Geometrics G-882 Magnetometer

Science Center Objects

In geophysical surveys from a ship, a magnetometer measures the fluctuations in the magnetic signature of the rocks and sediment below the ocean floor.

Three men and one woman stand, smiling, on the fantail of a docked boat in a marina, holding an instrument used to collect data.

USGS Pacific Coastal and Marine Science Center field crew showing off the new marine magnetometer, named Magnetron, on fantail of R/V Parke Snavely. Credit: Sam Johnson, USGS

Description  

The G-882 is a high resolution cesium vapor marine magnetometer, used to detect ferrous objects (e.g., anything made of iron, like pipelines, sunken ships, etc.) as well as for geophysical studies. The magnetometer detects variations in the total magnetic field based on the composition of the seafloor. Survey design and tow configuration is dependent on the goal of the study. Detecting ferrous objects requires the magnetometer to be towed a few meters above the seafloor in tightly spaced survey lines, whereas geophysical studies can use the magnetometer towed at the surface with larger distances between the survey lines. It can sample at up to 20 Hz and has a heading error <1 nT. 

Specifications 

  • Manufacturer: Geometrics 
  • Model: G-882 Marine Magnetometer 
  • Weight: 40 lbs, up to 100 lbs with use of five weight collars 
  • Dimensions: 2.75x2.75x 54” 
  • Power Requirements: 24 to 32 VDC 
  • Tow Cable Breaking Strength: 1630 kg 
Geophysical equipment sits on the deck of a boat.

Marine magnetometer (in storage box on left) and chirp sub-bottom profiler on the back deck of R/V Coral Sea. Credit: Janet Watt, USGS

Operational Characteristics 

  • Minimum Operational Depth: 20 m 
  • Maximum Operational Depth: The magnetometer is depth rated for 4000 psi, but in practice may be limited by the length of the tow cable 
  • Sediment Type: Any 
  • Limitations:  The magnetometer should be towed at a distance four times the vessel length away from the ship.  Therefore, on a 60 ft vessel, a tow cable of at least 250 feet is required. 
  • Power Outputs / Freq. Ranges: Passive 
  • Ship’s Requirements 
  • The magnetometer is light enough to be hand deployed by one person