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Title: Comparison of polar formatting and back-projection algorithms for spotlight-mode SAR image formation.

Abstract

No abstract prepared.

Authors:
 [1]; ;
  1. (.,
Publication Date:
Research Org.:
Sandia National Laboratories
Sponsoring Org.:
USDOE
OSTI Identifier:
884731
Report Number(s):
SAND2006-1861C
TRN: US200616%%31
DOE Contract Number:
AC04-94AL85000
Resource Type:
Conference
Resource Relation:
Conference: Proposed for presentation at the SPIE Defense and Security Symposium held April 17-21, 2006 in Orlando, FL.
Country of Publication:
United States
Language:
English
Subject:
47 OTHER INSTRUMENTATION; ALGORITHMS; OPTICAL RADAR; IMAGES; DATA ANALYSIS

Citation Formats

Jakowatz, Charles V., Jr., .), and Doren, Neall E. Comparison of polar formatting and back-projection algorithms for spotlight-mode SAR image formation.. United States: N. p., 2006. Web.
Jakowatz, Charles V., Jr., .), & Doren, Neall E. Comparison of polar formatting and back-projection algorithms for spotlight-mode SAR image formation.. United States.
Jakowatz, Charles V., Jr., .), and Doren, Neall E. Wed . "Comparison of polar formatting and back-projection algorithms for spotlight-mode SAR image formation.". United States. doi:.
@article{osti_884731,
title = {Comparison of polar formatting and back-projection algorithms for spotlight-mode SAR image formation.},
author = {Jakowatz, Charles V., Jr. and .) and Doren, Neall E.},
abstractNote = {No abstract prepared.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Mar 01 00:00:00 EST 2006},
month = {Wed Mar 01 00:00:00 EST 2006}
}

Conference:
Other availability
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  • 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
  • No abstract prepared.
  • 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
  • Synthetic Aperture Radar image formation algorithms typically use transform techniques that often requires trading between image resolution, algorithm efficiency, and focussed image scene size limits. This is due to assumptions for the data such as simplified (often straight-line) flight paths, simplified imaging geometry, and simplified models for phase functions. Many errors in such assumptions are typically untreatable due to their dependence on both data domain positions and image domain positions. The result is that large scenes often require inefficient multiple image formation iterations, followed by a mosaicking operation of the focussed image patches. One class of image formation algorithms thatmore » performs favorably divides the spatial and frequency apertures into subapertures, and perhaps those subapertures into sub-subapertures, and so on, in a tiered subaperture fashion. This allows a gradual shift from data domain into image domain that allows correcting many types of errors that limit other image formation algorithms, even in a dynamic motion environment, thereby allowing larger focussed image patches without mosaicking. This paper presents and compares focussed patch diameter limits for tiered subaperture (TSA) image formation algorithms, for various numbers of tiers of subapertures. Examples are given that show orders-of-magnitude improvement in non-mosaicked focussed image patch size over traditional polar format processing, and that patch size limits increase with the number of tiers of subapertures, although with diminishing returns.« less