Synthetic Aperture
A Revolution in
Underwater Sensing



Matthew Nelson and Ralph Chatham
Dynamics Technology, Inc.
1555 Wilson Blvd. Suite 320
Arlington, VA 22209
tel: (703) 841-0990
email: ,

Abstract The coherent combination of data from multiple tramsmissions in the form of synthetic aperture processing revolutionized radar imaging over the past 30 years. A key feature of the synthetic aperture approach is that cross range resolution becomes independent of range. During the past eight years Dynamics Technology, Inc. has been applying that revolution to sonar: first with medium stability measurements, the development of SAS emulators, adaptions of SAR imaging and autofocusing algorithms to many-element real apertures, and more recently as the processing house for DARPA's Synthetic Aperture Sonar program. 50 KHz data from a spring 1987 experiment has been processed to produce images of mine shadows at 230 m and greater ranges with 10 cm cross range resolution, resoluton which is only possible for current mine classification sonars at 30 meters range. We have also imaged the interior structure of a water-filled sunken airplane at 350 meters. Other images show the same cross range resolution out to a kilometer. This represents over an order of magnitude better resolution/range combination than ever achieved with sonar. A program to explore this concept further and to develop a hands-off real-time SAS processor for mine hunting applications is just starting under DARPA funding.



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