Abstract: The invention relates to a method of mapping subsurface resistivity contrasts by making multichannel transient electromagnetic (MTEM) measurements on or near the earth's surface using at least one source, receiving means for measuring the system response and at least one receiver for measuring the resultant earth response. All signals from the or each source-receiver pair are processed to recover the corresponding electromagnetic impulse response of the earth and such impulse responses, or any transformation of such impulse responses, are displayed to create a subsurface representation of resistivity contrasts. The invention enables subsurface fluid deposits to be located and identified and the movement of such fluids to be monitored.

Abstract: The invention relates to a method of mapping subsurface resistivity contrasts by making multichannel transient electromagnetic (MTEM) measurements on or near the earth's surface using at least one source, receiving means for measuring the system response and at least one receiver for measuring the resultant earth response. All signals from the or each source-receiver pair are processed to recover the corresponding electromagnetic impulse response of the earth and such impulse responses, or any transformation of such impulse responses, are displayed to create a subsurface representation of resistivity contrasts. The invention enables subsurface fluid deposits to be located and identified and the movement of such fluids to be monitored.

Abstract: In order to accumulate data from which the signature of an array of n interacting seismic sources 21 to 27, for instance marine seismic sources in the form of air guns, can be determined, the array is actuated and the emitted pressure wave is measured at n independent points whose positions will respect to the array are known by hydrophones 31 to 37. Data from the measured pressure wave is stored for subsequent processing to produce n equivalent signatures of the n sources taking into account the interactions therebetween. The signature of the array is then determined merely by superposing the n equivalent signatures.

Abstract: The invention relates to a method of determining the location in the earth of sub-surface boundaries and/or the acoustic properties of sub-surface features substantially in the absence of the far field source wavelet and noise and with errors due to reflections of sound waves from the water being substantially compensated for. The invention uses point sound sources or arrays thereof at a first depth and then scales the energy, pressure and spacing of a similar source at a second depth to provide data which is used to obtain a seismic record.

Abstract: A seismic method and apparatus utilizes two point sound sources located at the same location on the earth to produce sound waves at different amplitudes and times. The reflections of the sound waves are analyzed to determine the acoustic properties and rock boundaries within the earth.

Abstract: A method is provided of ascertaining the far field signature of an array of sound source units, each of which is small compared with the wavelength of the highest frequency of interest. The units are fired so that the interactions between them is negligible. This is achieved by firing the units sequentially so that each generates all its significant radiation before the next is fired, and/or by firing more than one unit at a time and separating the units by at least one wavelength of the lowest frequency of interest. The far field signature of each unit is measured by a pressure-sensitive detector close to the unit but in a region where the phase spectrum of the pressure field is independent of azimuth and range. The far field signature of the array is derived from the measured signatures by summation.

Abstract: In order to determine the signature of an array of n seismic sources 21 to 27, for instance marine seismic sources in the form of air guns, the array is actuated and the emitted pressure wave is measured at n independent points whose positions will respect to the array are known by hydrophones 31 to 37. The measurements are processed to produce n equivalent signatures of the n sources taking into account the interactions therebetween. The signature of the array is then determined merely by superposing the n equivalent signatures.

Abstract: A method and apparatus for determining the acoustic properties of the earth utilizes one or more identical, non-interacting, first spaced arrays of point sound sources and one or more identical, non-interacting, second spaced arrays of point sound sources with corresponding arrays of the first and second sources containing the same number of point sound sources in the same spatial relationship, with the spacing between the point sources of the second array or arrays being a factor .alpha. greater than the spacing between corresponding point sources of the first array or arrays. The energy of the radiation emitted by each point source of the first array(s) is greater than that emitted by the corresponding point sources in the second array(s) by a factor of .alpha..sup.3.