Method for detecting surface motions and mapping small terrestrial or planetary surface deformations with synthetic aperture radar
First Claim
1. A method for detecting surface motions or mapping small terrestrial or planetary surface deformation changes over large areas using synthetic aperture radar comprising the steps ofmaking two synthetic aperture radar images sequential in time, but of the same area with flight paths substantially duplicated,processing said synthetic aperture radar images for azimuth focusing, co-registration, motion compensation, and yaw, pitch and roll, of the platformforming a difference interferogram of said area from said two synthetic aperture radar images, after processing in the previous step,unwrapping phases of pixels of said difference interferogram by finding the 2π
- multiples of phase, if any, that disappear in the making of said difference interferogram, andobserving line of sight surface motion or deformation changes in said terrestrial or planetary surface from said unwrapped difference interferogram, where said line of sight is of said synthetic aperture radar while making said images.
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Abstract
A technique based on synthetic aperture radar (SAR) interferometry is used to measure very small (1 cm or less) surface deformations with good resolution (10 m) over large areas (50 km). It can be used for accurate measurements of many geophysical phenomena, including swelling and buckling in fault zones, residual, vertical and lateral displacements from seismic events and prevolcanic swelling. Two SAR images are made of a scene by two spaced antennas and a difference interferogram of the scene is made. After unwrapping phases of pixels of the difference interferogram, surface motion or deformation changes of the surface are observed. A second interferogram of the same scene is made from a different pair of images, at least one of which is made after some elapsed time. The second interferogram is then compared with the first interferogram to detect changes in line of sight position of pixels. By resolving line of sight observations into their vector components in other sets of interferograms along at least one other direction, lateral motions may be recovered in their entirety. Since in general, the SAR images are made from flight tracks that are separated, it is not possible to distinguish surface changes from the parallax caused by topography. However, a third image may be used to remove the topography and leave only the surface changes.
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Citations
13 Claims
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1. A method for detecting surface motions or mapping small terrestrial or planetary surface deformation changes over large areas using synthetic aperture radar comprising the steps of
making two synthetic aperture radar images sequential in time, but of the same area with flight paths substantially duplicated, processing said synthetic aperture radar images for azimuth focusing, co-registration, motion compensation, and yaw, pitch and roll, of the platform forming a difference interferogram of said area from said two synthetic aperture radar images, after processing in the previous step, unwrapping phases of pixels of said difference interferogram by finding the 2π - multiples of phase, if any, that disappear in the making of said difference interferogram, and
observing line of sight surface motion or deformation changes in said terrestrial or planetary surface from said unwrapped difference interferogram, where said line of sight is of said synthetic aperture radar while making said images. - View Dependent Claims (2, 5, 6)
- multiples of phase, if any, that disappear in the making of said difference interferogram, and
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3. A method for mapping small terrestrial or planetary surface deformation changes over large areas with synthetic aperture radar comprising the steps of
making three sequential synthetic aperture radar images of the same scene with phase coherence between corresponding pixels of said images, at least one of which is made significantly later than the other two processing said synthetic aperture radar images for azimuth focusing, co-registration, motion compensation, and yaw, pitch and roll, of the platform forming a first single-difference interferogram from a first pair of synthetic aperture images after processing in the second step, said first pair being selected from said three sequential synthetic radar images, forming a second single-difference interferogram from a second pair of synthetic aperture images after processing in the second step, said second pair being distinct from said first pair selected from said three sequential synthetic aperture radar images, unwrapping phases of pixels of said first and second single-difference interferograms by finding the 2π - multiples of phase that disappear in the making of said first and second single-difference interferograms,
forming a double-difference interferogram from said first single-difference interferogram and said second single-difference interferogram, thereby removing phase changes from corresponding pixels due to topography, leaving an image of nonzero phases only in areas where surface deformation has changed in the time between said first pair of images and said second pair of images, and observing surface deformations in said terrestrial or planetary surface from said double-difference interferogram. - View Dependent Claims (4, 7)
- multiples of phase that disappear in the making of said first and second single-difference interferograms,
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8. A method for mapping small terrestrial or planetary surface deformations over large areas using synthetic aperture radar comprising the steps of
making multiple sequential synthetic aperture radar images of the same scene with phase coherence between corresponding pixels, processing said synthetic aperture radar images for azimuth focusing, forming a first single-difference interferogram from a first image of a first pair and a second image of said first pair, said first pair of images being selected from sequential ones of said multiple sequential synthetic radar images, forming a second single-difference interferogram from a first synthetic aperture radar image of a second pair and a second synthetic aperture radar image of said second pair, said second pair of synthetic aperture radar images being selected from sequential ones of said multiple sequential synthetic radar images, where each of said first and second synthetic aperture radar images of said second pair of synthetic aperture radar images is distinct from said first pair of synthetic aperture radar images, and at least one synthetic aperture radar image of said second pair is significantly later in sequence than both synthetic aperture radar images of said first pair, unwrapping phases of each pixel of said first and second single-difference interferograms by finding the 2π - multiples of phase that disappear in the making of said first and second single-difference interferograms,
forming a double-difference interferogram from said first single-difference interferogram and said second single-difference interferogram, thereby removing phase changes between corresponding pixels due to topography, leaving an image of nonzero phases only in areas where surface deformation has changed in the time between said first pair of synthetic aperture radar images and said later observation, and observing surface deformation changes in said terrestrial or planetary surface from said double-difference interferogram. - View Dependent Claims (9, 10, 11, 12, 13)
- multiples of phase that disappear in the making of said first and second single-difference interferograms,
Specification