractPairwise comparison is basically used to prioritize alternatives and select a solution in product development. Decision errors can happen when the amount of processing information increases. This research proposes an assisted decision tool to prioritize alternatives by using the pairwise comparison technique and a Quicksort algorithm. This software was evaluated in the product development workshop that aims to select the component to further develop in the new product generation. This tool provides high-reliability results, reduces procedure time and is a user-friendly interactive interface.

Determination of the Geopotential Difference between Atomic Clock Ensemble in Space (ACES) and Ground Station using the Tri-Frequency Combination (TFC) Method

2021 ◽  
Author(s):  
Mostafa Ashry ◽  
Wenbin Shen ◽  
Ziyu Shen ◽  
Hussein A. Abd-Elmotaal ◽  
Abdelrahim ruby ◽  
...  
Keyword(s):  
Natural Science ◽  
Doppler Effect ◽  
High Performance ◽  
Atomic Clock ◽  
Space Station ◽  
Earth Tide ◽  
Relativity Theory ◽  
Atomic Clocks ◽  
Clock Signal ◽  
Ku Band

<p>According to general relativity theory, a precise clock runs at different rates at positions with different geopotentials. Atomic Clock Ensemble in Space (ACES) is a mission using high-performance clocks and links to test fundamental laws of physics in space. The ACES microwave link (MWL) will make the ACES clock signal available to ground laboratories equipped with atomic clocks. The ACES-MWL will allow space-to-ground and ground-to-ground comparisons of atomic frequency standards. This study aims to apply the tri-frequency combination (TFC) method to determine the geopotential difference between the ACES and a first order triangulation station in Egypt. The TFC uses the uplink of carrier frequency 13.475 GHz (Ku band) and downlinks of carrier frequencies 14.70333 GHz (Ku band) and 2248 MHz (S-band) to transfer time and frequency. Here we present a simulation experiment. In this experiment, we use the international space station (ISS) orbit data, ionosphere and troposphere models, regional gravitational potential and geoid for Africa, solid Earth tide model, and simulated clock data by a conventionally accepted stochastic noises model. The scientific object requires stabilities of atomic clocks at least 3 × 10 <sup>−16</sup> /day, so we must consider various effects, including the Doppler effect, second-order Doppler effect, atmospheric frequency shift, tidal effects, refraction caused by the atmosphere, and Shapiro effect, with accuracy levels of decimetres. This study is supported by the National Natural Science Foundations of China (NSFC) under Grants 42030105, 41721003, 41804012, 41631072, 41874023, Space Station Project (2020)228, and the Natural Science Foundation of Hubei Province of China under Grant 2019CFB611.</p>

FUNDAMENTAL PHYSICS ACTIVITIES IN THE HME DIRECTORATE OF THE EUROPEAN SPACE AGENCY

2007 ◽  
Vol 16 (12a) ◽  
pp. 1957-1966
Author(s):  
LUIGI CACCIAPUOTI ◽  
OLIVIER MINSTER
Keyword(s):  
Inertial Sensors ◽  
European Space Agency ◽  
Atomic Clock ◽  
Space Station ◽  
Matter Wave ◽  
Microgravity Environment ◽  
Atomic Clocks ◽  
Space Applications ◽  
Fundamental Physics ◽  
Space Agency

The Human Spaceflight, Microgravity, and Exploration (HME) Directorate of the European Space Agency is strongly involved in fundamental physics research. One of the major activities in this field is represented by the ACES (Atomic Clock Ensemble in Space) mission. ACES will demonstrate the high performances of a new generation of atomic clocks in the microgravity environment of the International Space Station (ISS). Following ACES, a vigorous research program has been recently approved to develop a second generation of atomic quantum sensors for space applications: atomic clocks in the optical domain, aiming at fractional frequency stability and accuracy in the low 10-18 regime; inertial sensors based on matter-wave interferometry for the detection of tiny accelerations and rotations; a facility to study degenerate Bose gases in space. Tests of quantum physics on large distance scales represent another important issue addressed in the HME program. A quantum communication optical terminal has been proposed to perform a test of Bell's inequalities on pairs of entangled photons emitted by a source located on the ISS and detected by two ground stations. In this paper, present activities and future plans will be described and discussed.

Optic-fiber gravity frequency transfer network

2021 ◽  
Author(s):  
Anh The Hoang ◽  
WenBin Shen
Keyword(s):  
Optical Fibers ◽  
Rapid Development ◽  
Space Station ◽  
Orthometric Height ◽  
Relativity Theory ◽  
Gravity Potential ◽  
General Relativity Theory ◽  
Long Time ◽  
High System ◽  
Frequency Transfer

<p>According to<strong> </strong>Einstein’s general relativity theory (GRT), a clock at a position with higher potential runs faster than a clock at a position with lower potential. Hence, inversely, one can determine the gravity potential (geopotential) and orthometric height based on precise clocks. If a clock with an accuracy of 10<sup>-18</sup> is used, the geopotential difference between two points can be determined with an accuracy of centimeters level.<strong> </strong>With the rapid development of science and technology, optical clocks achieve 10<sup>-18</sup> stability, which opens up opportunity for scientists to practically determine geopotential as well as orthometric height using optical clocks. One of the challenges of classical geodesic in the long time has been the unification of local hight systems. To complete this task is very difficult because each country has a regional high system. This problem can be solved if using a clock network, which overcomes the weaknesses of the spirit leveling method. Here we provide a formulation to establish a model of a network using optical clocks linked together by optical fibers for the purpose of determining the geopotential and establishing a unified world hight system at centimeter accuracy level. This study is supported by National Natural Science Foundation of China (NSFC) (grant Nos. 41721003, 42030105, 41631072, 41874023, 41804012), and Space Station Project (2020)228.</p><p><strong>Key words:</strong><strong> </strong>GRT, optical clocks network, frequency transfer, geopotential, orthometric height</p>

Design and Kinematic Analysis of a New Grapple Mechanism

2012 ◽  
Vol 605-607 ◽  
pp. 239-243
Author(s):  
Fei Deng ◽  
Jin Bao Chen ◽  
Meng Chen ◽  
Fu Jun Peng
Keyword(s):  
Kinematic Analysis ◽  
High Reliability ◽  
Space Station ◽  
Simple Construction ◽  
Working Process ◽  
End Effector ◽  
Parameter Variations ◽  
New Type ◽  
Working Principle

Combined with China's demand for space station construction, a new type of lock system for end effector is developed. This grapple mechanism makes grappling, pulling and rigidization in one mechanism which is simple construction and high reliability. The composition and the working principle of this grapple mechanism are introduced. Then, the singularity of the mechanism is analyzed and its kinematics equations are established. The parameter variations are obtained by using PROE. The results show that the working process adapts to the variation of the motion and force between the end effector and target adapter perfectly.

scholarly journals A Quasigeoid-Derived Transformation Model Accounting for Land Subsidence in the Mekong Delta towards Height System Unification in Vietnam

2020 ◽  
Vol 12 (5) ◽  
pp. 817
Author(s):  
Dinh Toan Vu ◽  
Sean Bruinsma ◽  
Sylvain Bonvalot ◽  
Dominique Remy ◽  
Georgios S. Vergos
Keyword(s):  
Mekong Delta ◽  
Equipotential Surface ◽  
Transformation Model ◽  
Gravity Potential ◽  
Third Order ◽  
Vertical Datum ◽  
Height System ◽  
Gravimetric Quasigeoid ◽  
Local Vertical Datum

A vertical offset model for Vietnam and its surrounding areas was determined based on the differences between height anomalies derived from 779 Global Navigation Satellite System (GNSS)/levelling points and those derived from a dedicated high-resolution gravimetric-only quasigeoid model called GEOID_LSC. First, the deterministic transformation model to effectively fit the differences between the quasigeoid and GNSS/levelling heights was based on a third-order polynomial model. Second, the residual height anomalies have been interpolated to a grid employing Least-Squares Collocation. Finally, the distortions were restored to the residual grid. This model can be used for combination with a gravimetric quasigeoid model in GNSS levelling. The quality of GNSS/levelling data in Vietnam was analyzed and evaluated in this study. The annual subsidence rate from ALOS-1 was also used to analyze the effects of subsidence on the quality of GNSS/levelling data in the Mekong Delta. From this we made corrections to improve the accuracy of GNSS/levelling data in this region. The offset model was evaluated using cross-validation technique by comparing with GNSS/levelling data. Results indicate that the offset model has a standard deviation of 5.9 cm in the absolute sense. Based on this offset model, GNSS levelling can be carried out in most of Vietnam’s territory complying third-order levelling requirements, while the accuracy requirements for fourth-order levelling networks is met for the entire country. This model in combination with the developed gravimetric quasigeoid model should also contribute to the modernization of Vietnam’s height system. We also used high-quality GNSS/levelling data and the determined quasigeoid model to determine the geopotential value W0 for the Vietnam Local Vertical Datum. The gravity potential of the Vietnam Local Vertical Datum is estimated equal to W 0 LVD = 62,636,846.81 ± 0.70 m2s−2 with the global equipotential surface realized by the conventional value W0 = 62,636,853.4 m2s−2.

Sign in / Sign up

Export Citation Format

Share Document