Evaluation Of Gravity Field Models: Eigen-6c4 And Goco03s Combined With Egm08 Using Gnss-Levelling

Abstract

This Study Has Evaluated The Accuracy Of Tow High Resolution Geopotential Models. The Objective Of The Study Is To Evaluate The Accuracy Of These Global Geopotential Models Such As Eigen-6c4, And Goco03s Combined With The 2008 Earth Gravity Model (Egm08) Using An Independent Global Navigation Satellite System (Gnss) And Levelling Data. Goco03s And Egm08 Are Combined By Using Butterworth Filter To Synthesis A Combined Model That Can Recover Long Wavelengths From Gravity For Steady-State Ocean Circulation Explorer (Goce) Satellite. Goco03s Is Truncated To Spherical Harmonics Up To Degree And Order Of 240. The Eigen-6c4 Combines Egm08 And New Gravitational Information From Goce Satellite When Compared To Goco03s. Space Domain Spherical Harmonic Analysis Was Used To Determine Geopotential Heights And Geoid Heights From Goco03s Plus Egm08, And Eigen-6c4 At Five Gnss-Levelling Bench Marks Across 10.742 Km Baseline Between Addis Ababa And Legedadi ?�? Levelled Heights Are Connected To The Blue Nile Bench Marks. Gnss Data Was Initially Processed By Gamit/Globk, Auspos Service, Rtx (Real Time Extended) Service And Lgo (Leica Geo Office) With A Tie To Itrf08 Reference Frame; Accuracy Was Assessed And Later Geodetic Coordinates (Longitude, Latitude, Ellipsoidal Height) From Gamit/Globk Were Used For The Computation Of Geopotential Heights And Geoid Heights At Gnss-Levelling Bench Marks. The Accuracy Of The Geopotential Heights Computed From The Eigen-6c4 Geopotential Model Was Evaluated By Comparing It With The One Derived From Goco03s Combined With Egm08 And Precise Levelled Heights. The Geoid Heights Computed From The Two Geopotential Models Are Also Compared With Geoid Heights Derived From Gnss-Levelling Data. The Eigen-6c4 Model Is In A Good Agreement With A Standard Deviation Of 0.002m And 0.111m Relative To Goco03s Plus Egm08 And Levelling, Respectively. Moreover, The Residual Between Levelled Heights And Orthometric Heights Computed From Goco03s And Egm08 Has Standard Deviation Of 0.110m. Besides, The Residual Between The Gravimetric Geoid Heights And Geoid Heights Derived From Gnss-Levelling Has A Mean Of (0.111m For Eigen-6c4 And 0.073m For Goco03s Plus Egm08) And Standard Deviation Of (0.110m For Eigen-6c4 And 0.109m For Goco03s Plus Egm08). The Absolute Height Separation Between The Levelling Datum And The Geoid Is 0.082m And 0.044m For Eigen-6c4, And Goco03s Plus Egm08 Respectively. The Results Of The Study Showed That The Combined Geopotential Model Best Simulates To The Gnss-Levelling Data Compared To Eigen-6c4 Model. The Discrepancy Of -0.038m Between The Eigen-6c4 And Goco03s And Egm08 Models May Arise From The Computational Methods Employed In The Synthesisation Of Stoke's Cosine And Sine Coefficients.