Method for generating orthogonal sweep signals

• US 4,686,654 A
• Filed: 07/31/1986
• Issued: 08/11/1987
• Est. Priority Date: 07/31/1986
• Status: Expired due to Term

• Current Assignee: WesternGeco LLC (Schlumberger NV)
• Original Assignee: Western Geophysical Company of America (Schlumberger NV)
• Inventors: Savit, Carl H.
• Primary Examiner(s): Kyle, Deborah L.
• Assistant Examiner(s): Griffiths, John E.
• Application Number:
  US06/891,475
• Time in Patent Office: 376 Days
• Field of Search: 367/38-42, 367/189, 367/190, 364/421, 364/422, 342/201, 342/132, 380/33-36, 370/19, 370/21, 370/22
• US Class Current: 367/41
• CPC Class Codes: G01V 1/375 Correlating received seismic signals with the emitted source signal

Abstract

A first sweep signal consists of a plurality of waveforms having non-invariant fundamental periods exhibiting a monotonic frequency progression of at least one octave over the duration of the sweep. Each waveform may consist of an ordered set of asymmetrical pulses distributed within the period of the waveform in a prescribed sequence as a function of time. A second sweep signal is orthogonalized with respect to the first by time-reversing the distribution-sequence of the pulse set.

Claims

1. A method for enhancing the orthogonality, with respect to each other, of at least two swept-frequency signals, while retaining common amplitude and phase spectra, comprising the steps of:

providing a first swept-frequency signal including a plurality of time periods within the duration of said first swept-frequency signal, each said time period including a set of asymmetrical pulses distributed in a first sequence as a function of time; and

providing at least a second swept-frequency signal including a plurality of time periods within the duration of said second swept-frequency signal that correspond to the time periods of said first signal, at least one of said time periods of said second swept-frequency signal including a set of asymmetrical pulses that are distributed as a function of time in a reverse sequence with respect to the pulse distribution within the corresponding fundamental period of said first swept-frequency signal.

3. The method of claim 1 wherein the time periods included within the duration of said second swept-frequency signal form a time-randomized sequence with respect to the time periods included within the duration of said first swept-frequency signal.

2. The method of cliam 1 wherein the time periods included within the duration of said first and second swept-frequency signals form a monotonic sequence.

4. A method for enhancing the orthogonality, with respect to each other, of at least two swept-frequency signals, while retaining common amplitude and phase spectra, comprising the steps of:

providing a first swept-frequency signal including a plurality of time periods within the duration of said first swept-frequency signal, each said time period including a set of asymmetrical pulses distributed in a first sequence as a function of time; and

providing at least a second swept-frequency signal including a plurality of time periods within the duration of said second swept-frequency signal that correspond to the time periods of said first signal, each of said time periods of said second swept-frequency signal including a set of asymmetrical pulses that are distributed as a function of time in a reverse sequence with respect to the pulse distribution within the corresponding time periods of said first swept-frequency signal.