scholarly journals Strategy for the realisation of the International Height Reference System (IHRS)

2021 ◽  
Vol 95 (3) ◽  
Author(s):  
Laura Sánchez ◽  
Jonas Ågren ◽  
Jianliang Huang ◽  
Yan Ming Wang ◽  
Jaakko Mäkinen ◽  
...  
Keyword(s):  
Gravity Field ◽  
Reference System ◽  
International Association ◽  
Accuracy Assessment ◽  
Equipotential Surface ◽  
Precise Determination ◽  
Gravity Models ◽  
Reference Network ◽  
Global Gravity Models

AbstractIn 2015, the International Association of Geodesy defined the International Height Reference System (IHRS) as the conventional gravity field-related global height system. The IHRS is a geopotential reference system co-rotating with the Earth. Coordinates of points or objects close to or on the Earth’s surface are given by geopotential numbersC(P) referring to an equipotential surface defined by the conventional valueW0 = 62,636,853.4 m2 s−2, and geocentric Cartesian coordinatesXreferring to the International Terrestrial Reference System (ITRS). Current efforts concentrate on an accurate, consistent, and well-defined realisation of the IHRS to provide an international standard for the precise determination of physical coordinates worldwide. Accordingly, this study focuses on the strategy for the realisation of the IHRS; i.e. the establishment of the International Height Reference Frame (IHRF). Four main aspects are considered: (1) methods for the determination of IHRF physical coordinates; (2) standards and conventions needed to ensure consistency between the definition and the realisation of the reference system; (3) criteria for the IHRF reference network design and station selection; and (4) operational infrastructure to guarantee a reliable and long-term sustainability of the IHRF. A highlight of this work is the evaluation of different approaches for the determination and accuracy assessment of IHRF coordinates based on the existing resources, namely (1) global gravity models of high resolution, (2) precise regional gravity field modelling, and (3) vertical datum unification of the local height systems into the IHRF. After a detailed discussion of the advantages, current limitations, and possibilities of improvement in the coordinate determination using these options, we define a strategy for the establishment of the IHRF including data requirements, a set of minimum standards/conventions for the determination of potential coordinates, a first IHRF reference network configuration, and a proposal to create a component of the International Gravity Field Service (IGFS) dedicated to the maintenance and servicing of the IHRS/IHRF.

Towards a Global Unified Physical Height System

2021 ◽  
Author(s):  
Laura Sanchez ◽  
Jianliang Huang ◽  
Riccardo Barzaghi ◽  
Georgios S. Vergos
Keyword(s):  
Gravity Field ◽  
Reference Frame ◽  
Reference System ◽  
International Association ◽  
Equipotential Surface ◽  
Terrestrial Reference Frame ◽  
Global Network ◽  
Main Challenge ◽  
Physical Height

<p>The International Association of Geodesy (IAG), as the organisation responsible for advancing Geodesy, introduced in 2015 the International Height Reference System (IHRS) as the global conventional reference system for the determination of gravity field-related vertical coordinates. The definition of the IHRS is given in terms of potential parameters: the vertical coordinates are geopotential numbers (C<sub>P</sub> = W<sub>0</sub> ‐ W<sub>P</sub>) referring to an equipotential surface of the Earth's gravity field realised by the conventional value W<sub>0</sub> = 62 636 853.4 m<sup>2</sup>s<sup>‐2</sup>. The spatial reference of the position P for the potential W<sub>P</sub> = W(<strong>X</strong>) is given by coordinates <strong>X</strong> of the International Terrestrial Reference Frame (ITRF). At present, the main challenge is the realisation of the IHRS; i.e., the establishment of the International Height Reference Frame (IHRF): a global network with regional and national densifications, whose geopotential numbers referring to the global IHRS are known. According to the objectives of the IAG Global Geodetic Observing System (GGOS), the target accuracy of these global geopotential numbers is 3 x 10<sup>-2</sup> m<sup>2</sup>s<sup>-2</sup>. In practice, the precise realisation of the IHRS is limited by different aspects; for instance, there are no unified standards for the determination of the potential values W<sub>P</sub>; the gravity field modelling and the estimation of the position vectors <strong>X</strong> follow different conventions; the geodetic infrastructure is not homogeneously distributed globally, etc. This may restrict the expected accuracy of 3 x 10<sup>-2</sup> m<sup>2</sup>s<sup>-2 </sup>to some orders lower (from 10 x 10<sup>-2</sup> m<sup>2</sup>s<sup>-2</sup> to 100 x 10<sup>-2</sup> m<sup>2</sup>s<sup>-2</sup>). This contribution summarises advances and present challenges in the establishment of the IHRS/IHRF.</p>

ASTROD–AN OVERVIEW

2002 ◽  
Vol 11 (07) ◽  
pp. 947-962 ◽  
Author(s):  
WEI-TOU NI
Keyword(s):  
Angular Momentum ◽  
Solar System ◽  
Gravitational Wave ◽  
Reference System ◽  
Precise Determination ◽  
The Sun ◽  
Gravitational Wave Detection ◽  
Wave Detection ◽  
The Earth

The objectives of the Astrodynamical Space Test of Relativity using Optical Devices (ASTROD) Mission concept are threefold. The first objective is to discover and explore fundamental physical laws governing matter, space and time via testing relativistic gravity with 3-6 orders of magnitude improvement. Relativistic gravity is an important cornerstone of physics, astronomy and cosmology. Its improved test is crucial to cosmology and modern theories of gravitation including superstring theories. Included in this objective is the precise determination of the relativistic parameters β and γ, the improved measurement of Ġ and a precise determination of an anomalous, constant acceleration directed towards the Sun. The second objective of the ASTROD mission is the high-precision measurement of the solar-system parameter. This includes: (i) a measurements of solar angular momentum via Lense-Thirring effect and the detection of solar g-mode oscillations via their changing gravity field, thus, providing a new eye to see inside the Sun; (ii) precise determination of the planetary orbit elements and masses; (iii) better determination of the orbits and masses of major asteroids. These measurements give better solar dynamics and probe the origin of our solar system. The third objective is to detect and observe gravitational waves from massive black holes and galactic binary stars in the frequency range 50 μHz to 5 mHz. Background gravitational -waves will also be explored. A desirable implementation is to have two spacecraft in separate solar orbit carrying a payload of a proof mass, two telescopes, two 1-2 W lasers, a clock and a drag-free system, together with an Earth reference system. the two spacecraft range coherently with the Earth reference system using lasers. When they are near, they range coherently to each other. The Earth reference system could be ground stations, Earth satellites and/or spacecraft near Earth-Sun Lagrange points. In this overview, we discuss the payload concept, the technological requirements, technological developments, orbit design, orbit simulation, the measurement of solar angular momentum, the gravitational-wave detection sensitivity, and the solar g-mode detection possibility for this mission concept. A simplified mission, Mini-ASTROD with one spacecraft ranging optically with ground stations, together with Super-ASTROD with four spacecraft of 5 AU (Jupiter-like) orbits, will be mentioned in the end. Super-ASTROD is a dedicated low-frequency gravitational-wave detection concept. For Mini-ASTROD, the first objective of ASTROD will be largely achieved; the second objective will be partially achieved; for gravitational wave detection, the sensitivity will be better than the present-day sensitivity using Doppler tracking by radio waves.

Optical clocks for gravity field observation and further geodetic applications

2020 ◽  
Author(s):  
Hu Wu ◽  
Jürgen Müller ◽  
Annike Knabe
Keyword(s):  
Gravity Field ◽  
Rapid Development ◽  
Satellite Orbit ◽  
Equipotential Surface ◽  
Gravity Potential ◽  
Height Difference ◽  
The Earth ◽  
Temporal Gravity ◽  
Reference Clock

<p>In the past three decades, optical clocks and frequency transfer techniques have experienced a rapid development. They are approaching a fractional frequency uncertainty of 1.0x10<sup>-18</sup>, corresponding to about 1.0 cm in height. This makes them promising to realize “relativistic geodesy”, and it opens a new door to directly obtain gravity potential values by the comparison of clock frequencies. Clocks are thus considered as a novel candidate for determining the Earth’s gravity field. We propose to use a spaceborne clock to obtain gravity potential values along a satellite orbit through its comparison with reference clocks on ground or with a co-orbital clock. The sensitivity of clock measurements is mapped to gravity field coefficients through closed-loop simulations.</p><p>In addition, clocks are investigated for other geodetic applications. Since they are powerful in providing the height difference between distant sites, clocks can be applied for the unification of local/regional height systems, by estimating the offsets between different height datums and the systematic errors within levelling networks. In some regions like Greenland, clocks might be a complementary tool to GRACE(-FO) for detecting temporal gravity signals. They can be operated at locations of interest and continuously track changes w.r.t. reference clock stations. The resulting time-series of gravity potential values reveal the temporal gravity signals at these points. Moreover, as the equipotential surface at a high satellite altitude is more regular than that on the Earth’s surface, a couple of clocks in geostationary orbits can realize a space-based reference for the determination of physical heights at any point on the Earth through clock comparisons.</p><p>We gratefully acknowledge the financial support by the Deutsche Forschungsgemeinschaft (DFG) under Germany’s Excellence Strategy EXC-2123/1 (Project-ID: 390837967).</p>

scholarly journals Indoor height determination of the new absolute gravimetric station of L'Aquila

2020 ◽  
Vol 63 (Vol 63 (2020)) ◽  
Author(s):  
Marco Fortunato ◽  
Augusto Mazzoni ◽  
Giovanna Berrino ◽  
Filippo Greco ◽  
Federica Riguzzi ◽  
...  
Keyword(s):  
Gravity Field ◽  
Equipotential Surface ◽  
Absolute Gravity ◽  
Post Processing ◽  
Height Difference ◽  
Geoidal Undulation ◽  
Height Determination ◽  
Topographic Survey ◽  
Gravity Measurements

In this paper we describe all the field operations and the robust post-processing proceduresto determine the height of the new absolute gravimetric station purposely selected to belong to a new absolute gravimetric network and located in the Science Faculty of the L’Aquila University. This site has been realized indoor in the Geomagnetism laboratory, so that the height cannot be measured directly, but linking it to the GNSS antenna of AQUI benchmark located on the roof of the same building, by a classical topographic survey. After the topographic survey, the estimated height difference between AQUI and the absolute gravimetric site AQUIgis 14.9700.003 m. At the epoch of the 2018 gravimetric measures, the height of AQUI GNSS station was 712.9740.003 m, therefore the estimated ellipsoidalheight of the gravimetric site at the epoch of gravity measurements is 698.0040.005 m. Absolute gravity measurements are referred to the equipotential surface of gravity field, so that the knowledge of the geoidal undulation at AQUIg allows us to infer the orthometric height as 649.32 m.

Gravity Field Implied Density Modeling of Topography, for Precise Determination of the Geoid

2008 ◽  
Vol 8 (19) ◽  
pp. 3371-3379 ◽  
Author(s):  
M. Sedighi ◽  
M. Najafi-ala ◽  
S.H. Tabatabaie
Keyword(s):  
Gravity Field ◽  
Precise Determination ◽  
Density Modeling

scholarly journals Operational infrastructure to ensure the long-term sustainability of the IHRS/IHRF

2020 ◽  
Author(s):  
Riccardo Barzaghi ◽  
Laura Sanchez ◽  
George Vergos
Keyword(s):  
Global Change ◽  
Gravity Field ◽  
Reference System ◽  
International Association ◽  
Field Service ◽  
Future Developments ◽  
Vertical Datum ◽  
System Changes ◽  
Local Levels

<p>An objective of the International Height Reference System (IHRS) and its realization (the IHRF) is to support the monitoring and analysis of Earth’s system changes. The more accurate the IHRS/IHRF is, the more phenomena can be identified and modelled. Thus, the IHRS/IHRF must provide vertical coordinates and their changes with time as accurately as possible. As many global change phenomena occur at different scales, the global frame should be extended to regional and local levels to guarantee consistency in the observation, detection, and modelling of their effects. From this perspective, an operational infrastructure is needed to ensure the long-term sustainability of the IHRS/IHRF. In this contribution, we discuss the possibility of establishing such as infrastructure within the International Association of Geodesy (IAG) and its International Gravity Field Service (IGFS). Some aspects to be considered are:</p><ul><li>- Improvements in the IHRS definition and realization following future developments in geodetic theory, observations and modelling.</li> <li>- Refinement of the IHRS/IHRF standards/conventions based on the unification of the standards/conventions used by the geometric and gravity IAG Services.</li> <li>- Development of strategies for collocation of IHRF stations with existing gravity and geometrical reference stations at different densification levels.</li> <li>- Identification of the geodetic products associated with the IHRF and description of the elements to be considered in the corresponding metadata.</li> <li>- Servicing the vertical datum needs of other geosciences such as, e.g., hydrography and oceanography.</li> <li>- Implementation of a registry containing the existing local/regional height systems and their connections to the global IHRS/IHRF.</li> </ul>

PRECISE DETERMINATION OF THE IRRATIONAL PRE-FERRED INTERFACE ORIENTATION BY TEM

2010 ◽  
Vol 46 (4) ◽  
pp. 411-417 ◽  
Author(s):  
Yang MENG ◽  
Lin GU ◽  
Wenzheng ZHANG
Keyword(s):  
Precise Determination ◽  
Interface Orientation

Nauwkeurige methode voor de aanwasbepaling van het grondvlak met behulp van de Pressler-boor

1968 ◽  
Vol 12 ◽  
Author(s):  
R. Goossens
Keyword(s):  
Basal Area ◽  
Precise Determination ◽  
Maximum Diameter ◽  
Precise Method ◽  
Maximum Radius ◽  
The Core ◽  
Two Parameters

A precise method for the determination of the increment of the  basal area using the PressIer bore. Refering to  previous research showing that the basal area of the corsica pine could be  characterized by an ellips, we present in this paper a precise method for the  determination of the increment of the basal area. In this method we determine  the direction of the maximum diameter, we measure this diameter and we take a  core in one of the points of tangency of the caliper with the measured tree.  The determination of the diameter perpendicular to the maximum diameter  finishes the work wich is to be done in the forest. From the classical  measurements effectuated on the core and from the measured diameters we can  then determine the form (V) and the excentricity (e). Substituting these two  parameters in the formula 2 or 2', we can also calculate the error of a  radius measured on the core with respect to the representative radius, This  error with them allow us to correct the measured value of the minimum or the  maximum radius and we will be able to do a precise determination of the  increment.

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