Abstract: A system for geophysical exploration uses a single source (30) which emits signals over multiple octaves. The source is driven by a composite sweep signal having two or more sweeps, one of which covers the lower octave (10) while the other sweeps cover the remainder of the bandwidth. The signals covering the lower portion are reduced in the case of a sweep which varies linearly with time in proportion to the square root of the ratio of the sweep rate of the signals covering the upper end to the sweep rate of the signals covering the lower end. The signals are transmitted simultaneously. Because of the composite sweep the same energy spectrum is transmitted as with a sine wave sweep which extends over the entire frequency band, while reducing the peak power and radiator displacement required at lower frequencies to maintain a flat spectrum. The size of the equipment can be reduced.

Abstract: A pneumatic gun having a fast-acting sliding sleeve valve member reciprocating between two axial positions, first to open an exhaust port for the explosive release of gas from a pressurized charge chamber in a stationary housing while simultaneously closing a pressurized intake port to said chamber, and then to close said exhaust port while simultaneously opening said pressurized intake port for recharging said charge chamber, all for the purpose of generating repetitive trains of impulsive sounds at a rapid rate with increased efficiency. The sliding valve member comprises a sleeve and may include a piston in a cylinder within the housing. The sliding valve member has a sealing flange which forms a lip seal with a stationary annular mating surface of the gun to close an exhaust port. A wall of the charge chamber is provided with an intake port in communication with a source of high-pressure gas.