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Know the Earth…Show the Way

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY

Towards the Next Earth Gravitational Model to Degree 2160:

Status and Progress

Towards the Next Earth Gravitational Model to Degree 2160:

Status and Progress

Dynamic Planet 2005Cairns, Australia

22-26 August 2005

Dynamic Planet 2005Cairns, Australia

22-26 August 2005

Steve Kenyon, John Factor, NGANikolaos Pavlis, Jarir Saleh, Simon Holmes, Raytheon IS

24 Aug 05 2



Earth Gravitational Model 2006

• CHAMP and GRACE satellite gravity missions– 100x improvement in the accuracy

with which large regional features of the gravitational field can be modeled

• Need for higher-resolution model of the gravitational field and geoid– 5’ x 5’ resolution– n=m=2160– 15 cm global RMS accuracy

goal for geoid

24 Aug 05 3



Progression of EGMs

EGM96• 30’x30’ resolution• 50 cm RMS accuracy• 70 x 70 error

propagation• 40 satellites used

for long ’s• 30 M surface gravity

values• 29 elevation codes• 130 K coefficients

EGM06• 5’x5’ resolution• 15 cm RMS accuracy• 2160 x 2160 error

propagation• CHAMP and GRACE

used for long ’s• 52 M surface gravity

values• SRTM, ICESAT• 4.7 M coefficients

24 Aug 05 4



10-3

10-2

10-1

100

101

102

103

0 20 40 60 80 100 120 140 160

EGM96 Geoid SignalEGM96 Geoid ErrorEGM96S Geoid ErrorGGM01S Geoid ErrorGGM02S Geoid Error DOT Signal (POCM_4B, Rapp 1998)GRACE Geoid Error (UT/CSR Simulation)

0 20 40 60 80 100 120 140 160

[ D

egre

e V

aria

nce

] 1/

2

(mm

)Spherical Harmonic Degree

24 Aug 05 5



EGM06 Geoid Goals

• EGM06 Geoid Error Goal - 15 cm Global RMS

• 5 cm commission error from GRACE out to n=m=100

• 3 cm omission error beyond 2160 following Kaula's Rule

• NGA’s detailed gravity data are expected to meet an ~14 cm geoid commission error requirement for degrees 101-2160

24 Aug 05 6



EGM06 Geographic Accuracy Breakdown

• Ocean areas with good altimetric data: from +/- 5 cm to +/- 10 cm

• Land areas with good surface gravity data: from +/- 10 cm to +/- 15 cm

• Land areas with poor surface gravity data: from

+/- 15 cm to +/- 50 cm

• Land areas with no surface gravity data: from +/- 50 cm to +/- 120 cm

24 Aug 05 7



Data Collection MethodsData Collection MethodsUNCLASSIFIED

24 Aug 05 8



24 Aug 05 9



24 Aug 05 10



Statistics of 5’x5’ g (v081005)

Source Area Min. Max. RMS ArcGP 4.0 186.0 235.6 31.3 8.1

Altimetry 67.0 -360.4 377.9 29.2 3.1

Terr. 15’ 18.0 -284.5 443.8 42.3 6.1

Fill-in 3.2 -196.9 256.4 32.3 24.6

Actual 5’ 78.8 -360.4 669.8 29.6 3.6

All 100.0 -360.4 669.8 32.3 6.0

(, ) 19.5, 293.5 19.5, 204.5

The Fill-in anomalies for v081005 have decreased from 16.7 to 3.2 of the world compared to PGM2004A

24 Aug 05 11



Mongolian Aerogravity Project

24 Aug 05 12



JGP95E 5’x 5’ Global Elevation Source Codes

24 Aug 05 13



SRTM World Coverage Map

Coverage between latitudes 60 N - 54 S80% of the Earth’s landmass

24 Aug 05 14



KINEMATIC GPS GROUND CONTROL POINT COMPARISON WITH SRTM

CONTINENT

MEAN

DIFF. (M)

STD DEV.

(M)

90% ABSOLUTE

ERROR (M)

AFRICA 1.3 3.8 6.0

AUSTRALIA 1.8 3.5 6.0

EURASIA -0.7 3.7 6.6

N. AMERICA 0.1 4.0 6.5

S. AMERICA 1.7 4.1 7.5

NEW ZEALAND 1.4 5.9 10.0

24 Aug 05 15



RMS = 2.9 mgal in comparison with NGA’s “Best” Marine 5’x5’ File

KMS 2002 2’x2’g

24 Aug 05 16



GPS/Leveling Comparisons (±2 m edit threshold)

Model (Nmax)All

(10767)

NGS

(4649)

All

(10767)

NGS

(4649)

EGM96 (360)

PGM2004A (2159)

G99SSS (1’→10800)

PGM2005A (2159)

29.3

15.5

-

15.6

21.4

9.7

9.1

9.7

25.8

12.6

-

12.5

18.1

7.3

5.7

7.3

Linear Trend Removal

Before After

Weighted Mean Std. Deviation (cm)

24 Aug 05 17



GPS Leveling Comparisons over Some Areas with New g

Area (Npts)

PGM2004A PGM2005A

Mean Diff.

(cm)

Std. Dev. (cm)

Mean Diff.

(cm)

Std. Dev. (cm)

Tasmania (46)

Greece (36)

Japan (826)

Switzerland (115)

-25.2

-69.2

-22.0

-59.8

60.1

22.6

18.7

13.4

-20.2

-73.1

-21.1

-53.6

12.6 17.5 17.0 28.5 ?

Statistics before bias removal. 2 m edit applied.

24 Aug 05 19



Upcoming EGM06 Activities

• Spherical harmonic synthesis software will be made available at end of 2005– Official EGM06 project software – Provides ability to efficiently compute geodetic

quantities to n=m=2160– Test sets to be provided– Available thru http://earth-info.nga.mil/GandG/

• Validation of new EGM06– GPS/leveling, orbits, DOVs, etc. – International participation is welcome– Spring 2005 timeframe leading to final EGM06

selection

24 Aug 05 20



Summary

• EGM06 is planned for June 2006– New surface and airborne gravity collected until Jan 06– Goal of EGM06 is 15 cm– n=m=2160– 5’x5’ resolution

• Latest GRACE model, Surface Gravity, Satellite Altimetry, SRTM and ICESAT data will be utilized

• Error Propagation to n=m=2160• 5’x5’ gravity data from unsurveyed areas

is welcome

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