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Calculating of Adjusted Geoid Undulation Based on EGM08 and Mean Sea Level for Different Regions in Iraq

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Calculating of Adjusted Geoid Undulation Based on EGM08 and Mean Sea Level for Different Regions in Iraq MATEC Web of Conferences 162, 03028 (2018) https://doi.org/10.1051/matecconf/201816203028 BCEE3-2017 Calculating of adjusted geoid undulation based on EGM08 and mean sea level for different regions in Iraq Ali Fanos1,*, Rusul Tahir 2, Suad Mohammed1, and May Mahmood 1 1 Ministry of Water Resources, State Commission of Survey, Baghdad, Iraq 2 Civil Engineering Department, Al Esraa University College, Baghdad, Iraq Abstract. In last decades Global Navigation Satellite System (GNSS) or as known Global Positioning System (GPS) technique is considered a revolutionary technique in the field of geodetic survey in comparison with traditional techniques (level, theodolite and total station). The height obtained from GNSS technique is ellipsoid height and to have a physical meaning in a surveying or engineering application it must be transformed to orthometric height. Therefore, a geoid model has to be used to do this transformation process. In Iraq there is no specific geoid that can be used in order to get proper orthometric height. This research aims to calculate adjusted geoid undulation based on Earth Gravitational Model 2008 (EGM08) through observation of Iraqi official vertical network using GNSS technique. Different regions in Iraq have been chosen to perform this research. The result of this research can assist a lot to enhance the accuracy of elevations obtained from GNSS and support the establishment of Iraq geoid. 1 Introduction the geoid and close to it, but lacking the physical interpretation of an equipotential surface. Most surveying, engineering and scientific work, The distance H along a plumb line from the point to orthometric heights related to the geoid, a close the geoid is the orthometric height of a point. Orthometric approximation to mean sea level (M.S.L), are needed [1]. height is for practical purposes height above sea level Combining of data acquired by the global navigation (Fig.1). satellite system (GNSS), leveling and geoid information has been a key process for different geodetic applications. Despite the fact that these three height types are significantly varies, basically in terms of physical meaning, reference surface realization/definition, accuracy and observational methods, they should fulfill the simple geometrical relationship [2] N = h – H + ɛ (1) In which h is ellipsoidal height derived by GNSS technique, H is orthometric height obtained by spirit Fig.1. The difference between the orthometric and ellipsoidal leveling and gravimetric, N is geoid height and ε is small height. quantity because of the curvature of the plumb line and the deflection of the vertical. The geoid is the shape that the sea’s surface would take Normal height is height above the mean sea level and it under rotation and the effect of earth's gravity, in the is one of many height types that are all computed by other effects absenteeism such as winds and tides. The slightly different methods. The others are: orthometric surface is expanded through the continents. The points on height and dynamic height. The normal height of a point the geoid have the similar potential energy of gravity is computed from geopotential numbers by dividing the (centrifugal potential energy and the sum of gravitational point's geopotential number, for instance, its geopotential potential energy). Gravity force acts everywhere variance with which of sea level, by the mean, normal perpendicular to the geoid, which means water levels gravity computed along the plumbline of the point. parallel to the geoid and plumb lines point perpendicular Therefore, normal height is dependent upon the chosen of [3]. reference ellipsoid. Normal heights figure prominently in the theory of the Earth's gravity field. The reference Particularly, the geoid is the equipotential surface surface which normal height is measured from is called which could correspond with the mean sea surface if the the quasi-geoid. The representation of M.S.L similar to atmosphere and sea were in equilibrium [4]. * Ali Mutar Fanos: [email protected] © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). MATEC Web of Conferences 162, 03028 (2018) https://doi.org/10.1051/matecconf/201816203028 BCEE3-2017 The geoid surface is lower than the referece ellipsoid any new poits were estalished. A series of six whereer there is a negative graity aomaly mass Continuously perating Referece tations COR is deficit ad higher tha the referece ellipsoid wherever actig as the ackbone of the GR that have een there is a positive graity anomaly mass ecess) 5]. utilied to eted the coverage of the IGR primary Ali 2016) 6], calculated the geoidal height for control etwork. differet groud control poits GCPs) distriuted in side The COR network ig.2 is operated oitl y the Baghdad iersity campus ased on the difference ational eodetic Survey, which is part of the US between the ellipsoidal height ad the orthometric height ational ceaographic and Atmospheric dmiistration of the same poit EGM08 has been used to calculate the (NOAA) NGS) ad the ra iistry of ater maimum and the minimum values of the geoid Resources tate Commission on urvey. igh ccuracy udulation. owever, the calculation of geoidal height or Reference etwork HARN) poits hae been estalished geoid undulation eeds to e performed for wide area relatie to the OR network forming the GR control with well poits distriution. network consists. In last decade techniue has een widely used i ra. owever, regardig the elevation, the local eleations i Ira are related to the mean sea leel (M.S.L) ad the ero poit is located i l aw south of Ira. eawhile there is o specific geoid that can e used i order to get proper eleation or orthometeric height Thus, this research is tryig to find the adjustmet value of geoid undulation based on GM08 through observe the local vertical network using 2 Geodetic referencing in Iraq The most significant datum in ra are arbala 1979 ad The Ira eospatial Referece ystem IGRS) 2.1. Karbala 1979 Fig.2. The distribution of initial CORS stations in Iraq. A completely ew geodetic network was estalished i the 1970s y the Cartography OKART ad olish Initially the geodetic surveying work of the IGRS tate nterprise for eodesy (Polservice coverig all of network was managed by British and US Army Ira. This was a conventional astro-geodetic control engineers. In this phase a series of 64 HARN points have etwork which cosist of aroud 78 points with a been established in southern Iraq (Fig.3). The aim of this aerage inter-point distance of k. new spirit- work was to make a beginning for a nationwide HARN leeled vertical network, tied to two tide gauges at the network with a distance of about 50 km between each port of Al-aw, supplemented the horiontal etwork. two points. Observations of gravity were made along all precise leeling lines The original poit of the horiontal network was moved to arbala istead of ahrwa. The coordiates change of ay poit in ra is important in the Baghdad region the shift between arbala 1979 ad ahrwa coordiates is around 00 eters. arbala 1979 was utilied i combiation with the T map projections system and with a dedicated T projection as well 2.2 The Iraq Geospatial Reference System (IGRS) USA armies after the first ulf ar estalishes the beginings of a new geodetic network, the Irai eospatial Referece ystem IGRS), an effort in which the Irai iistry of Water esources tate Commission on urvey played a ke role eeral poits of the arbala 1979 etwork that still eisted were Fig. 3. The distribution of 64 HARN points in southern Iraq. observed utiliing high accuracy SS techniue ad 167 2 MATEC Web of Conferences 162, 03028 (2018) https://doi.org/10.1051/matecconf/201816203028 BCEE3-2017 After that Ministry of Water Resource / State Commission on Survey installed 7 CORS stations (Fig.4) and continued establishing the HARN points for whole Iraq provinces. Fig. 5. The study area. Fig. 4. The distribution of CORS stations in Iraq. 4 Methodology and material At this phase of IGRS the orthometric height of points The methodology of this research can e diided into two was obtained by subtracting geoid undulation based on aspects the first one is the recoaissace ad observation the EGM96 model from the ellipsoidal height that of the local vertical network y GNSS techniue the derived using GNSS technique. In that time, EGM96 second one is measurig of HARN poits y ad model was the most accurate global geoid. Geoid by precise level based on local ertical poits. undulation accuracy based on EGM96 is estimated to be not better than 0.5 meters. Therefore, orthometric height 4.1 Reconnaissance and observation of the local accuracy derived via EGM96 will be of the same vertical network magnitude order as the model itself (0.5 meter). This is The local vertical network is ased on aw ean sea much larger than the accuracy of ellipsoidal height that leel ad consist of may leveling lines coverig whole can be obtained through GNSS technique. Ira ig.6) Each lie has may poits and each point has a number prited on it The number consists of two 3 Study area parts the first one refers to the lie number and the other refers to the poit number for istace, 5 - 10 it eans The methodology of this research has een performed i lie number 5 ad the teth poit i the lie. The shape different regions in ra ad focus on the most importat of the poits are pyramid on a cube (ig.7). provices namely Baylon, arbala aaf, ut ad ioaia (ig.5).
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