A Vertical Seismometer With Built-In Retroreflector for Absolute Gravimetry

Classical absolute gravimeters are widely used in many areas, including metrology, seismology, geophysics, and exploration. These gravimeters apply a free-fall method to measure absolute gravitational acceleration using a laser interferometer. In practice, the measurement precision is affected by ground vibrations. Vibration correction is an important way to deal with these ground vibrations for absolute gravity measurement. Most vibration correction methods use a commercial seismometer to measure the motion of a reference retroreflector indirectly. A vertical seismometer with a built-in retroreflector is designed to directly measure the motion of the retroreflector, which is fixed on the proof mass of the seismometer. The motion of the retroreflector relative to the ground vibration is measured through capacitance detection. A voice coil actuator is employed to drive the retroreflector to track the ground vibration. The sensitivity of the homemade vertical seismometer is approximately 15751 V/g. The bandwidth of the system is 80 Hz. The homemade vertical seismometer is integrated into the homemade T-1 absolute gravimeter to test its performance. The standard deviation of the measurement results is reduced by a factor of 16, when compared with the results obtained without any vibration treatment. Absolute gravimeters with the homemade vertical seismometer are expected to be used in field measurements.