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Title: Beamforming as a foundation for spotlight-mode SAR image formation by backprojection.


No abstract prepared.

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Publication Date:
Research Org.:
Sandia National Laboratories
Sponsoring Org.:
OSTI Identifier:
Report Number(s):
TRN: US200824%%3
DOE Contract Number:
Resource Type:
Resource Relation:
Conference: Proposed for presentation at the SPIE Defense and Security Symposium held March 16-20, 2008 in Orlando, FL.
Country of Publication:
United States

Citation Formats

Yocky, David Alan, Wahl, Daniel Eugene, and Jakowatz, Charles V., Jr.. Beamforming as a foundation for spotlight-mode SAR image formation by backprojection.. United States: N. p., 2008. Web.
Yocky, David Alan, Wahl, Daniel Eugene, & Jakowatz, Charles V., Jr.. Beamforming as a foundation for spotlight-mode SAR image formation by backprojection.. United States.
Yocky, David Alan, Wahl, Daniel Eugene, and Jakowatz, Charles V., Jr.. 2008. "Beamforming as a foundation for spotlight-mode SAR image formation by backprojection.". United States. doi:.
title = {Beamforming as a foundation for spotlight-mode SAR image formation by backprojection.},
author = {Yocky, David Alan and Wahl, Daniel Eugene and Jakowatz, Charles V., Jr.},
abstractNote = {No abstract prepared.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2008,
month = 2

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  • In recent papers the authors discussed the advantages of forming spotlight-mode SAR imagery from phase history data via a technique that is rooted in the principles of phased-array beamforming, which is closely related to back-projection. The application of a traditional autofocus algorithm, such as Phase Gradient Autofocus (PGA), requires some care in this situation. Specifically, a stated advantage of beamforming is that it easily allows for reconstruction of the SAR image onto an arbitrary imaging grid. One very useful grid, for example, is a Cartesian grid in the ground plane. Autofocus via PGA for such an image, however, cannot bemore » performed in a straightforward manner, because in PGA a Fourier transform relationship is required between the image domain and the range-compressed phase history, and this is not the case for such an imaging grid. In this paper we propose a strategy for performing autofocus in this situation, and discuss its limitations. We demonstrate the algorithm on synthetic phase errors applied to real SAR imagery.« less
  • No abstract prepared.
  • Beamforming is a methodology for collection-mode-independent SAR image formation. It is essentially equivalent to backprojection. The authors have in previous papers developed this idea and discussed the advantages and disadvantages of the approach to monostatic SAR image formation vis--vis the more standard and time-tested polar formatting algorithm (PFA). In this paper we show that beamforming for bistatic SAR imaging leads again to a very simple image formation algorithm that requires a minimal number of lines of code and that allows the image to be directly formed onto a three-dimensional surface model, thus automatically creating an orthorectified image. The same disadvantagemore » of beamforming applied to monostatic SAR imaging applies to the bistatic case, however, in that the execution time for the beamforming algorithm is quite long compared to that of PFA. Fast versions of beamforming do exist to help alleviate this issue. Results of image reconstructions from phase history data are presented.« less
  • Wavefront curvature defocus effects can occur in spotlight-mode SAR imagery when reconstructed via the well-known polar formatting algorithm (PFA) under certain scenarios that include imaging at close range, use of very low center frequency, and/or imaging of very large scenes. The range migration algorithm (RMA), also known as seismic migration, was developed to accommodate these wavefront curvature effects. However, the along-track upsampling of the phase history data required of the original version of range migration can in certain instances represent a major computational burden. A more recent version of migration processing, the Frequency Domain Replication and Downsampling (FReD) algorithm, obviatesmore » the need to upsample, and is accordingly more efficient. In this paper the authors demonstrate that the combination of traditional polar formatting with appropriate space-variant post-filtering for refocus can be as efficient or even more efficient than FReD under some imaging conditions, as demonstrated by the computer-simulated results in this paper. The post-filter can be pre-calculated from a theoretical derivation of the curvature effect. The conclusion is that the new polar formatting with post filtering algorithm (PF2) should be considered as a viable candidate for a spotlight-mode image formation processor when curvature effects are present.« less
  • In this paper, the authors introduce a general formulation for wavefront curvature correction in spotlight-mode SAR images formed using the polar-formatting algorithm (PFA). This correction is achieved through the use of an efficient, image domain space-variant filter which is applied as a post-processing step to PFA. Wavefront curvature defocus effects occur in certain SAR collection modes that include imaging at close range, using low center frequency, and/or imaging very large scenes. The formulation is general in that it corrects for wavefront curvature in roadside as well as squinted collection modes, with no computational penalty for correcting squint-mode images. Algorithms suchmore » as the range migration technique (also known as seismic migration), and a recent enhancement known as frequency domain replication, FReD, have been developed to accommodate these wavefront curvature effects. However, they exhibit no clear computational advantage over space-variant post-filtering in conjunction with polar formatting (PF2). This paper will present the basic concepts of the formulation, and will provide computer results demonstrating the capabilities of space-variant post-filtering.« less