SWOT INTERFEROMETRIC PROCESSING OF FRESH WATER BODIES FOR SWOT Ernesto Rodríguez, JPL/CalTech Delwyn Moller, Remote Sensing Solution Xiaoqing Wu, JPL/CalTech Kostas Andreadis, JPL/CalTech 1-1 IGARSS July 27, 2011 SWOT Study Area • ~1000 km reach of the Ohio River basin • Drains an area of ~220,000 km2 • Topography from National Elevation Dataset (30 m) • River vector maps from HydroSHEDS • Channel width and depth from developed power-law relationships • Explicitly modeled rivers with mean widths at least 50 m 1-2 IGARSS July 27, 2011 SWOT Hydrodynamic Modeling • • • • • LISFLOOD-FP raster-based model 1-D solver for channel flow 2-D flood spreading model for floodplain flow Kinematic, Diffusive and Inertial formulations Requires information on topography, channel characteristics and boundary inflows • Needed to coarsen spatial resolution to 100 m • Simulation period of 1 month • Boundary inflows from USGS gauge measurements SWOT Hydrology Virtual Mission Meeting, Paris, 221-3 Sep 2010 IGARSS July 27, 2011 SWOT Data from the SWOT Land Simulator Range Along-Track The SWOT simulator produces data with the correct signal to noise ratio, layover and geometric decorrelation scattering properties. Notice for SWOT the land SNR is low, while surface water stands out. 1-4 IGARSS July 27, 2011 SWOT Challenges for near-nadir interferometry over land • Topographic layover and low land SNR makes conventional phase unwrapping approaches unfeasible • Notice that fringes are well defined over the water, since the water is flat and quite bright at nadir incidence. • The signal from topography may contaminate the signal over the water (see next slide) 1-5 IGARSS July 27, 2011 SWOT Radar Layover and its Effect on Interferometry Surface Layover Volumetric Layover (trees) Points on dashed line arrive at the same time Correlation Ratio (land less correlated than water) PLand Land arg1 exp iLand W ater PW ater W ater Brightness Ratio (land darker than water) 1-6 IGARSS July 27, 2011 SWOT NASA SWOT Land Processing Approach • Processing approach relies on having a fair estimate of topography and water body elevation – Estimate can be derived from a priori data or previous SWOT passes (to account for dynamics) • A priori information is used to generate reference interferograms for phase flattening and estimation of layover (to avoid averaging in land) 1-7 IGARSS July 27, 2011 SWOT Interferogram after phase flattening with reference interferogram Noisy interferogram Noisy interferogram after flattening with reference 1-8 IGARSS July 27, 2011 SWOT Noisy interferogram Layover region identification Noisy interferogram after flattening with reference 1-9 IGARSS July 27, 2011 SWOT Land Processing Flow to Geolocation 1-10 IGARSS July 27, 2011 SWOT Layover mask All pixels with any layover are red Mid-Swath Near-Swath 1-11 IGARSS July 27, 2011 SWOT What if we accept pixels whose expected error is < 5 cm? 1-12 IGARSS July 27, 2011 From raw heights to hydrologic variables SWOT Manning’s equation Discharge Width Flow Depth (height from bottom) 1-13 Slope IGARSS July 27, 2011 SWOT Water Classification 1-14 IGARSS July 27, 2011 SWOT River Channel Mask . Pavelsky and L. Smith, “Rivwidth: A software tool for the calculation of river widths from remotely sensed imagery,” IEEE Geoscience and Remote Sensing Letters, vol. 5, no. 1, p. 70, 2008. 1-15 IGARSS July 27, 2011 SWOT Center Line Mask 1-16 IGARSS July 27, 2011 SWOT Get Center Line . Pavelsky and L. Smith, “Rivwidth: A software tool for the calculation of river widths from remotely sensed imagery,” IEEE Geoscience and Remote Sensing Letters, vol. 5, no. 1, p. 70, 2008. 1-17 IGARSS July 27, 2011 SWOT Project to Local Coordinates • Spline interpolate center line to constant separation points downstream • Use spline to obtain local tangent plane coordinate system at each point s c • For each point: -Use KDTree algorithm to find closest centerline point - Project point into local coordinate system to get along and across-track distance 1-18 IGARSS July 27, 2011 SWOT Measured Noisy Elevation 1-19 IGARSS July 27, 2011 SWOT Unsmoothed Elevation Errors 1-20 IGARSS July 27, 2011 SWOT Height Error vs Downstream Distance 1-21 IGARSS July 27, 2011 SWOT Height Error vs Downstream Distance with Downstream Averaging 1-22 IGARSS July 27, 2011 SWOT Measurement Errors Downstream Averaging: 200 m 1-23 IGARSS July 27, 2011 SWOT Measurement Errors Downstream Averaging: 1 km 1-24 IGARSS July 27, 2011
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