Measurement and Analysis of Vibration Effect of Free-falling Corner Cube Driving Mechanism in Free Fall Absolute Gravimeter

The vibration interference of the reference corner cube runs through the free flight process of the free-falling corner cube,which is superimposed on the whole laser interference fringes.Thus,it is necessary to solve the interference fringes with the entire fringe to analyze the quantitative influence of vibration on gravity measurements.

First acceptance testing of multiple A10 absolute gravimeters in China and analysis of the comparison results

Three A10 absolute gravimeters(AGs) were first acquired in China by the Hubei Earthquake Agency under the Belt and Road Seismic Monitoring Network Project. Although AG measuring and testing technique is not new, the purchase and simultaneous testing of 3 A10 absolute gravimeters is unprecedented in China. This study conducted the first acceptance testing of the AGs at 3 locations(the Jiufengshan Gravity Observation Station, the Global Navigation Satellite System Observation Station in Wuhan, and the Jiugongshan Observation Station in Xianning). The results were compared using a method based on expert validation, and the acceptance testing scheme was formulated by referring to the Technical Regulations for Tectonic Environment Monitoring Networks in China and Specifications for Gravimetry Control. Based on the repeatability, precision, and consistency of the measured g values, the results from each instrument were evaluated using the air pressure precision test. Comparing the instrument reference values, the final test results can identify the indicator parameters for 3 A10 AGs, the effects of the surrounding environment, and the related parameters on measurement precision. The precision of A10-059, A10-058, and A10-057 exceeded 0.78 μGal, 0.79 μGal, and 0.42 μGal, respectively.This testing scheme can be used as a reference for conducting acceptance testing of AGs in the future and obtaining absolute gravimetric measurements.

Optimal zero-crossing group selection method of the absolute gravimeter based on improved auto-regressive moving average model

An absolute gravimeter is a precision instrument for measuring gravitational acceleration, which plays an important role in earthquake monitoring, crustal deformation, national defense construction, etc. The frequency of laser interference fringes of an absolute gravimeter gradually increases with the fall time. Data are sparse in the early stage and dense in the late stage. The fitting accuracy of gravitational acceleration will be affected by least-squares fitting according to the fixed number of zero-crossing groups. In response to this problem, a method based on Fourier series fitting is proposed in this paper to calculate the zero-crossing point. The whole falling process is divided into five frequency bands using the Hilbert transformation. The multiplicative auto-regressive moving average model is then trained according to the number of optimal zero-crossing groups obtained by the honey badger algorithm. Through this model, the number of optimal zero-crossing groups determined in each segment is predicted by the least-squares fitting. The mean value of gravitational acceleration in each segment is then obtained. The method can improve the accuracy of gravitational measurement by more than 25% compared to the fixed zero-crossing groups method. It provides a new way to improve the measuring accuracy of an absolute gravimeter.

Calibration of a compact absolute atomic gravimeter

Compact atomic gravimeters are the potential next generation precision instruments for gravity survey from fundamental research to broad field applications.We report the calibration results of our home build compact absolute atomic gravimeter USTC-AG02 at Changping Campus,the National Institute of Metrology(NIM),China in January 2019.The sensitivity of the atomic gravimeter reaches 35.5μGal/√Hz(1μGal=1×10-8 m/s2)and its long-term stability reaches 0.8μGal for averaging over 4000 seconds.Considering the statistical uncertainty,the dominant instrumental systematic errors and environmental effects are evaluated and corrected within a total uncertainty(2σ)of 15.3μGal.After compared with the reference g value given by the corner cube gravimeter NIM-3A,the atomic gravimeter USTC-AG02 reaches the degree of equivalence of 3.7μGal.

Movable precision gravimeters based on cold atom interferometry

High precision atom interferometers have shown attractive prospects in laboratory for testing fundamental physics and inertial sensing.Efforts on applying this innovative technology to field applications are also being made intensively.As the manipulation of cold atoms and related matching technologies mature,inertial sensors based on atom interferometry can be adapted to various indoor or mobile platforms.A series of experiments have been conducted and high performance has been achieved.In this paper,we will introduce the principles,the key technologies,and the applications of atom interferometers,and mainly review the recent progress of movable atom gravimeters.

Accurate determination of calibration factor for tidal gravity observation of a GWR-superconducting gravimeter

It is recognized widely nowadays that the superconducting gravimeter (SG) is a kind of best relative gravimeter with high observing precision, good continuity and stability. However, it is necessary to calibrate the direct output (change in voltage) by using scale value (calibration factor) before getting the change of the real gravity field. Studies show that the accuracy of the scale value will influence the late analysis and explanation of the observations. By using absolute gravity measurements of a FG5 absolute gravimeter (AG) at Wuhan international tidal gravity fundamental station (two campaigns each for 3 days) and by using known tidal parameters at the same station, the calibration factors of the SG and their precision are studied in detail in this paper.

Field measurements of absolute gravity in East Antarctica

This paper reports the results of field-based absolute gravity measurements aimed at detecting gravity change and crustal displacement caused by glacial isostatic adjustment. The project was initiated within the framework of the 53rd Japanese Antarctic Research Expedition （JARE53）. Absolute gravity measurements, together with GPS measurements, were planned at several outcrops along the Prince Olav Coast and S6ya Coast of East Antarctica, including at Syowa Station. Since the icebreaker Shirase （AGB 5003） was unable to moor alongside Syowa Station, operations were somewhat restricted during JARE53. However, despite this setback, we were able to complete measurements at two sites： Syowa Station and Langhovde. The absolute gravity value at the Syowa Station IAGBN （A） site, observed using an FG-5 absolute gravimeter （serial number 210; FG-5 #210）, was 982 524 322.7＋0.1 ktGal, and the gravity change rate at the beginning of 2012 was -0.26 gGal.a-1. An absolute gravity value of 982 535 584.2~0.7 ktGal was obtained using a portable A-10 absolute gravimeter （serial number 017; A-10 #017） at the newly located site AGS01 in Langhovde.

Gravity and GPS Measurements at South-West Part of Baikal Rift

Measurements of non-tidal variations of gravity （Ag）, which were obtained from 1992 to 2012 at the Talaya seismic station （located in the south-western part of the Baikal region）, are interpreted together with GPS （Global Position System） observation data, which were obtained from 2000 to 2013 at the same station. An absolute gravimeter was used for gravity observation. The strongest precision requirements concern tidal gravity prediction. It is the reason why we investigated tidal effect by LCR （LaCoste ＆ Romberg） gravimeter from 1996 to 1997 at the same station. We use tested tidal model for correction of gravity change. The linear component of gravity variations corresponds to changes in the elevation of the site. The correlation coefficient is close to the normal value of the vertical gradient of gravity. At this site, coseismic gravity variations at the time of the Kultuk earthquake （August 27, 2008, Mw = 6.5） were caused by a combined effect of the change of the site＇s elevation and deformation of the crust. Our estimations of the coseismic effects are consistent with results obtained by modeling based on the available seismic data.