H. Mahdizadeh; Y. Djamour
Abstract
Today, with the use of Global Positioning System (GPS), it is possible to determine the geodetic height (relative to a Reference Ellipsoid) in easy mode with less time and cost. Despite of some advantages for leveling with GPS (GPS/Levelling) relative to traditional leveling, there is an important limitation ...
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Today, with the use of Global Positioning System (GPS), it is possible to determine the geodetic height (relative to a Reference Ellipsoid) in easy mode with less time and cost. Despite of some advantages for leveling with GPS (GPS/Levelling) relative to traditional leveling, there is an important limitation which indicates the difference between Ellipsoid (as the reference datum for geodetic height) and Geoid (as the reference datum for orthometric height) named geoidal height. In order to achieve maximum accuracy in height component and then evaluating the quality results, different aspects of GPS/Levelling are considered in this study. In order to study the Feasibility of replacing precise levelling with GPS in Iran, a part of 55 km physical geodesy and geodynamic network in Azerbaijan region as well as the dense geodetic multipurpose network in Qeshm island were used. Based on different distances between each couple of points, this information, consisting of Orthometric and Geodetic heights for each point, is classified in 5 groups. The last Geoid model of Iran (IRGeoid10) with an absolute average accuracy of ±26 cm and a relative average accuracy of ±2.8 ppm are used for geoidal height. Obtained results show the accuracy of leveling height difference with GPS would be reduced by increasing the length of baseline. Index K as a criterion for determining level degree was calculated. This index shows that levelling with GPS in Iran could provide a precision of 4th degree leveling which can serve many engineering applications.
M Talebian; M Shahpasand-Zadeh; Y jamour; M.R Sepahvand; A Arabpour
Abstract
Determination of inter-seismic deformations such as fault slip-rate can usually be achieved by using geodetic observations, earthquake geology and paleo-seismology, as well as mechanical, empirical and numerical modeling. In these models, combination of the fault seismic parameters and the GPS data can ...
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Determination of inter-seismic deformations such as fault slip-rate can usually be achieved by using geodetic observations, earthquake geology and paleo-seismology, as well as mechanical, empirical and numerical modeling. In these models, combination of the fault seismic parameters and the GPS data can help estimate the fault slip-rate, the elastic thickness of the lithosphere, the earthquakes recurrence time, the relaxation time of the asthenosphere, the elapsed time of earthquake and the locking depth of the fault. In this study, we utilize the geodetic data of the North Tabriz Fault (NTF) by using random Bootstrap sampling and conducting numerical modeling by code writing in the R and MATLAB softwares. In this concern, the fault slip-rate and elastic layer thickness are estimated to be ~4-6.5±1 mm/yr and ~5-25 km, respectively, for the NW segment of the NTF. Similarly, model results for the SE segment of the fault indicate a slip-rate of ~3.5-5.5±1 mm/yr and elastic layer thickness of ~8-16 km. For the NW segment of the NTF, the asthenosphere relaxation time, earthquake recurrence time and elapsed time are estimated to be ~160-185 years, ~650-950 years and ~200-1400 years, respectively. Model results for the SE segments of the NTF indicate an asthenosphere relaxation time of ~220-340 years, an earthquake recurrence time of ~750-1050 years and an elapsed time of ~200-1500 years, respectively. The results are well consistent with the other paleoseismological and geological results.
o Memarian Sorkhabi; Y Djamour
Abstract
In order to study the crustal movements in Iran, establishment of several campaign GPS networks in 1998 seriously initiated geodynamical activities. After that in 2005, a network of ~120 permanent GPS stations named Iranian Permanent GPS Network (IPGN) has been installed to complete the campaign GPS ...
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In order to study the crustal movements in Iran, establishment of several campaign GPS networks in 1998 seriously initiated geodynamical activities. After that in 2005, a network of ~120 permanent GPS stations named Iranian Permanent GPS Network (IPGN) has been installed to complete the campaign GPS networks already existing in Iran. Thanks to all campaign and continuous GPS sites, there are many geodetic velocity vectors indicating kinematic behavior of the crust at their positions. Now, the main question is about geodetic velocity for any other arbitrary station. Evidently, the best reliable solution is installing more GPS stations and recording satellite signals, which need considerable cost and time. Another solution, which could be an appropriate alternative, is applying some modern and smart estimation methods such as “Artificial Neural Networks (ANN)”. The main advantages of ANN method are capability learning of networks, parallel processing and computation flexibility. Based on 42 GPS velocity vectors existing in NW Iran, we estimated new velocity vectors for some arbitrary positions in study area by using two estimation methods: “Back Propagation Artificial Neural Networks (BPANN)” and “Collocation”. This estimation was run in 2 models including 2 different reference stations but the same check points. The results from model 1 (with fewer reference points) showed BPANN’s RMSE in E and N components is ±2 mm and ±3.5 mm respectively, which is less than Collocation’s RMSE. The results from model 2 (with more reference points) showed BPANN’s RMSE in E and N components increased to ±1 mm and ±1.5 mm respectively. Therefore, it seems BPANN method could be considered as a good alternative to estimate geodetic velocity field relative to other classical estimation methods.
E Bekri; HR Nankali; Z Rahimi
Abstract
In the 11th August 2012 two Earthquakes trembled Azarbayjan that their scales were 6 Mw and 6.2 Mw. The locking depth of these two earthquakes is about 10 km, the epicenter of the first one is 38.55 N and 46.87 E, and the second one is 38.87 N and 46.87 E. In this research displacement of the earth crust ...
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In the 11th August 2012 two Earthquakes trembled Azarbayjan that their scales were 6 Mw and 6.2 Mw. The locking depth of these two earthquakes is about 10 km, the epicenter of the first one is 38.55 N and 46.87 E, and the second one is 38.87 N and 46.87 E. In this research displacement of the earth crust during trembling on these stations was determined by using permanent GPS stations in Ahar Earthquake 2012. The cosiesmic offset due to the Ahar earthquake has been studied using permanent GPS Network of Azarbayjan (a sub network of Iranian permanent GPS Network). Here, we explore these issues using data processing and times series analysis of the GPS sites. We found 0.5 to 2 cm offset that the GPS site (near and far) showed from the main rapture due to earthquake.
P. Haghighatmehr; M. J. Valadanzouj; R. Tajik; S. Jabari; M. R. Sahebi; R. Eslami; M. Ganjiyan; M. Dehghani
Abstract
A large area in Hashtgerd plain, in southwest of Tehran, is subject to the land subsidence induced by overexploitation of groundwater. In this paper, in order to study the subsidence SAR interferometry (InSAR) and global positioning system (GPS) are used. The small baseline subset (SBAS) algorithm is ...
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A large area in Hashtgerd plain, in southwest of Tehran, is subject to the land subsidence induced by overexploitation of groundwater. In this paper, in order to study the subsidence SAR interferometry (InSAR) and global positioning system (GPS) are used. The small baseline subset (SBAS) algorithm is used for deformation time series analysis. Time series analysis is performed using 6 interferograms calculated from 4 ENVISAT ASAR data spanning 4 months in 2008. A smoothing constraint that reduces the atmospheric noise, unwrapping and orbital errors whereas it preserves the non-linear deformation features is added to the least-squares solution. The time series results revealed that the area is subsiding continuously. Mean LOS deformation velocity map obtained from time series analysis demonstrated a considerable subsidence rate of 47 (mm/month). In order to assess the time series analysis results a dense GPS network consisting of 18 measuring stations is then established. The network design is carried out based on the subsidence spatial pattern extracted from an interferogram calculated from radar data of 2003-2004. The GPS stations are collecting the data simultaneously with radar data acquisitions. Horizontal and vertical components of the subsidence are extracted from GPS measurements. The comparison of InSAR and GPS time series shows the high compatibility of the results demonstrating the high performance of InSAR technique.
S. Adham Khiabani; M. R. Mobasheri; M. J. Valadanzoej; M. Dehghani
Abstract
SAR interferometry has shown its abilities in measuring the surface deformation in various applications. Atmospheric signals as an important factor affecting the interferometric measurements have temporally uncorrelated and complicated behavior. In this paper, a model based on the error source is presented ...
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SAR interferometry has shown its abilities in measuring the surface deformation in various applications. Atmospheric signals as an important factor affecting the interferometric measurements have temporally uncorrelated and complicated behavior. In this paper, a model based on the error source is presented to reduce the atmospheric contributions on the interferometric measurements in Mashhad subsidence area. In this model, the Full-Resolution (RF) MODIS data and meteorological information were used in order to estimate the water vapor and reduce the pressure effect, respectively. Moreover, water drops as well as the clouds effects were considered in the proposed model. Utilizing error propagation, model error was estimated as 7.2 mm. The Root Mean Square Error (RMSE) as a quantitative comparison between GPS measurements and interferometric results showed an improvement from 9 mm (before atmospheric correction) to 2 mm after applying the correction model.
Yahya Djamour; S. Hashemi Tabatabaei; M. Sedighi; H. R. Nankali
Abstract
In previous decades, using traditional geodetic observations such as distance and angle measurements was prevalent in the earth surface displacement studies. After accessing to satellite positioning systems with a high precision ability such as GPS, we encountered to an upheaval in the earth surface ...
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In previous decades, using traditional geodetic observations such as distance and angle measurements was prevalent in the earth surface displacement studies. After accessing to satellite positioning systems with a high precision ability such as GPS, we encountered to an upheaval in the earth surface displacement studies. Indeed using temporal variations of the earth surface deformation, the seismotectonics of the area can be distinguished. Deformation modeling of the area can be accessed using the analyzing of repeated geodetic measurements. In Tehran area the earthquake studies is an important task and in this paper we are going to use GPS measurements for this field. Here 35 GPS stations cover whole of Tehran which consists North Tehran fault. These stations were occupied at least 2 annual epochs and some of them were measured more than 4 times. After processing the acquired data and analyzing the results, the velocity field was obtained. Deformation analysis of the velocity field shows a small left lateral movement about 0.5-2 mm/year and more or less the same value for shortening in the northern band Tehran area. This value is not constant along the northern band and it seems the eastern part where we reach the Mosha fault the deformation is more significant than western part. The observed rate is equal to a total movement of ~5km during 2.5-10 my which is consistent with geological studies carried out in this area.
Yahya Djamour
Abstract
Today, the best coordinates of stations on the ground are obtained by using Global Navigation Satellite Systems (GNSS) such as Global Positioning System (GPS). There are many error sources affecting the GNSS observations that limit the required accuracies. But differential positioning methods, like double ...
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Today, the best coordinates of stations on the ground are obtained by using Global Navigation Satellite Systems (GNSS) such as Global Positioning System (GPS). There are many error sources affecting the GNSS observations that limit the required accuracies. But differential positioning methods, like double difference, are big helps to us to achieve an accuracy of millimeter. Differential operation of GNSS is based on placing a reference station with a GNSS receiver at a known location. One of such errors is the coordinate error of reference station and its propagation on unknown stations. In fact the coordinates of a reference station should be known in a reference system coordinate, such as WGS84 used in GPS, which we usually assume is exactly known. In practice, the position of the reference station in the reference system coordinate may not be exactly known due to different reasons. Therefore, in this study, the effect of the reference station position errors on various ranges from ~4 km to ~90 km, in static mode and using double difference carrier phase, is investigated. The results show this effect could be of the order of a few ppm depending on error magnitude of reference position and the range of baseline.