Adaptive monofrequency pilot signals

Claim 2

In a seismic prospecting method of the type where seismic waves are radiated into the earth from an electronically controllable multifrequency seismic source, the improvement comprising: a. detecting said seismic waves on a near-field detector located near said seismic source, said near-field detector producing a near-field electrical signal corresponding to the said radiated seismic waves; b. comparing a function of said near-field electrical signal with only a part of a predetermined multifrequency control signal; and c. automatically modifying at least one of the duration, frequency or amplitude characteristics of said multifrequency control signal when said comparison in step (b) indicates a predetermined ratio thereof has been reached.

Claim 3

In a method of seismic prospecting using an electronically controllable multifrequency seismic source to radiate seismic signals into the earth, the improvement comprising: a. generating for said seismic source an electrical control signal having a predetermined amplitude-frequency spectrum; b. detecting said radiated seismic signals on a near-field detector located relative to said seismic source such that the signal produced by said near-field detector essentially contains at least the attenuation in said radiated signal introduced by near-surface material immediately adjacent to said seismic source; c. measuring a near-field amplitude-frequency spectrum of said near-field detector electrical signal; d. comparing said near-field amplitude-frequency spectrum with said predetermined amplitude-frequency spectrum; and e. continuously and automatically modifying said electrical control signal until said comparison step indicates said near-field spectrum essentially equals said predetermined spectrum.

Claim 4

In a method of seismic prospecting using an electronically controllable multifrequency seismic source to radiate seismic signals into the earth, the improvement comprising: a. generating for said seismic source an electrical control signal having a predetermined amplitude-frequency spectrum; b. detecting said radiated seismic signals on a near-field detector located relative to said seismic source such that the signal produced by said near-field detector essentially contains at least the attenuation in said radiated signal introduced by near-surface material immediately adjacent to said seismic source; c. measuring a near-field amplitude-frequency spectrum of said near-field detector electrical signal; d. comparing said near-field amplitude-frequency spectrum with said predetermined amplitude-frequency spectrum; and e. continuously and automatically modifying said electrical control signal until said comparison step indicates said near-field spectrum essentially equals said predetermined spectrum.

Claim 5

A method of seismic prospecting as recited in claim 2 wherein said generating step comprises the generation of a sequence of individual electrical control signal segments, each having individual predetermined spectra which when composited form a signal having a predetermined amplitude-frequency spectrum.

Claim 6

A method as recited in claim 3 wherein said individual electrical control signal segments are generated in a juxtaposed time sequence to form an elongated signal with essentially no time elapsing between adjacent individual signal segments.

Claim 7

A method as recited in claim 3 wherein said individual signal segments are generated in a separated time sequence such that the time elapsing between said individual signal segments is at least equal to the traveltime of seismic wave from said controllable seismic source to the deepest reflecting interface of interest and back to a conventional reflection spread seismometer which is located the farthest distance from said seismic source.

Claim 8

A method as recited in claim 3 wherein said spectrum modification step is performed by changing the amplitude of said individual electrical control signal segments.

Claim 9

A method as recited in claim 3 wherein said spectrum modification step is performed by changing the duration of said individual electrical control signal segments.

Claim 10

A method as recited in claim 3 wherein said spectrum modification step is performed by changing the frequency of said individual electrical control signal segments.

Claim 11

A method as recited in claim 2 wherein said detecting step is accomplished by locating said near-field detector within the earth in a hole substantially beneath said seismic source.

Claim 12

An improved method of seismic prospecting of the type where a sequence of truncated sinusoids is radiated into the earth by a controllaBle seismic vibrator wherein the improvement comprises: a. initiating the generation of a predetermined first-frequency sinusoidal vibrator drive signal having a predetermined amplitude and frequency; b. detecting said first-frequency radiated signal on a near-field detector located relative to said vibrator such that its output signal essentially contains the distortion in the radiated signal caused by the near-surface earth materials substantially beneath said controllable seismic vibrator; c. forming from said near-field detector output signal a first-frequency spectrum value proportional to the cumulative energy of said radiated signal at said frequency after near-surface distortion has occurred; d. comparing said first-frequency spectrum value with a predetermined first standard value; e. stopping said first-frequency signal when said first near-field cumulative value equals said predetermined first standard value; and f. repeating steps (a) through (e) for additional predetermined frequencies and corresponding standard values until a desired composite signal bandwidth is obtained.

Claim 13

An improved method of seismic prospecting of the type where a sequence of truncated sinusoids is radiated into the earth by a controllaBle seismic vibrator wherein the improvement comprises: a. initiating the generation of a predetermined first-frequency sinusoidal vibrator drive signal having a predetermined amplitude and frequency; b. detecting said first-frequency radiated signal on a near-field detector located relative to said vibrator such that its output signal essentially contains the distortion in the radiated signal caused by the near-surface earth materials substantially beneath said controllable seismic vibrator; c. forming from said near-field detector output signal a first-frequency spectrum value proportional to the cumulative energy of said radiated signal at said frequency after near-surface distortion has occurred; d. comparing said first-frequency spectrum value with a predetermined first standard value; e. stopping said first-frequency signal when said first near-field cumulative value equals said predetermined first standard value; and f. repeating steps (a) through (e) for additional predetermined frequencies and corresponding standard values until a desired composite signal bandwidth is obtained.

Claim 14

A method as recited in claim 10 wherein said generating step for each different frequency sinusoid is preformed sequentially such that an elongated signal comprising a sequence of juxtaposed repetitive sinusoids with little time interval between each two frequency sinusoids is formed, compared to the duration of either of said two frequency sinusoids.

Claim 15

A method as recited in claim 10 wherein said generating step is performed sequentially such that each different frequency sinusoid is separated from the previous one by a time interval at least as long as the traveltime required for seismic waves to travel from said controllable seismic vibrator to the deepest reflecting interface of interest and back to a seismometer in a conventional spread adjacent said vibrator which is farthest removed from said vibrator location.

Claim 16

A method as recited in claim 10 further comprising: a. measuring the time interval that elapses between initiation and stopping of each frequency sinusoid to establish a signal duration time; b. taking the reciprocal of said signal duration time to determine a new signal frequency increment; c. adding said new frequency signal increment to the previous signal frequency to establish a new signal frequency which will be the predetermined frequency employed in step (f) of claim 14; and d. stopping said repeating step (f) in claim 14 when said new signal frequency exceeds a predetermined final frequency.

Claim 17

A method as described in claim 10 further comprising: a. measuring the amplitude of said first-frequency vibrator drive signal from a given frequency individual sinusoid; b. comparing said first frequency vibrator drive signal amplitude measured in step (a) with a predetermined first maximum amplitude chosen such that said vibrator will remain coupled to the ground; c. adjusting the amplitude of said first frequency vibrator drive signal until it at least equals said predetermined maximum amplitude; and d. repeating steps (a) through (c) for additional predetermined frequencies and maximum amplitudes until a predetermined composite signal bandwidth is obtained.

Claim 18

A method as recited in claim 10 wherein said spectrum forming step is performed by accumulating the square of the amplitude of said near-field detector signal.

Claim 19

A method as recited in claim 10 wherein said spectrum forming step is performed by accumulating the absolute values of said near-field signal.

Claim 20

An improved method of seismic prospecting of the type where a number of predetermined equal-length sinusoids are radiated into the earth by a controllable seismic vibrator wherein the improvement comprises: a. Generating for control of said seismic vibrator a first sinusoidal vibrator drive signal having a predetermined amplitude and duration chosen to produce a first predetermined spectrum value at a predetermineD first frequency, said first frequency being chosen to define one limit of a predetermined bandwidth; b. detecting said first frequency radiated signal on a near-field detector located relative to said seismic vibrator such that it produces an electrical output signal which essentially contains the distortion in the radiated signal caused by the near-surface earth materials near said seismic vibrator; c. determining a first frequency near-field spectrum value proportional to the cumulative energy in said near-field detector output signal; d. forming a ratio of said predetermined first frequency spectrum value to said cumulative near-field spectrum value; e. multiplying the first of said predetermined signal lengths of said ratio determined in step (d) to produce a first frequency correction value; f. taking the reciprocal of said first frequency correction value to produce a first frequency increment; g. adding said first frequency increment to said predetermined first frequency to establish a second frequency; h. storing said second frequency for subsequent use in establishing a third frequency; i. comparing said second frequency with a predetermined final frequency chosen to define the other limit of said desired bandwidth; j. generating for control of said seismic vibrator a second sinusoidal vibrator drive signal having the same predetermined amplitude and duration as said first frequency sinusoidal vibrator drive signal but at said second frequency as determined in step (g) above; and (k) repeating steps (b) through (k) for additional frequencies until an nth frequency at least equal to said predetermined final frequency value is reached; and (1) stopping said signal generation when said comparison in step (i) above indicates said nth frequency at least equals said predetermined final frequency.

Claim 21

An improved method of seismic prospecting of the type where a number of predetermined equal-length sinusoids are radiated into the earth by a controllable seismic vibrator wherein the improvement comprises: a. Generating for control of said seismic vibrator a first sinusoidal vibrator drive signal having a predetermined amplitude and duration chosen to produce a first predetermined spectrum value at a predetermineD first frequency, said first frequency being chosen to define one limit of a predetermined bandwidth; b. detecting said first frequency radiated signal on a near-field detector located relative to said seismic vibrator such that it produces an electrical output signal which essentially contains the distortion in the radiated signal caused by the near-surface earth materials near said seismic vibrator; c. determining a first frequency near-field spectrum value proportional to the cumulative energy in said near-field detector output signal; d. forming a ratio of said predetermined first frequency spectrum value to said cumulative near-field spectrum value; e. multiplying the first of said predetermined signal lengths of said ratio determined in step (d) to produce a first frequency correction value; f. taking the reciprocal of said first frequency correction value to produce a first frequency increment; g. adding said first frequency increment to said predetermined first frequency to establish a second frequency; h. storing said second frequency for subsequent use in establishing a third frequency; i. comparing said second frequency with a predetermined final frequency chosen to define the other limit of said desired bandwidth; j. generating for control of said seismic vibrator a second sinusoidal vibrator drive signal having the same predetermined amplitude and duration as said first frequency sinusoidal vibrator drive signal but at said second frequency as determined in step (g) above; and (k) repeating steps (b) through (k) for additional frequencies until an nth frequency at least equal to said predetermined final frequency value is reached; and (1) stopping said signal generation when said comparison in step (i) above indicates said nth frequency at least equals said predetermined final frequency.

Claim 22

An improved method of seismic prospecting of the type using an electronically controllable seismic source to radiate seismic signals into the earth wherein the improvement comprises: a. generating for said seismic source an electrical control signal having a predetermined spectrum value for each operating frequency; b. detecting said radiated signal on a near-field detector located relative to said seismic source such that an electrical signal is produced by said near-field detector which essentially reflects the radiated signal distortion introduced by the near-surface material immediately adjacent to said vibrator source; c. continuously determining near-field spectrum values from said near-field detector electrical signal; d. continuously forming a ratio of said near-field spectrum values to said predetermined spectrum values; and e. continuously adjusting the amplitude of said electrical control signal in response to said ratio formed in step (d) above such that said radiated seismic signal has a spectrum value for each operating frequency which approximately equals the predetermined spectrum value.

Claim 23

An improved method of seismic prospecting of the type using an electronically controllable seismic source to radiate seismic signals into the earth wherein the improvement comprises: a. generating for said seismic source an electrical control signal having a predetermined spectrum value for each operating frequency; b. detecting said radiated signal on a near-field detector located relative to said seismic source such that an electrical signal is produced by said near-field detector which essentially reflects the radiated signal distortion introduced by the near-surface material immediately adjacent to said vibrator source; c. continuously determining near-field spectrum values from said near-field detector electrical signal; d. continuously forming a ratio of said near-field spectrum values to said predetermined spectrum values; and e. continuously adjusting the amplitude of said electrical control signal in response to said ratio formed in step (d) above such that said radiated seismic signal has a spectrum value for each operating frequency which approximately equals the predetermined spectrum value.