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Precise Gravimetric Geoid Model for Iran Based on GRACE and SRTM Data and the Least-Squares Modification of Stokes’ Formula: with Some Geodynamic Interpretations
KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301).
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Iran is one of the most complicated areas in the world from the view of rough topography, tectonic activity, large lateral density and geoidal height variations. The computation of a regional gravimetric geoid model with high accuracy in mountainous regions, especially with sparse data, is a difficult task that needs a special attention to obtain reliable results which can meet the needs of the today geodetic community.

In this research different heterogeneous data has been used, which includes gravity anomalies, the high-resolution SRTM Digital Elevation Model (DEM), recently published GRACE Global Geopotential Models (GGMs), geological maps and GPS/levelling data. The above data has been optimally combined through the least-squares modification of Stokes formula with additive corrections. Regarding the data evaluation and refinement, the cross-validation technique has been used for detection of outliers. Also, several GGMs and DEMs are evaluated with GPS/levelling data. The impact of utilizing a high resolution SRTM DEM to improve the accuracy of the geoid model has been studied. Also, a density variation model has been established, and its effect on the accuracy of the geoid was investigated. Thereafter a new height datum for Iran was established based on the corrective surface idea. Finally, it was found that there is a significant correlation between the lateral geoid slope and the tectonic activities in Iran.

We show that our hybrid gravimetric geoid model IRG04 agrees considerably better with GPS/levelling than any of the other recent local geoid models in the area. Its RMS fit with GPS/levelling is 27 cm and 3.8 ppm in the absolute and relative senses, respectively. Moreover, the relative accuracy of the IRG04 geoid model is at least 4 times better than any of the previously published global and regional geoid models in the area. Also, the RMS fit of the combined surface model (IRG04C) versus independent precise GPS/levelling is almost 4 times better compared to the original gravimetric geoid model (IRG04). These achievements clearly show the effect of the new gravity database and the SRTM data for the regional geoid determination in Iran based on the least-squares modification of Stokes’ formula.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , viii, 89 p.
Series
TRITA-INFRA, ISSN 1651-0216 ; 06-003
Keyword [en]
Gravity database, least-squares modification of Stokes, geoid determination, SRTM, GRACE, GPS/levelling, density variation model, height datum, geodynamics, Iran
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:kth:diva-4125ISBN: 978-91-85539-06-2 OAI: oai:DiVA.org:kth-4125DiVA: diva2:10840
Public defence
2006-10-27, D1, Lindstedtsvägen 17, 2tr, 13:00
Opponent
Supervisors
Note

QC 20100906

Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2017-02-23Bibliographically approved
List of papers
1. Qualification and refinement of the gravity database based on cross-validation approach, A case study of Iran
Open this publication in new window or tab >>Qualification and refinement of the gravity database based on cross-validation approach, A case study of Iran
2007 (English)In: Acta Geodaetica et Geophysica, ISSN 1217-8977, Vol. 42, no 3, 285-295 p.Article in journal (Refereed) Published
Abstract [en]

In this article, we propose a technique for the precise cleaning of the gravity anomaly database based on the cross validation approach. The terrestrial gravity anomalies were compared versus a global geopotential model and take into account the effect of topography in this comparison. The efficiency of the cross-validation technique is illustrated in outlier detection as well as in choosing the proper gridding technique as a case study in construction of the Iranian new gravity database. In order to reduce the effect of topography and the discretisation error, a special interpolation scheme is used for gridding of the free-air gravity anomalies. The final grid file was created based on the Kriging method with 80" x 90" block resolution. The overall accuracy for the new Iranian gravity database is estimated in the order of 10 mGal.

Keyword
cross-validation; geoid; gravity anomaly; Iran; outlier; residual terrain model
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-6190 (URN)10.1556/AGeod.42.2007.3.3 (DOI)000258337800003 ()2-s2.0-34548009131 (Scopus ID)
Note
QC 20100906Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2010-09-06Bibliographically approved
2. Comparison of the qualities of recent global and local gravimetric geoid models in Iran
Open this publication in new window or tab >>Comparison of the qualities of recent global and local gravimetric geoid models in Iran
2005 (English)In: Studia Geophysica et Geodaetica, ISSN 0039-3169, Vol. 49, no 3, 289–304- p.Article in journal (Refereed) Published
Abstract [en]

A number of regional gravimetric geoid models have recently been determined for the Iran area, and a common problem is to select the best model, e.g. for engineering applications. A related problem is that in order to improve the local geoid models, the selection of the best Global Geopotential Model (GGM) model for the region is essential, to be used in a combined solution from GGM and local gravimetric data. We discuss these problems by taking advantage of 260 GPS/levelling points as an external tool for validation of different global and local geoid models in the absolute and relative senses. By using relative comparisons of the height differences between precise levelling and GPS/geoid models we avoid possible unknown systematic effects between the different types of observables.

The study shows that the combination of the newly released GRACE model (GGM02C) with EGM96 geoid model fits the GPS/levelling data in Iran with the best absolute and relative accuracy among the GGMs. Among the local geoid models, the newly gravimetric geoid model IRG04 agrees considerably better with GPS/levelling than any of the other recent local geoid models. Its rms fit with GPS/levelling is 55 cm. Hence, we strongly recommend the use of this new model in any surveying engineering or GPS/levelling projects in the area.

Keyword
geoid, GRACE, GGM, accuracy, GPS/levelling
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-6191 (URN)10.1007/s11200-005-0011-7 (DOI)000230691400003 ()2-s2.0-23344440297 (Scopus ID)
Note
Tidigare titel: The qualities of Iranian gravimetric geoid models versus recent gravity field missions QC 20100906 Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2010-09-06Bibliographically approved
3. Effect of the SRTM global DEM on the determination of a high-resolution geoid model: a case study in Iran
Open this publication in new window or tab >>Effect of the SRTM global DEM on the determination of a high-resolution geoid model: a case study in Iran
2005 (English)In: Journal of Geodesy, ISSN 0949-7714, E-ISSN 1432-1394, J. Geodesy, Vol. 79, no 9, 540-551 p.Article in journal (Refereed) Published
Abstract [en]

Any errors in digital elevation models (DEMs) will introduce errors directly in gravity anomalies and geoid models when used in interpolating Bouguer gravity anomalies. Errors are also propagated into the geoid model by the topographic and downward continuation (DWC) corrections in the application of Stokes's formula. The effects of these errors are assessed by the evaluation of the absolute accuracy of nine independent DEMs for the Iran region. It is shown that the improvement in using the high-resolution Shuttle Radar Topography Mission (SRTM) data versus previously available DEMs in gridding of gravity anomalies, terrain corrections and DWC effects for the geoid model are significant. Based on the Iranian GPS/levelling network data, we estimate the absolute vertical accuracy of the SRTM in Iran to be 6.5 m, which is much better than the estimated global accuracy of the SRTM (say 16 m). Hence, this DEM has a comparable accuracy to a current photogrammetric high-resolution DEM of Iran under development. We also found very large differences between the GLOBE and SRTM models on the range of -750 to 550 m. This difference causes an error in the range of -160 to 140 mGal in interpolating surface gravity anomalies and -60 to 60 mGal in simple Bouguer anomaly correction terms. In the view of geoid heights, we found large differences between the use of GLOBE and SRTM DEMs, in the range of -1.1 to 1 m for the study area. The terrain correction of the geoid model at selected GPS/levelling points only differs by 3 cm for these two DEMs.

Keyword
digital elevation model (DEM), geoid, Iran, Shuttle Radar Topography Mission (SRTM)
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-6192 (URN)10.1007/s00190-005-0006-8 (DOI)000233737600005 ()2-s2.0-30344485185 (Scopus ID)
Note
QC 20100906Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2010-09-06Bibliographically approved
4. A strategy for determining the regional geoid in developing countries by combining limited ground data with satellite-based global geopotential and topographical models: A case study of Iran
Open this publication in new window or tab >>A strategy for determining the regional geoid in developing countries by combining limited ground data with satellite-based global geopotential and topographical models: A case study of Iran
2006 (English)In: Journal of Geodesy, ISSN 0949-7714, E-ISSN 1432-1394, J. Geodesy, Vol. 79, no 10,11, 602–612- p.Article in journal (Refereed) Published
Abstract [en]

The computation of regional gravimetric geoid models with reasonable accuracy, in developing countries, with sparse data is a difficult task that needs great care. Here we investigate the procedure for gathering, evaluating and combining different data for the determination of a gravimetric geoid model for Iran, where limited ground gravity data are available. Heterogeneous data, including gravity anomalies, the high-resolution Shuttle Radar Topography Mission global digital terrain model and different global geopotential models including recently published Gravity Recovery and Climate Experiment models, are combined through least-squares modification of the Stokes formula. The new gravimetric geoid model, IRG04, agrees considerably better with GPS/levelling than any of the other recent local geoid model in the area. Its RMS fit with GPS/levelling is 0.27 m and 3.8 ppm in the absolute and relative view, respectively. The relative accuracy of IRG04 is four times better than the most recently published global and regional geoid models available in this area. This progress shows the practical potential of the method of least-squares modification of Stokes's formula in combination with heterogeneous data for regional geoid determination.

Keyword
gravity database, least-squares modification of Stokes's formula, regional geoid determination, SRTM, GRACE, GPS/levelling, Iran
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-6193 (URN)10.1007/s00190-005-0009-5 (DOI)000235270800004 ()2-s2.0-33746648141 (Scopus ID)
Note
QC 20100906Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2010-09-06Bibliographically approved
5. Hybrid precise gravimetric geoid model for Iran based on recent GRACE and SRTM data and the least squares modification of Stokes formula
Open this publication in new window or tab >>Hybrid precise gravimetric geoid model for Iran based on recent GRACE and SRTM data and the least squares modification of Stokes formula
2006 (English)In: J. Physics of Earth and Space, Vol. 32, no 1, 7-23 p.Article in journal (Refereed) Published
Abstract [en]

Since 1986, several gravimetric geoid models have been published in the Iran region. It was found thatthe standard deviation of fitting between these models versus GPS/levelling data in most cases was worsethan the currently available global geopotential models. A new hybrid gravimetric geoid model computed(IRG04) by using the least squares modification of Stokes formula based on the recent published GRACEbased global geopotential model, the high-resolution Shuttle SRTM global digital terrain model and anew Iranian gravity anomaly database. The absolute and relative accuracies of the new geoid model testedversus the GPS/levelling points and they are estimated about 0.27 m and 3.8 ppm, respectively.Additional comparison between the IRG04 and the recent published gravimetric geoid models shows thatthe relative accuracy of the IRG04 is almost 4 times better than the most recent published models in thisarea.

Keyword
Gravity database, Least-squares modification of Stokes function, Geoid determination, SRTM, GRACE, GPS/levelling, Iran
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-6194 (URN)
Note

QC 20100906

Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2017-04-12Bibliographically approved
6. A new height datum for Iran based on combination of the Gravimetric and GPS/levelling geoid models
Open this publication in new window or tab >>A new height datum for Iran based on combination of the Gravimetric and GPS/levelling geoid models
2007 (English)In: Acta Geodaetica et Geophysica, ISSN 1217-8977, Vol. 42, no 1, 69-81 p.Article in journal (Refereed) Published
Abstract [en]

A new geoid model for Iran (IRG04) was computed based on the least squares modification of the Stokes formula. IRG04 was derived from the most recent gravity anomaly database, SRTM high resolution Digital Elevation Model (DEM) and GRACE GGM02 global geopotential model. In order to define a new height datum for Iran, we attempted to combine this high resolution gravimetric geoid model with GPS/levelling data using the corrective surface approach. The corrective surface was constructed from 224 GPS/levelling points and then evaluated with 35 independent points. Different interpolation techniques were tested for the creation of the corrective surface; among them the Kriging method was selected as it gave the smallest RMS and 'noise level' at the comparisons with GPS/levelling data. The RMS fit of the new combined geoid model versus the independent GPS/levelling data is 0.09 m, it is near four times better compared to the original gravimetric geoid model. The combined model should be more convenient and useful in definition of the new height reference surface, specifically in engineering and GPS/levelling projects.

Keyword
Corrective surface, Geoid, GPS/levelling, GRACE, Kriging, Least squares modification, SRTM
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-6195 (URN)10.1556/AGeod.42.2007.1.4 (DOI)000258221700004 ()2-s2.0-33847154669 (Scopus ID)
Note
QC 20100906Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2010-09-06Bibliographically approved
7. The Impact of lateral density variation model in the determination of precise gravimetric geoid in mountainous areas: A case study of Iran
Open this publication in new window or tab >>The Impact of lateral density variation model in the determination of precise gravimetric geoid in mountainous areas: A case study of Iran
2006 (English)In: Geophysical Journal International., ISSN 0956-540X, Vol. 167, no 2, 521-527 p.Article in journal (Refereed) Published
Abstract [en]

The existence of topography above the geoid violates the basic assumption of Stokes' formula for the determination of the geoid. Usually a constant density of 2.67 g cm(-3) is used in the determination of the geoid. However, we know that the density of the topographical mass departs by about 10-20 per cent from the actual mean value of the crustal density. Iran has one of the largest relief and density variations in the world and the geoid computation in this area is affected the most by topographical density effects. The influence on the geoid height coming from the actual and Pratt-Hayford's isostatic models are studied. Numerical results show that the differences in the geoid height due to actual and isostatic density models can reach up to 0.22 and 0.29 m, respectively, which is not negligible in a precise geoid determination with centimetre accuracy. Our results suggest that the effect of topographical density lateral variations is significant enough and ought to be taken into account specially in mountainous regions in the determination of a precise geoid model.

Keyword
geoid, GPS, levelling, Iran; isostasy, lateral density variation
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-6196 (URN)10.1111/j.1365-246X.2006.03143.x (DOI)000241766800004 ()2-s2.0-33750682012 (Scopus ID)
Note
QC 20100906Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2010-09-06Bibliographically approved
8. Impact of the precise geoid model in studying tectonic structures- a case study in Iran
Open this publication in new window or tab >>Impact of the precise geoid model in studying tectonic structures- a case study in Iran
2006 (English)In: Journal of Geodynamics, ISSN 0264-3707, J. Geodynamics, Vol. 42, no 1-3, 1-11 p.Article in journal (Refereed) Published
Abstract [en]

Iran is one of the most active regions in the world with respect,to earthquakes and tectonic motions in the lithosphere. In order to study the impact of the geoid model in detecting plate tectonic boundaries and in the establishment of an accurate height datum for future geodynamic observations, a new combined gravimetric geoid model for Iran (IRG04C) was computed by the method of least squares modification of Stokes formula based on the most recent gravity anomaly database, SRTM high resolution Digital Elevation Model (DEM), GRACE GGM02 Global Geopotential Model and GPS/levelling data. The RMS fit of the new geoid model versus GPS/levelling data is 9 cm, which is a 10 times better fit compared to the most recent published gravimetric geoid model in the area. An integrated approach, combining gravity, geoid and seismology data as well as a digital elevation model, was used to find possible correlations between these parameters. Our investigation indicates that all earthquakes with magnitude over 6.0 in the Richter scale are located in areas with a geoid slope exceeding 7.5%. The study shows a significant correlation between the horizontal gradient of the geoid and plate tectonic activities.

Keyword
lateral geoid slope, plate tectonics, SRTM, GRACE, GPS/levelling, Iran
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-6197 (URN)10.1016/j.jog.2006.04.001 (DOI)000240874700001 ()2-s2.0-33747805901 (Scopus ID)
Note
QC 20100906Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2010-09-06Bibliographically approved
9. Analysis of Surface Deformation Patterns Analysis Using 3D Finite Elements Method: A case study in Skåne area, Sweden
Open this publication in new window or tab >>Analysis of Surface Deformation Patterns Analysis Using 3D Finite Elements Method: A case study in Skåne area, Sweden
2005 (English)In: J. Geodynamics, ISSN 0264-3707, Vol. 39, no 4, 403-412 p.Article in journal (Refereed) Published
Abstract [en]

The application of geodetic techniques to study crustal deformations associated with the geodynamic activity of a region is considered as a fundamental tool in seismic risk mitigation and in earthquake prediction research. In principle, the crustal deformation analysis is a purely geodetic problem as it concerns alteration of the Earth shape, so that deformations of the crust are directly connected with geodetic observables. The Tornquist zone across Skane in southern Sweden is a classical fault zone that separates the Precambrium gneisses of the Baltic shield in the north from Phanerozoic Europe to the south. In this region, a Global Positioning Network (GPS) was established to study possible crustal motions. The aim of this article is to improve on previous study in to estimate the possible crustal strains and dilation parameters by a finite element analysis. Results show that the areas with maximum shear strain and dilation are located exactly in the active fault zones and their intersections. However, further observations in a dense network as well as integration with geological and geophysical data are needed to fully explore the recent crustal motions over the Tornquist zone.

Keyword
tectonic activity, fault deformation, finite element method, Skane, Sweden
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-6198 (URN)10.1016/j.jog.2005.03.001 (DOI)000229921800005 ()2-s2.0-18744411538 (Scopus ID)
Note
QC 20100906Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2011-09-01Bibliographically approved

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