We designed a system to enable the signature of an air gun array to be calculated at any point in the water from a number of simultaneous independent measurements of the near‐field pressure field [subject of a patent application]. The number of these measurements must not be less than the number of guns in the array. The underlying assumption in our method is that the oscillating bubble produced by an air gun is small compared with the wavelengths of seismic interest. Each bubble thus behaves as a point source, both in the generation of seismic waves and in its response to incident seismic radiation produced by other nearby bubbles. It follows that the interaction effects between the bubbles may be described in terms of spherical waves. The array of interacting guns is equivalent to a notional array of noninteracting guns whose combined seismic radiation is identical. The seismic signatures of the equivalent independent elements of this notional array can be determined from the near‐field measurements. The seismic radiation pattern emitted by the whole array can be computed from these signatures by linear superposition, with a spherical correction applied. The method is tested by comparing far‐field signatures computed in this way with field measurements made in deep water. The computed and measured signatures match each other very closely. By comparison, signatures computed neglecting this interaction are a poor match to the measurements.

The signal from an air gun is assumed to behave as if it were derived from an oscillating spherical air bubble in water. The theory of the oscillations of spherical bubbles according to Gilmore is used in conjunction with experimental evidence to derive the complete set of equations necessary to calculate the shape of the radiated pressure waveform anywhere in the water. It is believed that this method will be useful in the design of signal processing techniques and also to improve the design of existing air gun profiling systems.

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We describe the acquisition, processing, and inversion of a multitransient electromagnetic (MTEM) single-line survey, conducted in December 2004 over an underground gas storage reservoir in southwestern France. The objective was to find a resistor corresponding to known gas about [Formula: see text] below the survey line. In data acquisition, we deployed a [Formula: see text] inline bipole current source and twenty [Formula: see text] inline potential receivers in various configurations along the [Formula: see text] survey line; we measured the input current step and received voltages simultaneously. Then we deconvolved the received voltages for the measured input current to determine the earth impulse responses. We show how both amplitude and traveltime information contained in the recovered earth impulse responses reveal the lateral location and approximate depth of the resistive reservoir. Integrating the impulse responses yields step responses, from which the asymptotic DC values were estimated and used in rapid 2D dipole-dipole DC resistivity inversion to find the top of the reservoir. A series of collated 1D full-waveform inversions performed on individual common midpoint gathers of the step responses position the top and bottom of a resistor corresponding to known gas in the reservoir and also obtain the transverse resistance. The results imply that the MTEM method can be used as a tool for hydrocarbon exploration and production.