Abstract: An apparatus (10) for determining while drilling in the earth with a drill bit (12) the positions of seismic wave reflecting geologic formations (15, 17) has seismic wave sensors (A, B) positioned in the earth near its surface (42). The sensors (A, B) are disposed at known positions with respect to the borehole. The drill bit (12) generates the seismic waves. The sensors (A, B) receive the seismic waves both directly and by reflection from the geologic formations (15, 17). Adaptive filters (20, 26) are connected to each of the sensors (A, B). A summing circuit (34) receives outputs from the adaptive filters (20, 26). The converged impulse responses of the adaptive filters provide information about the amplitude of the reflected waves and their arrival times at the surface, thus allowing detection of the reflecting horizons and their location and physical characteristics.

Abstract: A pair of sensitive microphones or transducers are mounted on a user's body, spaced apart by a distance equal to one-half a wavelength of the center frequency of a range of frequencies to be emphasized. By summing the outputs of the two microphones, sound in the broadside or look direction (i.e., the direction the listener faces, the microphones being on a line perpendicular to this direction) are emphasized; sounds in the endfire or side directions are nulled or produce a substantially null response in the region of the center frequency defined by the microphone spacing. A third microphone may be added that is not equally spaced from the microphones on either side, but is spaced to provide half wavelength distances which define maximum and null responses centered at the other points within the frequency range (1-4 KHz) desirable for highly effective hearing. The summed signal from each mircophone pair is bandpass filtered. Three bandpass filters are used.

Abstract: Seismic exploration method and apparatus in which interference signals received by the sensing geophones from the seismic vibration source are cancelled by employing a signal representative of the seismic vibration source and combining it with the output from the sensing geophones.

Abstract: A technique utilizing a combination of adaptive noise cancelling and conventional signal processing is developed to enhance electrocardiographic monitoring in the operating room by reducing the noise interference that is created by an electrosurgical instrument. Significant amounts of interference are eliminated by radio frequency shielding, passive and active lowpass filtering and optical isolation. A digital adaptive canceller using the least-mean-square algorithm is used to reduce the remainder of the interference, yielding an improvement in signal-to-noise ratio of approximately 100 dB.

Abstract: Apparatus for determining the position of a gas-saturated porous rock in the vicinity of a deep borehole in the earth. The apparatus includes a source of seismic waves of selected characteristic, positioned at a selected point in the borehole, with an array of geophones positioned on the earth in known positions around the borehole. These geophones are adapted to receive the seismic waves generated by the source in the borehole, after traveling downwardly through the earth to the formation and reflected from the formation, and to produce corresponding facsimile electrical signals. If the seismic waves from the source in their downward movement impinge upon a gas-saturated porous rock they will reflected, and therefore the signals from the geophones which are in path of the reflected waves will show a change of character. If the reflection is observed while drilling at two or more known depths, the depth, azimuth, and radial position from the borehole of the gas-saturated rock can be determined.

Abstract: Apparatus for determining the position of a gas-saturated porous rock in the vicinity of a deep borehole in the earth, drilled to a selected depth below the expected position of the porous rock. The apparatus includes a source of seismic waves of selected characteristic, positioned at a selected point in the borehole, with an array of geophones positioned on the earth in known positions around the borehole. These geophones are adapted to receive the seismic waves generated by the source in the borehole, after traveling upwardly through the earth, and to produce corresponding facsimile electrical signals. If the seismic waves from the source, in their upward movement to the surface, pass through a gas-saturated porous rock they will be attenuated, and therefore the signals from the geophones which are in the shadow of this gas-saturated rock will show a change of character and/or an attenuation.

Abstract: A correlator which is capable of correlating two or more signals of unknown frequency and bandwidth receives inputs on each of two or more channels. For the case of a two-channel, or pairwise, correlator the two channels are designated a first channel and a second channel. For the pairwise correlator, a first adaptive linear predictive (ALP) filter filters the input signal from the first channel and a second ALP filter filters the input signal from the second channel, the two output signals of the filters being x(k) and y(k). The adaptive linear predictive filter is an adaptive time-domain digital filter which adapts its impulse response according to a certain algorithm. The filter output represents an adaptive linear predictive estimate of the current input value, based on many past inputs. The input signals to the two channels of the pairwise correlator may correspond to sensor outputs from two or more widely separated sensors.

Abstract: An adaptive detector comprises an adaptive linear prediction filter (ALPF) nd a detection processor.The adaptive filter comprises an input filter, adapted to receive an input signal x(k) and delay it by a time .DELTA.. An L-point, or L-tap, adaptive filter has an input connected to the output of the input filter, a signal r(k) appearing at the output of the filter. A means for summing has two inputs, one for receiving the signal x(k) and the other for receiving an inverted signal from the adaptive filter, the output of the summer being an error signal .epsilon.(k). A feedback amplifier, whose input is connected to the output of the summer, takes a portion 2.mu., of the output signal .epsilon.(k) and feeds it back to the adaptive filter, thereby modifying the tap weights of the adaptive filter.The detection processor comprises a circuit, whose input is connected to the output of the adaptive filter, to receive the signal r(k), for performing a K-point discrete Fourier transform (DFT) on the signal r(k).

Abstract: An input signal X(j) is fed directly to the positive port of a summing function and is simultaneously fed through a parallel channel in which it is delayed, and passed through an adaptive linear transversal filter, the output being then subtracted from the instantaneous input signal X(j). The difference, X(j)-Y(j), between these two signals is the error signal .epsilon.(j). .epsilon.(j) is multiplied by a gain .mu. and fed back to the adaptive filter to readjust the weights of the filter. The weights of the filter are readjusted until .epsilon.(j) is minimized according to the recursive algorithm: ##EQU1## where the arrow above a term indicates that the term is a signal vector. Thus, when the means square error is minimized, W.sub.(j+1) =W.sub.(j), and the filter is stabilized.