In 1947, Roy Paslay, George Pavey and Pershing Wipff invented the towed marine streamer (Lawyer et al, 2001; Paslay et al, 1956) Since that time, there have been many improvements in streamer technology However, one aspect of that technology has remained fixed during the intervening 60 years; the type of seismic detector has remained the hydrophone As a consequence, every recorded and finally processed reflection wavelet from marine streamers has been accompanied by a ghost reflection from the ocean’s surface And the resulting filter effect on the recorded data has restricted streamer towing depths to a range of about six to nine meters In this paper, we report on the successful addition of particle velocity sensors to a new dual-sensor towed marine streamer, and the geophysical improvements and advantages that result

A Dual-Sensor, Towed Marine Streamer; Its Viable Implementation And Initial Results

The present invention provides a downconverter method and apparatus for downconverting a multiphase modulated signal. The downconverter can be implemented in a multi-phase receiver such as a quadrature receiver. An analog-to-digital converter (103) converts an intermediate frequency signal to a digital signal at a sampling rate. A Hilbert transformation filter (104) and a delay element (105) connected in parallel provide respective passband quadrature and in-phase components of the digital signal. A digital translator (107) alters the passband quadrature and in-phase components based on a predetermined pattern to provide a baseband quadrature signal and a baseband in-phase signal. The digital translator (107) can be a pseudorandom sequence demodulator for demodulating a code division multiple access (CDMA) signal. Various types of DC estimation can also be provided in addition to automatic gain control.

Method and apparatus for multi-phase component downconversion

A method of producing a seismic signal indicative of the substrata beneath a body of water comprising the steps of: supplying acoustic energy to the body of water; sensing at a predetermined depth the pressure wave reflected from the substrata beneath the body of water and the secondary pressure wave caused by a secondary reflection of the pressure wave from the air-water interface and generating a first signal indicative thereof; sensing at the predetermined depth the particle velocity of the water accompanying the pressure wave reflected from the substrata and the secondary pressure wave and generating a second signal indicative thereof; filtering the second signal such that portions of the second signal that have a frequency that is less than a first frequency are attenuated by the filtering to generate a third signal, the first frequency being less than a second frequency which is equal to the wave propagation velocity of the body of water divided by two times the predetermined depth; and combining the first and third signals to produce a signal indicative of the substrata beneath the body of water.

Marine seismic system

A QPSK modulated wave is inputted to an in-phase detector and an orthogonal detector. The detected components are converted to substantially a base band, and each component is digital-converted by A/D converters. Each digital component is spectrum-shaped by digital LPFs. The outputs of digital LPFs are inputted to a complex multiplier and calculated by use of first and second reproduction carriers and expressed as first and second calculation outputs, and inputted to a phase detector. The phase detector obtains phase difference data between the phase expressed by the first and second calculation outputs and a predetermined phase and quadrant data of the phase. The phase difference data is used for a PLL. The phase difference data is is inputted to a frequency error detection circuit detecting a frequency error. The frequency error output is smoothed by a filter of an AFC loop, and used as a control signal controlling the oscillation frequency of the local oscillation unit. If the frequency error is large, the frequency error detection circuit controls the AFC loop to be in an operation state and the PLL loop and the PLL loop to be in a fixed state. If the frequency error is small, the frequency error detection circuit contains the control state of the AFC loop and switches the PLL loop to be the operation state.

Demodulator for digitally modulated wave

An adaptive mode control system is provided which includes a transmitter including apparatus for inputting format information regarding the waveform structure of an AM compatible digital broadcast signal. The transmitter also includes apparatus for inputting user data such as the information to be broadcast. The transmitter selects the waveform parameters in response to the format information and produces control channel information. The transmitter uses this control channel information in combination with the user data to produce composite data. The transmitter generates an over-the-air signal waveform using the composite data and waveform parameters. Each receiver includes apparatus for detecting the over-the-air signal waveform and composite data generated by the transmitter. The receiver further includes apparatus for parsing the composite data into user data and control channel information. The receiver regenerates the waveform parameters from the control channel information and folds the waveform parameters into the receiver's detection apparatus so that the waveform parameters can reconfigure the receiver for receipt of subsequent transmissions.

Adaptive mode control system for AM compatible digital broadcast

A modulated carrier is received on a node (10) and then the I- and the Q-channels extracted with a local carrier clock (16) that is free-running relative to the modulated carrier. The I- and the Q-channels are then input to a digital signal processor (26) wherein a composite phase signal is generated representing the phase difference between the modulated carrier and the local carrier clock (16). The composite phase is output from a look-up table in an EPROM (30) and then the free-running phase the local carrier clock (16) and the modulated carrier is discriminated from the composite phase. The free-running phase is then subtracted from the composite phase to yield the phase modulation on the carrier.

Carrier and data recovery and demodulation system

The specification discloses a pressure-sensitive transducer including two spaced pressure-sensitive subassemblies having matched parameters and which are electrically coupled together in a manner to minimize the effect of acceleration on the transducer. In one embodiment, each subassembly comprises a pair of piezoelectric crystals attached to opposite sides of a conductive mounting plate. The two plates are supported on opposite sides of an insulated annular spacer ring in a manner to face like poled surfaces of the crystals in the same directions. The crystals are electrically coupled together in parallel by conductors which couple each pair of crystals of a subassembly together and to the mounting plate of the other assembly.

Transducer having enhanced acceleration cancellation characteristics

Methods, systems, and devices for conducting a seismic survey. The system includes at least one seismic sensor configured to supply a signal responsive to reflections of acoustic energy from an earth surface; and at least one processor configured to: mitigate sensor offset from a sequence of samples representative of the signal by filtering the sequence of samples using a symmetrical-in-time finite impulse response (FIR) filter. The FIR filter may approximate a sinc-in-frequency filter. The at least one processor may be configured to process the sequence of samples using a plurality of filter stages that are rectangular in time. The length of one filter stage of the plurality of filter stages may be different than the length of another filter stage of the plurality of filter stages.

Removing offset from seismic signals

The invention discloses a method, system and device used for executing earthquake survey. The system comprises at least an earthquake sensor used for supplying a signal responsing to sound energy reflection from a ground surface, at least a processor. A finite impulse response (FIR) filter symmetrical in time is employed to reduce sensor deviation in a sample sequence representing the signal. The FIR filter is similar to a sinc frequency filter. The at least one processor can be arranged to be a plurality of filters which are rectangular in the usage time to process a sample sequence. The length of one of the plurality of filters can be different from the length of another filter in the plurality of filters.

William T. McDavid

Papers

Carrier and data recovery and demodulation system

Transducer having enhanced acceleration cancellation characteristics

Removing offset from seismic signals

Deviation removal from earthquake