Acoustic Imaging Using a 750 kHz Thin Lens System

These images were taken using a test system we are developing at the University of Washington's Applied Physics Lab. The system is a single-channel sonar which uses two thin acoustic lenses to focus sound. The system is scanned across the underwater landscape on a ram mounted in the R/V J.E. Henderson , one of APL's research vessels. These images were taken in Lake Union and at Shilshole Marina.

Also see images with varying resolution and 3-D images taken with a 3 MHz conical-beam system.

The test lens system. The electronics are in the green cylinder. The orange faceplate contains the transducers. The two lenses are mounted on rails so that they can be adjusted to focus the system.
Another view of the system.

Large Sector Scan of bottom of Lake Union

Map of the Large Sector Scan above.

Barge is in blue, docks are light blue, the bridge footings and piers are in gray and black, the targets are in red, and interesting targets of opportunity (i.e. we didn't put them there) are in light green.

Sector Scan of bottom of Lake Union

A slightly closer-range view of the left side of the full scan above. Note the automobile tires (upper left corner), beer keg (bright spot to right of tires), and ladder (just to the left and above the bright section near the bottom). There are some other targets as well, but they are very hard to see. For example, the bright spot in the midst of the tire graveyard is a full propane cylinder, and the slightly dimmer spot near it is an empty propane cylinder.

Close-Up of Ladder

Upside-down Rowboat in Lake Union

Small boat at Shilshole Marina

Barrel and five tires in Lake Union

Close-up of "tire graveyard" in Lake Union. The barrel "rings" when hit by the sound waves from the sonar, giving it a characteristic tail. We are also investigating the possibility of identifying targets by an aural signal from the sonar. For example, the tires sound like a click, whereas the barrel sounds more like a cricket.

Close-up of Test Barrel

The barrel had one open and one closed end. The closed end, which is the end in the picture, has angle iron welded on it in a "T" pattern, which can be seen in the image. The barrel also has an assortment of odd pipes and fins on its sides. The "rain" in the picture is 60 Hz noise which we've since eliminated.

Barrel and two pilings at long (approximately 50 m) range (Shilshole Marina)

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