Airgun Release in the Name of Geophysics!
Seismic surveying offshore requires an airgun as pressure source.
Seismic surveying offshore requires an airgun as pressure source.
The device has a pressure chamber, which is continuously loaded and released in an instant.
The release causes a pressure wave travel trough the water column down to the sea floor and throug the rock layers.
In this experiment, the hydrophone was lowered into the borehole and the one-way travel time can be measured.
Typically, in most surveys there are no boreholes available and the two-way-travel time can be measured from hydrophones straming behind a survey vessel.
In this instance IODP Expedition 356 conducted a Vertical Seismic Profile (VSP)
In a VSP experiment, a borehole seismic tool (VSI) is anchored against the borehole wall at regularly spaced intervals and records the full waveform of elastic waves generated by a seismic source positioned just below the sea surface. These “check shot” measurements relate depth in the hole to traveltime in reflection seismic profiles. The VSI used on the ship contains a three-axis geophone. In a VSP survey, the VSI was anchored against the borehole wall at approximately 25 m station intervals (where possible), with 5–10 air gun shots typically taken at each station.
Quote from: IODP Expedition 356 Proceedings
