Geodesy Part of the ACES Mission: GALILEO on Board the International Space Station

Transcription

1 Geodesy Part of the ACES Mission: GALILEO on Board the International Space Station 1 Svehla D, 2 Rothacher M, 3 Salomon C, 2 Wickert J, 2 Helm A, 2 Beyerle, G, 4 Ziebart M, 5 Dow J 1 Institute of Astronomical and Physical Geodesy Technische Universität München, Germany 2 GeoForschungsZentrum Potsdam, Germany 3 Laboratoire Kastler Brossel, Paris, France 4 University College London, UK 5 ESA/ESOC, Darmstadt, Germany

2 ACES Scientific Objectives - Geodesy 1) Precise orbit determination for the International Space Station 2) GPS/GALILEO time and frequency transfer combined with ACES MW-link 3) First demonstration of relativistic geodesy 4) GPS/GALILEO coherent reflectometry/radio-occultation (GNSS-R/RO) 5) GPS/GALILEO incoherent reflectometry/scatterometry (GNSS-R) 6) First demonstration of a tsunami early warning concept from the LEO orbit ESA Topical Team on Geodesy

3 GNSS Reflectometry/Radio-Occultation Signal from ground pseudolites? flight direction ACES GALILEO/GPS improving performance of the GPS tracking (weak signal) use of the zero-difference approach no need for the slave GPS satellite to remove receiver clock parameter clocks of high stability over short period (are essential) ocean surface LEO < GALILEO/GPS

4 Kinematic Positioning GRACE Mission Kinematic vs. Reduced Dynamic GRACE-A, day 200/2003 Daily RMS: Kinematic vs. Reduced Dynamic GRACE-A, days /2003

5 Orbit Validation using SLR Kinematic orbit CHAMP satellite Reduced-dynamic orbit CHAMP satellite

6 GPS Satellite ISS Simulation with Beta Angle 90 Simulation with Beta Angle 0

7 Paradox with number of GPS satellites that can be tracked from Space Station β=0 Top of Columbus β=90 Visibility thrus 15 Removed by antenna tilting thrus 15 Columbus Columbus ACES

8 The Optimal Place for the GPS Antenna THE BEST PLACE: Top of Columbus, β=0 GPS Antenna tilted by 15

9 Orbit Determination of the CHAMP Satellite Using the ISS Visibility Masks CHAMP: Top of Columbus β=90

10 ISS Orbit Error and Frequency Transfer 15 min The CHAMP radial orbit error from previous slide was converted into time units and is assumed to be clock error. The radial orbit component is the less determined component for LEOs and highly correlated with the estimated clock parameter. This figure shows that if the ISS orbit is estimated with an accuracy 5 cm this will provide a relative accuracy of in the frequency transfer after h (ACES clock:

11 Frequency Comparison using GPS Phase Clocks (Colorado Springs USNO) ( /day) 7 mm Stability of GPS receiver and H-maser Root 200 s Only phase clocks estimated. Troposphere (TZD), station coord., EOPs, etc., fixed to IGS white noise drift 1/ f Clear white noise up to 200 s 200 s

12 Two-way Links ACES Mission GPS/GALILEO optical link MW - link

13 ACES MWL EM: Code & Carrier ADEV 1,0E-11 1,0E-12 PN Code Carrier, Modulation Off Carrier Modulation On Code, Modulation Off Code, Modulation On (Schäfer, 2008) see talk given by W. Schäfer ADE 1,0E-13 1,0E-14 Carrier Frequency Stability (ADEV) Code: s Carrier: s 1,0E-15 1,0E Tau(s) 1E-16/d... Data modulation has no significant impact on ADEV 1E-18? 1E-17/10d

14 Improvements in Optical Frequency Standards 1.0E E-10 Essen s Cs clock Iodine-stabilised HeNe Fractional uncertainty 1.0E E E-13 Cs redefinition of the second H 1.0E-14 Hg +, Yb +, Ca Sr 1.0E-15 Hg + Yb Hg Cs fountain clocks + 1.0E =10 cm Sr in geoid height Al + Hg + 1.0E Microwave Year Optical (absolute frequency measurements) (Margolis, 2008) Optical (estimated systematic uncertainty) H Ca Femtosecond combs H

15 Relativistic Geodesy ACES link (x,y,z) B (x,y,z) A B B geoid ellipsoid clock frequency 50 m C D Gravitational potential ν B /ν A = T A / T B = 1 + (V B -V A )/c 2 Geometry measured with GPS Gravitational potential measured with optical clocks and ACES two-way links Demonstrated accuracy of the ground optical clocks 2.6x10-17 (over only few hours) E Unification of the geometrical (GNSS) and gravitational positioning (optical clocks on the ground)

16 Relativistic Geodesy first demonstration of the relativistic geodesy frequency transfer based on the combination of the ACES two-way optical/mwlink and GPS/GALILEO receiver between optical clocks on the ground. First optical clocks with stability ~10-17 over few hours (NIST). goal: gravitational potential differences between ground optical clocks with an accuracy below 10 cm in terms of the geoid heights Such a novel measurement type can be used to help establishing a unified global height system across national height systems and different continents and complement the current space geodetic missions such as CHAMP, GRACE and GOCE and altimetry missions such as ENVISAT, JASON-1 and JASON-2 reference potential differences for the world height system and benchmarking climatological monitoring over long time period. Unification of the geometrical (GNSS) and gravitational positioning (optical clocks)

17 SLR Time/Frequency Transfer SLR Corner Cubes (CHAMP & GRACE mission) MWL and GPS/GALILEO receiver to be used to time tag signal from the Photo-Diode Main problem: time tag Secondary scientific objectives: comparison between range measured in optical and microwave band (SLR vs. MWL and GNSS) and independent range measured by GNSS/MWL first accurate measurement of the water vapor delay first accurate measurement of the higher-order iono-effects calibration of so-called "local tie" in the combination of space geodesy techniques between SLR and GPS calibration of the SLR range biases between different ILRS stations validation of the ISS orbits based on GPS combined GNSS/SLR/MW time and frequency transfer independent and combined (GNSS+MWL+SLR) time/frequency comparison

18 Einstein Gravity Explorer Alternatives: GIOVE Follow-on GRACE Follow-on ranging below 1 µm only with the good clock 3 µm 10 fs s EGE S/C Ku-Band, Down-link Power Tx: 1 W Carrier: GHz PN-Code: 100 MChip/s 1pps: 1 time marker /s Data: 5 kbit/s Ka-Band, Down-Link Power Tx: 1 W Carrier: 32 GHz Tone: 250 MHz PN-Code: 20 MChip/s 1pps: 1 time marker /s Data: 5 kbit/s Ku-Band, Up-link Power Tx: 5 W Carrier: GHz PN-Code: 100 MChip/s 1pps: 1 time marker /s Data: 1 kbit/s/channel S/C: 10 Rx Channels S-Band, Down-link Power Tx: 1 W Carrier: 2248 MHz PN-Code: 1 MChip/s 1pps: 1 time marker /s Data: 5 kbit/s Ka Ku S Ka-Band, Up-link Power Tx: 5 W Carrier: 34.5 GHz Tone: 250 MHz PN-Code: 20 MChip/s 1pps: 1 time marker /s Data: 1 kbit/s/channel S/C: 10 Rx Channels G/S Antenna diameter Major station: 2 m User station: 1 m ACES terminal: 0.6 m Proposal for an optical clock mission (Fundamental Physics) in the ESA s Cosmic Vision Program. (Schiller, Salomon et al. 2007)

19 Orbit Design: Einstein Gravity Explorer Orbit Scenario 1. Apogee Altitude: km (-10 ) Perigee Altitude: km (+10 ) Semi-major axis: km Period: 16 h Eccentricity: 0.67 Inclination: 63.4 Argument of perigee: 170 RAAN: 25 True Anomaly: 220 Perigee drift 800 km/ 2 months Orbit Scenario 2: Apogee Altitude: km (+30 ) Perigee Altitude: km (-30 ) Semi-major axis: km Period: 16 h Eccentricity: 0.72 Inclination: 30 Argument of perigee: 270 RAAN: 215 True Anomaly: 135 Perigee drift 800 km/ 2 months ACES and Future GNSS-Based Earth Observation and Navigation, May 2008, Munich, Germany

20 EGM 2008: GPS/Leveling Test spherical harmonicsdegree/order = 2160 resolution = 5 10/20 km Thinned set consisting of points. ±2 m edit applied. Conversion of Height Anomalies to Geoid Undulations applied in EGMs using DTM elevation coefficients to commensurate Nmax. Bias Removed Linear Trend Removed Model (Nmax) Number Passed Edit Weighted Std. Dev. (cm) Number Passed Edit Weighted Std. Dev. (cm) EGM96 (360) GGM02C_EGM96 (360) EIGEN-GL04C (360) EGM2008 (360) EGM2008 (2190) (Pavlis et al. 2008)

21 Local geoid model Topography 1-cm Geoid accuracy m km Deflections of vertical GPS/levelling (Svehla and Colic 1998) (Svehla and Colic 1998)

22 Local geoid model 80 cm Global gravity models like EGM2008 (degree/order 2160) cannot see the mountain of 900 m (80 cm) over a distance of 20 km 20 km (Svehla and Colic 1998)

23 United European Levelling Network Height system biases in [cm] levelling connection via Euro Tunnel (Adam et al. 2002) Formal a posteriori errors after estimating 3063 parameters out of 4263 measurements

24 Two-Way Optical Link Using Frequency Combs Frequency Comb Basic Idea: Can we connect frequency combs via SLR and make use of fs-lasers? Frequency Comb Terra-Sat X: Optical Data Link demonstrated between LEO-ground, LEO-LEO, LEO-GEO

25 Navigation System Based on MW or Optical Links with Frequency Combs Optical reference frequency optical frequency (optical carrier) frequency comb in GEO frequency comb in MEO (generation of microwave frequency) possible optical frequency dissemination from the ground (difficult, but should work with the microwave link ) microwave frequency optical link microwave frequency

26 Thank You