Time variable gravity from kinematic orbits of LEO ... - Graz University

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Time variable gravity from kinematic orbits of LEO satellites A 15+ years series of monthly solutions without gaps N. Zehentner, T. Mayer-Gürr, S. Strasser Institute of Geodesy Graz University of Technology IAG-IASPEI 2017 3. August 2017 u ifg.tugraz.at

Satellite-to-satellite tracking  High-low satellite-to-satellite tracking  Well known approach for gravity field recovery  Two-step method: 1. Kinematic orbit estimation 2. Gravity field recovery  Independent of dedicated gravity field missions

 New developments ahead:  Additional GNSS  Additional frequencies  Increasing number of available satellites

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N. Zehentner, T. Mayer-Gürr, S. Strasser

Satellite missions

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N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach  Precise point positioning approach  Undifferenced observations  No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers

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N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach GOCE

 Precise point positioning approach  Undifferenced observations  No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers

Units: cm 5

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach GOCE

 Precise point positioning approach

GRACE 1

 Undifferenced observations  No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers

Units: cm 5

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach GOCE

 Precise point positioning approach

GRACE 1

 Undifferenced observations

Jason 3

 No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers

Units: cm 5

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach GOCE

 Precise point positioning approach

GRACE 1

 Undifferenced observations

Jason 3

 No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers

Units: cm 5

N. Zehentner, T. Mayer-Gürr, S. Strasser

Sentinel 3A

Kinematic orbit estimation  Raw observation approach  Precise point positioning approach  Undifferenced observations  No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

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N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach SVN 38

 Precise point positioning approach  Undifferenced observations  No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

Units: cm 6

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach SVN 38

 Precise point positioning approach SVN 45  Undifferenced observations  No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

Units: cm 6

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach SVN 38

 Precise point positioning approach SVN 45  Undifferenced observations

SVN 55

 No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

Units: cm 6

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach SVN 38

 Precise point positioning approach SVN 45  Undifferenced observations

SVN 55 SVN 66

 No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

Units: cm 6

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach  Precise point positioning approach  Undifferenced observations  No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

 For phase and code observations

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N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach GOCE

 Precise point positioning approach  Undifferenced observations  No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

 For phase and code observations

Units: m 7

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach GOCE

 Precise point positioning approach

GRACE 1

 Undifferenced observations  No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

 For phase and code observations

Units: m 7

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach GOCE

 Precise point positioning approach

GRACE 1

 Undifferenced observations

Jason 3

 No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

 For phase and code observations

Units: m 7

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach GOCE

 Precise point positioning approach

GRACE 1

 Undifferenced observations

Jason 3

 No ionosphere-free combination

Sentinel 3A

 Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

 For phase and code observations

Units: m 7

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach  Precise point positioning approach  Undifferenced observations  No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

 For phase and code observations  Azimuth and elevation dependent weighting scheme  Individual for each receiver and observation type

8

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach GOCE

 Precise point positioning approach  Undifferenced observations  No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

 For phase and code observations  Azimuth and elevation dependent weighting scheme  Individual for each receiver and observation type Units: cm 8

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach GOCE

 Precise point positioning approach

GRACE 1

 Undifferenced observations  No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

 For phase and code observations  Azimuth and elevation dependent weighting scheme  Individual for each receiver and observation type Units: cm 8

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach GOCE

 Precise point positioning approach

GRACE 1

 Undifferenced observations

Jason 3

 No ionosphere-free combination  Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

 For phase and code observations  Azimuth and elevation dependent weighting scheme  Individual for each receiver and observation type Units: cm 8

N. Zehentner, T. Mayer-Gürr, S. Strasser

Kinematic orbit estimation  Raw observation approach GOCE

 Precise point positioning approach

GRACE 1

 Undifferenced observations

Jason 3

 No ionosphere-free combination

Sentinel 3A

 Antenna center variations  Azimuth and elevation dependent for receivers and transmitters  Individual corrections for each transmitter

 For phase and code observations  Azimuth and elevation dependent weighting scheme  Individual for each receiver and observation type Units: cm 8

N. Zehentner, T. Mayer-Gürr, S. Strasser

Gravity field recovery  Short arc integral approach  Monthly solutions  Max D/O 60  Individual solutions for each LEO  Combination on level of normal equations

 Monthly time series of more than 15 years  January 2002 – May 2017  18 satellites included:  CHAMP, C/NOFS, GOCE, GRACE 1 & 2, JASON 1, 2 & 3, KOMPSAT 5, METOP A & B, SAC-C, Sentinel 3A, Swarm 1, 2 & 3, TanDEM-X, TerraSAR-X

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N. Zehentner, T. Mayer-Gürr, S. Strasser

Degree amplitudes  Degree amplitudes for all months in 2016

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N. Zehentner, T. Mayer-Gürr, S. Strasser

Degree amplitudes  Degree amplitudes for all months in 2016

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N. Zehentner, T. Mayer-Gürr, S. Strasser

Linear trend CSR-RL05 solution

Equivalent water height [cm/year]  750 km Gaussian filter applied 11

N. Zehentner, T. Mayer-Gürr, S. Strasser

Linear trend IfG solution CSR-RL05 solution

Equivalent water height [cm/year]  750 km Gaussian filter applied 11

N. Zehentner, T. Mayer-Gürr, S. Strasser

Seasonal signal - Amplitude CSR-RL05 solution

Equivalent water height [cm]  750 km Gaussian filter applied 12

N. Zehentner, T. Mayer-Gürr, S. Strasser

Seasonal signal - Amplitude IfG solution CSR-RL05 solution

Equivalent water height [cm]  750 km Gaussian filter applied 12

N. Zehentner, T. Mayer-Gürr, S. Strasser

Area mean values

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N. Zehentner, T. Mayer-Gürr, S. Strasser

Area mean values

Area ~6 000 000 km²

Correlation: ITSG-GRACE2016 – IfG: 0.89 14

N. Zehentner, T. Mayer-Gürr, S. Strasser

Area mean values

Area ~400 000 km²

Correlation: ITSG-GRACE2016 – IfG: 0.58 15

N. Zehentner, T. Mayer-Gürr, S. Strasser

Correlation  Correlation of ITSG-GRACE2016 and IfG time series for the 56 larges basins

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N. Zehentner, T. Mayer-Gürr, S. Strasser

Summary  Kinematic orbits  Raw observation approach applied  18 satellites  Freely available at ifg.tugraz.at

 Monthly gravity field time series  Based on kinematic orbits only  Unconstrained

 Consistent  Complete  More than 15 years  Good agreement to Grace 17

N. Zehentner, T. Mayer-Gürr, S. Strasser

Questions or visit ifg.tugraz.at

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N. Zehentner, T. Mayer-Gürr, S. Strasser