Absolute vector gravimeter and methods of measuring an absolute gravity vector

An absolute vector gravimeter for measuring at least one component of a non-ballistic acceleration vector, the absolute vector gravimeter comprising:

• a first single axis gimbal operatively connected to the base;
• a first single axis accelerometer operatively connected to the first single axis gimbal;
• a second single axis gimbal operatively connected to the base;
• a second single axis accelerometer operatively connected to the second single axis gimbal;
• and
• a processor operatively connected to the first single axis gimbal, to the first single axis accelerometer, to the second single axis gimbal, and to the second single axis accelerometer;
• wherein, in response to rotation signals from the processor, the first single axis gimbal is rotatable to at least three different first accelerometer orientations in a first plane;
• wherein the first single axis accelerometer is operable to take a static co-planar measurement at each of the at least three first accelerometer orientations;
• wherein, in response to rotation signals from the processor, the second single axis gimbal is rotatable to at least two different second accelerometer orientations in a second plane;
• wherein the second single axis accelerometer is operable to take a static co-planar measurement at each of the at least two second accelerometer orientations;
• and
• wherein the processor is configured to:
• generate the rotation signals to rotate the first single axis gimbal and the second single axis gimbal;
• calculate a first estimated non-ballistic acceleration vector component along a first in-plane axis in the first plane, a second estimated non-ballistic acceleration vector component along a second in-plane axis in the first plane wherein the second in-plane axis is perpendicular to the first in-plane axis, and an estimated bias in the first single axis accelerometer, using the measurements from the first single axis accelerometer at each of the at least three first accelerometer orientations;
• and
• calculate a third estimated non-ballistic acceleration vector component along a third axis perpendicular to both the first in-plane axis and the second in-plane axis, and an estimated bias in the second single axis accelerometer using the measurements taken by the second single axis accelerometer in the at least two second accelerometer orientations.

A method of measuring at least one component of a non-ballistic acceleration vector comprising:

• i. positioning a first single axis accelerometer pointing in a first direction along a first axis of measurement;
• ii. using the first single axis accelerometer to take a first measurement in the first direction;
• iii. rotating the first single axis accelerometer to point in a second direction, wherein the second direction is oriented at an angle of 180 degrees to the first direction, wherein the first and second directions point in opposite directions along the first axis of measurement;
• iv. using the first single axis accelerometer to take a second measurement in the second direction;
• and
• v. using the first and second measurements to calculate an estimated non-ballistic acceleration component along the first axis of measurement;
• vi. rotating the first single axis accelerometer to point in a third direction along a second axis of measurement, wherein the second axis of measurement is perpendicular to the first axis of measurement;
• vii. using the first single axis accelerometer to take a third measurement in the third direction;
• viii. using the third measurement and the first estimated bias to calculate a second estimated non-ballistic acceleration component along the second axis of measurement;
• ix. pointing a second single axis accelerometer in a fourth direction along a third axis of measurement;
• x. using the second single axis accelerometer to take a fourth measurement in the fourth direction;
• xi. rotating the second single axis accelerometer to point in a fifth direction along the third axis of measurement, wherein the fifth direction is oriented at an angle of 180 degrees to the fourth direction;
• xii. using the second single axis accelerometer to take a fifth measurement in the fifth direction;
• and
• xiii. using the fourth and fifth measurements to calculate a second estimated bias in the second single axis accelerometer and a third estimated non-ballistic acceleration component along the third axis of measurement.

A method of measuring at least one component of a non-ballistic acceleration vector using a processor operatively connected to a first single axis gimbal and a second single axis gimbal, the first single axis gimbal having a first single axis accelerometer mounted thereon and the second single axis gimbal having a second single axis accelerometer mounted thereon, the processor being connected to the first single axis accelerometer by a first hard-wired connection and to the second single axis accelerometer by a second hard-wired connection, the method comprising:

• rotating the first single axis gimbal to slew the first single axis accelerometer to at least three different first accelerometer orientations in a first plane;
• operating the first single axis accelerometer to take a static co-planar measurement at each of the at least three first accelerometer orientations;
• and
• using the measurements from the first single axis accelerometer, calculating a first estimated non-ballistic acceleration component along a first in-plane axis in the first plane, a second estimated non-ballistic acceleration vector component along a second in-plane axis in the first plane wherein the second in-plane axis is perpendicular to the first in-plane axis, and an estimated bias in the first single axis accelerometer;
• rotating the second single axis gimbal to slew the second single axis accelerometer to at least two different second accelerometer orientations in a second plane;
• operating the second single axis accelerometer to take a static co-planar measurement at each of the at least two second accelerometer orientations;
• and
• using the measurements from the second single axis accelerometer in the at least two second accelerometer orientations, calculating a third estimated non-ballistic acceleration component along a third axis perpendicular to both the first in-plane axis and the second in-plane axis, and an estimated bias in the second single axis accelerometer.

An absolute vector gravimeter comprising:

• a base;
• a plurality of single-axis gimbals mounted to the base;
• a plurality of single-axis accelerometers, each single-axis accelerometer mounted on one of the single-axis gimbals in the plurality of single-axis gimbals;
• and
• a processor electrically connected to each single-axis gimbal and each single-axis accelerometer;
• wherein, in response to rotation signals from the processor, each single-axis gimbal is rotatable to point the corresponding single-axis accelerometer in a plurality of directions within a corresponding plane;
• wherein each single-axis accelerometer is operable to take a plurality of static measurements, each static measurement taken when the single-axis accelerometer is pointed in one of the directions in the plurality of directions;
• and
• the processor is configured to:
• generate the rotation signals to rotate each of the single-axis gimbals;
• determine an estimated bias for each of the single-axis accelerometers from the static measurements taken by that single-axis accelerometer when pointed in the plurality of directions;
• and
• determine three perpendicular components of a non-ballistic acceleration vector from the plurality of static measurements taken by the plurality of single-axis accelerometers.