GNSS Reflectometry at GFZ: ocean altimetry and land surface monitoring

Transcription

1 GNSS Reflectometry at GFZ: ocean altimetry and land surface monitoring M. Semmling 1 S. Vey 1 J. Beckheinrich 1 V. Leister 1,2 J. Saynisch 1 J. Wickert 1 1 Research Centre for Geoscience GFZ, Potsdam 2 Technical University, Berlin Geodätische Woche Stuttgart 2015 Foto: C. Hübner, NPI, 2013/09/19

2 Introduction to GNSS Reflectometry Motivation General Concept GNSS Processing Outline Monitoring on Ground Soil Moisture in South Africa Snow Depth in Central Europe River Monitoring at the Mekong Ocean Altimetric Approach ZOIS & HALO experimental airborne studies GEROS simulation of a spaceborne mission Summary 2

3 Introduction to Reflectometry 3

4 GNSS satellite Motivation GNSS satellite specular land reflection specular water reflection Ny-Ålesund Ny-Ålesund Zeppelinfjellet Station 4

5 Motivation land surface: soil moisture snow depth vegetation coverage sea surface: sea level topography wind speed sea ice coverage 5

6 HALO aircraft Semmling et al., 2014 ref. stations International Space Station Vey et al., 2015 Zeppelin airship Wickert et al., 2011 Semmling et al., 2013 Ionosphere General Concept GNSS km space borne 400 km Differential Path Delay ground based: short delay, atmo. Troposphere ground based airborne 3.5 km Sea Level effect cancels spaceborne: long delay, significant atmo. effect 6

7 Sutherland ~2h coverage slant General Concept GNSS satellite zenith a max ~ 70m Vey et al., 2015 GNSS receiver GEROS-ISS ~30min coverage a max ~ 5km Saynisch et al., 2015 slant Specular point nadir Sea Level 7

8 SNR Approach SNR of geodetic receivers (RINEX format) for small delays (<1chip) superposition of direct and reflected signal interferometric pattern at low elevation angles spectral analysis... Larson et al., 2010 GNSS Processing 8

9 Master-Slave Approach adapted receiver with open-loop tracking for long delays (up to 12 chip tested) separation of direct and reflected signal in Master and Slave channels interferometric pattern at low elevation angles spectral analysis... GNSS Processing Semmling et al.,

10 Monitoring on Ground 10

11 Ny-Ålesund Wettzell Can Tho Sutherland Sea Ice Coverage Snow Depth River Level Soil Moisture Ground Setups 11

12 Sutherland Setup Soil Moisture Study signal penetrates into soil depends on water content dry soil deeper peneration h phase offset observed Soil moisture volts / volts SNR=A cos ( 4 πh λ sin e+φ ) h antenna height λ GNSS signal wavelength e elevation angle phase offset Larson et al.,

13 Sutherland Setup Soil Moisture Results long term variations resolved by GNSS sensor hydrological sensors (TDRv15) co-located agreement of sensor estimates in upper 15cm with mean deviation of 10% Vey et al.,

14 Wettzell Setup Snow Depth Study snow depth reduces antenna height over ground snow penetration disregarded h Doppler shift is observed Snow depth volts / volts SNR=A cos ( 4 πh λ h antenna height λ GNSS signal wavelength e elevation angle sin e+φ ) Doppler frequeny 14

15 Wettzell Setup Snow Depth Results Doy 2013 seasonal variation resolved by GNSS sensor ultra sonic sensor co-located agreement of sensor estimates with 1.7 cm RMS deviation Vey et al.,gnss+r 2015, Potsdam 15

16 Can Tho Setup River Level Study smooth water surface reflects signal specularly penetration is insignificant Doppler shift is observed h Water level volts / volts SNR=A cos ( 4 πh λ h antenna height λ GNSS signal wavelength e elevation angle sin e+φ ) Doppler frequency 16

17 Can Tho Setup Monitoring Results severe multipath due to buildings, trees and passing ships river level estimated applying Emperical Mode Decomposition (EMD) agreement with near tide gauge improves from 12 to 5cm standard deviation Beckheinrich et al.,

18 high frequency modes Can Tho Setup low frequency modes empirically selected modes 18

19 Ocean Altimetric Approach 19

20 ZOIS Experiment Semmling et al., 2013 RHCP antenna signal LHCP antenna signal surface height model Interferometric Pattern affected by receiver/transmitter motion, atmosphere and surface height changes Altimetric Phase Residual correction of motion and atmosphere effects residual related to surface height changes 20

21 ZOIS Experiment Geoid (GCG-05) [m] G. Liebsch et al., 2006, DVW. RHCP antenna signal reflection track ΔH = 0.2m LHCP antenna signal Lake Surface Model surface affected by geoid example reflection track along 20cm geoid anomaly Semmling et al., 2014 Phase Altimetry anomaly resolved by phase residuals with 5 and 7cm standard deviation 21

22 MSSH [m] HALO Experiment 2012 Jun 8 PRN 23 Example Event ~400km ground track large sea surface variations affect coherence of phase residuals Sea Surface Model mean of sea surf. height H (MSS) geoid undualtion ~10m variation mean of dyn. topography T (MDT) <1m variation geoid H ellipsoid Andersen et al., geoid as reference sea surface for phase retrieval 22

23 HALO Experiment topography model MSSH [m] Phase Altimetric Residual correction of motion, atmosphere and geoid undulation residual sensitive to dynamic topography changes T total level affected by ambiguity bias Semmling et al.,

24 GEROS Simulation ISS Global Ocean Coverage spacial bin. 1 deg x 1 deg GPS 32 GPS sat. observed at ISS (low elevation) dense coverage after one day for mid and low latitudes up to 100 obs. per bin Spaceborne Reflection Geometry receiver aboard International Space Station (ISS) in ~400km orbit height transmitter GPS sat. in ~20200km orbit height further GNSS transmitter included (GLONASS, Galileo, BeiDou) Leister et al., Geodätische Woche

25 GPS Sat /03/06 GEROS Simulation SSH Assimilation Study Regional Ocean Model System (ROMS) run with track assimilation run without track assimilation improvement in SSH recovery Saynisch et al., 2015 Regional Ocean Coverage Agulhas region spacial bin 0.2 x 0.25 (lat x lon) 32 GPS observed at ISS (all elevation) dense coverage after one day up to 20 obs. per bin lat -30 [deg] w.o. assim. SSH model deviation w. assim lon [deg] lon [deg] [m] 25

26 Motivation sensing water surface (sea level, surface topography, ice coverage) sensing land surface (soil moisture, snow depth) Summary GNSS Processing SNR approach using conventional geodetic receivers (ground-based) Master-Slave approach using an adapted reflectometry receiver (airborne tested) Monitoring on Ground 4 year soil moisture study (Sutherland, South Africa) seasonal variations of snow depth (Wettzell, Central Europe) river level study and multipath mitigation (Can Tho, Mekong Delta) Ocean Altimetric Approach geoid undulation resolved (5cm precision) Zeppelin airship flight (Lake Constance) sea surface topography detected (7cm precision) GEOHALO mission (Mediterranean Sea) altimetric module for GEROS-ISS mission simulator under construction successful assimilation of simulated ISS data in ocean model Thank you, for your attention! 26

27 Ocean Altimetric Approach References G. Liebsch, 2006: Quasigeoidbestimmung für Deutschland, DVW-Schriftenreihe O. B. Andersen & P. Knudsen, 2009: DNSC08 mean sea surface and mean dynamic topography models, J. Geophys. Res. J. Wickert, et al., 2011: GNSS REflectometry, Radio Occultation and Scatterometry for long-term monitoring on-board the International Space Station Proposal in response to Call ESA Research Announcement for ISS Experiments relevant to study of Global Climate Change M. Semmling et al., 2013: A Zeppelin experiment to study airborne altimetry using specular GNSS reflections, Radio Science. M. Semmling et al., 2014: Airborne GNSS Reflectometry using Crossover Reference Points for Carrier Phase Altimetry Proc. IEEE International Geoscience and Remote Sensing Symposium (IGARSS) M. Semmling et al., 2014: Sea surface topography retrieved from GNSS reflectometry phase data of the GEOHALO flight mission, Geophys. Res. Lett. J. Saynisch et al., 2015: Potential of space-borne GNSS reflectometry to constrain simulations of the ocean circulation Ocean Dynamics, accepted for publication 27

28 Monitoring on Ground References K. M. Larson, et al., 2010: GPS Multipath and Its Relation to Near-Surface Soil Moisture Content IEEE J. Sel. Top. Appl. Earth Observ. Remote Sens. J. Beckheinrich et al., 2014: Water Level Monitoring of the Mekong Delta using GNSS Reflectometry Technique Proc. IEEE International Geoscience and Remote Sensing Symposium (IGARSS) S. Vey et al., 2015: Long-term soil moisture dynamics derived from GNSS interferometric reflectometry: a case study for Sutherland, South Africa, accepted for publication in GPS Solut. 28