Sampling requirements and alias-free processing in stripmap SAS systems

pp. 199-210, vol. 17, 2014

Marcin Szczegielniak
University of Technology and Life Sciences, Bydgoszcz, Poland

Damian Szczegielniak
University of Technology and Life Sciences, Bydgoszcz, Poland

Key words: synthetic aperture sonar; high-resolution acoustic imaging; spatial filtering

Abstract: Synthetic Aperture Sonar (SAS) is the high-resolution acoustic imaging technique which allows us to improve along-track resolution. In the era of digital processing, the proper sampling of signals and alias-free processing have an enormous influence on the efficiency of modern SAS systems. SAS processing without taking into account the aliasing phenomenon can cause a serious degradation of the reconstructed SAS image. Therefore, understanding the causes of this phenomenon in real SAS systems and ways of suppressing or avoiding its harmful effects seems to be indispensable. The aim of this paper is the comprehensive discussion of the along-track sampling problem, taking into account the slow-time Doppler support of the raw SAS signal, along-track mapping, effective target area and spatial filtering process as well as practical limitations of the along-track sampling connected with the SAS platform velocity or an maximum unambiguous range to imaged objects. The discussion was extended by mathematical dependencies derived or presented by authors. Moreover, numerical simulations in the Matlab environment was carried out by authors and the results are presented and discussed in this paper. The received raw signal was generated for a stripmap SAS system. Then, the spatial filtering by means of the Polar Formatting with the subdivision of the synthetic aperture was applied to filter out undesirable SAS signal contributions - the reason of the aliasing appearance in real SAS images. The final reconstructed SAS images were obtained by the omega-k algorithm. The carried out experiments confirmed the effectiveness of the presented approach for assumed SAS system parameters.

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© Polish Acoustical Society - Gdansk Department, Polish Academy of Sciences. This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported. (CC BY-NC-SA 3.0)