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Title: Space-Variant Post-Filtering for Wavefront Curvature Correction in Polar-Formatted Spotlight-Mode SAR Imagery

Abstract

Wavefront curvature defocus effects occur in spotlight-mode SAR imagery when reconstructed via the well-known polar-formatting algorithm (PFA) under certain imaging scenarios. These include imaging at close range, using a very low radar center frequency, utilizing high resolution, and/or imaging very large scenes. Wavefront curvature effects arise from the unrealistic assumption of strictly planar wavefronts illuminating the imaged scene. This dissertation presents a method for the correction of wavefront curvature defocus effects under these scenarios, concentrating on the generalized: squint-mode imaging scenario and its computational aspects. This correction is accomplished through an efficient one-dimensional, image domain filter applied as a post-processing step to PF.4. This post-filter, referred to as SVPF, is precalculated from a theoretical derivation of the wavefront curvature effect and varies as a function of scene location. Prior to SVPF, severe restrictions were placed on the imaged scene size in order to avoid defocus effects under these scenarios when using PFA. The SVPF algorithm eliminates the need for scene size restrictions when wavefront curvature effects are present, correcting for wavefront curvature in broadside as well as squinted collection modes while imposing little additional computational penalty for squinted images. This dissertation covers the theoretical development, implementation and analysis of themore » generalized, squint-mode SVPF algorithm (of which broadside-mode is a special case) and provides examples of its capabilities and limitations as well as offering guidelines for maximizing its computational efficiency. Tradeoffs between the PFA/SVPF combination and other spotlight-mode SAR image formation techniques are discussed with regard to computational burden, image quality, and imaging geometry constraints. It is demonstrated that other methods fail to exhibit a clear computational advantage over polar-formatting in conjunction with SVPF. This research concludes that PFA in conjunction with SVPF provides a computationally efficient spotlight-mode image formation solution that solves the wavefront curvature problem for most standoff distances and patch sizes, regardless of squint, resolution or radar center frequency. Additional advantages are that SVPF is not iterative and has no dependence on the visual contents of the scene: resulting in a deterministic computational complexity which typically adds only thirty percent to the overall image formation time.« less

Authors:
Publication Date:
Research Org.:
Sandia National Labs., Albuquerque, NM (US); Sandia National Labs., Livermore, CA (US)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
14165
Report Number(s):
SAND99-2706
TRN: AH200136%%338
DOE Contract Number:
AC04-94AL85000
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 1 Oct 1999
Country of Publication:
United States
Language:
English
Subject:
47 OTHER INSTRUMENTATION; ALGORITHMS; EFFICIENCY; RADAR; SPATIAL RESOLUTION; DATA ANALYSIS; IMAGE PROCESSING

Citation Formats

DOREN,NEALL E. Space-Variant Post-Filtering for Wavefront Curvature Correction in Polar-Formatted Spotlight-Mode SAR Imagery. United States: N. p., 1999. Web. doi:10.2172/14165.
DOREN,NEALL E. Space-Variant Post-Filtering for Wavefront Curvature Correction in Polar-Formatted Spotlight-Mode SAR Imagery. United States. doi:10.2172/14165.
DOREN,NEALL E. Fri . "Space-Variant Post-Filtering for Wavefront Curvature Correction in Polar-Formatted Spotlight-Mode SAR Imagery". United States. doi:10.2172/14165. https://www.osti.gov/servlets/purl/14165.
@article{osti_14165,
title = {Space-Variant Post-Filtering for Wavefront Curvature Correction in Polar-Formatted Spotlight-Mode SAR Imagery},
author = {DOREN,NEALL E.},
abstractNote = {Wavefront curvature defocus effects occur in spotlight-mode SAR imagery when reconstructed via the well-known polar-formatting algorithm (PFA) under certain imaging scenarios. These include imaging at close range, using a very low radar center frequency, utilizing high resolution, and/or imaging very large scenes. Wavefront curvature effects arise from the unrealistic assumption of strictly planar wavefronts illuminating the imaged scene. This dissertation presents a method for the correction of wavefront curvature defocus effects under these scenarios, concentrating on the generalized: squint-mode imaging scenario and its computational aspects. This correction is accomplished through an efficient one-dimensional, image domain filter applied as a post-processing step to PF.4. This post-filter, referred to as SVPF, is precalculated from a theoretical derivation of the wavefront curvature effect and varies as a function of scene location. Prior to SVPF, severe restrictions were placed on the imaged scene size in order to avoid defocus effects under these scenarios when using PFA. The SVPF algorithm eliminates the need for scene size restrictions when wavefront curvature effects are present, correcting for wavefront curvature in broadside as well as squinted collection modes while imposing little additional computational penalty for squinted images. This dissertation covers the theoretical development, implementation and analysis of the generalized, squint-mode SVPF algorithm (of which broadside-mode is a special case) and provides examples of its capabilities and limitations as well as offering guidelines for maximizing its computational efficiency. Tradeoffs between the PFA/SVPF combination and other spotlight-mode SAR image formation techniques are discussed with regard to computational burden, image quality, and imaging geometry constraints. It is demonstrated that other methods fail to exhibit a clear computational advantage over polar-formatting in conjunction with SVPF. This research concludes that PFA in conjunction with SVPF provides a computationally efficient spotlight-mode image formation solution that solves the wavefront curvature problem for most standoff distances and patch sizes, regardless of squint, resolution or radar center frequency. Additional advantages are that SVPF is not iterative and has no dependence on the visual contents of the scene: resulting in a deterministic computational complexity which typically adds only thirty percent to the overall image formation time.},
doi = {10.2172/14165},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Oct 01 00:00:00 EDT 1999},
month = {Fri Oct 01 00:00:00 EDT 1999}
}

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