Remote Sensing Technology Institute 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 2 Microwaves & Radar Institute 3 University Erlangen-Nuremberg 7th CNES/DLR Workshop on Information Extraction and Scene Understanding for Meter Resolution Images

Remote Sensing Technology Institute 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.

Remote Sensing Technology Institute d A1A1 v s, az, Flight Track Ground Track x, v x y, v y R ground R0R0 z h  A2A2 Moving Target Interferometric phase: SAR Along-Track Interferometry

Remote Sensing Technology Institute The „Train Off the Track Effect“ 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 vyvy rg az

Remote Sensing Technology Institute Over smooth water the microwaves are reflected away from the sensor Higher return over rough surface Considerable Surface Roughness is Required

Remote Sensing Technology Institute ESAR Aircraft

Remote Sensing Technology Institute 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: m sensor velocity:88 m/s incidence angle:20 – 60 deg SLC resolution:1.50 x 0.09 m

Remote Sensing Technology Institute 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

Remote Sensing Technology Institute Puppling Test Site I

Remote Sensing Technology Institute ESAR Data of Puppling Test Site Amplitude Coherence ATI Phase az slant range

Remote Sensing Technology Institute SAR Amplitude Image of the Puppling Site

Remote Sensing Technology Institute 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.

Remote Sensing Technology Institute 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

Remote Sensing Technology Institute 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%.

Remote Sensing Technology Institute Simulation of Azimuth Displacement for E-SAR Case river surface velocity [m/s] river flow direction 70 m azimuth displacement rg az The azimuth displacement method is not affected by clutter!

Remote Sensing Technology Institute Original SAR image The two SAR channels are used for clutter cancellation Remaining amplitude after complex subtraction of the two channels (DPCA)

Remote Sensing Technology Institute SAR Amplitude Image of the Puppling Site

Remote Sensing Technology Institute Scene after Clutter Cancellation

Remote Sensing Technology Institute 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%!

Remote Sensing Technology Institute Wolfratshausen 2006 Data Takes trafic0210x1_t01 06trafic0211x1_t01 06trafic0209x1_t01 06trafic0208x1_t01

Remote Sensing Technology Institute 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 SectionRef. Measurement [m/s] N

Remote Sensing Technology Institute

Amplitude image of DT0210x1 Results from : corrected DPCA modeling Illumination flight direction

Remote Sensing Technology Institute Clutter reduction by DPCA filtering Results from : corrected DPCA modeling Illumination flight direction

Remote Sensing Technology Institute Displaced river surface (red line) versus actual flow (blue line) Results from Illumination flight direction

Remote Sensing Technology Institute Surface velocity from displacement Sectio n Ref. Measurement [m/s] Results from Illumination flight direction

Remote Sensing Technology Institute Results from Sectio n Ref. Measurement [m/s] Illumination flight direction Surface velocity from displacement

Remote Sensing Technology Institute Illumination Results from Illumination flight direction Surface velocity from displacement

Remote Sensing Technology Institute Results from Illumination flight direction Amplitude image of DT0211x1

Remote Sensing Technology Institute Results from Illumination flight direction Clutter reduction by DPCA filtering

Remote Sensing Technology Institute Illumination flight direction Displaced river surface (red line) versus actual flow (blue line)

Remote Sensing Technology Institute Sectio n Ref. Measurement [m/s] Illumination flight direction Surface velocity from displacement

Remote Sensing Technology Institute Results from , daz reference = area with greatest roughness; slightly corrected DPCA modeling Sectio n Ref. Measurement [m/s] Illumination flight direction Surface velocity from displacement

Remote Sensing Technology Institute Results from , daz reference = area with greatest roughness; slightly corrected DPCA modeling Illumination flight direction Surface velocity from displacement

Remote Sensing Technology Institute 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.