Abstract: A method of estimating the angles of arrival .theta.1 and .theta.2 of two closely spaced radar targets of which one target may be the virtual image of the other target. The targets are illuminated with a radar beam of wavelength WL, and the resulting echos from the targets are received at three directive antennas whose apertures are coplanar and whose phase centers are colinear and spaced a distance D apart. The received echos are converted to complex numbers S1, S2 and S3 representing the magnitude and phase of the respective echos received by the three directive antennas. If the plane of symmetry of the two targets is known, the value of a parameter WD is determined which minimizes L=.vertline.S1-WB(WD+WD*)S2+WB.sup.2 S3.vertline..sup.2, where WB=exp (j2.pi.D.theta.B/WL) and .theta.B is the known angle bisecting the angles of arrival of the two targets. If the plane of symmetry of the two targets is not known, the values of WD and WB are determined by solving for WD and WB which minimize L.

Abstract: A remotely operated downhole switching apparatus, particularly adapted to selectively connect a downhole device such as a sensor circuit to a cable which supplies power to a downhole motor includes a switch for connecting the downhole device to a neutral node of the motor, a latch coil responsive to a latching signal carried by the cable for closing the switch, and a delatch coil connected to the cable through a frequency responsive circuit which is responsive to a delatching signal carried by the cable for passing current through the delatch coil. A diode connected to the delatch coil prevents current flow through the delatch coil in a direction which causes the switch to close. An AC signal may be employed for closing the switch, and a voltage pulse may be employed for opening the switch.

Abstract: The invention concerns a procedure and a circuit arrangement for a coherent, high-resolution pulse radar applicable to distances from several tens of meters down to less than one meter and which evinces at the same time an accuracy in the cm range; the application is in particular to industrial monitoring operations.Two highly stable pulse sequences are generated in the transmitter and differ only slightly with respect to their pulse repetition frequencies. Both sequences are shaped into microwave pulse bundles and one sequence is processed into transmitter pulses, the other sequence being processed into scanning pulses for a time-expansion procedure. Heterodyning with the scanning pulses takes place in the receiver mixer, the result being a combined formation of intermediate-frequency (IF) and time-expansion. In this manner the signal bandwidth is already decreased by the time-expansion factor in the IF part. This is made possible in that coherent phases are used, i.e.

Abstract: The target simulation system includes a reflector 18 located within a closed and shielded room 10. An array 30 of transmitting elements is located within an opening 22 of the room so that the array is centered at a first focal point F.sub.1 of an ellipsoidal reflecting surface 18A of the reflector, and a receiving element of the target seeker 34 to be tested is located within an opening 24 so that the receiving element is centered at a second focal point F.sub.2 of the ellipsoidal reflecting surface. Phased array control system 32 causes the array to simultaneously and independently transmit a plurality of beams of radiation toward the reflector and each transmitted beam results in a corresponding reflected beam whose beam axis passes through the second focal point of the array so that each reflected beam simulates radiation coming from a distinct target. In the case where the radiation is electromagnetic radiation in the MMW range, the phased array control system (FIGS.

Abstract: A method and system for detecting objects having preferential polarization plane reflection characteristics. The method includes the steps of: (a) transmitting from a first given location, a first plane-polarized electromagnetic wave that is oriented in a predetermined reference plane; (b) transmitting from the first given location a second electromagnetic wave having the same frequency and intensity as the first wave and not being oriented in the predetermined reference plane: (c) receiving at a second given location, reflections of the first transmitted wave to provide a first received signal; (d) receiving at the second given location, reflections of the second transmitted wave to provide a second received signal; and (e) comparing the first received signal to the second received signal for detecting an object that preferentially reflects the transmitted radiation in a distinct plane so as to distinguish such object from other objects not having such characteristics.

Abstract: A device for determining the arrival time of a fast or slow rising front pulse is provided comprising a first comparator to which are applied at its inputs a delayed pulse and an attenuated non-delayed pulse, and a second comparator connected in parallel across the first, through an AND logic circuit receiving the pulse applied to the input of the device through a circuit connected to one of its inputs, acting on the noise and/or the signal.This circuit is either a low-pass filter or a divider circuit.

Abstract: An electronic roll-a-long switch for use in a seismic exploration system and method of seismic exploration are disclosed. For a group of N sequentially numbered receiver points, N/2 input channels are provided. Each input channel receives input from one of two receiver points which are spaced N/2 receiver points apart. The input channels are multiplexed to a data bus in an order corresponding to the sequential numbers of the receiver points comprising the input channels.

Abstract: A group-complementary codes provide sets of binary word groups which have the combined properties of optimized aperiodic autocorrelation and optimized cross-correlation between word sets. The optimized aperiodic autocorrelation property allows the implementation of pulse compression processing in sensor systems to achieve zero value temporal or range sidelobes within the principal interpulse period without resorting to weighting techniques for sidelobe reduction. The orthogonal nature of group-complementary codes, apparent from their absence of cross-correlation between sets, allows sensors to be deployed in close proximity, using the same carrier frequency without direct path mutual interference when synchronized.

Abstract: An accurate radio frequency ranging system is provided for measuring the time required for a signal to be transmitted from a ground station to a remote station and to be returned to the ground station. The ground station is provided with a master reference clock that is employed to drive a first pseudonoise generator. The ranging system in the ground station is started by a unique and predetermined start epoch signal produced by the first pseudonoise generator. The first pseudonoise generated signals are transmitted to the remote station where they are tracked and sensed. When the original start epoch signal is sensed at the remote station, it is employed as a trigger or read signal to initiate the generation of a stop epoch signal. The stop epoch signal is retransmitted to the ground station and stored in a register where it is compared with pseudonoise generated signals being retransmitted from the remote station to the ground station.

Abstract: A device for the elimination of n.sup.th trace moving echoes and radar interference echoes in a radar system operating by bursts and comprising a display device for moving targets. The device comprises means for detecting first and n.sup.th trace echoes of which the amplitudes exceed, respectively, two given thresholds S.sub.1 and S.sub.2, and means for comparing these echoes with each other. The device finds particular utilization in a surveillance radar or in a radar landing system operating by pulses.

Abstract: Earthquake simulator making it possible to produce seismic waves and apply them to a sample, wherein it comprises a generator able to produce shock waves, whose frequencies are similar to the shock wave frequencies produced in a natural earthquake, the ratio of similitude being equal to 1/.lambda. in which .lambda. is a positive integer, said generator being formed by a cylinder, sealed at one of its ends by one of the walls of a cell containing the sample and at the other end by a thick wall to which are fixed means making it possible to produce shock waves within the cylinder, said waves being transmitted from the interior of the cylinder to the interior of the cell by means of openings made in the wall of the latter causing movements of the sample similar to those encountered during natural earthquakes.

Abstract: A docking system for positioning a vehicle relative to a selective location employs a baseband communication link between the vehicle and the selected location. Transmitters located at specific points at the selective location are activated upon command from the docking vehicle and synchronized with reference signals radiated therefrom. Time delays between the arrival of each signal radiated by the transmitter and the initiation of a reference signal are determined to establish measures to the different points at the selected location. These measures are then processed to provide relative positioning information.

Abstract: An improved duty cycle controlled filter, wherein a resistance is included in every circuit path that exists between a switch terminal and an amplifier terminal. Such improved filter produces low distortion and has been found to be especially useful in data acquisition circuits of seismic exploration systems.

Abstract: An automatic adaptive sensitivity time control for a ground mapping radar comprises the dynamic range of radar returns for presentation on a video display. A feedback loop including a differential amplifier senses the magnitude of a signal presented to a limit amplifier and compares the same with a clutter threshold reference potential. A low-pass filter in the feedback loop then smooths or averages the clutter deviation from the reference potential to adjust the clutter level out of a log IF amplifier so that the nominal clutter signal level of close-in returns does not exceed a predetermined magnitude. A second embodiment includes a dual time constant filter in the feedback loop. A comparator circuit senses the leading edge of clutter return signals and switches the feedback loop to its faster time constant mode allowing dynamic compression of smaller time constant pulses.

Abstract: A pulse expansion and compression system, especially useful for radar rang, comprising a pulse coder for expanding an input pulse and a pulse compressor of the matched-filter type. The coder consists of a plurality of delay stages into which the input pulse is fed, a discrete Fourier transform (DFT) circuit to which the output signals of the delay stages are fed by way of respective phase weights and for which every other frequency port is inverted prior to entry to a time-dispersion-means (TDM) comprising an arrangement of adders interconnected by delay stages for differently delaying the output signals from the DFT. The adders are connected in N/2-fold cyclically permutated order to the frequency ports, where N is the number of frequency ports if that number is even, and N is the number of frequency ports less one if that number is odd. The TDM output is fed to a phase modulator and then to the transmitter.

Abstract: The present invention relates to a method for initiating an underwater implosive seismic source which comprises the steps of: measuring the instantaneous pressure at the location of the source; determining, from this measured pressure, the bubble period separating the firing signal from the implosion peak of the shock wave; and initiating the source with a delay or advance of a value equal to the difference between the bubble period corresponding to the instantaneous pressure and that corresponding to the mean pressure. The invention also provides a device for carrying out this method which device comprises; means for measuring the instantaneous pressure in the neighborhood of the source; comparator means (C5) for comparing this pressure with a mean value; and time delay means (C3, C4) for delaying a firing signal (S1) by a value which is a function of the result of this comparison.

Abstract: An anechoic chamber utilizes an expanded central area resembling two flared horns with their rims fastened together, with the general vertex area of one of the horns forming the source area of the chamber and the other end the test or receiver end, there being adequate room beneath the two ends to include as part of the chamber rooms outside the chamber shell for housing the transmitter and receiver equipment. The purpose of the flare is to reduce shallow angle incidence on the walls of the chamber to improve performance by decreasing reflectivity.

Abstract: The aftermath of a nuclear explosion generates a large amount of heat or infrared energy. When this heat is received by a parabolic reflector type antenna, the level of heat concentrated on the focal area of the feed is very intense. The present invention utilizes a highly heat conductive ceramic plug between the splash plate at the focal area of the feed and the waveguide so that heat can be readily conducted away from the splash plate and thereby minimize operational destruction of this splash plate due to thermal overload. The heat conductor material is a ceramic which is substantially transparent to RF signals being received by, or transmitted from the waveguide of the antenna system.

Abstract: The invention includes a method and apparatus for detecting geophysical phenomena by the use of a synthetic pulse radar. A radar transmitter generates a plurality of component signals of different frequencies which approximate at least a portion of the Fourier transform of a radar short pulse. These component signals are transmitted simultaneously for modulation by the geophysical phenomena, and the modulated component signals are substantially simultaneously received in a receiver. The receiver divides the component signals, and as to each determines representative parameters. The invention also includes a heterodyne receiver which operates with a fixed IF frequency and incorporates a single frequency quadrature system.

Abstract: Water inflow inside a seismic streamer may create parasitic electric connections between lines supplying current to the electronic devices of the streamer and lines transmitting seismic informations, thus damaging the electronic apparatus and making these informations inaccurate. In accordance with the invention streamer sections including sections of supply lines and transmission lines are provided with water inflow detection assemblies, each comprising a closed circuit element surrounding the supply lines, a conducting line connected to a DC voltage generator, and means for detecting any DC voltage therebetween resulting from parasitic connections between the supply lines and the closed circuit element, created by a water inflow.