A Zeppelin-based Study on GNSS Reflectometry for Altimetric Application

Transcription

1 A Zeppelin-based Study on GNSS Reflectometry for Altimetric Application M. Semmling 1 G. Beyerle 1 J. Beckheinrich 1 J. Wickert 1 M. Ge 1 S. Schön 2 1 GFZ Deutsches GeoForschungsZentrum, Potsdam 2 IfE Institut für Erdmessung, Hannover Geodätische Woche Berlin 2014 Image: Zeppelin NT in action (ZOIS, 2010)

2 Outline Motivation Ocean Altimetry GNSS-R Experiments Zeppelin Experiment Airborne Setup Differential Data Model Requirements Lake Altimetry Reflection Event Height Retrieval Crossover Calibration Summary & Outlook 2

3 Motivation 3

4 MDT [m] O. B. Andersen & P. Knudsen, 2009, J. Geophys. Res. Ocean Altimetry Jason-2 Altimeter track ISS GNSS reflection tracks Sea Surface Topography characterises ocean circulation indicator for change of Earth energy budget improved observation coverage required Coverage single track Jason-2 Altimetry (Ocean Surface Topography Mission) 2014/04/19 6h57 9h00 UTC tracks potential ISS Reflectometry (proposed GEROS Mission) 2014/04/19 6h05 7h42 UTC 4

5 GNSS-R Experiments GNSS-R Concept synchronized system of transmitters X passive receiver R on various platforms precise carrier phase data Zeppelin M. Semmling et al., 2013, Radio Science. campaigns over Lake Constance and X Mediterranean Sea X R X HALO M. Semmling et al., 2014, Geophys. Res. Lett. ISS Wickert et al., 2014, Geophys. Res. Abstracts GNSS-R Platforms Zeppelin over Lake Constance reflection tracks HALO over Mediterranean Sea Internat. Space Station (proposed) 5

6 Zeppelin Experiment 6

7 Airborne Setup up up up down down down down down down CTRL Antennas direct signal acquisition co-pol. (RHCP) antenna up reflected signal acquisition co-pol. (RHCP) antenna down cross-pol. (LHCP) antenna down nav. GORS diff. diff. M. Semmling et al., 2013, Radio Science. Receiver GORS unit for real-time navigation data (up signal) GORS unit for differential data (down - up signal) control pc for data recording and reflection tracking 7

8 Differential Data Master (up) direct peak Slave (down) specular peak diff. data I Q time t specular model τ 0 τ 0 +τ A delay Doppler frequency f Master and Slave sampling diff. data 8

9 X Model Requirements M. Semmling et al., 2013, Radio Science. Specular Model broadcast ephemerides X differential range p(x,s,r) - p(x,r) R trajectory, attitude and antenna baselines R S troposphere refraction apriori surface height (e.g. gauge stations) geoid undulation Height Definition G = H - Q gauge height Q lake surface height H ellipsoidal heights H geoid G normal height Q ellipsoid 9

10 Lake Altimetry 10

11 Reflection Event Geoid (GCG-05) [m] G. Liebsch et al., 2006, DVW. aircraft trajectory reflection track ΔH = 0.5m mean lake level Event PRN 31 13h00 observed starboard sat. at elevation 24-17deg length 15 km and duration 16 min 11

12 M. Semmling et al., 2013, Radio Science diff. data Height Retrieval spec. model doppler compensation (1) (2) specular model (1) (2) apriori water level ancillary data geoid undulation data retrieval Diff. Data Spectrum co- and cross polarization (cpol, xpol) narrow peak (1) refer to direct signal broader peak (2) refer to reflected signal identified by specular model 12

13 M. Semmling et al., 2014, Geophys. Res. Lett. spec. model diff. data doppler compensation phase unwrap res. phase track height conversion dots (cpol) crosses (xpol) Height Retrieval 0.5m apriori water level ancillary data geoid undulation data retrieval Residual Phase & Height Variation continuous phase tracks (ambiguity) converted to height tracks (offset bias) height variation in geoid range (0.5m amplitude) 13

14 M. Semmling et al., 2014, Geophys. Res. Lett. spec. model diff. data doppler compensation phase unwrap res. phase track Crossover Calibration height conversion reference height ancillary data crossover calibration geoid undulation data retrieval Reference Height given at crossover point calibrated height scale validate with geoid model 14

15 Crossover Calibration gauge station reference track cross point PRN 31 Calibration & Validation cal. tracks between gauge stations obs. track crossover point val. track deduced from Geoid model bias precision G (cpol) 7 cm 3 cm G (xpol) 5 cm 4 cm 15

16 Zeppelin Experiment airborne setups: Zeppelin airship, three antennas, GORS receiver differential data: Master samples direct signal & Slave samples reflected signal model requirement: specular reflection, ancillary data (receiver trajectory etc.) Summary Lake Altimetry specular reflection event observed during Zeppelin flight (500m above lake surface) geoid undulation resolved (centimetre-precision) using carrier phase data bias mitigated by crossover calibration using gauge data Outlook crossover calibration with boat and Zeppelin measurements study specular reflection conditions for airborne application study space-based options (GEROS mission) Zeppelin flight track 2014/05/20 boat track 16

17 Support from our partners is gratefully acknowledged. swisstopo Thank you, for your attention! 17

18 O. B. Andersen & P. Knudsen, 2009: DNSC08 mean sea surface and mean dynamic topography models, J. Geophys. Res. References M. Semmling et al., 2013: A Zeppelin experiment to study airborne altimetry using specular GNSS reflections, Radio Science. M. Semmling et al., 2014: Sea surface topography retrieved from GNSS reflectometry phase data of the GEOHALO flight mission, Geophys. Res. Lett. G. Liebsch et al., 2006: Quasigeoidbestimmung für Deutschland DVW-Schriftenreihe. J. Wickert et al., 2014: GEROS-ISS: Innovative Ocean Remote Sensing using GNSS Reflectometry onboard the International Space Station, Geophys. Res. Abstracts, EGU