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.

Abstract: A seismic signal source apparatus is mounted on the bed of a vehicle by means of a support structure. The apparatus includes a base plate coupled to ground surface beneath the vehicle as well as a seismic signal transducer to inject sweep signals into the ground through the base plate. A restraining means is connected between the upper end of the transducer support structure and the vehicle bed to prevent rocking motion of the seismic signal source. The restraining means includes a double-acting hydraulic piston. The piston is provided with at least two spring-loaded, oppositely-directed check valves. The spring loaded valves open to allow the transducer base plate to adjust itself to the local ground contours when the transducer base plate is pressed to the ground by the weight of the vehicle. The valves remain closed during a sweep cycle to provide a rigid restraining link which prevents destructive rocking movements of the transducer and base plate during a sweep cycle.

Abstract: An apparatus for generating a series of seismic acoustic pulses in a body of water. The series is characterized by having continuously-variable, non-repetitive time intervals between successive pulses during a continuous seismic recording. The preferred generator is an air gun comprising a variable-speed motor with a rotating cam for actuating a sleeve valve which alternately opens and closes exhaust ports in a high-pressure chamber. As the valve repeatedly opens, jets of high-pressure air are impulsively expelled into the surrounding water, thereby generating an underwater acoustic pulse train.

Abstract: The apparatus provides a means for time-varying the signal sample rate and the subsurface coverage during a single seismic reflection recording cycle. A number of seismic sensor arrays are connected to a multichannel seismic recording apparatus through a data-signal transmission means such as a multiconductor cable or a telemetric link. Each seismic sensor array is, of course, connected to a corresponding input channel, including a preamplifier, in the multichannel recording apparatus. Included in the recording apparatus is a set of addressable multiplexer switches. The multiplexer switches (or for simplicity, simply multiplexers) are divided into at least two groups. Separate sets of anti-aliasing filters, each set having a different pass band, are connected to the input terminals of the respective subgroups of multiplexers. One half of the input channels are connected to both sets of filters; all of the input channels are connected to one set of filters and multiplexers.

Abstract: A single time-multiplexed channel for telemetry of seismic data from a plurality of remote, spaced-apart sensors to a central recording device. All of the sensors are identical and interchangeable. A unique polling signal is transmitted over a telemetry link to each sensor. Upon receipt of the polling signal, each sensor in turn transmits its accumulated data over the telemetry link to a recording device. The time-delay due to polling-signal propagation between successive sensors provides a time window during which each sensor can transmit data.