Multichannel seismic telemeter system and array former

• US 4,072,923 A
• Filed: 03/08/1976
• Issued: 02/07/1978
• Est. Priority Date: 03/08/1976
• Status: Expired due to Term

• Current Assignee: Western Atlas International Incorporated (Northrop Grumman Corporation)
• Original Assignee: Western Geophysical Company of America
• Inventors: Siems, Lee E., Morgan, Paul M.
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US05/664,617
• Time in Patent Office: 701 Days
• Field of Search: 340/15.5 DP, 340/15.5 TS, 340/151, 340/152 T, 340/183, 179/15 BL, 179/15 A, 179/15 AL
• US Class Current: 367/6
• CPC Class Codes: G01V 1/22 Transmitting seismic signals to recording or processing apparatus
• CPC Class Codes: G01V 1/38 specially adapted for water-covered areas G01V1/28 takes precedence
• CPC Class Codes: H04J 3/04 Distributors combined with modulators or demodulators pulse distributors in general H03K5/15; pulse counters H03K21/00 - H03K29/06; for telegraphy H04L5/22, H04L13/00 - H04L23/00, H04L25/45; for telephony H04Q11/04
• CPC Class Codes: H04J 3/10 Arrangements for reducing cross-talk between channels

Abstract

It is a purpose of this invention to dispose a large number, such as 500, of elemental seismic sensor units over the earth'"'"'s surface in a desired pattern. The sensors are arranged preferably in a linear pattern, at increasing distances, remotely with respect to a central station. Each elemental seismic sensor unit comprises a short subarray consisting of three seismic detectors, electrically interconnected. Each elemental sensor unit is a separate source of seismic signals. At regular intervals the analog seismic signals from the elemental sensor units are sampled in sequence and are digitized as a 20-bit binary number. The binary numbers are representative of the analog signal levels. The binary numbers are encoded in a self-clocking, return-to-zero pulse code as digital data words. The data words from the respective elemental sensor units are time-delay multiplexed into a wide band transmission channel for transmission to the central station in a constant current mode. Spaced along the transmission link are a series of transceiver units to each of which several separate sensor units are connected. The transceiver units are connected in series and include a repeater network which receives and retransmits data words from down-link transceivers, as well as data words derived from each of the locally-connected sensor units. Each repeater network also includes a word detection circuit, a local clock, and synchronizing circuitry. In the central station, the respective data words are stored as a matrix, in a core memory in sequential order. A formatter extracts from the core memory, data words that originated from selected groups of the elemental subarrays. The data words are combined to form new composite data words representative of seismic signals originating from desired longer arrays. The composite data words are transferred to a recording medium, such as a magnetic tape, for storage or future use.

Claims

1. In a seismic data system comprising a central station;

a plurality of remote transceivers, each having a plurality of input channels;

a broadband transmission link including an interrogation channel connecting said transceivers in series to said central station;

means in each said transceiver, coupled to said interrogation channel for applying a fixed delay to said interrogation signals, for regenerating said interrogation signals, and for transmitting said interrogation signals down-link to the next-in-series transceiver, the fixed delay being less than the sum of the digital-data-word length plus the two-way signal propagation delay through the interrogation channel;

a plurality of spaced elemental seismic sensor units connected to supply analog seismic signals to corresponding input channels in each said transceiver;

means in each said transceiver for sampling input seismic signals and for converting the amplitudes and polarities thereof into multibit, self-clocking, floating-point, phase encoded digital data words having a predetermined length in time, the respective bit values being defined by coded phase reversals, each said digital data word being divided into a number of bit intervals having a width equal to an integral submultiple of the digital data word length;

control means in each said transceiver coupled to said interrogation channel for applying digital data words from each channel of each said transceiver to said broadband transmission link, in constant current mode, in response to interrogation signals received from said central station over said interrogation channel, the improvement wherein;

the leading edge of the leading bit of each said data word always has the same given polarity trend, the improvement further including;

first means in each said transceiver for receiving digital data words from respective down-link transceivers, and for regenerating and retransmitting said digital data words up-link;

second means in said central station for receiving digital data words from said respective transceivers; and

sensing means included in said first means and said second means for sensing said given polarity trend as the beginning of a digital data word and means for detecting the end of a digital data word by counting the number of phase reversals in the direction of said given polarity trend that occur within a prescribed multiple of the bit interval.

2. The system as defined in claim 1 including:

means coupled to said second means and to said interrogation channel for measuring the elapsed time interval between the time of transmission of an interrogation signal over said interrogation channel and the time of receipt of the respective digital data words from said transceivers;

means in said central station for converting said elapsed time intervals to corresponding binary address words; and

means for storing the resultant binary address words associated with said received digital data words for source identification.

3. In a seismic data aquisition system including a central station, having a master controller, a plurality of remote transceivers each having a plurality of input channels, a broadband data transmission link and interrogation link connecting said transceivers in series to said central station, a plurality of elemental seismic sensor units connected to supply analog seismic signals to corresponding input channels in each said transceiver, means in each said transceiver for sampling input seismic signals and for converting the amplitudes and polarities thereof to multibit, self-clocking, floating-point, phase-encoded digital data words, control means in each said transceiver for applying the digital data words from each said transceiver to said data transmission link in transceiver-sequential, channel-sequential order, in response to interrogation signals received from said master controller in said central station over said interrogation link, the improvement comprising:

data receiver means in said central station coupled to said master controller, for measuring the elapsed time interval between the time of application of an interrogation signal to said interrogation link and the time of receipt of the respective digital data words from said transceivers;

means for converting each of said elapsed time intervals to a corresponding binary address word defining the transceiver from which each said digital data word originated;

remap memory means in said central station coupled to said data receiver means for converting the arrangement of the received digital data words from transceiver-sequential, channel-sequential order to consecutive channel-sequential order in accordance with the respective corresponding binary address words.

means, coupled to said remap memory, for combining digital data words from selected groups of input channels to programmably reconfigure the array response of the associated elemental seismic sensor units; and

a weighting coefficient memory for weighting the digital data words as they are being combined.

4. A system as defined in claim 3 wherein said broad-band data transmission link is more than one mile in length, has a frequency pass-band of a least 100 MHz, and wherein said control means for applying digital data words to said broadband data transmission link has a pulse repetition rate of more than 20,000,000 pulses per second and includes circuit means for retransmitting said words in return-to-zero pulse code form.