extraction of the surface velocity of rivers with sar-ati
DESCRIPTION
7th CNES/DLR Workshop on Information Extraction and Scene Understanding for Meter Resolution Images. Extraction of the surface velocity of rivers with SAR-ATI. H. Runge 1 , S. Suchandt 1 , R. Horn 2 , T. Eiglsperger 3 German Aerospace Center (DLR) 1 Remote Sensing Technology Institute - PowerPoint PPT PresentationTRANSCRIPT
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Extraction of the surface velocity of rivers with
SAR-ATI
H. Runge1, S. Suchandt1, R. Horn2, T. Eiglsperger3
German Aerospace Center (DLR)
1Remote Sensing Technology Institute
2Microwaves & Radar Institute
3University Erlangen-Nuremberg
7th CNES/DLR Workshop on Information
Extraction and Scene Understanding for
Meter Resolution Images
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Why do we need measurement of river surface currents with remote sensing?
The surface velocity is one important parameter to measure the river run-off
River discharge is the only parameter in the water cycle that can be measured integrated over a large area.
River discharge is a sensitive parameter for climate changes.
With the rapid growth of world population the fresh water resources are of vital interest.
Gauging stations can not be maintained in all parts of the world.
From some countries run-off data are not made available.
In case of flooding better run-off predictions are necessary.
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d
A1
vs, az, Flight Track
Ground Track
x, vx
y, vy
Rground
R0 zh
A2
Moving Target
s
yATI v
vd
sin2
Interferometric phase:
SAR Along-Track Interferometry
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The „Train Off the Track Effect“
][sin
0 mv
vRaz
s
y
A moving target with across-track motion appears displaced in azimuth direction in the SAR image.
The signal from the water surface will appear displaced & superimposed on clutter at the river bank in the focused SAR image.
az
vy
rg
az
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Over smooth water the microwaves are reflected away from the sensor
Higher return over rough surface
Considerable Surface Roughness is Required
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ESAR Aircraft ESAR Aircraft
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ESAR ATI System Parameter
E-SAR ATI system
frequency band: X (9.6 GHz)
range bandwidth:
100 MHz
pulse repetition frequency:
1000 Hz / channel
antenna separation:
0.87119 m
sensor velocity: 88 m/s
incidence angle: 20 – 60 deg
SLC resolution: 1.50 x 0.09 m
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Gauge „Puppling“
Drainage Basin of the River Isar
site „Lenggries“
site „Kochel“
DLR test sites where in-situ measurements have been performed by the Bavarian Hydrological Office
Munich
DLR
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Puppling Test Site I
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ESAR Data of Puppling Test Site
Amplitude Coherence ATI Phase
az
slant range
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SAR Amplitude Image of the Puppling Site
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ATI Phase Analysis
Pixel with non-zero phase are back projected to their “original” position.
Only pixel which are then positioned over the river will be considered.
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Result from ATI Analysis
Result for ATI current velocity:
Pixel analyzed: 61
Min/Max: 2.27 / 0.56 m/s
Mean: 1.22 m/s
Result from in-situ measurement:
Mean: 1,70 m/s
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Result from ATI Analysis
Result for the current velocity from ATI method:
Pixel analyzed: 61
Min/Max: 2.27 / 0.56 m/s
Mean: 1.22 m/s
Result from in-situ measurement:
Mean: 1,70 m/s
Due to the superposition with stationary clutter the ATI measurements are biased to lower velocities. The error is 28%.
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Simulation of Azimuth Displacement for E-SAR Case
2.5
2.0
1.51.0
0.5
river surface velocity [m/s]
river flow direction
70 m
azimuth displacement
rg
az
The azimuth displacement method is not affected by clutter!
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Original SAR image
The two SAR channels are used for clutter cancellation
Remaining amplitude after complex subtraction of the two channels (DPCA)
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SAR Amplitude Image of the Puppling Site
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Scene after Clutter Cancellation
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Result for the current velocity from the displacement method plus DPCA clutter suppression:
Mean displacement: 86m
Corresponding velocity : 1.90 m/s
Result from in-situ measurement:
Mean: 1,70 m/s
The difference to the reference measurement has been reduced to 12%!
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Wolfratshausen 2006 Data Takes
1
3
2
4
06trafic0210x1_t01
06trafic0211x1_t01
06trafic0209x1_t01 06trafic0208x1_t01
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Isar 12/05/06 - Ground Truth Measurements
1-4:Sections where ground truth data where acquired with floaters.
Main river stream with greatest surface roughness
Section
Ref. Measurement
[m/s]
1 2.43
2 2.37
3 1.90
4 2.04
N
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Amplitude image of DT0210x1
Results from 24.11.06: corrected DPCA modeling
Illumination
flightdirectio
n
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Clutter reduction by DPCA filtering
Results from 24.11.06: corrected DPCA modeling
Illumination
flightdirectio
n
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Displaced river surface (red line) versus actual flow (blue
line)
Results from 21.03.07
Illumination
flightdirectio
n
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Surface velocity from displacement
Section
Ref. Measurement
[m/s]
1 2.43
2 2.37
3 1.90
4 2.04
Results from 21.03.07
Illumination
flightdirectio
n
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Results from 21.03.07
Section
Ref. Measurement
[m/s]
1 2.43
2 2.37
3 1.90
4 2.04
Illumination
flightdirectio
n
Surface velocity from displacement
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Illumination
Results from 21.03.07
Illumination
flightdirectio
n
Surface velocity from displacement
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Results from 18.10.06
Illumination
flightdirectio
n
Amplitude image of DT0211x1
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Results from 18.10.06
Illumination
flightdirectio
n
Clutter reduction by DPCA filtering
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Illumination
flightdirectio
n
Displaced river surface (red line) versus actual flow (blue line)
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Section
Ref. Measurement
[m/s]
1 2.43
2 2.37
3 1.90
4 2.04
Illumination
flightdirectio
n
Surface velocity from displacement
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Results from 21.03.07, daz reference = area with greatest roughness; slightly corrected DPCA modeling
Section
Ref. Measurement
[m/s]
1 2.43
2 2.37
3 1.90
4 2.04
Illumination
flightdirectio
n
Surface velocity from displacement
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Results from 21.03.07, daz reference = area with greatest roughness; slightly corrected DPCA modeling
Illumination
flightdirectio
n
Surface velocity from displacement
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Conclusions
Due to strong clutter on the river bank the ATI measurements are biased to lower velocities
Clutter cancellation led to a SAR velocity measurement which differ in the order of only 10 to 15% from the in-situ measurements
A 3-channel SAR will allow to do both DPCA and ATI.
With such a system no auxillary information concerning the actual flow direction is required.