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Feature Article

Deployment of a Deep Tow Synthetic Aperture Sonar System
PROSAS Surveyor 60 Operates at Longer Ranges, Greater Depths than Similar SAS Systems

Andy Wilby
Chief Engineer
Raytheon Applied Signal Technology Inc.
Sunnyvale, California

Deepwater exploration and surveying is dominated by specialized equipment and extreme technological challenges. Difficulties with communications, sensor tracking and data monitoring are exacerbated by the physical separation between the sensor, the seabed and the host surveying platform. In recent years, the introduction of AUV technology has seemed to offer the most cost-efficient solution to deepwater surveying. The time required to move from survey line to survey line is short when compared with the turning circles of a ship with a towfish on a long umbilical. Even when considering the need to recover the vehicle every few hours to recharge batteries and upload data, AUVs still win out as a cost-effective technology for deep water.

Furrow bedforms, 50 meters apart and 1 meter high, are shown at 4,000 meters' depth. Using data collected by the PROSAS Surveyor 60 deployed off the U.S. East Coast, the SAS imagery is draped over interferometric bathymetry at a 500-meter range.

In 2011, a new sensor technology, the PROSAS Surveyor 60 (PS60), was deployed in more than 4,000 meters of water off the U.S. Eastern Seaboard and demonstrated operating at 1,100 meters per side (2,200-meter total swath width). The use of such technology might at least cause a pause for thought before jumping to the conclusion that AUVs are the answer to every surveyor's prayer.

Development and Initial Deployments
The PS60 is a deep tow synthetic aperture and bathymetric imaging system designed by Raytheon Applied Signal Technology Inc. in conjunction with Williamson & Associates (Seattle, Washington) and SL Hydrospheric (Whitefish, Montana). The system provides imagery at resolutions on the order of 10 centimeters by 10 centimeters at ranges of up to 1,500 meters per side.

On this initial deployment, two synthetic aperture sonar (SAS) records were broken. The system was operating at a longer range than any previous SAS imaging system and at a greater depth than any similar system had previously been deployed.

The system can survey 177 square kilometers of seabed in a 24-hour period, operate in water depths of up to 6,000 meters and collect simultaneous side scan, SAS and bathymetric data. Consistently producing high-resolution imagery across wide swaths was the primary goal of the PS60 system.

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Andy Wilby is chief engineer for sensor systems at Raytheon Applied Signal Technology and lives in Redondo Beach, California. Educated in the U.K., he has worked in the sonar industry for 25 years, delivering sensors and sensor processing systems across the full spectrum of the underwater acoustic domain.

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