Dynamic Planet 2005 Cairns, Australia 22-26 August 2005 Towards the Next Earth Gravitational Model to Degree 2160: Status and Progress Dynamic Planet 2005 Cairns, Australia 22-26 August 2005 Steve Kenyon, John Factor, NGA Nikolaos Pavlis, Jarir Saleh, Simon Holmes, Raytheon IS

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 Joint Navigation Conference Yes_____ No_____ CHAMP (Challenging Mini-Satellite Program) is a… GRACE (Gravity Recovery and Climate Experiment) is a joint NASA/TBD program to measure the Earth’s gravitational field at wavelengths of TBD and larger with unprecedented accuracy. The improvements to the long wavelength promise improvements in determining the orbits of LEO satellites. GOCE (?) is a 24 Aug 05

Progression of EGMs EGM96 EGM06 30’x30’ resolution 5’x5’ 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

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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

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

Data Collection Methods UNCLASSIFIED Data Collection Methods To satisfy the geodetic and geophysical (G&G) requirements of our DoD and IC customers, we have developed a broad range of data collection sources. Some data can be acquired from orbital sensors, for example Global Positioning System, Shuttle Radar Topographic Mission and Satellite Altimetry ocean data. For surface data, surveys are required. NGA is the depository of all DoD surveyed gravity data. In addition, much of our information is obtained through informal data exchange with other organizations that have conducted surveys (oil and geophysical companies, universities and foreign agencies). We do have some external assistance funds to support data acquisition in void areas. These funds are used to support field surveys or the cost of providing existing data to NGA. We also partner with other organizations in the scientific community (like the International Association of Geodesy or Society of Exploration Geophysicists) to acquire data. 24 Aug 05

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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

Mongolian Aerogravity Project 24 Aug 05

JGP95E 5’x 5’ Global Elevation Source Codes 24 Aug 05

SRTM World Coverage Map Coverage between latitudes 60 N - 54 S 80% of the Earth’s landmass 24 Aug 05

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 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

RMS = 2.9 mgal in comparison with NGA’s “Best” Marine 5’x5’ File KMS 2002 2’x2’g KMS 2002 Dgs. Comparisons with these Dgs and NGA’s survey data with accuracies < 10 milligals were used to estimate these RMS = 2.9 mgal in comparison with NGA’s “Best” Marine 5’x5’ File 24 Aug 05

GPS/Leveling Comparisons (±2 m edit threshold) Weighted Mean Std. Deviation (cm) Model (Nmax) 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 25.8 12.6 12.5 18.1 7.3 5.7 Linear Trend Removal Before After 24 Aug 05

GPS Leveling Comparisons over Some Areas with New g Statistics before bias removal. 2 m edit applied. Area (Npts) PGM2004A PGM2005A 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 ? 24 Aug 05

Comparisons With Astronomic Deflections over CONUS 3561 stations compared. Units (arc-seconds) Model (Nmax) RMS ∆ ∆ EGM96 (360) PGM2004A (2159) DEFLEC99 (1’→10800) PGM2005A (2159) 2.80 1.22 0.91 1.24 3.22 1.28 0.92 1.29 24 Aug 05

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

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 24 Aug 05