Synthetic vibration isolation system for freefall gravimeter

A computer-implemented method of measuring the acceleration in inertial space of a free-falling mass, the method comprising the steps of:

• measuring, using an axis, a first displacement of a reference device relative to a base during an increment of time;
• measuring, using the axis, a second displacement of a free-falling mass relative to the reference device during the same increment of time;
• filtering the first displacement;
• subtracting, with a processor, the filtered first displacement from the second displacement;
• computing, with the processor, the relative displacement of the falling mass in inertial space and storing the relative displacement and time increment;
• repeating the above steps of measuring, filtering, subtracting, and computing;
• calculating, with the processor, a best-fit estimate of the acceleration of the free-falling mass from the stored relative displacements and time increments made during a single drop;
• repeating the drop and repeating the above steps of measuring, filtering, subtracting, computing, repeating, and calculating;
• and
• calculating, with the processor, an overall acceleration of the mass by averaging the best-fit estimates of the acceleration from all the drops.

A non-transitory computer-readable medium having computer-executable instructions stored thereon for execution by a processor to perform a method of measuring the relative position of a falling mass in inertial space, the method comprising the steps of:

• measuring a first displacement of a reference device relative to a base during an increment of time, wherein the base comprises a retroreflector;
• measuring a second displacement of a free-falling mass relative to the reference device during the same increment of time;
• filtering the first displacement;
• subtracting the filtered first displacement from the second displacement;
• computing the relative displacement of the falling mass in inertial space and storing the relative displacement and time increment;
• repeating the above steps of measuring, filtering, subtracting, and computing;
• calculating a best-fit estimate of the acceleration of the free-falling mass from the stored relative displacements and time increments made during a single drop;
• repeating the drop and repeating the above steps of measuring, filtering, subtracting, computing, repeating, and calculating;
• and
• calculating an overall acceleration of the mass by averaging the best-fit estimates of the acceleration from all the drops.