Science Center Objects

A sub-bottom profiler like the EdgeTech SB-516 Chirp emits acoustic pulses to produce an image of the layers of sediment below the seafloor.

The EdgeTech SB-516, or “Chirp,” is a sub-bottom profiler. The Chirp produces frequency-modulated acoustic pulses in the 0.5-16 kHz range and records their reflections to create two-dimensional images (cross-sections or “profiles”) of the sediment layers beneath the seafloor. See the gray illustration below for an example. The Chirp’s acoustic penetration can range from 40-250 m, and vertical resolution can be as good as 6 cm, depending on factors such as sediment type and sea state.  The system consists of a tow vehicle (fish) that has both transmit and receive arrays, as well as the electronics to interface with the sonar and convert between analog and digital signals, a 100 m data cable, and a deck unit with a PC and the Starmux III Digital Telemetry Link.

An instrument rests on the deck of a ship, its cables suspended above it, while a scientist looks on.

Chirp 516

A man guides a data collection instrument, that is strapped to two large pontoons, out into water from the stern of a boat.

USGS scientist Jackson Currie deploys the Chirp attached to its Cataraft, from research vessel Parke Snavely in San Pablo Bay, California. The cataraft's pontoons keep the equipment from running aground in the shallow waters of the Bay.

Photo credit: Janet Watt, USGS Pacific Coastal and Marine Science Center

 

Two identical illustrations show the sediment layers under the seafloor, one as raw data and the other with interpretive labels.

Illustration shows an example of the geophysical information collected from a chirp sub-bottom profiler. Top frame shows just the processed data, then the bottom frame shows a scientist's interpretations of the features.

Credit: Katie Maier, USGS

Specifications

  • Manufacturer: EdgeTech
  • Model: SB-516
  • Weight:  650 lbs in air
  • Dimensions: 62x53x18”, 68x54x28” shipped
  • Power Requirements: 90-260 VAC

Operational Characteristics

  • Minimum Operational Depth: 3 m (with use of cataraft)
  • Maximum Operational Depth: 2000 m
  • Tow Height: 3-5 m above sea floor OR 15 m or greater below sea surface
  • Sediment Type: Any, penetration will vary from 40 m in coarse sand to 250 m in clays
  • Limitations: Tow height of the fish is limited by the length of data cable (100 m). On large vessels the topside unit must be located sufficiently close to the tow point of the fish that the there is enough data cable to reach desired tow depth.
  • Power Outputs / Frequency Ranges 2000 W, 0.5 – 16 kHz
  • Ship’s Requirements
    • Winch and over-boarding gear with 2000lb SWL
    • Can be deployed with A-frame, davit, j-frame, with one block for winch line
    • 1 person must be able to stand sufficiently close to the wire during deployment to marry the data cable to the tow cable with zip ties
    • 62”x53” footprint

Additional Equipment required

  • In shallow water, the Chirp can be used with a Cataraft - a buoyed frame that can be used for surface-towing the Chirp.
  • The Chirp topside PC needs software, like EdgeTech’s 'Discover' software (free), to collect and view data in real-time.

Complementary Systems

The Chirp 516 can be equipped with a magnetometer connected to the electronics bottle on the fish.  This allows the magnetic data to be passed to the topside for output on a COM (communications) port.  Magnetic data can provide additional geophysical constraints to the sub-bottom data that the Chirp provides.