Method and device for separating seismic signals from seismic sources

Abstract

System and method for actuating first and second marine acoustic sources in a firing sequence, the firing sequence including at least a first actuation of the first source followed by a first actuation of the second source followed by a second actuation of the first source and a second actuation of the second source. The method includes towing the first source at a depth in water substantially equal to a depth of the second source; establishing a series of reference time instants; actuating the first source with a variable first time delay relative to the series of reference time instants; and actuating the second source with a variable second time delay relative to the series of reference time instants such that time intervals between consecutive activations of the first and second sources are also variable.

1 . (canceled) 
     
     
         2 . A method for actuating at least first and second marine acoustic sources in a firing sequence, the method comprising:
 towing the first and second sources in water;   establishing a series of reference time instants;   actuating the first source with a variable first time delay relative to the series of reference time instants so that a first portion of a first underwater reflector is illuminated; and   actuating the second source with a variable second time delay relative to the series of reference time instants so that a first portion of a second underwater reflector is illuminated,   wherein the variable second time delay is different from the variable first time delay, and   the first portion of the first underwater reflector and the first portion of the second underwater reflector extend one next to the other along a cross-line direction.   
     
     
         3 . The method of  claim 2 , wherein the first and second time delays are random. 
     
     
         4 . The method of  claim 2 , wherein the first and second time delays are semi-random. 
     
     
         5 . The method of  claim 2 , wherein the first and second time delays are systematically varying. 
     
     
         6 . The method of  claim 2 , further comprising
 towing a low-frequency source while the first and second sources are high-frequency sources.   
     
     
         7 . The method of  claim 2 , wherein the first and second sources emit different frequencies. 
     
     
         8 . The method of  claim 2 , further comprising:
 towing plural streamers with a same vessel that tows the first and second sources; and   simultaneously recording reflected seismic waves corresponding to the first and second sources.   
     
     
         9 . The method of  claim 2 , further comprising:
 when comparing at a same instant and at a same underwater location an envelope of a far-field signature of the first source with an envelope of a far-field signature of the second source, the two envelopes substantially overlap.   
     
     
         10 . A computing device for actuating at least first and second marine acoustic sources in a firing sequence, the computing device comprising:
 an interface for receiving a series of reference time instants; and   a processor connected to the interface and configured to,   actuate the first source with a variable first time delay relative to the series of reference time instants so that a first portion of a first underwater reflector is illuminated; and   actuate the second source with a variable second time delay relative to the series of reference time instants so that a first portion of a second underwater reflector is illuminated,   wherein the variable second time delay is different from the variable first time delay, and   the first portion of the first underwater reflector and the first portion of the second underwater reflector extend one next to the other along a cross-line direction.   
     
     
         11 . The device of  claim 10 , wherein the first and second time delays are random. 
     
     
         12 . The device of  claim 10 , wherein the first and second time delays are semi-random. 
     
     
         13 . The device of  claim 10 , wherein the first and second time delays are systematically varying. 
     
     
         14 . The device of  claim 10 , further comprising
 towing a low-frequency source while the first and second sources are high-frequency sources.   
     
     
         15 . The device of  claim 10 , wherein the first and second sources emit different frequencies. 
     
     
         16 . The device of  claim 10 , wherein plural streamers are towed with a same vessel that tows the first and second sources; and
 reflected seismic waves corresponding to the first and second sources are recorded simultaneously.   
     
     
         17 . The device of  claim 10 , wherein, when comparing at a same instant and at a same location underwater an envelope of a far-field signature of the first source with an envelope of a far-field signature of the second source, the two envelopes substantially overlap. 
     
     
         18 . The device of  claim 10 , wherein the series of reference time instants is calculated based on an assumption that no other source except the first source is present and thus there is no need for a waiting time necessitated by the actuation of the other source before firing again the first source, and time intervals between any two consecutive reference time instants are fixed to a predetermined value. 
     
     
         19 . The device of  claim 10 , wherein the first and second sources have a substantially same inline position. 
     
     
         20 . A non-volatile computer readable medium including computer executable instructions, wherein the instructions, when executed by a processor, implement a method for actuating at least first and second marine acoustic sources in a firing sequence, the method comprising:
 establishing a series of reference time instants;   actuating the first source with a variable first time delay relative to the series of reference time instants so that a first portion of a first underwater reflector is illuminated; and   actuating the second source with a variable second time delay relative to the series of reference time instants so that a first portion of a second underwater reflector is illuminated,   wherein the variable second time delay is different from the variable first time delay, and   the first portion of the first underwater reflector and the first portion of the second underwater reflector extend one next to the other along a cross-line direction.   
     
     
         21 . The medium of  claim 20 , wherein the first and second time delays are random.