Abstract: The analog signals provided by a seismic-velocity well logger, resulting from the transmission of seismic impulses from a transmitter to a receiver in a logging sonde in a well by paths that include travel through the rock walls of the borehole, are digitally recorded. These seismic impulses and the resulting received seismic signals, or traces, are repeated approximately 20 times per second. The recording apparatus digitizes these analog traces by determining signal amplitudes at intervals of approximately 10 microseconds and temporarily stores the digital values. The apparatus includes a programmable-gain amplifier, an analog-to-digital converter, a computer, and a memory in which are, in addition to the data, also stored the values of gain which are to be used in digitizing the next signal. That is, on each digitizing interval a stored gain "program" is read out of the computer and sets the gain of the amplifier.

Abstract: Seismometer group recorders amplify and make reproducible recordings of one or more seismometers employed in geophysical prospecting. There is no recording of the various groups at the controller instrument truck, as is common in the prior art. The operator needs assurance prior to collecting data through such recorders that the selectively activated group recorders (always considerably less than the total number placed in the field) are ready for the recording. This disclosure describes means for accomplishing such a status display which identifies those group recorders which have been turned on by the radio transmission system or equivalent, verifying that as to each recorder there is available recording medium, proper switching on of the power source, etc.

Abstract: In seismic group recording, each seismic trace is initially digitally recorded by a small, portable, magnetic recorder placed near the corresponding seismometer recorder group. A large number of such groups and corresponding recorders are placed over an area or along a profile line, and from a control point, only those specific recorders needed for a given set of record traces are turned on at any time by transmitting a set of coded signals over a communications link which is usually a radio link. The bandwidth restrictions of licensed geophysical radio channels can cause difficulty in this communications system from control point to the various seismometer groups. Accordingly, this disclosure covers an improvement in the communication method employed in a seismic group recorder system. U.S. Pat. No. 3,806,864 teaches the employment of audio frequency encoding on a frequency-modulated band-limited channel with a maximum audio frequency of approximately 3 kilohertz.

Abstract: Seismic waves are generated by detonating an explosive gas mixture in an earth cavity formed by driving a short earth auger to a desired depth, leaving most of the augered earth in the hole surrounding the auger shaft, and then pulling the auger and shaft upwardly to lift and compress the augered earth and pack it around the auger shaft, thereby forming and sealing the cavity below the auger. The gas mixture is then introduced through the hollow auger shaft and detonated, preferably by ignition propagation through the connecting hose and the auger shaft. Upon completion of as many gas fills and detonations as may be desired, the auger is reversed and withdrawn, leaving the ground surface virtually undisturbed.

Abstract: This is a seismic digital recording system for use where the seismic amplifiers are placed near the geophone locations and their outputs transmitted by common cable to the recording truck or recorded on magnetic tape at the geophone location. In such a digital recording system, it is impractical to use a high-speed, high gain-ranging amplifier of 15 or 16 bits range. In our design the gain-ranging amplifier is high-speed but employs fewer bits total range. The extra range is made up in a preamplifier which has a variable range of gain, which can be automatically set, but at slower speed. The invention involves a control system which is responsive to the output of an A/D converter which is connected to the output of the gain-ranging amplifier.