Radargrammetry of High-Resolution Synthetic Aperture Radar A Theoretical Study

1. ISRS2007, Lamada Plaza Hotel, Jeju, Korea, 31 October - 2 November 2007 Radargrammetry of High-Resolution Synthetic Aperture Radar A Theoretical Study Hoonyol Lee Department of Geophysics Kangwon National University Email: hoonyol@kangwon.ac.kr Homepage: http://sar.kangwon.ac.kr

2. Contents Overview of KOMPSAT-5 COSI Radargrammetry of KOMPSAT-5 COSI Conclusion

3. Overview of KOMPSAT-5 COSI • X-band • Altitude: 550km • Inclination: 97.6 deg • Dawn-dusk orbit • 06:00 am Mean Local Time of Ascending Node • 15+1/28 revolutions per day • Nodal Period: 95.78 minutes • 28D421R (28 days revisit time after 421 revolutions) • Ground speed: 6.97 km/s • Successive Orbit Distance: 2665 km (no image overlap between two successive orbits) • Distance between adjacent pass: 95 km at equator

4. KOMPSAT-5 Orbit Elements Note some parameters may be changed due to a new launch schedule in May 2010.

5. Ascending Node Pass (Dawn) Orbit Number 2665 km © KARI Day Number

6. Descending Node Pass (Dusk) Orbit Number 95 km © KARI Day Number

7. Spot Mode • Imaging Time of 1 Scene = 3 sec • In-Cal and Fin-Cal Time = (0.25+0.25) sec • Maximum Time btw. Target Change (20-45 deg) = 2 sec • Minimum Number of HR Images in 2 minutes = 22 © KARI

8. Stripmap Mode • Imaging Time = 2 continuous minutes • Maximum Time btw. Target Change (20-45 deg) = 1.5 sec © KARI

9. ScanSAR Mode • Imaging Time = 2 continuous minutes • Maximum Time btw. Target Change (20-45 deg) = 4 sec © KARI

10. Radargrammetry Stereographic mapping with two SAR images taken at different incidence angles All weather, day & night, high-resolution SAR Horizontal Resolution: ~ 8x8 pixels for cross-correlation Vertical Resolution ~ incidence angles and their difference Severe topographic distortion

11. Spaceborne Topographic Mappers

12. SSR vs. OSR Incidence angles Same-Side Radargrammetry (SSR) Opposite-Side Radargrammetry (OSR) Vertical Resolution: OSR is better than SSR Severe topographic distortion: SSR is better than OSR • Opposite-Side Radargrammetry • High sensitivity to height • Severe distortion • Error in textureless area • Same-Side Radargrammetry • Moderate sensitivity to height • Moderate distortion • Error in textureless area

13. SSR Geometry

14. OSR Geometry

15. Radargrammetry – An example Magellan SAR data of Lullin Impact Crater, Venus (Lee et al. 2003) Left-look, 44.2 ° Left-look, 25.1 ° Right-look, -24.9 °

16. SSR vs. OSR • Same-Side Radargrammetry • Moderate sensitivity to height • Moderate distortion • Error in textureless area • Opposite-Side Radargrammetry • High sensitivity to height • Severe distortion • Error in textureless area Anaglyph DEM

17. KOMPSAT-5 COSI Imaging Modes Adjacent Pass 95 km 0 km Nadir 185 km 490 km Altitude 550km Nominal 675 km Spot (1 m), 5km, 22 scenes Extended Strip map (3 m), 30 km x 800 km ScanSAR (20m), 100 km x 800 km 20 ° 185 km Nominal 305 km 45 ° 55 ° Coverage 490 km Extended 185 km

18. Number of Pass for a Ground Target • Condition for Complete Coverage of SSR: N=C/A>2 N: number of pass, C: Image Coverage width, A: Adjacent pass distance(=95km at equator)

19. Uniqueness of K-5 COSI for SSR

20. Uniqueness of COSI for SSR • Radarsat-1 has been unique for SSR • Limited SSR availability of TerraSAR-X and COSMO-SkyMed unless significant satellite maneuvering • SSR will be valuable before the widespread of single-pass interferometers (e.g., TanDEM-X). • KOMPSAT-5 COSI is dedicated to SSR.

21. z (up) K5 Orbit Geometry for Radargrammetry Left Look Right Look R: Earth radius H: Altitude of satellite Xg: Ground distance of adjacent pass n: Pass number from nadir x: Image location from nadir to east |x|<Xg/2 θi: Incidence angle Nominal: 20° < θi < 45 ° Extended: 45 ° < θi < 55 ° θl: Look angle Rg: Ground range Nominal: 185 km < Rg < 490 km Extended: 590 km < Rg < 675 km Rs: Ground range n =0 -1 1 -2 2 3 4 Satellite Pass θi θl H = 550Km Earth Surface (Equatorial plane) x Xg =95 km at equator East R = 6378Km δ Earth Center

22. Incidence angle as a function of x (position from Nadir)

23. z (up) Radargrammetric Geometry (x = -47.5 km) Left Look Right Look Nominal Mode Extended Mode -2 -1 n=0 1 2 3 4 5 6 7 8 Xa=95 km Altitude H = 550Km x = -47.5 km x (east) -47.5 0 +47.5

24. z (up) Radargrammetric Geometry (x = 0 km) Left Look Right Look Nominal Mode Extended Mode -2 -1 n=0 1 2 3 4 5 6 7 8 Xa=95 km Altitude H = 550Km x=0 km x (east) -47.5 0 +47.5

25. z (up) Radargrammetric Geometry (x = +47.5 km) Left Look Right Look Extended Mode Nominal Mode -2 -1 n=0 1 2 3 4 5 6 7 8 Xa=95 km Altitude H = 550Km x=+47.5 km x (east) -47.5 0 +47.5

26. Height Sensitivity of Parallax

27. Height Sensitivity of Parallax

28. Days of SSR Orbits

29. Arctic : More passes but rotated

30. Antarctic : More passes but rotated and with a hole

31. Conclusions • The orbit and imaging modes of KOMPSAT-5 COSI is dedicated to radargrammetry. • At least 3 passes are available for a ground target (5: extended). • Orbit pairs of 5-3 and 3-2 are recommended for radargrammetric nominal mission • Height sensitivity of parallax: 0.6-0.9 • Height resolution: 1-2 pixels • Wider selection of pairs are theoretically provided. • Combination of ASC/DES, and L/R-looking will provide more opportunity. • Note that all calculations are true at equator. Further analysis is necessary for global configuration. • TerraSAR-X and COSMO-SkyMed data may provide tests of high-resolution examples, but not so versatile as KOMPSAT-5 COSI.