Heave compensation system

Claim 2

An underwater seismic system for producing sound signals in water and for recording echoes from the bottom beneath the surface of such water, comprising: (1) a body adapted to travel through said water and including (a) a sound source for generating a sound signal, said source including input trigger means responsive to a trigger pulse received thereat for generating said sound signal, (b) a receiver for receiving echoes from said bottom, (2) a recorder connected to said receiver for recording said echoes, said recorder including repetitive sweep means, and means for generating a first start signal upon commencement of each sweep, (3) delay means including: (a) an accelerometer located in said body, said accelerometer including means for generating an output signal indicative of the vertical acceleration of said body, (b) integration means for double integrating said output signal within a frequency range having a predetermined low frequency rolloff, to produce a position signal approximately indicative of the position of said body for accelerations within said frequency range, said position signal having a steady state value in the absence of acceleration within said frequency range, said position signal changing in a first sense from said steady state value for upward acceleration of said body and changing in an opposite sense from said steady state value for downward acceleration of said body, (c) means connected to said recorder for receiving said first start signal from said recorder, (d) means connected to said integration means for receiving said position signal and also connected to said means (c) and responsive to receipt of said first start signal for thereon generating a second start signal at a time delayed from said first start signal by a time interval which has a predetermined value when said position signal has said steady state value and which decreases from said predetermined value when said position signal changes in said first sense and which increases from said predetermined value when said position signal changes in said opposite sense, (e) means connecting said means (d) to said input trigger means for said second start signal to constitute said trigger pulse, so that vertical acceleration of said body within said frequency range will cause compensating variations in the time of operation of said source.

Claim 3

A system according to claim 1 and further including pressure compensation means comprising a pressure transducer located in said body and including means for producing a pressure signal indicative of the depth of said body, second delay means connected to said first mentioned delay means for receiving said second start signal therefrom and also connected to said pressure transducer and responsive to receipt of said second start signal for generating a third start signal at a time delayed from that of said second start signal by a time dependent at least in part on said pressure signal, and means connecting said second delay means to said input trigger means for said third start signal in place of said second start signal to constitute said trigger pulse.

Claim 4

A system according to claim 2 including a low pass filter connected between said pressure transducer and said second delay means to attenuate pressure signals above said low frequency.

Claim 5

A system according to claim 3 wherein said first mentioned delay means includes switch means for switching either of said first and said second start signals to said second delay means, and said second delay means includes further switch means for switching either the signal received from said first delay means or said third start signal to input trigger means.

Claim 6

A system according to claim 2 including a blocking capacitor connected between said accelerometer and said integration means.

Claim 7

A system according to claim 2 including a blocking capacitor connected between said accelerometer and said integration means, and wherein said integration means comprises two integrators, each integrator comprising an operational amplifier having a feedback loop therein, said feedback loop being a high pass filter.

Claim 8

A system according to claim 2 wherein said low frequency is 0.01 Hz.

Claim 9

An underwater seismic system for producing sound signals in water and for recording echoes from the bottom beneath the surface of such water, comprising: (1) a body adapted to travel through said water and including: (a) a sound source for generating a sound signal, said source including input trigger means responsive to a trigger pulse received thereat for generating said sound signal, (b) a receiver for receiving echoes from said bottom, (2) a recorder connected to said receiver for recording said echoes, said recorder including repetitive sweep means, and means for generating a first start signal upon commencement of each sweep, (3) delay means including: (a) an accelerometer located in said body, said accelerometer including means for generating an output signal indicative of the vertical acceleration of said body, (b) integration means for double integrating said output signal within a frequency range having a predetermined low frequency rolloff, to produce a position signal approximately indicative of the position of said body for accelerations within said frequency range, said position signal having a steady state value in the absence of acceleration within said frequency range, said position signal changing in a first sense from said steady state value for upward acceleration of said body and changing in an opposite sense from said steady state value for downward acceleration of said body, (c) a pressure transducer located in said body and including means for producing a pressure signal indicative of the depth of said body, (d) a low pass filter for receiving said pressure signal and for attenuating variations therein above said low frequency, (e) means connected to said recorder for receiving said first start signal from said recorder, (f) means connected to said integration means for receiving said position signal and to said low pass filter for receiving the pressure signal therefrom and responsive to receipt of said first start signal therefrom and responsive to receipt of said first start signal for then generating a second start signal at a time delayed from said first start signal for a time interval which has a predetermined value when said position signal has said steady state value and when said pressure signal has a preset value, and which decreases from said predetermined value when said position signal changes in said first wave or when said pressure signal decreases at a rate below said low frequency, and which increases from said predetermined value when said position signal changes in said opposite sense or when said pressure signal increases at a rate below said low frequency, (g) means connecting said means (f) to said input trigger means for said second start signal to constitute said trigger pulse, so that both vertical accelerations of said body within said frequency range and changes in the pressure at said body at a rate below said low frequency will cause compensating variations in the time of operation of said source.

Claim 10

An underwater seismic system for producing sound signals in water and for recording echoes from the bottom beneath the surface of such water, comprising: (1) a body adapted to travel through said water and including: (a) a sound source for generating a sound signal, said source including input trigger means responsive to a trigger pulse received thereat for generating said sound signal, (b) a receiver for receiving echoes from said bottom, (2) a recorder connected to said receiver for recording said echoes, said recorder including repetitive sweep means, and means for generating a first start signal upon commencement of each sweep, (3) delay means including: (a) an accelerometer located in said body, said accelerometer including means for generating an output signal indicative of the vertical acceleration of said body, (b) integration means for double integrating said output signal within a frequency range having a predetermined low frequency rolloff, to produce a position signal approximately indicative of the position of said body for accelerations within said frequency range, said position signal having a steady state value in the absence of acceleration within said frequency range, said position signal changing in a first sense from said steady state value for upward acceleration of said body and changing in an opposite sense from said steady state value for downward acceleration of said body, (c) a pressure transducer located in said body and including means for producing a pressure signal indicative of the depth of said body, (d) a low pass filter for receiving said pressure signal and for attenuating variations therein above said low frequency, (e) means connected to said recorder for receiving said first start signal from said recorder, (f) means connected to said integration means for receiving said position signal and to said low pass filter for receiving the pressure signal therefrom and responsive to receipt of said first start signal therefrom and responsive to receipt of said first start signal for then generating a second start signal at a time delayed from said first start signal for a time interval which has a predetermined value when said position signal has said steady state value and when said pressure signal has a preset value, and which decreases from said predetermined value when said position signal changes in said first wave or when said pressure signal decreases at a rate below said low frequency, and which increases from said predetermined value when said position signal changes in said opposite sense or when said pressure signal increases at a rate below said low frequency, (g) means connecting said means (f) to said input trigger means for said second start signal to constitute said trigger pulse, so that both vertical accelerations of said body within said frequency range and changes in the pressure at said body at a rate below said low frequency will cause compensating variations in the time of operation of said source.

Claim 11

A system according to claim 8 including a blocking capacitor connected between said accelerometer and said integration means.

Claim 12

A system according to claim 9 wherein said low frequency is 0.01 Hz.