DESCRIPTION

EdgeTech and Applied Signal Technology, Inc. (AST) have teamed to offer our customers high-resolution side scan sonar images produced by using Synthetic Aperture Sonar processing technology.

AST (www.appsig.com) is acknowledged as one of the world's leading experts in synthetic aperture technology applied to underwater acoustic imaging. Their expertise in this field is now joined with EdgeTech's industry leading side scan sonar Full Spectrum “chirp” capability.

The result is the first commercially available operational synthetic aperture side scan sonar. Not a promise, or a Product Bulletin, or an “announcement” meeting… just a working system with results from the field.

Systems are available for towed, ROV and AUV platforms, in different frequency ranges and for depths to full-ocean.

Topside Display Processor
The Model 564 topside display processor and ProSAS computers are 19" rack mountable units, which accept the raw sonar data produced by the FS-SAS data acquisition electronics. The 564 includes a keyboard, trackball, and two high-resolution 19" flat panel LCD monitors.

Command and control of ProSAS comes from the 564. Raw unprocessed sonar data is sent to the ProSAS sub-system for SAS processing. Processed SAS side scan sonar imagery is returned to the 564 for data display and logging as the final sonar product. The only connection to ProSAS is an Ethernet link to the Model 564.

This topside combination produces both conventional side scan sonar imagery and high-resolution focused geo-located, synthetic aperture sonar images. These images are available for local display on the Model 564. Two data files are created. The first an EdgeTech native format “.jsf” contains the raw data from each of the sub-elements along with navigation and time stamps. The second file is an EdgeTech defined format “.sas”. This file contains the synthetic aperture side scan data. Both files can be exported via the 564 DVD-R/W or Ethernet port for display on third party side scan sonar post-processing systems.

SAS Arrays
The two SAS sensor arrays are mounted on the port and starboard sides of the vehicle. Each array is made up of a number of sub-elements. The length of the sub-element dictates the resolution of the sonar. For example, the SAS 120/6 has 6 (six) 20 cm. sub-elements. The sonar resolution is ½ the sub-element length or in this case 10 cm. Other frequencies, number of sub-elements and the sub-element lengths are available. The arrays are symmetric so that end over end mounting is not required for port and starboard installations.

 

FS-SAS Electronics
The FS-SAS Sonar and Data Acquisition electronics are housed in an EdgeTech supplied pressure housing or may be integrated into a customer’s pressure housing. There are watertight connections for the arrays and vessel control and motion sensor information. 48 VDC is required to power the system.

All data and command interfaces with the FS-SAS are implemented using TCP/IP (Transport Control Protocol/Internet Protocol) over Ethernet, and are in accordance with the EdgeTech published standard for interfacing to the Full Spectrum “chirp” family of systems. This allows at a minimum for sub-system control, (On/Off, Pulse selection, ping rate, etc) as well as system configuration.

The raw sonar data produced by the system comprises 12 channels of coherent, range compressed data samples, 6 channels per side, port and starboard.

The interfaced sensor data (assumed to be DVL, Motion/Attitude and position) is locally time stamped and logged in the same data stream as the side scan sonar data. This will ensure the motion data and the sonar data have minimal timing errors and is independent of inter-system time set errors. The data stream is available over the Ethernet. With the current system specifications (12 channels, 10cm resolution, complex data Nyquist sampled data) the expected data rate is approximately 5Mbit/s (+/-20%).

For AUV deployments the raw sonar data can be minimally processed to produce a low-resolution image data stream for QC purposes. Sub-element data from each array is coherently combined, decimated in range and in ping number, to produce this data stream. The along and across track decimation factors are user configurable via "ini" file settings or the control interface. This data is available as a separate data message.