Post on 13-Jul-2020
WISDOM: GNSS-R flood monitoring, Jamila Beckheinrich, TU München 2012
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WISDOM: GNSS-R based flood monitoring
J. Beckheinrich1, G. Beyerle1, M. Semmling1, S. Schön2, J. Wickert1, H. Apel1
1. GFZ, German Research Center for Geosciences, Potsdam, Germany
2. Leibniz University Hannover, Institute of Geodesy, Hannover, Germany
WISDOM
GNSS-Reflectometry
GORS Receiver
Experimental setup
Preliminary results
Outlook
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WISDOM
Water related Information System for the sustainable Development Of the Mekong delta.
Climate changes have caused severe changes in the Mekong Delta:
extreme flood events
drinking water availability
soils salinization, acidification
…
Build an information system to support and assist the decision of makers, planners and local authorities for a optimized and integrated resource management.
WISDOM: GFZ Contribution
Flood monitoring of the coastal areas with dense population, like on the banks of the Mekong Delta.
Space-based radar and laser altimeters: high altimetric accuracy
insufficient spatial and temporal resolution
Ground-based instrumentation: high temporal resolution but for a point location only
GNSS-Reflectometry could fill this gap.
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GNSS Reflectometry
Main advantages of GNSS:
large and increasing number of available GNSS signals
signals for civilian are for free
High quality signals: dual frequency, long-term availability
and stability
Inexpensive: passive system
dense global coverage
Some surfaces like water, ice or wet soil show high
reflectivity for the GNSS L-Band signals.
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GNSS-Reflectometry
Multiple simultaneous measurements with high
temporal and spatial resolution.
A bistatic radar technique using GNSS as sources of
opportunity for the monitoring of reflective surfaces.
Potential applications:
Atmosphere (ionosphere, troposphere)
Surface Roughness (wave form, wind speed and direction)
Surface Dielectric Properties (salinity, pollution, soil moisture)
Target detection on sea surface
Altimetry
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GNSS-Reflectometry
GNSS signals scatter off the reflecting surface.
The reflected signal has to travel a longer path
relative time delay Δt
phase offset Δf
w.r.t. to the direct signal
iidr Nttctc f
Reflecting Surface
direct
signal
Reflected
signal
h Ehsin2
E
E
ρ
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GORS Receiver
GNSS Occultation, Reflectometry and Scatterometry
Dual-frequency receiver developed at
GFZ in collaboration with JAVAD
Four front end receiver: Tracking of reflected and direct signal
Up to 10 channels run in parallel (master and slave correlators)
10 reflections can be recorded simultaneously
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GORS Receiver
Modified firmware that allows for an open loop
tracking of GPS signals
provides a complex vector:
In- (I) and Quadrature (Q)-phase correlations sums
sampling rate of 200 Hz
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GORS Receiver:
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GORS Receiver
Modified firmware that allows for an open
loop tracking of GPS signals
provides a complex vector:
In- (I) and Quadrature (Q)-phase correlations sums
sampling rate of 200 Hz
Based on the measurement of phase offset
Coherency between direct and reflected signal is
needed
Coherent altimetry
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Coherent Altimetry:
Specular reflection change into diffuse scattering
depending on:
Signal wavelength
surface roughness
Elevation angle
Rayleigh criterion:
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specular
diffuse
Coherent altimetry:
Coherent altimetry:
Coherency causes the typical rotation of the Phasor
Incoherent Altimetry:
The lapse t is measured between the two correlation
peaks
the direct and the reflected signal
Incoherent altimetry
t
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Measurements setting:
Measurements at the An Bihn Hotel in Can Tho city
in Vietnam
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Measurements setting:
Measurements at the An Bihn Hotel in Can Tho city
in Vietnam
Two different antenna heights above the reflecting
surface:
Terrace with 10 m
Roof with 20 m
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Measurements Setting
Two antennas:
RHCP oriented to the zenith (direct signal)
LHCP tilted 175° w.r.t the nadir (reflected signal)
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Fresnel equations:
The Fresnel equations show the fraction of the
reflected signal that can be recorded by a Right Hand
Circular Polarization (RHCP) and a Left Hand Circular
Polarization (LHCP) antenna.
Brewster’s
angle
Source [2]
Measurement Settings:
Tides water level changes
leveling bare
Better measurement instrument is needed for the next
measurement campaign
Reflection events:
Preliminary results:
Reflection events:
Preliminary results:
Preliminary results:
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rcvidirectiii
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rcv
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rcvreflected EhNionotroptropttc iiiii sin2int.int.int.
Signal preprocessing:
Detection of cycle slips
Reconstruction of missing data
Preliminary results:
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Excess path:
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Preliminary results:
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i
sat
rcvi
sat
rcv
sat
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rcvidirectiii
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Signal preprocessing:
Detection of cycle slips
Reconstruction of missing data
cosAIMOD
sinAQMOD
MOD
MODMOD
I
Q1tan
Preliminary results:
Preliminary results:
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Outlook:
Separation between direct and reflected signal
Outlook:
Time delay: > 1 chip
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Outlook:
Time delay: < 1 chip
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Outlook and conclusion:
Improvement of cycle slip detection and reconstruction of missing data method.
Elimination of direct signal from the reflected one
Ambiguity resolution
GNSS-R could significantly contribute in fields where observations with high temporal and spatial resolution is needed
Optimization receiver and antennas for GNSS-R applications
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Thank you for your attention
jamila.beckheinrich@gfz-potsdam.de
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References
[1] Fabra, F: Phase Altimetry with Dual Polarization GNSS-R over Sea Ice, IEEE Trans. Geosci. And Remote Sens., Accepted for publication, 2011. doi: 10.1109/TGRS.2011.2172797.
[2] Helm, A.: Ground-based GPS altimetry with the L1 OpenGPS receiver using carrier phase-delay observations of reflected GPS signals, GFZ German
Research Centre for Geosciences, Scientific Technical Report, vol. 8, No. 10, PhD Thesis, doi:10.2313/GFZ.b103-08104, 2008.
[3] Imamura F.: IUGG/IOC Time Project Numerical method of Tsunami Simulation with the Leapfrog Scheme, UNESCO, IOC anuals and Guides, 35, 1997.
[4] Semmling A. M.: Detection of Arctic Ocean tides using interferometric GNSS-R signals, Geophys. Res. Letters, 38:L04103, 2011. doi: 10.1029/2010GL046005.
[5] Stosius, R.: Simulation of space borne tsunami detection using GNSS-Reflectometry applied to tsunamis in the Indian Ocean, Natural Hazards and Earth System Sciences, 10, pp. 1359-1372, 2010.
[6] Stosius, R.: The impact on tsunami detection from space using GNSS-reflectometry when combining GPS with GLONASS and Galileo on GNSSReflectometry tsunami detection from space, Advances in Space Research, 47, 5, pp 843-853, 2011
[7] Martin-Neira, M.: A Passive Reflectometry and Interferometric System (PARIS): Application to Ocean Altimetry, ESA Journal, Vol.17, pp. 331-355, Dec 1993.
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