EdgeTech manufactures a hydrographic survey quality combined side scan sonar and sub-bottom profiler specifically designed for small, limited payload AUV's.
Systems are availabale for:
* Hydroid's Remus (2200-S REMUS)
* Hafmynd's GAVIA (2200-S GAVIA)
* Bluefin Robotics's BLUEFIN 12 (2200-S BLUEFIN 12)
* Others as they become available
A system consists of a drop-in payload module that contains the sonar electronics, a built-in sub-bottom profiler transmitter and side scan sonar arrays with integrated sub-bottom profiler hydrophones. A large capacity hard drive is used to store sonar data. The average data flow is dependent on the sampling frequency, the data window size, the ping rate of the sub-bottom profiler and the range scale setting of the side scan sonar.
Careful attention has been paid to keeping the power consumption low for the 2200-S. The amplifiers are turned off between transmissions. The amplifier power output can be controlled and the ping rate can be adjusted via the payload control interface.
On the surface, a portable PC with DISCOVER software displays and stores the sonar data that is offloaded from the AUV.
The system is available as a combined dual frequency side scan sonar and sub-bottom profiler. Integration between the two sonars permits them to be triggered in such a way as to eliminate or minimize acoustic interference between the two.
The system can be ordered as a side scan sonar or sub-bottom profiler only. It can be upgraded later by adding an electronics kit and sonar arrays.
Side Scan Sonar
The 2200-S is a dual frequency Full Spectrum CHIRP side scan sonar with a choice of either 120/410 kHz or 300/600 kHz frequencies. Additionally an 850 kHz Dynamically Focused frequency is also available.
The 2200-S processor transmits a linearly swept, frequency-modulated pulse with resolution proportional to transmit bandwidth, not pulse length. The transmission of a longer duration wide bandwidth pulse results in higher resolution sonar images and, because more energy is projected into the water, greater SNR resulting in extended range. The extended range and resolution provides for better system efficiency.
* Less interference from side lobes due to the frequency modulated pulse.
* Low frequency range is up to 30% greater than conventional systems at the same frequency.
* High frequency range is up to 50% greater than conventional systems at the same frequency.
* Narrow beam side scan sonar transducers result in sharp, high-resolution, along-track sonar imagery.
The 2200-S is a 4-24 kHz Full Spectrum chirp sub-bottom profiler. A number of selectable pulses are available within this frequency range. By changing the center frequency of the pulse it is possible to select the penetration and resolution of the sub-bottom profiler.
The sub-bottom profiler uses a specially designed transmitter with low Q wideband characteristics best suited for chirp transmissions.
In addition, the pulses do not make the transducer ring so data can be collected close to the bottom without this interference.
DISCOVER Display Processor
EdgeTech's DISCOVER Software is a modular acquisition and processing software package for the model 2200-S combined side scan and sub-bottom profiler sonars. It is part of a family of sonar control, image processing, display, storage and printer control for the EdgeTech family of Sub-bottom Profilers and Side Scan Sonars. DISCOVER runs on portable PC running Microsoft's Windows Operating System.
Sonar data are stored on a high-capacity hard drive on the AUV and are offloaded from the drive via an external Ethernet connection. A DVD-R/W drive permits archiving the data to DVD and/or data can be accessed through a network connection on the portable. A hard copy of the data may be printed on a continuous feed thermal gray scale printer. Most industry standard printers are supported.
Displays- DISCOVER displays data as a waterfall in a dedicated window. Navigation and other sonar information, if stored with the data, is monitored and displayed in a status window.
On-line Help, Warnings and Error Messages- A comprehensive context sensitive help feature lets a user get assistance without having to consult the manual.
Navigation Correlation- Data stored on line can be correlated with the AUV navigation by two methods. The first is for vehicle position information to be sent to the 2200-S via an Ethernet or RS-232 connection. The other is for the AUV to synchronize the 2200-S internal real time clock so that the data is time tagged for later correlation with time tagged navigation data. Navigation information is stored in the trace header of the sonar data. During replay in DISCOVER, the navigation message is displayed on the screen and can be printed on the thermal printer.
Printer- DISCOVER includes software drivers to a variety of printers. The hard copy is printed in shades of gray. The operator has control over the printer settings independent of the video display settings. Control of the printer includes gain, contrast, TVG, and other settings means that the operator can customize the settings to get the best print-out possible.
Data Recording- Recorded in the AUV in EdgeTech native format (.jsf). In DISCOVER, the .jsf files can be transcribed to .xtf and SEG-Y formats.
Annotation- Input via keyboard or RS-232 port. Annotation goes to screen, printer and mass storage device.
Replay- Software can be installed royalty free on most any PC for data replay.
Side Scan Sonar
Processing- Includes speed and altitude correction, pseudo color palettes, contrast enhancement and compression.
Display- One or two channels, zoom across or along track, geo-referenced cursor position.
Target Mensuration- Size and altitude off the bottom, target database with stored image, true target zoom.
Processing- Includes removal of swell effect, adaptive automatic gain control and time variable gain.
Reflection Coefficient- Since the EdgeTech sonar is linear, the measured refelection coefficient can be used to identify the type of material (i.e. sand, clay. mud, etc.) on the bottom. A graph of the reflection coefficient is displayed in real time.
TVG Gain Control- The TVG gain control is a processing that improves visualization of seismic signals. The general principle is to compensate the variations in the signal envelope by the means of different functions:
a) Positive TVG
b) Negative TVG
c) TVG Gain
d) TVG Slope