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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i

sat

rcvi

sat

rcv

sat

rcvsatrcv

sat

rcv

sat

rcvidirectiii

i

ii Nionotropttc

i

sat

rcvi

sat

Porefl

rcv

Porefl

sat

Porefl

sat

rcv

sat

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

rcvsatrcv

sat

rcv

sat

rcvidirectiii

i

ii Nionotropttc

i

sat

rcvi

sat

Porefl

rcv

Porefl

sat

Porefl

sat

rcv

sat

rcvreflected EhNionotroptropttc iiiii sin2int.int.int.

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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