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 tha the referece ellipsoid a ew poits were estalished series of si whereer there is a egatie grait aoal ass otiuousl peratig eferece tatios is deficit ad higher tha the referece ellipsoid whereer actig as the ackoe of the that hae ee there is a positie grait aoal ass ecess utilied to eted the coerage of the priar li calculated the geoidal height for cotrol etwork differet groud cotrol poits s distriuted i side The etwork ig is operated oitl the aghdad iersit capus ased o the differece atioal eodetic ure which is part of the etwee the ellipsoidal height ad the orthoetric height atioal ceaographic ad tospheric diistratio of the sae poit has ee used to calculate the ad the ra iistr of ater aiu ad the iiu alues of the geoid esources tate oissio o ure igh ccurac udulatio oweer the calculatio of geoidal height or eferece etwork poits hae ee estalished geoid udulatio eeds to e perfored for wide area relatie to the etwork forig the cotrol with well poits distriutio etwork cosists last decade techiue has ee widel used i ra oweer regardig the eleatio the local eleatios i ra are related to the ea sea leel ad the ero poit is located i l aw south of ra eawhile there is o specific geoid that ca e used i order to get proper eleatio or orthoeteric height Thus this research is trig to fid the adustet alue of geoid udulatio ased o through osere the local ertical etwork usig

2 Geodetic referencing in Iraq The ost sigificat datu i ra are arala ad The ra eospatial eferece ste

2.1. Karbala 1979

Fig.2. The distribution of initial CORS stations in Iraq. copletel ew geodetic etwork was estalished i the s the artograph T ad olish Initially the geodetic surveying work of the IGRS tate terprise for eodes olserice coerig all of network was managed by British and US Army ra This was a coetioal astrogeodetic cotrol engineers. In this phase a series of 64 HARN points have etwork which cosist of aroud poits with a been established in southern Iraq (Fig.3). The aim of this aerage iterpoit distace of k ew spirit work was to make a beginning for a nationwide HARN leeled ertical etwork tied to two tide gauges at the network with a distance of about 50 km between each port of law suppleeted the horiotal etwork two points. seratios of grait were ade alog all precise leelig lies The origial poit of the horiotal etwork was oed to arala istead of ahrwa The coordiates chage of a poit i ra is iportat i the aghdad regio the shift etwee arala ad ahrwa coordiates is aroud eters arala was utilied i coiatio with the T ap proectios sste ad with a dedicated T proectio as well

2.2 The Iraq Geospatial Reference System (IGRS) aries after the first ulf ar estalishes the egiigs of a ew geodetic etwork the rai eospatial eferece ste a effort i which the rai iistr of ater esources tate oissio o ure plaed a ke role eeral poits of the arala etwork that still eisted were Fig. 3. The distribution of 64 HARN points in southern Iraq. osered utiliig high accurac techiue ad 167

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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 ethodolog of this research ca e diided ito two was obtained by subtracting geoid undulation based on aspects the first oe is the recoaissace ad oseratio the EGM96 model from the ellipsoidal height that of the local ertical etwork techiue the derived using GNSS technique. In that time, EGM96 secod oe is easurig of poits ad model was the most accurate global geoid. Geoid precise leel ased o 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 ertical etwork is ased o aw ea sea much larger than the accuracy of ellipsoidal height that leel ad cosist of a leelig lies coerig whole can be obtained through GNSS technique. ra ig ach lie has a poits ad each poit has a uer prited o it The uer cosists of two 3 Study area parts the first oe refers to the lie uer ad the other refers to the poit uer for istace it eas The ethodolog of this research has ee perfored i lie uer ad the teth poit i the lie The shape differet regios i ra ad focus o the ost iportat of the poits are praid o a cue ig proices ael alo arala aaf ut ad ioaia ig techiue has ee widel used i these regios due to the icrease of proects that hae ee carrig out i these proices i ters of oil costructio idustrial ad other proects That is wh this research focus o these regios

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Fig. 6. Precise leveling lines.

Fig. 8. Observation process for local vertical points.

Fig.7. A precise leveling point. 4.2 Measuring of HARN points tate oissio o ure has estalished a ecoaissace has ee perfored to the lies i poits distriuted i all ra ig This process cocerig proice ased o poits sketch that prepared has ee perfored ased o stadard desig that preiousl the copa that estalished the ertical follows ig ad also ased o aiu ad etwork olserice This process has ee carried out i iiu distace etwee each two poits order to kow the eistig poits ecause soe poits hae ee daaged or reoed fter that a pla has ee ade to specif which poits will e osered i a specific lie The the poits hae ee easured usig techiue Topco ad Trile ig ach poit has ee osered for fie hours The the raw data has ee set to after oe oth fro the oseratio date to do postprocessig ased o ra statio ad get er accurate iforatio i ters of logitude latitude ad altitude i additio to The has ee used i order to get geodetic height or orthoetric height which supposed to e sae the aw fter that the differece etwee the height otaied ad the actual height for each poit has ee calculated which represets the adustet alue of geoid udulatio

Fig. 9. The distribution of HARN points which established by S.C.S.

Fig. 10. Design of HARN points. ll poits hae ee osered usig dual freuec receier ig i two sessios each 169

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oe for hours ad the data processig has ee carried out progra through wesite

Fig. 11. Observing of HARN points.

lost all the poits ppedi hae ee easured ased o the earest local ertical poit This process has ee carried out usig two precise leel ad two operators ad do the doule check to get accurate easureets The the differece etwee the orthoetric height otaied ad precise leel has ee calculated for each poit ad added to the geoid udulatio which otaied applig to get adusted for each poit fter that the aerage of the differece has ee calculated to represet the adustet alue of otaied usig i each proice oot ea suare error is a freuetl used easure of the differeces etwee alues easured or calculated alue ad actual alue has ee applied i order to check the accurac

which n is the uer of poits is the orthoetric height ased o aw ea sea leel ad is the orthoetric otaied fro ased o

5 Results and discussion igure illustrates the differece etwee ellipsoidal height orthoetric height ased o aw ea sea leel ad orthoetric height otaied usig This figure shows the differece for the fie proices alo arala aaf ut ad ioaia all proices the orthoetric height ased o aw ea sea leel ad is alost sae with a sall differece The differece etwee orthoetric height oth aw ad ad ellipsoidal height is cleared i this figure The sallest differece etwee orthoetric height ad ellipsoidal height is i arala ad the highest differece is i ut

Fig. 12. The difference between orthometric height based on Faw M.S.L and EGM08 and ellipsoidal height

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The root ea suare error has ee calculated for each proice ased o aw orthoetric height ad the orthoetric height otaied fro ased o Tale shows the alue of for each proice The highest alue is i ut proice ad the lowest alue is i aaf proice

Table 1. The of ach roice

No. Province RMSE T

ccordig to results oe ust ot rel o ust without cosiderig the correctio alue of each proice Thus i order to get accurate eleatio this correctio has to e added igure illustrates the geoid udulatio ased o ad the adusted oe ased o the oseratio related to aw ea sea leel i each proice alo proice the adustet alue is ragig aroud to arala proice it is ragig to additio the figure clears that the geoid udulatio ca e positie or egatie which eas the geoid ca e higher tha ellipsoid ad ice ersa t is ragig fro to i aaf proice ad fro to i ut proice ad fro to i ioaia proice Fig. 13. Geoid undulation based on EGM08 and Faw M.S.L.

Tale clarifies the aerage adustet alue for each proice that should e added to the geoid udulatio otaied techiue ased o These alues ased o the oseratio of local ertical etwork ad the poits that easured techiue ad precise leel related to the earest local ertical poit aw s a result ca e used as secod order i arala ad aaf proice ad as third order i the ra iddle proices the orther proices ril uhok ad uliaia caot e used due to the high differeces

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Table 2. The erage dustet alue for each proice 4. C. Conrad, "Lecture 3: Earth's figure, gravity, and geoid", GG612 Accelerated Introduction to Geology Province Average ajustement value II, SOEST - University of Hawaii (2012) 5. C.A. Stein, Eos 72, 427 (1991) 6. A.M. Ali, ARJ 2, 403 (2016) T T T

6 Conclusions

loal aigatio atellite ste is cosidered as a adaced techiue i the field of geodetic sureig due to the capailit of this techiue oer the coetioal techiues theodolite leel ad total statio i ters the uer of operators tiesaig iterisiilit ad accurac oweer regardig the height this techiue easures the ellipsoidal height whereas the ost sigificat height i all applicatio is the orthoetric height To do this trasforatio ellipsoid to orthoetric height a geoid odel has to e used ra there is o specific geoid that ca e used to get

proper orthoetric height which supposed to e ased o aw ea sea leel this research has ee used to calculate the adusted geoid udulatio ased o the differece i orthoetric height related to aw ad the oe otaied ased o The result

shows that ca e utilied as secod order i arala ad aaf proice ad as third order i the other proices The adusted geoid udulatio has ee calculated i this research for differet proices i ra The results of

curret research ca iproe the accurac of the orthoetric height or eleatio otaied techiue ad ca support the estalishig of ra geoid

or future work grait oseratio ca e coied with the height oseratio to iproe the accurac ad estalishig ra geoid additio this research ca e iproed icrease the uer of oseratios for local ertical etwork

e ackowledge r isa dulkadhi ussei for his support our research

References

1. P. Banerjee, G.R. Foulger, C.P. Dabral, JGEOD 73, 79 (1999) 2. C. Kotsakis, M.G. Sideris , JGEOD 73, 412 (1999) 3. T. Statella, S.M. Figueiredo, P. Pina, In EPSC, Proc. (2015) in Nantes, France, 10, 722

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Appendix 1. The coordinates of observed HARN points

Point Easting Northing Point Easting Northing

Point Easting Northing Point Easting Northing

Point Easting Northing

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