Marine Seismic Surveys and the Environment

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Marine Seismic Methods
Seismic methods, as employed in marine applications, differ little in theory from ground based seismic surveys. A sound wave generating device is used to transmit a sound wave, while receiving devices measure the amplitude and arrival times of the returned (reflected /refracted) signals. However, practical applications of field techniques, field equipment, and geographic control can vary greatly between surface and marine surveys.

In the case of marine surveys, the instrumentation is generally a towed transmitter and array of geophones (figure 1). In some shallow water applications, a specialized array that rests on the ocean floor during acquisition is used (figure 2). Given the difficulty associated with establishing straight survey lines while in a vessel on a body of water, and with the necessity to image deep structures, the field equipment can be cumbersome. Figure 3 demonstrates the scale of field equipment necessary for marine seismic acquisition. Positional control is generally provided by a global positioning system (GPS) where the GPS sensor is mounted on the vessel towing the magnetometer, with a constant offset equal to the distance from the GPS sensor to the geophone array.