Position Correction Using Echoes From a Navigation Fix for Synthetic Aperture Sonar Imaging
Journal article, 2009

In synthetic aperture sonar (SAS), the platform position must be known sufficiently accurately for signals to be added coherently along the synthetic aperture. Often, the onboard navigation system is insufficiently accurate by itself, so corrections are needed. A well-known method is the displaced phase center antenna (DPCA) procedure for correcting platform position using seabed echoes. DPCA methods have the advantage of insensitivity to changing interference patterns, moving specular reflection, and changing occlusion, with aspect. However, when seabed echoes are unusable, either because they are too weak, or because they are corrupted by multipath, the seabed DCPA method may fail. Therefore, we present an alternative DPCA method using sonar echoes from a suitable navigation fix, based on an object detected after standard beamforming. In our proposed system, look angle is obtained by tracking the centroid of the rectified image of the fix object. When the standard DPCA correction equations are modified for a fixed reflector, it turns out that they provide incremental range and look-angle errors, precisely the values required when the target itself is used as the navigation fix. Moreover, the values obtained are then self-compensating for errors in estimating seabed depth or forward motion of the platform. The navigation fix is selected by bracketing in range, and beamforming overlapping subsets of the receiver array. In this paper, we present experimental results at transmitter frequencies of 25 and 100 kHz where our method enabled well-focused SAS images to be generated with little recourse to other navigation information. Hence, SAS can be carried out, even when a sophisticated inertial navigation system (INS) is not available.

Autofocus

autopositioning

displaced phase center antenna (DPCA)

synthetic aperture sonar (SAS)

shallow-water acoustics

micronavigation

autofocus

Author

Geoffrey Shippey

Chalmers, Signals and Systems, Signal Processing and Biomedical Engineering

Mattias Jonsson

Swedish Defence Research Agency (FOI)

J. N. B. Pihl

Swedish Defence Research Agency (FOI)

IEEE Journal of Oceanic Engineering

0364-9059 (ISSN)

Vol. 34 3 294-306

Subject Categories

Signal Processing

DOI

10.1109/JOE.2009.2022578

More information

Latest update

2/27/2018