1. The use of absolute gravity data for validation of GOCE-based GGMs – A case study of Central Europe 1), 2) Walyeldeen Godah 2) Jan Krynski 2) Malgorzata Szelachowska 2) Przemyslaw Dykowski 2) Marcin Sekowski 2) Institute of Geodesy and Cartography (IGiK), Warsaw, Poland 5th INTERNATIONAL GOCE USER WORKSHOP 1 25-28 November 2014, UNESCO, Paris, France 1) University of Khartoum, Sudan

2. I.Objectives & Motivations II. Data used III. Validation of GOCE-based GGMs GOCE-based GGMs vs. EGM08 GOCE-based GGMs vs. GNSS/levelling GOCE-based GGMs vs. absolute gravity data IV. Conclusions V. Future works Overview The use of absolute gravity data for validation of GOCE-based GGMs – A case study of central Europe 5th INTERNATIONAL GOCE USER WORKSHOP 2 25-28 November 2014, UNESCO, Paris, France

3.  Main objectives  To discuss the use of absolute gravity measurements for the validation of gravity functionals determined from GGMs  To prove that  Motivation  A sub-region of Central Europe (Poland) is chosen as study area Objectives & Motivation The use of absolute gravity data for validation of GOCE-based GGMs – A case study of central Europe 5th INTERNATIONAL GOCE USER WORKSHOP 3 25-28 November 2014, UNESCO, Paris, France the 5 th release GOCE-based GGMs at spatial resolution d/o ~200 provide 1-2 cm geoid heights 1 mGal gravity anomalies availability of high quality and homogenous ground truth data (absolute gravity data, GNSS/levelling, etc.) high performance of EGM08 due to

4.  GOCE-based GGMs investigated Data used (1) The use of absolute gravity data for validation of GOCE-based GGMs – A case study of central Europe 5th INTERNATIONAL GOCE USER WORKSHOP 4 25-28 November 2014, UNESCO, Paris, France  EGM08  satellite data – SLR + CHAMP + GRACE + altimetry-derived Δg  Digital Terrain Model – DTM2006.0  terrestrial data – 5' × 5' Δg provided by IGiK height anomalies of 1.9 - 3.7 cm accuracy for the area of Poland GGMDIR-R5TIM-R5 ESA’s nameGO_CONS_GCF_2_DIR_R5GO_CONS_GCF_2_TIM_R5 Maximum d/o300280 GOCE GPS-SST data & GOCE SGG data whole mission data 01/11/2009 – 20/10/2013 whole mission data 01/11/2009 – 20/10/2013 GRACE GPS-SST & K-band range-rate data 10 years 2003 – 2012 – LAGEOS-1/2 SLR data 25 years 1985 – 2010 – Global Geopotential Models (GGMs)

5. GNSS/levelling data The use of absolute gravity data for validation of GOCE-based GGMs – A case study of central Europe 5th INTERNATIONAL GOCE USER WORKSHOP 5 25-28 November 2014, UNESCO, Paris, France  Height anomalies ζ from three data sets (1)POLREF network sites  315 stations (blue dots)  3 – 4 cm accuracy (2) EUVN network sites  56 stations (brown dots)  ~2 cm accuracy (3) GNSS/level. control traverse sites  185 stations (green dots)  1 – 2 cm accuracy Data used (2)

6. Absolute gravity data The use of absolute gravity data for validation of GOCE-based GGMs – A case study of central Europe 5th INTERNATIONAL GOCE USER WORKSHOP 6 25-28 November 2014, UNESCO, Paris, France  168 gravity stations – modernized Polish gravity control in 2012-2014  absolute gravity value – absolute gravimeter A10-020  vertical gravity gradient – LaCoste&Romberg G relative gravimeters Data used (3)

7. GOCE-based GGMs vs. EGM08 The use of absolute gravity data for validation of GOCE-based GGMs – A case study of central Europe 5th INTERNATIONAL GOCE USER WORKSHOP 8 25-28 November 2014, UNESCO, Paris, France δζ = ζ EGM08 – ζ GOCE δζ [m] δΔg [mGal] GGMDIR-R5TIM-R5DIR-R5TIM-R5 N max = d/o 2000.0340.0330.860.84 N max = d/o 2800.1400.1465.555.80 N max = d/o 3000.152–6.31– δΔg =Δg EGM08 – Δg GOCE Validation of GOCE-based GGMs (1)

8. The use of absolute gravity data for validation of GOCE-based GGMs – A case study of central Europe 5th INTERNATIONAL GOCE USER WORKSHOP 7 25-28 November 2014, UNESCO, Paris, France The STD values of δζ 1 ( GOCE-based GGMs “only” ) at d/o 200 and the maximum d/o of the model [m] GGMsPOLREFEUVNContr. Trav. DIR-R5 N max = d/o 200 0.2550.2160.229 DIR-R5 N max = d/o 300 0.193 0.1690.187 TIM-R5 N max = d/o 200 0.2540.2150.227 TIM-R5 N max = d/o 280 0.1880.1810.159 (I) GOCE-based GGMs vs. GNSS/levelling data Validation of GOCE-based GGMs (2)

9. (II) GOCE-based GGMs vs. GNSS/levelling data The use of absolute gravity data for validation of GOCE-based GGMs – A case study of central Europe 5th INTERNATIONAL GOCE USER WORKSHOP 8 25-28 November 2014, UNESCO, Paris, France Note! The height anomalies signal beyond d/o 2190 does not exceed 3 mm – is neglected in this investigation The STD values of δζ 2 ( GOCE-based GGMs + EGM08 ) at d/o 200 and the maximum d/o of the model [m] GGMsPOLREFEUVNContr. Trav. DIR-R5 N max = d/o 200 0.0380.0350.036 DIR-R5 N max = d/o 300 0.1510.128 0.151 TIM-R5 N max = d/o 200 0.0340.0330.028 TIM-R5 N max = d/o 280 0.1450.1460.136 Validation of GOCE-based GGMs (3)

10. The use of absolute gravity data for validation of GOCE-based GGMs – A case study of central Europe 5th INTERNATIONAL GOCE USER WORKSHOP 10 25-28 November 2014, UNESCO, Paris, France  The evaluation of EGM08 (the reference GGM) using absolute gravity data MinMaxMeanSTD - 6.023.41- 0.841.71 Statistics of [mGal] where GOCE-based GGMs vs. absolute gravity data I – computed with the use of SRTM3 Validation of GOCE-based GGMs (4)

11. The use of absolute gravity data for validation of GOCE-based GGMs – A case study of central Europe 5th INTERNATIONAL GOCE USER WORKSHOP 11 25-28 November 2014, UNESCO, Paris, France  The evaluation of GOCE based GGMs with the use of absolute gravity data Statistics of at d/o 200 [mGal] GGM MinMaxMeanSTD DIR-R5 - 6.944.60-1.061.80 TIM-R5 - 6.634.30-1.061.75 GOCE-based GGMs vs. absolute gravity data II usingTIM-R5 to d/o 200 Validation of GOCE-based GGMs (5)

12. The use of absolute gravity data for validation of GOCE-based GGMs – A case study of central Europe 5th INTERNATIONAL GOCE USER WORKSHOP 12 25-28 November 2014, UNESCO, Paris, France 1. GOCE-based GGMs vs. EGM08  consistency for both GOCE-based GGMs (TIM-R5 and DIR-R5)  from d/o 200 onward the STD values increase gradually noise starts dominating the signal, regularization of the coefficients, etc.  with N max = d/o 200 the fit of GOCE-based GGMs to EGM08 in Δg : ~0.85 mGal & in ζ : ~3.3 cm 2. GOCE-based GGMs vs. GNSS/levelling data  fit of GOCE-based GGMs “only” (STD): 22 - 26 cm at N max = d/o 200 16 - 19 cm at N max = d/o 280/300  fit of GOCE-based GGMs extended with EGM08 (STD): < 4 cm for both GOCE-based GGMs from d/o 100 to d/o 200 2.8 – 3.8 cm at N max = d/o 200 Conclusions (1)

13. Conclusions (2) The use of absolute gravity data for validation of GOCE-based GGMs – A case study of central Europe 5th INTERNATIONAL GOCE USER WORKSHOP 13 25-28 November 2014, UNESCO, Paris, France 3. GGMs vs. absolute gravity data  fit of EGM08 (STD): 1.71 mGal  fit of GOCE-based GGMs + EGM08 + the topography potential (STD): 1.75 – 1.80 mGal at N max = d/o 200  GOCE-based GGMs agree (<0.1 mGal) with EGM08 up to d/o 200  Absolute gravity data seem valuable for the validation of GGMs Main advantages of absolute gravity over other ground truth data (e.g. GNSS/levelling, mean gravity anomalies, etc.): high accuracy, economical reasons, less time to develop a network, etc.

14. Future works The use of absolute gravity data for validation of GOCE-based GGMs – A case study of central Europe 5th INTERNATIONAL GOCE USER WORKSHOP 13 25-28 November 2014, UNESCO, Paris, France 1)Modification of the spectral enhancement method (SEM) o considering the correlation between the coefficients of GOCE-based GGMs and EGM08 2)More extensive investigation towards using absolute gravity data to validate GGMs o compensation of gravity signal beyond N max  medium to short gravity signal (e.g. from d/o 201 to 2190)  very short gravity signal (e.g. from d/o 2191 onward) 3)Study the performance of GOCE-based GGMs for developing a gravimetric geoid/quasigeoid model for the area of Poland o GOCE-based GGM + 5' × 5' Faye anomalies Some research are still needed

15. Backup slides

16. STD of free-air anomalies differences

17. (mean value has been removed) Outliers Old No.St. name KLC8 Kielce 246Sobótka 314 Zwardoń 320 Jabłonka Orawska 328Piwniczna KLD8Kłodzko ZYW8Żywiec Name and number of the outliers stations