Method for surfaces exploration adapted in particular to seismic prospecting and device therefor

Claim 2

Method for exploration at a distance from surfaces and discontinuities of a surveyed medium, adapted in particular to seismic prospecting of subterranean surfaces, comprising transmitting from at least one point and receiving in at least one point, waves selected from acoustic- or radio-waves, said transmission and reception points being remote from said surface, wherein at one transmission point is transmitted a wave-train of substantially constant frequency and of a length at least equal to the travel time of the waves over twice the distance between two limit points of the surveyed zone, at each receiving point, the reflected and diffracted waves are received and recorded after a delay, following the beginning of the transmission of the wave-train, which corresponds to the travel time of the waves over the path from the transmission point to said receiving point through a limit point of the surveyed zone and during a time interval at least as long as half a period of the transmitted wave-train, from each recording there are determined two characteristic numbers, one of the amplitude and the other of the phase of the recorded waves, and these numbers are used for restoring the diffraction points of the surfaces and the image of the transmission point with respect to the surfaces, acting as mirrors, of the considered medium, whereby said surfaces can be identified.

Claim 3

Method for exploration at a distance from surfaces and discontinuities of a surveyed medium adapted in particular to seismic prospecting of subterranean surfaces, comprising transmitting from at least one point and receiving in at least one point, waves selected from acoustic- or radio-waves, said transmission and reception points being remote from said surface, wherein there is successively transmitted from a plurality of transmission points wave-trains of substantially constant frequency and of a length at least equal to the travel time of the waves over twice the distance between two limit points of the surveyed zone, there is received and recorded at one reception point the reflected and diffracted waves after a delay, following the beginning of the transmission of each wave-train, which corresponds to the travel time of the waves over the path from the corresponding transmission point to said receiving point through a limit point of the surveyed zone, and during a time interval at least as long as half a period of the transmitted wave-train, there are determined from each recording two characteristic numbers, one of the amplitude and the other of the phase of the recorded waves, and these numbers are used for restoring the diffraction points and the image of the reception point with respect to the surfaces, acting as mirrors, of the considered medium, whereby said surfaces can be identified.

Claim 4

Method for exploration at a distance from surfaces and discontinuities of a surveyed medium adapted in particular to seismic prospecting of subterranean surfaces, comprising transmitting from at least one point and receiving in at least one point, waves selected from acoustic- or radio-waves, said transmission and reception points being remote from said surface, wherein there is successively transmitted from a plurality of transmission points wave-trains of substantially constant frequency and of a length at least equal to the travel time of the waves over twice the distance between two limit points of the surveyed zone, there is received and recorded at one reception point the reflected and diffracted waves after a delay, following the beginning of the transmission of each wave-train, which corresponds to the travel time of the waves over the path from the corresponding transmission point to said receiving point through a limit point of the surveyed zone, and during a time interval at least as long as half a period of the transmitted wave-train, there are determined from each recording two characteristic numbers, one of the amplitude and the other of the phase of the recorded waves, and these numbers are used for restoring the diffraction points and the image of the reception point with respect to the surfaces, acting as mirrors, of the considered medium, whereby said surfaces can be identified.

Claim 5

Method according to claim 1, wherein the recording time is equal to Delta t n/fo, fo being the transmission frequency and n the number of recorded periods of the received waves.

Claim 6

Method according to claim 1, wherein the length of the transmitted wave train is substantially equal to the travel time of the waves from the nearest to the farthest discontinuity and back, increased by internal t n/fo, fo being the transmission frequency and n the number of recorded periods of the received waves.

Claim 7

MeThod according to claim 1, wherein the transmission frequency of the wave train is selected from a frequency range whose width is in inverse ratio to the distance between the limit surface to be identified in the surveyed medium.

Claim 8

Method according to claim 1, wherein the waves are simultaneously transmitted from several points and that the phase/shift between the different waves remains constant during the transmission.

Claim 9

Method according to claim 1, wherein the transmitted waves have a higher amplitude at the beginning of the transmission period than at the end thereof.

Claim 10

Device for exploration at a distance from surfaces and discontinuities of a surveyed medium, particularly adapted to seismic prospecting of subterranean surfaces comprising in combination: means for transmitting substantially monochromatic waves, means for feeding with electric signals said transmitting means, means for limiting the transmission time of said waves to said time interval, means for receiving a signal corresponding to the waves reflected by the discontinuities of the surveyed medium, means for comparing the received signal to the received noise means for limiting the recording time of the received signal, depending on the ratio of the signal to the noise, to a selected number N of periods, means for measuring the maximum amplitude of said sine-signal, means for detecting the phase shift between the signal issued from the feeding means and the sine-signal issued from the summing means, means for recording, for each of the reception means, the value of the amplitude and of the phase shift, and means for restoring the images of the transmission sources or the reception points from said values of amplitude and phase shift.

Claim 11

Device for exploration at a distance from surfaces and discontinuities of a surveyed medium, particularly adapted to seismic prospecting of subterranean surfaces comprising in combination: means for transmitting substantially monochromatic waves, means for feeding with electric signals said transmitting means, means for limiting the transmission time of said waves to said time interval, means for receiving a signal corresponding to the waves reflected by the discontinuities of the surveyed medium, means for comparing the received signal to the received noise means for limiting the recording time of the received signal, depending on the ratio of the signal to the noise, to a selected number N of periods, means for measuring the maximum amplitude of said sine-signal, means for detecting the phase shift between the signal issued from the feeding means and the sine-signal issued from the summing means, means for recording, for each of the reception means, the value of the amplitude and of the phase shift, and means for restoring the images of the transmission sources or the reception points from said values of amplitude and phase shift.

Claim 12

Device for seismic prospecting of subterranean surfaces comprising the combination of transmission means of substantially monochromatic waves comprising at least two transmission units each of which transmits an identical signal at selected different times, means for feeding with electric current said transmission means, means for limiting the transmission time of each signal to said time interval, means for receiving each signal reflected from the sub-strata, means for comparing each received signal to the received noise, means for limiting the recording time of the received signal, in dependence with the ratio signal/noise, to a number n of periods, summation means successively issuing sine-signals, each corresponding to the average of the n periods of each received signal, means for measuring the maximum amplitude of each sine-signal, means for detecting the phase shift between the signal issued from the feeding means and each sine-signal and retarding means, associate with said summation means, for determining, by combining the amplitude and phase values, an amplitude value and phase value corresponding to the amplitude and the phase which would have been obtained by simultaneously transmitting waves from these different points.

Claim 13

Device for seismic prospecting of subterranean surfaces comprising the combination of transmission means of substantially monochromatic waves comprising at least two transmission units each of which transmits an identical signal at selected different times, means for feeding with electric current said transmission means, means for limiting the transmission time of each signal to said time interval, means for receiving each signal reflected from the sub-strata, means for comparing each received signal to the received noise, means for limiting the recording time of the received signal, in dependence with the ratio signal/noise, to a number n of periods, summation means successively issuing sine-signals, each corresponding to the average of the n periods of each received signal, means for measuring the maximum amplitude of each sine-signal, means for detecting the phase shift between the signal issued from the feeding means and each sine-signal and retarding means, associate with said summation means, for determining, by combining the amplitude and phase values, an amplitude value and phase value corresponding to the amplitude and the phase which would have been obtained by simultaneously transmitting waves from these different points.

Claim 14

Method according to claim 1, comprising receiving the waves reflected from the various surfaces acting as mirrors, at a plurality of points so located that the spacing between adjacent receivers decreases with an increasing distance thereof from the transmission point.

Claim 15

Method according to claim 2, wherein the recording time is equal to Delta t n/fo, fo being the transmission frequency and n the number of recorded periods of the received waves.

Claim 16

Method according to claim 2, wherein the length of the transmitted wave train is substantially equal to the travel time of the waves from the nearest to the farthest discontinuity and back, increased by internal t n/fo, fo being the transmission frequency and n the number of recorded periods of the received waves.

Claim 17

Method according to claim 2, wherein the transmission frequency of the wave train is selected from a frequency range whose width is in inverse ratio to the distance between the limit surface to Be identified in the surveyed medium.

Claim 18

Method according to claim 2, wherein the transmitted waves have a higher amplitude at the beginning of the transmission period than at the end thereof.