Abstract: In seismic profiling systems utilizing sweeps of signals which change in repetition frequency during the transmission interval, interference results from a spurious correlation against an interfering sweep, usually produced by the first break reflection of a simultaneously transmitted sweep which is in the opposite sense for 3-D surveying or from another source. The first break interfering sweep repeats while correlating with time slipped replicas in surveying for deeper and deeper reflecting interfaces and appears as correlation sidelobe interference which has a significant contribution to the correlator output only when the interfering sweep and the replica are in a condition where their frequencies are identical or nearly so. This condition is known as stationary phase.

Abstract: A vehicle such as a combine harvester or the like includes a main frame and a first and second undercarriages for supporting the main frame and individually having front and rear wheel assemblies and a track encircling the wheel assemblies. A suspension structure therefore includes a laterally spaced apart pair of pivot joints adjacent the front wheel assemblies for pivotally connecting the undercarriages to the main frame, and a coupling assembly adjacent the rear wheel assemblies for centrally supporting the main frame on the undercarriages. A hydraulic motor powerably rotates each of the rear wheel assemblies and an inside support device is provided therefor that includes a stabilizing beam. The coupling assembly includes an equalizer bar having outer ends, and the stabilizing beam extends rearwardly beyond the driven rear wheel assemblies for connection to the outer ends. Also, an outside support device releasably clamps the rear wheel assemblies to the undercarriages.

Abstract: A transmission from a hydroacoustic source, especially for underwater geophysical exploration, is generated in accordance with two binary codes (provided by two pulse trains or sequences having two levels and which provide a spectrum of harmonically related components). One of these codes has one more or one less harmonic component than the other. The transmission is provided with a frequency spectrum which extends between an upper and lower frequency limit by sweeping the pulse trains over an octave (2:1) frequency range, far shorter than the range of the spectrum, and utilizing one of the codes and then the other of the codes during the sweep. The spectrum of the transmission extends between two arbitrary frequencies which need not be harmonically related, notwithstanding that the sweep is limited to an octave in frequency range.

Abstract: A transmission which requires only a single source to transmit is generated in accordance with a code which is binary (a pulse train having two levels which produces a specific harmonic line spectrum). The pulses are generated by pulse time modulation of the position and duration of pulses in a sweep which extends to the upper end of the spectrum.

Abstract: Movable sensing arrangements are prone to damage, unable to position a load engaging device relative to a load for stacking purposes, and unable to controllably position the sensing arrangement. A movable sensing apparatus having a housing and first and second signaling devices mounted in the housing is provided. A guide rail assembly elevationally movably mounts the housing on a carriage assembly and an actuator controllably elevationally moves the housing along the guide rail assembly. A coupling connects the actuator to the housing and releases the housing from connection with the actuator in response to a force of a preselected magnitude being applied to the housing. Thus, the problems related to damage, stacking, and positioning are reduced. The movable sensing apparatus is particularly suited for use on an automatic guided unmanned vehicle having a lift mast assembly.

Abstract: A seismic array containing a large number of seismic sensors, which may be optical hydrophones, has successive sections, each of which contains a subarray of sensor channels, interconnected by a fiber optic signal transmission line via telemetry modules. Synchronizing signals for initiating successive scans of the sensors in the array and timing the multiplexing of the channels are transmitted along the signal transmission line from the tail end of the line through telemetry modules to the head end. Equipment for receiving, demultiplexing and processing the seismic data is provided at the head end. The array may be towed as a seismic streamer and the head end equipment located topside on the towing vessel. The telemetry modules provide hybrid optical/electrical operation such that array sections including the optical hydrophones and fiber optic links are coupled to each other exclusively by electrical connectors.

Abstract: Time Division Multiplex (TDM) telemetry of submultiplex sequences of signals which may be obtained from successive sections of sensors in a sensor array are transmitted synchronously by locking generators in each section, which determine the time slots in which samples of the sensor signals from each sensor in the array may be transmitted, to successive synchronizing pulses which are generated in the section of the array furthest from the head end of the array where the telemetered signals are received. The synchronizing signals are transmitted once per scan of all of the sensors in the array and phase or time the operation of clock generators and counters which establish the timing so that neither the time slots nor the sensor data signals which are transmitted therein to the collection point at the head end of the array interfere with one another. The sensor array may be a seismic array such as a seismic streamer or spread used in geophysical exploration.

Abstract: An array of optical waveguide transducers, especially suitable for use in a multi-channel hydrophone seismic streamer, contains optical waveguides which are deformed in response to the parameter being sensed (underwater acoustic energy in the case of the seismic streamer). Two optical signals are obtained from each transducer, amplitude modulated in opposite polarity in accordance with the parameter and returned to a collection point by way of optical signal highways, such as optical fiber waveguides. The optical signals are time division multiplexed on the return highways by successively providing light pulses to each of the transducers upon activation of separate light sources associated therewith which are electrically activated by electrical signals propagated along a transmission line wherein the electrical signals are successively delayed.

Abstract: An optical transducer with an optical waveguide having two paths for the propagation of light is deformed in response to acoustical pressure variations or other parameters to be sensed to modulate the amplitude of the light propagated along the two paths in opposite polarities. The light outputs of the two paths are sensed by photodetectors and applied to an electrical differencing circuit. The mean values of the photodetector outputs are balanced as by mechanically providing a predetermined bias deformation of the fiber, or by electrically matching outputs of the detectors such that, on the average, the output of the differencing circuit is zero. Dynamic deformation of the fiber in the transducer results in unbalanced outputs of the photodetectors which unbalance is sensed by the differencing circuit. This differential detection method minimizes optical and mechanical sources of noise in the light source and waveguide and leads to increased signal-to-noise and enhanced dynamic range of the transducer.

Abstract: Quasi periodic pulse trains are generated and swept in repetition frequency over an octave. Spectral harmonics of the pulse trains which prevent the trains from having a constant or "flat" power spectrum over a frequency range much greater than an octave are reduced or eliminated by adjusting the shape of the pulses in the trains. By means of selecting the timing of the pulses, other harmonics are reduced or preferentially augmented. The spectral energy of the signals which are generated during a transmission interval is of the type which possesses an autocorrelation function with a narrow main lobe and low side lobe levels which is especially suitable for echo location purposes such as in geophysical exploration in which seismograms are constructed by cross correlation of the signals which are transmitted with those which are received from the geological reflection surfaces.

Abstract: Methods and apparatus are described for generating and transmitting signals in accordance with a sequence which defines the time relationship of the signals. Each signal has a band width covering several octaves and may be a pulse. During a transmission interval the repetition frequencies of the signals monotonically sweep in a coherent relationship over bands restricted to an octave such that the spectrum of the sequence has substantially constant energy over a frequency range much larger than an octave. The autocorrelation function of the sequence is characterized by an absence of side lobes which would indicate false targets or produce a high noise level upon processing of the signals in an echolocation system, such as a geophysical exploration system in which the seismograms are constructed by cross correlation of the signals which are received from the geological reflection surfaces with a stored replica of the transmitted signals.