MICROGRAVIMETER FOR GEOPHYSICAL PROSPECTING

摘要

An apparatus and a method for measuring the gravitational acceleration on the ground, for example adapted to geophysical explorations applied to mining, comprising a base frame (31), a resonator (10) having a first disc of sapphire (2) integral to said base frame (31), an a second disc of sapphire (1) arranged at a minimum distance from said first mass (2) and aligned vertically with respect to said first mass (2) such that said first and said second disc (1 and 2) form a resonator for electromagnetic signals (10); a cantilever arm (41) connected to said base frame (31) and holding resiliently the second disc (1) in order to provide a steady elastic modulus; a magnetic probe (11) for applying an electromagnetic signal to said resonator (10) arranged according to a plane existing between the two discs (1 and 2); a linear electric probe (12), arranged under the fixed disc (2) aligned vertically with respect to its side edge, for measuring a resonance frequency of said resonator responsive to said electromagnetic signal, means for correlating the variation of said resonance frequency to a variation of distance between said discs (1 and 2), and means for correlating the variation of distance to local gravitational acceleration. The support (7) has variable length for adjusting the unexcited distance d between the discs (1 and 2). Preferably, a first (10) and a second resonator are provided as above defined coupled and mounted on two respective base frames integral to each other for measuring the gravitational acceleration gradient in a vertical direction. Furthermore, the resonators are contained in a closed box in which vacuum conditions are created.