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| USGS Earth Resources Observation and Science Center (EROS) |
The Spaceborne Imaging Radar-C (SIR-C) processor processed a pair of repeat-pass complex images to produce C-band (5.67 cm wavelength) and/or L-band (24.23 cm wavelength) raw interferograms.
Phases in the raw interferogram contain three components of information: a) phase contributed by orbital baseline separation effects, b) topography (and any ground surface deformation change between the two images), and c) noise. Figure 1 is an example of the photo image associated with the interferometric products, and Figure 2 is an example of a raw (unflattened) interferogram.
Figure 1:
Photo Image
Figure 2:
Raw InterferogramA "flattened" interferogram is generated by removing the orbital phase component from the raw interferogram. An example of flattened interferogram corresponding to the images in Figures 1 and 2 is shown in Figure 3. Earth flattening is not a necessary step to derive a Digital Elevation Model (DEM).
Figure 3:
Flattened InterferogramAn approximate estimation of baseline parameters for the interferometric pair is given in pr#####.pfile. However, applications such as DEM generation or deformation detection require baseline parameter accuracy on the centimeter level. Therefore, additional calculations using ground control points are needed to re-estimate the baseline parameters (e.g., Zebker et al., 1994; Rosen et al., 1996).
Because the measured phase in an interferogram falls between 0 and 2 pi, it needs to be unwrapped in order to derive a DEM. A suggested technique is the one proposed by Goldstein et al. [1988]. An example of DEM derived based on a raw interferogram is shown in Figure 4.
Figure 4:
Interferometry-Derived DEMA suggested flow chart for deriving a topographic map from an interferogram is shown in Figure 5. Estimating baseline parameters and deriving the DEM are coupled with each other, and phase unwrapping is a necessary step bridging the baseline estimation and DEM generation.
Figure 5: Deriving a DEM from an Interferogram
Goldstein, R. M., H. A. Zebker, and C. L. Werner, Satellite radar interferometry: Two-dimensional phase unwrapping, Radio Science, 23, 713-720, 1988.
Rosen, P., S. Hensley, H. Zebker, F. H. Webb, and E. J. Fielding, Surface deformation and coherence measurements of Kilauea volcano, Hawaii, from SIR-C radar interferometry, J. Geophys. Res., 101, 23109-23125, 1996.
Zebker, H. A., C. L. Werner, P. L. Rosen and S. Hensley, Accuracy of topographic maps derived from ERS-1 interferometric radar, IEEE Transactions on Geoscience and Remote Sensing, 32, 823-836, 1994.
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