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Alireza A. Ardalan - One of the best experts on this subject based on the ideXlab platform.

  • Molodensky potential telluroid based on a minimum-distance map. Case study: the quasi-geoid of East Germany in the World Geodetic Datum 2000
    Journal of Geodesy, 2002
    Co-Authors: Alireza A. Ardalan, Erik W. Grafarend, J. Ihde
    Abstract:

    A potential-type Molodensky telluroid based upon a minimum-distance mapping is derived. With respect to a reference potential of Somigliana–Pizzetti type which relates to the World Geodetic Datum 2000, it is shown that a point-wise minimum-distance mapping of the topographical surface of the Earth onto the telluroid surface, constrained to the gauge W(P)=u(p), leads to a system of four nonlinear normal equations. These normal equations are solved by a fast Newton–Raphson iteration.

  • Time Evolution of a World Geodetic Datum
    International Association of Geodesy Symposia, 2002
    Co-Authors: Erik W. Grafarend, Alireza A. Ardalan
    Abstract:

    Four fundamental Geodetic parameters, namely \(\{ GM,{W_0},\Omega ,{J_2}\} \) , determine a world Geodetic Datum. With respect to the Somigliana-Pizzetti Level Ellipsoid I International Reference Ellipsoid these fundamental parameters from best estimates at a reference epoch determine its semi-major axis a as well as its semi-minor axis b (or equivalently the linear eccentricity \(\varepsilon = \sqrt {{a^2} + {b^2}} \) . Satellite orbit analysis as well as sea level projects have indicated that the four fundamental Geodetic parameters are time-dependent, described for instance by \(\{ (CM\dot ),{\dot W},\dot \Omega ,{\dot J_2}\} \) . Here we have \(\{ (GM\dot ),{\dot W_0},\dot \Omega ,{\dot J_2}\} \) . Here we have analyzed the impact of best estimates of \(\{ {\dot W_0},{\dot J_2}\} \) on shape and size parameters, i.e., {ȧ,ḃ} and (ȧ±,), of the World Geodetic Datum 2000 (WGD2000). Based on the best estimate of time variations of \(\{ {\dot W_0},{\dot J_2}\} \) we have computed the best estimates ȧ = (0.3 ± 0.02) mm / year, ḃ= (-0.0002 ± 0.00008) mm/ year, and ɛ- = (3.7 ± 0.3) mm / year as the time variation of the shape and size parameters of the WGD 2000. The new results give a scientific basis for answering the question: Is there a need for a Geodetic Datum 2000?

  • World Geodetic Datum 2000
    Journal of Geodesy, 1999
    Co-Authors: Erik W. Grafarend, Alireza A. Ardalan
    Abstract:

    Based on the current best estimates of the fundamental Geodetic parameters, i.e., W 0 (Grafarend and Ardalan, Journal of Geodesy 71 (1997) 673-679), GM (Ries et al, Geophys. Res. Letters 19 (1992) 529-531), J 2 (Lemoine et al, GRAGEO-MAR 1996, International Association of Geodesy, Symposia 117, (1996) 461-469) and Ω (given in Internal Communications of IAG/IUGG Special Commission 3, Darmstadt (1997)), the form parameters of a Somigliana-Pizetti level ellipsoid, namely the semi-major axis a and semi-minor axis b (or equivalents the linear eccentricity ɛ = √a 2 - b 2 ) are computed. There are six parameters namely the four fundamental Geodetic parameters {W 0 , GM, J 2 , Ω} and the two form parameters {a, b} or {a, ɛ}, which determine the ellipsoidal reference gravity field of Somigliana-Pizetti type constraint to two nonlinear condition equations. Their iterative solution leads to best estimates a = (6378136.572 ±0.053)m, b = (6356751.920 ±0.052)m, ɛ= (521853.580 ±0.013)m for the tide-free geoid of reference and a = (6378136.602 ±0.053)m, b = (6356751.860 ± 0.052)m, ɛ= (521854.674 ±0.015)m for the zero-frequency tide geoid of reference. The best estimates of the form parameters of a Somigliana-Pizetti level ellipsoid, {a, b}, differ significantly by -0.398m, -0.454m, respectively, from the data of the Geodetic Reference System 1980.

Nic Donnelly - One of the best experts on this subject based on the ideXlab platform.

  • From geophysics to Geodetic Datum: updating the NZGD2000 deformation model
    New Zealand Journal of Geology and Geophysics, 2016
    Co-Authors: Chris Crook, Nic Donnelly, John Beavan, Chris Pearson
    Abstract:

    ABSTRACTThe deformation model is a critical component of New Zealand Geodetic Datum 2000 (NZGD2000), the official reference frame for New Zealand. The model is used to manage the relationship between the NZGD2000 and the global International Terrestrial Reference Frame (ITRF), in which precise Geodetic measurements are made. Consequently, the deformation model has a direct impact on NZGD2000 coordinates. With improved knowledge of the secular deformation field and models of significant earthquakes to have affected New Zealand since 2000 now being available, the decision was made to update the deformation model. At the same time, the 14-parameter transformation between ITRFs to be used in New Zealand was officially defined.

  • special feature managing the dynamics of the new zealand spatial cadastre
    Journal of Spatial Science, 2015
    Co-Authors: Donald Grant, Nic Donnelly, Chris Crook, Matt Amos, John Ritchie, Craig Roberts
    Abstract:

    In 1995, a dynamic cadastre, based on a dynamic Geodetic Datum, was proposed for New Zealand to recognise that all cadastral boundaries are in motion. Subsequently New Zealand implemented a semi-dynamic Geodetic Datum which is accompanied by a deformation model. In 2010 and 2011, the Canterbury region in the South Island of New Zealand was subjected to a sequence of earthquakes that resulted in some boundaries being ruptured by up to 4 metres. A set of localised deformation models was developed to model the seismic movements. The implementation of these models and their accuracy are addressed in this paper.

  • Special feature – managing the dynamics of the New Zealand spatial cadastre
    Journal of Spatial Science, 2014
    Co-Authors: Donald Grant, Nic Donnelly, Chris Crook, Matt Amos, John Ritchie, Craig Roberts
    Abstract:

    In 1995, a dynamic cadastre, based on a dynamic Geodetic Datum, was proposed for New Zealand to recognise that all cadastral boundaries are in motion. Subsequently New Zealand implemented a semi-dynamic Geodetic Datum which is accompanied by a deformation model. In 2010 and 2011, the Canterbury region in the South Island of New Zealand was subjected to a sequence of earthquakes that resulted in some boundaries being ruptured by up to 4 metres. A set of localised deformation models was developed to model the seismic movements. The implementation of these models and their accuracy are addressed in this paper.

  • Managing the dynamics of the New Zealand spatial cadastre
    2014
    Co-Authors: Donald Grant, Chris Crook, Nic Donnelly
    Abstract:

    In 1995, the concept of a dynamic cadastre, based on a dynamic Geodetic Datum, was proposed for New Zealand to recognize that all cadastral boundaries in New Zealand are in some form of motion - relative to each other and relative to the Geodetic Datum which is also in motion. Subsequently New Zealand implemented a semi-dynamic Geodetic Datum which is accompanied by a deformation model. Later, a survey conversion project resulted in the boundaries of 70% of the land parcels in New Zealand being coordinated to survey accuracy in terms of the semi-dynamic Datum. These boundaries continue to be adjusted by least squares as new cadastral survey observations and Geodetic control stations are integrated into the network. However the deformation model has not, in practice, been routinely applied to cadastral boundaries. In 2010 and 2011, the Canterbury region in the South Island of New Zealand was subjected to a sequence of earthquakes that caused widespread damage and resulted in some boundaries being ruptured by up to 4 metres. A set of localized deformation models was developed to model the seismic movements. Propagating these movements through to all affected cadastral boundaries has proved to be a major undertaking which is described in this paper

  • Maintaining Accurate Coordinates for Geospatial Datasets after a Geodetic Datum Update
    2009
    Co-Authors: Nic Donnelly
    Abstract:

    SUMMARY With ever-increasing demands for accuracy, Geodetic Datum updates are becoming more frequent. In its widest sense, a Geodetic Datum update can include anything from updating the coordinates of a single mark, to establishing a new Datum affecting hundreds of thousands of Geodetic marks. The Geodetic Datum provides the underlying spatial framework for numerous other geospatial datasets, including cadastral, engineering and topographic. Often significant effort is expended to ensure that these datasets are in terms of an accurate Geodetic Datum. However, maintaining the spatial accuracy of these datasets is a problem which is often given little attention. For any dataset using Geodetic mark coordinates as control, consideration needs to be given to updating the dataset’s coordinates whenever a Geodetic update or readjustment occurs. This is particularly crucial where coordinates in the dataset have associated accuracy values and coordinates are stated to comply with a given accuracy standard. This paper outlines potential techniques for updating coordinates. Several scenarios are identified which may trigger a Geodetic Datum update. These include nationwide Datum readjustment, updates in response to a deformation event (such as an earthquake) and updates to incorporate additional observations into the Geodetic network. Knowing the nature and extent of the Geodetic update is important, as this will affect the technique chosen to maintain the accuracy of geospatial datasets. An approach is suggested, which considers the problem in two parts: how to update coordinates and how to update the accuracy values on those coordinates. For some scenarios, both coordinates and accuracy values will need to be updated, in others only the coordinates. It is the characteristics of the Geodetic update which will determine what needs to be updated. Techniques for updating coordinates and accuracy values are identified, linking them to the Geodetic update scenarios for which they should be considered. The New Zealand cadastre is used as an example.

Chris Crook - One of the best experts on this subject based on the ideXlab platform.

  • From geophysics to Geodetic Datum: updating the NZGD2000 deformation model
    New Zealand Journal of Geology and Geophysics, 2016
    Co-Authors: Chris Crook, Nic Donnelly, John Beavan, Chris Pearson
    Abstract:

    ABSTRACTThe deformation model is a critical component of New Zealand Geodetic Datum 2000 (NZGD2000), the official reference frame for New Zealand. The model is used to manage the relationship between the NZGD2000 and the global International Terrestrial Reference Frame (ITRF), in which precise Geodetic measurements are made. Consequently, the deformation model has a direct impact on NZGD2000 coordinates. With improved knowledge of the secular deformation field and models of significant earthquakes to have affected New Zealand since 2000 now being available, the decision was made to update the deformation model. At the same time, the 14-parameter transformation between ITRFs to be used in New Zealand was officially defined.

  • special feature managing the dynamics of the new zealand spatial cadastre
    Journal of Spatial Science, 2015
    Co-Authors: Donald Grant, Nic Donnelly, Chris Crook, Matt Amos, John Ritchie, Craig Roberts
    Abstract:

    In 1995, a dynamic cadastre, based on a dynamic Geodetic Datum, was proposed for New Zealand to recognise that all cadastral boundaries are in motion. Subsequently New Zealand implemented a semi-dynamic Geodetic Datum which is accompanied by a deformation model. In 2010 and 2011, the Canterbury region in the South Island of New Zealand was subjected to a sequence of earthquakes that resulted in some boundaries being ruptured by up to 4 metres. A set of localised deformation models was developed to model the seismic movements. The implementation of these models and their accuracy are addressed in this paper.

  • Special feature – managing the dynamics of the New Zealand spatial cadastre
    Journal of Spatial Science, 2014
    Co-Authors: Donald Grant, Nic Donnelly, Chris Crook, Matt Amos, John Ritchie, Craig Roberts
    Abstract:

    In 1995, a dynamic cadastre, based on a dynamic Geodetic Datum, was proposed for New Zealand to recognise that all cadastral boundaries are in motion. Subsequently New Zealand implemented a semi-dynamic Geodetic Datum which is accompanied by a deformation model. In 2010 and 2011, the Canterbury region in the South Island of New Zealand was subjected to a sequence of earthquakes that resulted in some boundaries being ruptured by up to 4 metres. A set of localised deformation models was developed to model the seismic movements. The implementation of these models and their accuracy are addressed in this paper.

  • Managing the dynamics of the New Zealand spatial cadastre
    2014
    Co-Authors: Donald Grant, Chris Crook, Nic Donnelly
    Abstract:

    In 1995, the concept of a dynamic cadastre, based on a dynamic Geodetic Datum, was proposed for New Zealand to recognize that all cadastral boundaries in New Zealand are in some form of motion - relative to each other and relative to the Geodetic Datum which is also in motion. Subsequently New Zealand implemented a semi-dynamic Geodetic Datum which is accompanied by a deformation model. Later, a survey conversion project resulted in the boundaries of 70% of the land parcels in New Zealand being coordinated to survey accuracy in terms of the semi-dynamic Datum. These boundaries continue to be adjusted by least squares as new cadastral survey observations and Geodetic control stations are integrated into the network. However the deformation model has not, in practice, been routinely applied to cadastral boundaries. In 2010 and 2011, the Canterbury region in the South Island of New Zealand was subjected to a sequence of earthquakes that caused widespread damage and resulted in some boundaries being ruptured by up to 4 metres. A set of localized deformation models was developed to model the seismic movements. Propagating these movements through to all affected cadastral boundaries has proved to be a major undertaking which is described in this paper

Erik W. Grafarend - One of the best experts on this subject based on the ideXlab platform.

  • Molodensky potential telluroid based on a minimum-distance map. Case study: the quasi-geoid of East Germany in the World Geodetic Datum 2000
    Journal of Geodesy, 2002
    Co-Authors: Alireza A. Ardalan, Erik W. Grafarend, J. Ihde
    Abstract:

    A potential-type Molodensky telluroid based upon a minimum-distance mapping is derived. With respect to a reference potential of Somigliana–Pizzetti type which relates to the World Geodetic Datum 2000, it is shown that a point-wise minimum-distance mapping of the topographical surface of the Earth onto the telluroid surface, constrained to the gauge W(P)=u(p), leads to a system of four nonlinear normal equations. These normal equations are solved by a fast Newton–Raphson iteration.

  • Time Evolution of a World Geodetic Datum
    International Association of Geodesy Symposia, 2002
    Co-Authors: Erik W. Grafarend, Alireza A. Ardalan
    Abstract:

    Four fundamental Geodetic parameters, namely \(\{ GM,{W_0},\Omega ,{J_2}\} \) , determine a world Geodetic Datum. With respect to the Somigliana-Pizzetti Level Ellipsoid I International Reference Ellipsoid these fundamental parameters from best estimates at a reference epoch determine its semi-major axis a as well as its semi-minor axis b (or equivalently the linear eccentricity \(\varepsilon = \sqrt {{a^2} + {b^2}} \) . Satellite orbit analysis as well as sea level projects have indicated that the four fundamental Geodetic parameters are time-dependent, described for instance by \(\{ (CM\dot ),{\dot W},\dot \Omega ,{\dot J_2}\} \) . Here we have \(\{ (GM\dot ),{\dot W_0},\dot \Omega ,{\dot J_2}\} \) . Here we have analyzed the impact of best estimates of \(\{ {\dot W_0},{\dot J_2}\} \) on shape and size parameters, i.e., {ȧ,ḃ} and (ȧ±,), of the World Geodetic Datum 2000 (WGD2000). Based on the best estimate of time variations of \(\{ {\dot W_0},{\dot J_2}\} \) we have computed the best estimates ȧ = (0.3 ± 0.02) mm / year, ḃ= (-0.0002 ± 0.00008) mm/ year, and ɛ- = (3.7 ± 0.3) mm / year as the time variation of the shape and size parameters of the WGD 2000. The new results give a scientific basis for answering the question: Is there a need for a Geodetic Datum 2000?

  • World Geodetic Datum 2000
    Journal of Geodesy, 1999
    Co-Authors: Erik W. Grafarend, Alireza A. Ardalan
    Abstract:

    Based on the current best estimates of the fundamental Geodetic parameters, i.e., W 0 (Grafarend and Ardalan, Journal of Geodesy 71 (1997) 673-679), GM (Ries et al, Geophys. Res. Letters 19 (1992) 529-531), J 2 (Lemoine et al, GRAGEO-MAR 1996, International Association of Geodesy, Symposia 117, (1996) 461-469) and Ω (given in Internal Communications of IAG/IUGG Special Commission 3, Darmstadt (1997)), the form parameters of a Somigliana-Pizetti level ellipsoid, namely the semi-major axis a and semi-minor axis b (or equivalents the linear eccentricity ɛ = √a 2 - b 2 ) are computed. There are six parameters namely the four fundamental Geodetic parameters {W 0 , GM, J 2 , Ω} and the two form parameters {a, b} or {a, ɛ}, which determine the ellipsoidal reference gravity field of Somigliana-Pizetti type constraint to two nonlinear condition equations. Their iterative solution leads to best estimates a = (6378136.572 ±0.053)m, b = (6356751.920 ±0.052)m, ɛ= (521853.580 ±0.013)m for the tide-free geoid of reference and a = (6378136.602 ±0.053)m, b = (6356751.860 ± 0.052)m, ɛ= (521854.674 ±0.015)m for the zero-frequency tide geoid of reference. The best estimates of the form parameters of a Somigliana-Pizetti level ellipsoid, {a, b}, differ significantly by -0.398m, -0.454m, respectively, from the data of the Geodetic Reference System 1980.

Chris Pearson - One of the best experts on this subject based on the ideXlab platform.