Improvements in or relating to determination of far field signatures, for instance of seismic sources

Claim 1

. 1. A method of ascertaining the far field signature of an array of sound source units in a fluid, comprising: employing an array of sound source units, each of which is small compared with the wavelength of sound generated by the unit; locating at least one sound pressure detector at a known distance from the units of the array, which distance is small compared with the wavelength of sound generated by the units but sufficiently large for the phase spectra of the pressure fields of the units to be independent of azimuth and range; locating each source unit at a known distance below the fluid surface and at a distance from the fluid floor sufficiently greater than the distance between the detector and the sound unit for the reflection of the soundwave from the floor to be disregarded; generating from one sound source unit at a time a sound pressure wave with intervals between consecutive waves being greater than the time taken for the preceding wave to pass the detector substantially completely, and/or generating sound pressure waves from more than one of the sound source units at a time with the units being located at least one wavelength of the lowest frequency of significance apart; and deducing by summation the individual source unit signatures detected by the or each detector the far field signature of the array.

Claim 5

A method of determining the impulse response of the earth, comprising providing an array of marine seismic sources, ascertaining the far field signature of the array by means of a method as claimed in any one of the preceding claims, employing the array to obtain a measured response, and deconvolving the measured response from the far field signature of the array.