Geophysical Instruments

Geophysical Instruments are used by scientists and those seeking hard minerals and hydrocarbon deposits, to study those parts of the earth hidden from direct view. Instruments used underwater include magnetometers, which are described under their own listing, gravimeters, and seismometers. Another class of underwater geophysical equipment are seismic devices used to generate a shock waves so reflected signals can be used to detect structures under the sea floor. Dynamite was used in the early days to generate shock waves. Today mechanical devices such as air guns, bubble pulsers, boomers, and sparkers are utilized. The reflected signals are detected by hydrophones that can either be placed on the seafloor or towed behind a ship. Streamer cables are arrays of hydrophones that are wired together and contained in oil filled plastic hose.

In recent years three dimensional (3D) and three dimensional times series (4D) seismic survey techniques have been developed. The newest technique in this field is Continuous Source Electro-magnetic Measurements (CSEM). It involves towing a source of low frequency electromagnetic signals to an array of seafloor receivers. The received data is used to determine the resistivity structure of the subsurface. This is of interest as there is a significant contrast between resistive hydrocarbons reservoirs and conductive saline water saturated layers.

Click here to return to the Dummy's Guide to Marine Technology