Airborne Experiments to study GNSS-R Phase Observations as part of the GEOHALO Mission

Transcription

1 Airborne Experiments to study GNSS-R Phase Observations as part of the GEOHALO Mission M. Semmling1, G. Beyerle1, J. Beckheinrich1, J. Wickert1, F. Fabra2, S. Ribó2, M. Scheinert3 GFZ 2 IEEC 3 TUD 1 Deutsches GeoForschungsZentrum Potsdam, Germany Institut d'estudis Espacials de Catalunya, Spain Technische Universität Dresden, Germany SPACE REFLECTO 2013 Brest, France Image: Moon over the Mediterranean Sea (Sicily, 2012)

2 Outline Introduction Motivation GEOHALO Mission Polarimetric Experiment Phase Retrieval Case Study Altimetric Experiment Phase Retrieval Case Study Conclusion 2

3 Introduction 3

4 Motivation Current Limits single reflection track ~ sufficient for ocean tides, El Nino critical for ocean eddies, tsunamis latitude [deg] more tracks for tsunami early warning Radar Altimeter longitude [deg] reflection track M. Ablain et al., High resolution altimetry reveals new characteristics of the 2004 Indian Ocean tsunami, Geophys. Res. Lett.,

5 Motivation Chances for GNSS-R synchronized system passive receiver ZOIS multiple reflection tracks higher ocean coverage R. Stosius et al., Simulation of space-borne tsunami detection using GNSSReflectometry applied to tsunamis in the Indian Ocean, Natural Hazards and Earth System Science, 2010 GEOHALO GNSS-R Receiver GEROS-ISS Receiver Platforms airborne on Zeppelin and HALO reflection tracks spaceborne on Internat. Space Station (future) 5

6 GEOHALO Mission Flights first geoscientific mission of HALO research aircraft four mission flights (6-12 Jun 2012) total length 16,150 km height above sea level 3,500 m velocity 425 km/h Measurements gravimetry (two gravity meters) magnetometry (scalar & vector) GNSS positioning GNSS reflectometry laser altimetry 6

7 GEOHALO Mission receiver: G-REX GOLD-RTR GORS antenna link: down up & down up & side experiment: scatterometric polarimetric altimetric observation: sea state ocean salinity sea surface height 7

8 Motivation X R differential path XS + SR - XR S Altimetric Principle sea surface height (SSH) effects differential path phase data R reflected polarisation Ein Eref Polarimetric Principle sea surface salinity (SSS) Eref effects reflected polarisation (Fresnel) Ein phase data (R and L) 8

9 Polarimetric Experiment 9

10 Retrieval GOLD-RTR Receiver φdown(l) and φup(r) contain residual model information from internal GPS receiver Up-looking antenna (direct signal) Down-looking antennas (reflected signal) φdiff = φdown(l) - φup(r) contains altimetric information φdown(l) - φdown(r) contains polarimetric information 10

11 Case Study Sea Surface Salinity high salinity in Mediterranean reduced by fresh water of Po river in Northern Adriatic Sea Surface Salinity Map calculated from Mediterranean Forecasting System, Simulation salinity (const. temp. assumed) ]) φ( gle d-[ ) φ( R polarimetric phase dependent on sat. elevation and Cardellach, E.; Ribó, S. & Rius, A. Technical Note on POlarimetric Phase Interferometry (POPI) Institut de Ciències de l Espai (IEEC-CSIC),

12 Case Study - ) φ( R Balkan States Italy Reflection Events tracks in Northern Adriatic instrumental phase jumps corrected [cycle] Phase etric etric Polarim [cycle] ) φ( Phase Polarim L Northern Adriatic continuous phase tracks residuals of antenna effects? Second of Day (phase wind-up, phase centre variation) 12

13 Altimetric Experiment 13

14 Retrieval Master Sampling P direct peak I Slave Sampling Q reflected peak φ I Q delay Δt [chips] direct and reflected waveform time t [s] in-phase (I) and quad-phase (Q) samples 14

15 Retrieval X M. Semmling et al., A Zeppelin experiment to study airborne altimetry using specular GNSS reflections, Radio Science, 2013 R Path Model broadcast ephemerides X trajectory and attitude R troposphere refraction antenna baseline reference surface (geoid) differential path XS + SR - XR S' geoid Altimetric Method specular phase data φ model correction (omc) tracks of sea surface height (SSH) antenna baseline R1 R1R2,3 R2, Jun 8 PRN 23 15

16 Case Study Sea Surface Height 2012 Jun 8 PRN 23 example event PRN 5 MSS model DTU-10 gradient > 10 m Topography derived from phase residuals geoid model EIGEN-6c2 geoid ellipsoid SSH O. B. Andersen & P. Knudsen DNSC08 mean sea surface and mean dynamic topography models, J. Geophys. Res., 2009 SSH = geoid + topography data_and_models/downloaddata MSS = geoid + MDT 16

17 Case Study SSH MSS Preliminary Results residual phase tracks land topography tracks offset to MDT unresolved topography crosses (L) dots (R) SSH tracks agree with MSS I land II MDT ee phase ν land 17

18 Case Study SSH track [m] Specular Events SSH tracks reproduce gradient specular data filtered sea reflections recorded during 4 flights 18

19 Conclusion GEOHALO mission continuous phase tracks retrieved (length > 50 km) GOLD-RTR with polarimetric retrieval salinity masked by other effects (phase wind-up, phase centre?) GORS with altimetric retrieval specular data yield tracksof sea surface height topography deviation due to phase ambiguity Outlook apply phase correction to GEOHALO data (wind-up, centre, ambiguity) study other reflections (larger specular part expected) sea ice (ASIRIS) and shelf ice reflections (ANTHALO) 19

20 Summary Thank you, for your attention! 20