Development Of High-precision Laser Interference Absolute Gravity Gradiometer

The measurement of Earth gravity gradient(GG)has significance of application on the research of geoscience,earthquake forecasting,resource exploration and high precision inertia guidance systems.The development of gravity gradient measurement devices has been intensively studied in recent years since the idea of a portable gravity gradiometer is put forward by the U.S.air force in 1971 for the first time.However,few of the gravity gradient measurement devices under development in the laboratory has been sufficiently tested for productization.Currently,the rotating accelerometer gravity gradiometer from the Bell Lab in the U.S.is the only commercial gravity gradiometer.However,the measurement of gravity gradient is based on relative gravity values,while there is still not any published research information about absolute gravity gradiometer by other organizations.This paper thus focuses on developing an absolute gravity gradiometer based on the Michelson interference principle.By using the iodine stabilized laser as length measurement inference and the rubidium atomic clock for time measuring inference,the faller path is extracted and reconstructed via digital precise faller servo control and laser interference based faller tracking,obtaining the absolute gravity value.On such basis,a dual faller measuring synchronous servo control mechanism and a dual interference light path in vacuum system are designed to measure the absolute gravity of two fallers at the initial positions of absolute gravity acceleration.The vertical component of gravity gradient is computed by using the finite differentiation method.Primary achievements of the research in this paper are as follows:1)It develops the first laser interference absolute gravity and gradient measurement system in the world that measures the gravity gradient and absolute gravity value in an integrated way,measurement accuracy of absolute gravity value: 4.35?Gal,precision: 3.47?Gal,measured value of the vertical-to-the-earth component of the gravity gradient: 2590 E,precision: 80 E.2)It proposes a gravity gradient value algorithm based on median filtering,improving the precision of gravity gradient value from 80 E to 5E.3)It explores the two-stage feedback vibration isolation technique and guarantees that the uncertainty of the measurement of absolute gravity value to be less than 8?Gal.