Data Acquisition Equipment

DATA ACQUISITION EQUIPMENT

U.S. GEOLOGICAL SURVEY
WOODS HOLE FIELD CENTER (WHFC)

Sidescan-Sonar Towfish:

Datasonics model SIS-1000 (100 kHz).

Data Collection Platform:

Triton Elics International ISIS^Ž

Specifications for the Sidescan-Sonar portion of the SIS-1000:
(for more information, see Benthos, Inc.)

Sidescan Transducers: Multi-element array; single array transmit, dual array receivers -- 0.5-degree horizontal beam; 60-degree vertical beam

Frequency: 100 kHz band swept FM, port and starboard channels sweeping in opposite directions; 7.5 cm resolution

Processing: Calibrated transmit waveform stored in ROM; match filter FFT digital signal processing

Swath (range) Selection: +/- 50 meters to +/- 70 meters
Tow Vehicle Specifications:

Depth rating: 1000 meters
Vehicle dimensions: 18 inches OD x 64 inches long
Weight: in air: 300lbs; in water: 170 lbs

--Windows 95 based Pentium machine
--Saves sidescan-sonar data via network interface or on an Exabyte 8200 tape subsystem
--Will accept up to 5 channels of data
--Serial I/O ports (i.e., for navigation)
--Parallel (Centronics) ports for printing the sidescan-sonar data
--Array processor handling the digitized sidescan-sonar signal
--12-bit analog to digital converter OR: DSP card for digital signals

The topside data acquisition computer the USGS uses to collect and store the digital signal is the ISIS^(TM) system, which runs under the Windows 95 operating system and is built by Triton Elics International, Inc., Watsonville, CA using a 12-bit (72 db effective dynamic range) A/D converter in conjunction with an array processor. ISIS^(TM) is capable of digitizing up to four channels of information at aggregate rates of up to 750 kHz, thus preserving the content and the dynamic range of the sidescan-sonar signal. An installed Digital Signal Processing (DSP) board is an alternative to handling signals digitized at the towfish (SIS-1000). Port and starboard sidescan-sonar data are displayed in real-time on a high-resolution color display (1280 x 1024 pixels). Telemetry from navigation systems and the towfish, including full towfish attitude information, is displayed in separate windows. The backup data storage media used is 8 mm Exabyte tape. The USGS WHFC records directly to disc on separate computer systems using the Network File System (NFS) protocol and archives the data to DVD-ROM.

Sidescan-Sonar files collected using the ISIS^(TM) system have the following format (Q-MIPS):

     1st rec   ----    ----    ---- *** Data is stored in 
        |      ----    ----    ---- *** 1024 byte records for
        |        .                            each channel
        |        .                      (*** 256 byte trailer.)
        |        .
        |        .
        V        .
      End rec  ----    ----    ---- ***
               Chan    Chan2   ChanX  (*** = 256 byte trailer.)

Each data file contains a 2048 byte file header followed by the sidescan-sonar data stream which consists of at least two channels of sidescan-sonar information and a 256 byte trailer. The trailer contains parameters relevant to the collected sidescan-sonar, such as altitude, file name, pitch, roll, date of collection, time of day, etc. The isis header and Isis sonar formats for the ISIS are described on the Q-MIPS page.