Abstract: A seismic air gun includes a body, a main chamber, two ports, several air passageways, a shuttle, a return device, and a firing device. The main chamber is within the body. The two ports are in the main chamber. The ports lie along a common axis. The air passageways connect a high pressure air source to the return device, the main chamber, and the firing device. The shuttle slides along the common axis between an open position, in which the main chamber is open, and a closed position, in which the main chamber is closed. The return device biases the shuttle toward the closed position. The firing device causes the shuttle to move from the closed position to the open position whereby pressurized air is released simultaneously from the two ports and in opposite directions.

Abstract: A bus structure for a real-time multiprocessor computing system connects, for example, 16 processors, each having only two bus interfaces, without degrading processor performance or requiring partitioning by application programmers. The processors are divided into groups with each combination of two groups connected together and to memory and peripheral units via a different bus. In a computing system having first, second, third and fourth processor groups and first and second memory groups and peripheral groups, a first bus connects the first and second processor groups together and to first groups of memory and peripheral units, a second bus connects the first and fourth processors together and to second memory and peripheral groups, a third bus connects the second and third processors to the second memory and peripheral groups and a fourth bus connects the third and fourth processor groups to the first memory and peripheral groups.

Abstract: A seismic energy source air gun has a body with an air chamber formed therein that opens 360 degrees around the periphery of the body. A sleeve-type shuttle covers the opening in a pre-fire condition. When the air gun is fired, the shuttle moves rapidly away from the opening providing a large area for compressed air held in the chamber to escape. This very quick release maximizes the acoustic output. The movement of the shuttle is ultimately controlled by a solenoid which, when activated, causes the shuttle to move away from the 360 degree opening and when deactivated permits the shuttle to move back into the pre-fire position over the 360 degree opening.

Abstract: An adaptive filter for enhancing the discrimination of targets from clutter and noise and suitable for use in a pulse doppler radar signal processor which processes successive echo pulse period signalling in accordance with range cell samples is disclosed. One embodiment of the filter has a delayed lattice configuration including a plurality of cascadedly coupled lattice stages, each adapted to operate on the range cell samples of first and second complex signal inputs. The adaptive filter embodiment provides rapid and low cost updating of the lattice stage weighting coefficients so that varying clutter spectrums may be effectively dealt with. Moreover, the lattice filter embodiment is insensitive to average clutter motion and to transmitter phase and gain instabilities. It further permits the use of variable interpulse period operation in radars that are unambiguous in range.

Abstract: Spurious frequencies are eliminated in a direct frequency synthesizer by means of a feed forward correction circuit. The improved direct frequency synthesizer of the invention includes a series adder, clocked register, a D/A converter and a phase corrector. The adder is inputted by a digital control increment and the output of the register. The system clock frequency is divided down by a smoothing counter that in part controls the phase of the output signal. Spurious frequencies are manifested by overflow of the register. The register overflow is converted to an analog signal by the D/A converter. The system output is provided by a voltage controlled oscillator that is controlled by an amplifier which is responsive to both the smoothing counter output and the analog output of the D/A converter. Additionally, the D/A converter is sampled twice for every cycle of output frequency, resulting in a doubling of the output frequency for a given D/A converter.