"Zero-field" air-gun measurements for improved efficiency in marine seismic acquisition

Summary Complex measurement and control systems are needed for tuning and monitoring air-gun arrays to ensure they meet demanding specifications. Failure to meet these specifications can be a substantial source of production downtime for a multi-streamer seismic vessel. However, significant improvements in efficiency can be achieved with a pressure sensor used both as a “zero-field” hydrophone and as a time-break sensor. We show that a pressure sensor located centimeters from the air-gun ports in the “zero field” can be used for accurate measurement of both the firing time delay and the “zerofield” signature of the air-gun. The “zero-field” signature can then be used to compute the pressure field anywhere. Its amplitude is about 20 times that of conventional near-field pressure measurements, and therefore its discrimination between source signal and sea bottom reflections is 20 times better. The location and sensitivity of the sensor must be accurately known.