Abstract: This invention concerns a method of making airborne geophysical measurements. Such measurements may be made from fixed or moving wing airplanes or dirigibles. The method comprises the following steps: taking first real time measurements from one, or more, geophysical instruments mounted in an aircraft to produce geophysical data related to the ground below that instrument. Taking second real time measurements from navigation and mapping instruments associated with or carried by the aircraft. Computing a background response of each geophysical instrument using the second real time measurements to take account of its time varying altitude, and the time varying topography of the ground below it. Adjusting an operating or data processing condition of each geophysical instrument using the respective background response and the instrument's attitude to enhance the performance of that instrument.

Abstract: Gravity gradiometers (or gravity gradient instrument, GGI) measure one or more components of the gradient of gravity which is expressed as the gradient of a gravity vector. One or more feedback loops extend from the instrument output to one or more of the accelerometers (1–4) to compensate for errors. The feedback loops include one or more inputs in addition to the instrument output. The additional inputs include signals representing one or more of: components of attitude, velocity and acceleration, the physical environment and flight conditions, taken alone or in combination.

Abstract: This invention concerns gravity gradiometers for airborne surveys for minerals. The gravity gradiometer comprises an inertially stabilized platform, a rotor that is between 0.4 and 1.5 m in diameter mounted in the stabilized platform, and between twelve and seventy two accelerometers arranged in complements of four each on the rotor; and a signal processor operative to: (i) subtract noise calculated from the mass distribution of the aircraft and the inertially stabilised platform, and by the angles of the gimbals of the stabilised platform; (ii) use measures of the accelerations experienced by the gravity gradiometer to estimate the sensitivities of the gravity gradiometer to the acceleration, and use this estimate to correct the gravity gradiometer output; and (iii), use measures of the rotations to which the gravity gradiometer is subjected to calculate the contribution of rotation to the gravity gradiometer noise, and to remove the contribution of rotation to said gravity gradiometer noise.

Abstract: This invention concerns gravity gradiometers for airborne surveys for minerals. The gravity gradiometer comprises an inertially stabilised platform, a rotor that is between 0.4 and 1.5 m in diameter mounted in the stabilised platform, and between twelve and seventy two accelerometers arranged in complements of four each on the rotor; and signal a signal processor operative to: (i) substract noise calculated from the mass distribution of the aircraft and the inertial platform, and by the angles of the gimbals of the stabilised platform; (ii) use measures of the accelerations experienced by the gravity gradiometer to estimate the sensitivities of the gravity gradiometer to the acceleration, and use this estimate to correct the gravity gradiometer output; and (iii), use measures of the rotations to which the gravity gradiometer is subjected to calculate the contribution of rotation to the gravity gradiometer noise, and top remove it.

Abstract: This invention concerns an aircraft equipped for conducting airborne gravity surveys. In another aspect it concerns a process for creating airborne gravity surveys. The aircraft is equipped to perform the method using measured attitude data, laser range data and scan angle data, and aircraft position data.

Abstract: This invention concerns improvements to gravity gradient instruments (GGI) and in particular to the accelerometers that are paired within these instruments. Accelerometers have a proof mass suspended by a spring within a magnetic field. An internal feedback loop provides a signal related to movement of the proof mass back through a reaction coil retaining the proof mass in the magnetic field, to maintain the proof mass stationary. An external feedback loop adjusts the accelerometer scale factor. The internal feedback loop provides second order compensation to the proof mass and the spring stiffness. In a further aspect the invention is a method of matching accelerometer pairs.

Abstract: This invention concerns an aircraft equipped for conducting airborne gravity surveys. In another aspect it concerns a process for creating airborne gravity surveys. The aircraft is equipped to perform the method using measured attitude data, laser range data and scan angle data, and aircraft position data.

Abstract: This invention concerns improvements to gravity gradient instruments (GGI) and in particular to the accelerometers that are paired within these instruments. Accelerometers have a proof mass suspended by a spring within a magnetic field. An internal feedback loop provides a signal related to movement of the proof mass back through a reaction coil retaining the proof mass in the magnetic field, to maintain the proof mass stationary. An external feedback loop adjusts the accelerometer scale factor. The internal feedback loop provides second order compensation to the proof mass and the spring stiffness. In a further aspect the invention is a method of matching accelerometer pairs.

Abstract: This invention concerns improvements in the performance of a mobile gravity gradient instrument (GGI). Gravity gradiometers measure one or more components of the gradient of gravity which is expressed as the gradient of a gravity vector, or in other words a tensor. The instrument comprises a first, second, third and fourth accelerometer equally spaced around the circumference of a circle, with their sensitive axes tangential to the circle, and arranged in opposing pairs with the first accelerometer opposite the second, and the third accelerometer opposite the fourth. In use the accelerometers are spun around an axis normal to the circle which passes through its center. A summing amplifier receives the outputs of the accelerometers and combines them in a manner to cancel the common mode output signals and so produces all instrument output. One or more feedback loops extend from the instrument output to one or more of the accelerometers to compensate for errors.