Abstract: Inertial measurement system and method in which a gyroscope is periodically dithered about an axis perpendicular to its input axis, a signal from the gyroscope is delayed to provide a delayed signal which lags the gyroscope signal by one-half of the dithering period, and the delayed signal and the signal from the gyroscope are combined to provide an output signal from which the bias has been cancelled.

Abstract: System having one or more inertial sensors in which one or more of the sensor input axes are modulated in orientation about an axis substantially perpendicular to the input, or sensitive, axis of the sensor and, in some embodiments, by also enhancing the accuracy of such a system to provide improved signal to noise ratio and reduced sensitivity to errors in alignment of the sensor axes to the dither axes.

Abstract: Inertial measurement system and method in which a gyroscope is periodically dithered about an axis perpendicular to its input axis, a signal from the gyroscope is delayed to provide a delayed signal which lags the gyroscope signal by one-half of the dithering period, and the delayed signal and the signal from the gyroscope are combined to provide an output signal from which the bias has been cancelled.

Abstract: System having one or more inertial sensors in which one or more of the sensor input axes are modulated in orientation about an axis substantially perpendicular to the input, or sensitive, axis of the sensor and, in some embodiments, by also enhancing the accuracy of such a system to provide improved signal to noise ratio and reduced sensitivity to errors in alignment of the sensor axes to the dither axes.

Abstract: A borehole survey method is provided for processing continuous measurements of the earth's magnetic and gravitational fields obtained while drilling a borehole. The present invention improves borehole acquisition of targeted geological structures by substantially reducing continuous measurement errors attributable to noise, shock and vibrations from turning the drill bit against rock.

Abstract: The invention is, in its various aspects, a method and apparatus useful for strapdown inertial navigation and surveying in a borehole. The method comprises maneuvering a probe including three vibrating mass, Coriolis effect gyroscopes in a borehole and initializing the probe's attitude in the borehole within the probe's frame of reference. Three orthogonal, incremental rotation angles and three orthogonal, incremental velocities are determined for the probe within the probe's frame of reference. The incremental rotation angles are determined from the gyroscopes. The method then translates the three incremental velocities from the probe's frame of reference into the inertial frame of reference using the three incremental rotation angles. Next, a velocity vector in a local-vertical, wander-azimuth frame of reference is determined from the translated incremental velocities. A velocity error observation is then obtained.

Abstract: A borehole survey method is provided for processing continuous measurements of the earth's magnetic and gravitational fields obtained while drilling a borehole. The present invention improves borehole acquisition of targeted geological structures by substantially reducing continuous measurement errors attributable to noise, shock and vibrations from turning the drill bit against rock.

Abstract: A method for calculating a gyroscope survey is disclosed. The method includes measuring outputs of gyroscopes and accelerometers in a survey instrument. An instrument rotational movement is determined from the outputs of the gyroscopes. If the rotational movement exceeds a predetermined threshold, an instrument attitude is calculated from the gyroscope measurements, using the most recent alignment measurement to initialize the attitude measurement. Instrument alignment is calculated from the output of the accelerometers and gyroscopes when the threshold is not exceeded. In one embodiment, alignment is calculated using Kalman filtering. In a particular application, azimuth and inclination of a wellbore are determined at selected positions from the alignment and/or attitude measurements. The wellbore azimuth and inclination are used in one embodiment to calculate the wellbore trajectory along its length.