SAR processing UWB VHF data without a motion measurement system
Paper in proceedings, 2018

SAR processing usually requires very accurate navigation data, i.e. to form a focused image. The track must be measured within fractions of the centre wavelength. For high frequencies (e.g. X-band) this condition is too strict. Even with a cutting-edge motion measurement system, autofocus is a necessity. For low frequencies (e.g. VHF-band) a differential GPS (DGPS) is often an adequate solution (alone). However, for this case, it is actually conceivable to rely on autofocus capability over the motion measurement system. This paper describes how to form a SAR image without support from navigation data. That is within the scope of factorized geometrical autofocus (FGA). The FGA algorithm is a base-2 fast factorized back-projection realization with six free geometry parameters (per sub-aperture pair). These are tuned step-by-step until a sharp image is obtained. This procedure can compensate for an erroneous geometry (from a focus perspective). The FGA algorithm has been applied successfully on an ultra-wideband (UWB) data set, acquired at VHF-band by the CARABAS 3 system. The track is measured accurately by means of a DGPS. We however adopt and modify a basic geometry model. A linear equidistant flight path at fixed altitude is assumed and adjusted at several resolution levels. With this approach, we emulate a stand-alone processing chain without support from navigation data. The resulting FGA image is compared to a reference image and verified to be focused. This indicates that it is feasible to form a VHF-band SAR image without a motion measurement system.

UWB

Autofocus

Back-Projection

FGA

VHF

Synthetic Aperture Radar (SAR)

Author

Jan Torgrimsson

Chalmers, Space, Earth and Environment, Microwave and Optical Remote Sensing

Patrik Dammert

Saab Surveillance

H. Hellsten

Saab Surveillance

Lars Ulander

Chalmers, Space, Earth and Environment, Microwave and Optical Remote Sensing

Anders Åhlander

Saab Surveillance

Proceedings of SPIE - The International Society for Optical Engineering

0277786X (ISSN)

Vol. 10647 106470F

Algorithms for Synthetic Aperture Radar Imagery XXV 2018
Orlando, USA,

Subject Categories

Signal Processing

Computer Vision and Robotics (Autonomous Systems)

DOI

10.1117/12.2304615

More information

Latest update

12/28/2018