Differential interferometric ballistic gravity measurement apparatus and method

A differential interferometric gravity measurement apparatus for measuring a differential in gravity between a plurality of at least three physically separated locations, said apparatus comprising:

• a gravity sensor located at each physically separated location, each gravity sensor including a test mass selectively moveable into free-fall movement, the characteristics of the free-fall movement of the test mass resulting from the influence of gravity at the location of the gravity sensor;
• each gravity sensor having an input optical beam projecting onto the test mass during free-fall movement, the input optical beam of each gravity sensor being the same as the input optical beam of each other gravity sensor;
• each gravity sensor also developing a response signal related to the reflection of the input optical beam from the test mass during free-fall movement;
• each gravity sensor also including a selectively activatable launch mechanism for the test mass to initiate free-fall movement of the test mass when activated;
• a trigger generator connected to the launch mechanism of each gravity sensor to activate each launch mechanism to cause pairs of the test masses to experience free-fall movement simultaneously;
• and
• a signal processor connected to each gravity sensor and receptive of the response signal to compare the response signals originating from pairs of gravity sensors and to determine the difference in gravity at respectively different physically separated locations of the pair of gravity sensors.

A method of measuring a differential in gravity between a plurality of physically separated locations, comprising the steps of:

• locating a test mass at each physically separated location;
• generating an optical beam having predetermined frequency characteristics from a laser light source;
• positioning the laser light source at a physically separated location from each test mass;
• selectively moving each test mass into free-fall movement, the characteristics of the free-fall movement of each test mass resulting from the influence of gravity at the location of each test mass;
• guiding the optical beam through a fiber optic cable from the laser light source to each location of a test mass;
• projecting the optical beam from the fiber optic cable onto each test mass while in free-fall movement;
• reflecting the optical beam from the test mass during free-fall movement as a response light signal;
• guiding the response signal through a fiber optic cable to a detector;
• creating signals related to the response light signal by operating the detector;
• positioning the detector at a physically separated location from each test mass;
• comparing the signals from the detector which are related to the response light signals from at least one pair of test masses;
• and
• determining the difference in gravity from the comparison of each pair of signals.

A method of measuring a differential in gravity between a plurality of at least three physically separated locations, comprising the steps of:

• locating a test mass at each physically separated location;
• selectively moving pairs of the test masses into simultaneous free-fall movement, the characteristics of the free-fall movement of each test mass resulting from the influence of gravity at the location of each test mass;
• providing an optical beam at each test mass that is the same as the optical beam provided at each other test mass;
• projecting the optical beam onto each test mass while in free-fall movement;
• reflecting the optical beam from each test mass during free-fall movement as a response light signal;
• comparing signals related to the response signals originating from pairs of test masses;
• and
• determining the difference in gravity at respectively different physically separated locations from the comparison of signals from each pair of test masses.