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    21-Aug-2014
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Radar Course III
37. Bragg scattering
43. Texture and image analysis
42. Temporal averaging
12. Synthetic Aperture Radar (SAR)
34. Space, time and processing constraints
15. Slant range / ground range
8. Side-looking radars
19. Shadow
10. Real Aperture Radar: Range resolution
11. Real Aperture Radar: Azimuth resolution
9. Real Aperture Radar (RAR)
7. Radar principles
38. Radar image interpretation
35. The radar equation
36. Parameters affecting radar backscatter
16. Optical vs. microwave image geometry
25. Method
18. Layover
32. Landers Earthquake in South California
23. Introduction
27. Interferogramme of Naples (Italy)
29. Interferogramme and DEM of Gennargentu (Italy)
2. Independence of clouds coverage
40. Image interpretation: Speckle
41. Image interpretation: Speckle filters
39. Image interpretation: Tone
20. Geometric effects for image interpretation
22. Geocoding: Geometry
17. Foreshortening
26. First ERS-1/ERS-2 tandem interferogramme
6. Electromagnetic spectrum
30. Differential interferometry
45. Data reduction: 16 to 8 bit, blockaverage vs incrementing
4. Control of imaging geometry
3. Control of emitted electromagnetic radiation
24. Concept
28. Coherence image of Bonn area (Germany)
44. Classification of ERS-1 SAR images with Neural Networks
5. Access to different parameters compared to optical systems
13. SAR processing
33. SAR interferometric products
21. SAR image geocoding
14. ERS SAR geometric configuration
31. The Bonn experiment
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Method

The nearly exact repeat orbit allows formation of an interferometric baseline as shown in the figure. The ERS-1 sensor provides a platform to record SAR data which is useful for interferometry.
This exploitation of the orbit repeat feature is known as multi-pass INSAR.
For a point target that is at (x, y, z), the phase difference f between the signal s1 and s2 received at r1 and r2 is

Where is the radar signal wavelength. The interferometric phase is obtained by complex correlation of the first complex SAR image, obtained during the first overpass, relative to the second image, belonging to the second pass, after precise co-registration.

The interferometric phase can be used to determine the precise look angle by first solving the cosine of the angle between the baseline vector and the look vector:


The height z at the location r1 is determined from:


Where h is the altitude of the platform above the reference plane.

The phase in the interferogramme is known only modulo 2p, therefore it is necessary to determine the correct multiple of 2p to add to the phase to obtain consistent height estimates.

The correlation coefficient g of the complex backscatter intensities s1 and s2 at r1 and r2 is defined by:



In the following we will call g the interferometric correlation. The correlation coefficient g in terms of the baseline correlation factor a is equal to



where the geometrical baseline correlation factor a is given by:

where SNR is the signal to noise ratio, dr the slant range resolution, and alpha is the radar incidence angle.
The ERS-1 radar sensor has a slant range pixel spacing of 7.9m, nominal incidence angle of 23 degrees, and nominal range of 853 Km to the center of the image swath.
For an 8 look image with a SNR of 20, the theoretical height resolution is better than 2.5 m for a wide range of correlation values y.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry