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1. Title Radar Interferometry withPublic Domain Tools • Bert Kampes(TUDelft/DLR, Germany) • Ramon Hanssen (TUDelft, The Netherlands) • Zbigniew Perski (University of Silesia, Poland)

2. Introduction • "Radar Interferometry is a tool." • Public domain software is important to stimulate fast and free dissemination of ideas. • Limited effort and low costs benefits the science community. • We show how users can take advantage of readily available public domain software by an example processing with ENVISAT ASAR data. • Handling the data in the distributed format. • Interferometric processing (unwrapping, geo-referencing). • Coordinate conversion and data gridding. • Visualization of computed DEM. • GIS analysis. • We note drawbacks and missing elements of the software in the hope that these items will be (developed and) made available to the scientific community. • (Public domain software in this presentation are marked red the first time they are referenced.)

3. Processed ENVISAT data: • Las Vegas Area; • Topography: 0  3500 m; • Effective baseline: 100 m; • Master: 03 Jan. 2003; • Slave: 29 Nov. 2002; • Doppler difference 50 Hz; SRTM C-band DEM of Las Vegas Area Data Overview • Doris (Delft University) is used for the interferometric processing. • International user community (>70 registered users). • User manual; email list (FAQ). • Runs on all platforms (GNU GCC compiler). • Uses public domain software for common tasks (FFTW, LAPACK). • Quicklook images of intermediate products. • Convenient interface for running. • Modular setup allows for easy addition of new algorithms (C++).

4. Las Vegas Reading the ENVISAT Format • The ENVISAT data distribution format differs from the CEOS format used for the ERS satellites. • The ESA has made a C software library available to the public domain to handle the distributed data (BEAM Toolbox). • The Doris software includes utilities for the extraction of information and data from the distributed format using this library. These utilities are automatically called by Doris 100 km 100 km • The visualization of the magnitude is done with a utility also provided with Doris (cpxfiddle). EnviSAT ASAR data (SLC full scene, beam 2)

5. Co-registration • Alignment of slave on master • Precise orbits. • Coarse correlation. • FINE (many small patches). • Shown are FINE offset vectors. • A 2D polynomial is least-squares estimated to model the transformation. • This plot is created by Doris, using GMT. • The co-registration is automated, using outlier detection. • Manual intervention in the polynomial fitting is easy for optimal control using error plots (GMT). Transformation slave to master geometry

6. Interferogram Generation • This was the first interferogram computed with Doris from ASAR ENVISAT data. • Multi-looking factors: 1x5. • Ellipsoid reference phase corrected and again multi-looked with factors 4x4. Resolution ~80 x 80 m2. • Annotated orbits seem very accurate for ENVISAT. • Height of ambiguity: 80 m • Resampling can be performed with a number of kernels, e.g., NN, linear, 6 point cubic convolution, 16 point truncated sinc. Phase of complex interferogram

7. Doris' Capabilities • Magnitude/phase display; These plots are SUNraster format and automaticallygenerated by Doris. • Doris can also: • Coherence image. • Differential interferometry (3 and 4 pass, external DEM). • Geo-referencing. • Phase filtering using arbitrary kernels in spatial or spectral domain, or Goldstein's method. • Spectral filtering (azimuth and range). Magnitude/Phase display

8. Phase Unwrapping • SNAPHU (Stanford University) is used to unwrap the interferometric phase. • "Statistical-Cost, Network-Flow Algorithm for Phase Unwrapping": a sophisticated MCF algorithm using expected smoothness of unwrapped data. • Can use interferometric amplitude or coherence for improved cost computation. • SNAPHU is run automatically by Doris, without user intervention, but can be run (again) standalone. • (7 minutes,1297x1310 pixels) EnviSAT ASAR data (SLC full scene, beam 2)

9. azimuth range longitude latitude height range azimuth • PROJ.4 (USGS) was used to convert the WGS84 coordinates to UTM. • PROJ.4: "Cartographic Projections library'' that can perform forward and inverse transformation of cartographic data to or from Cartesian data with a wide range of selectable projection functions, including datum translations (e.g., WGS84 to UTM, Gauss-Krueger, etc.). • Utilities and example scripts are included in the Doris distribution. PROJ.4 UTM GMT GIS Coordinate Transformations • After the phase unwrapping, the height is estimated with respect to the reference ellipsoid (save a bias, 1 GCP required). • Then, the radar coordinates {range, azimuth} are geo-referenced {latitude, longitude} using the estimated heights. • This yields 3 matrices with for each pixel a latitude/longitude/height triplet (irregularly sampled data). WGS ascii

10. The Generic Mapping Tools • The Generic Mapping Tools (GMT, Soest University) can be used to grid the data (surface tension spline). • The GMT handle {x,y,z} data as UNIX filters, making them extremely flexible. • Each program performs a specific task, e.g., creating a vector plot, or data gridding. • The output of each program is a processed data file or postscript code. • Extremely well documented and large and lively user community. DEM interpolation and visualization with GMT

11. GRASS FREE GIS • GRASS (open source) is a free GIS which can be used for analysis of data from different sources and stored in different formats, and for data visualization. • "Geographic Resources Analysis Support System" • Shown is a watershed analysis using the computed DEM. • Data can be imported in GRASS via the netcdf format used with GMT. Graphical User Interface of the GRASS free GIS software

12. GRASS (NVIZ) LANDSAT DRAPE

13. input handling Doris(Delft) Precise orbits • Delft orbits (ERS) SLC data • BEAM Toolbox (ESA) coregistration • GMT (Soest) interferogram generation • optionally differential interferogram: • SRTM C-band DEM, GTOPO30(USGS) • SNAPHU (Stanford) phase unwrapping datum transformation PROJ.4 (USGS) GMT (Soest) gridding & visualization GRASS (open source) GIS analysis Summary

14. Conclusion • We have demonstrated the capability of public domain software to handle ENVISAT data: • Interferometric processing was performed on a 900 MHz laptop, 100 MB of RAM available (OS: Cygwin under MS windows XP). • Interferometric processing time was 1 hour (full-scene DEM). • GRASS GIS analysis was performed on a 3 GHz Linux PC. • Sollicited functionality: • Interactive visualization tool for Radar data (click and analyze). • Time series functionality. • Extention/experience of the tools to handle other ENVISAT products (ScanSAR, alternating polarization, MERIS, etc.) • ENVISAT precise orbits distribution as for ERS (Delft?) • Utilities/algorithms using SRTM C-band DEM need to be investigated (fast radarcoding, coherence estimation, co-registration, etc.) • Algorithms for orbit improvement (cq. trend removal). • ?