Introduction Background
Line of sight (LOS) interferogram
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Line of sight (LOS) interferogramSuppose there is only a ground displacement of the entire pixel as a component of the image (without pixel distortion) in the range direction of the line of sight (LOS) between the radar and the target. In that case, the displacement is immediately translated as a phase shift concerning the rest of the image. Moving the pixel in the range direction by half a wavelength and a wavelength of round trip distance for the radar signal produces one fringe (2-phase difference) (Figure 2.4). As a result, one fringe in an interferogram corresponds to a half-wavelength displacement in the ground displacement in the range direction. It is how ground surface "deformation" is measured with InSAR (Gabriel et ali. 1989). For the repeat-pass SAR, variable acquisition geometry results in phase difference, affecting the topography of the ground surface and interferogram. The spatial separation of the two antenna sites is the baseline for photos obtained at different times on different orbits. The orbital fringes refer to the orbital contribution to the phase difference. Figure (2.4): Image shows imaging geometry. Each pixel in the single SAR image represents the phase and intensity returned from the corresponding ground spot. A second satellite pass later provides a similar image for determining displacements. A red arrow indicates the displacement projected along the satellite line of sight (LOS), and the phase difference between the two images is proportional to this displacement. The angle represents the antenna's look. The interferometric phase (the difference in phase between the two registered phase images) follows the following format: the topographic contribution to the phase difference is referred to as "topographic fringes. “As a result, numerous factors impact the interferogram, including the distance between the antenna and the ground pixel, surface topography, satellite orbits, the dielectric characteristics of the ground surface, the atmosphere, and system noise (Bonforte et al. 2001). The two registered images used to generate the interferogram in repeat-pass interferometry are obtained from the satellite between consecutive passes with baseline B. The first image (reference image) is referred to as the master image, while the second image is referred to as the slave image. Where (ΔΦ) in an interferogram is measured in radians between 0 and 2π. It is a result of the contribution from surface deformation (ΔϕDispl), the difference in atmospheric path delay (Δϕatm), topography (ΔϕTopo), the inaccuracies in the orbit state vectors (Δϕorb) and other noise contributions (Δϕnoise) (Bechor and Zebker, 2006). To find the surface deformation component (ΔϕDispl) in the target in terms of line of sight (LOS) of the absolute phase difference in an interferogram (Δϕ), topographic contributions (ΔϕTopo) are removed using a Digital Elevation Model (DEM). The inaccuracies come from the sensor and the data processing ( ). Suppose the atmosphere has similar spatial conditions between the two scan times. In this case, its contribution tends to be zero, and the distortion map can be obtained after eliminating the two-dimensional phase ambiguity in the phase shift of the interferometric model. In the following expression, the rest of the differential interferogram is displayed. We keep the topographic phase (second term to the right of 1) to illustrate the perpendicular baseline B’s dependence. We can obtain. Download 0.84 Mb. Share with your friends:
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