GS-15型重力仪记录比值的标定

昆明台对 GS-15型重力仪在自动记录时测定记录比值的方法有二个步骤:第一,用拉读数弹簧的方法求出仪器输出的电讯号与重力值的关系;第二,输入一个直流电讯号给记录器,求出记录器上的单位长度与电讯号的关系。再通过这二个关系,求得记录器上单位长度所表示的重力值——记录比值。 记录比值标定的要求 地震观测系统中,GS-15型重力仪所观测到的资料,一是利用重力值随时间的变化来研究它与地震的关系,二是利用来研究重力固体     

重力仪高频信息和地脉动的观测研究

本文介绍了应用电磁反馈零位检测技术改装的重力仪进行高频信息的观测。阐述重力仪高频信息频谱分布特征、数据采集、数字计算和随机信息的处理方法。利用高频信息可以很好地观测和研究地脉动,给出北京香山地震台利用重力仪高频信息观测所得的地脉动功率谱。分析了地脉动特征及其与台风过程的关系;讨论了某些大地震前所出现的地脉动异常现象。得出北京地区正常地脉动频率分布范围为0.13-0.32Hz,优势频率为0.2Hz,相应的卓越周期为5s的脉动频率异常,也可能在地脉动的正常频率处（0.2Hz左右）,出现幅度很大的脉动幅度异常,后者又往往与台风引起的幅度异常相混淆。     

新疆数字化重力观测台站的场地勘选、建设、运行及其资料评价

简要介绍了新疆数字化重力台站的勘选和建设情况,建成后的台站完全达到了设计目标,取得了令人满意的观测结果.GS-15型重力仪的改造是成功的,但气压干扰问题有待进一步解决.PET潮汐重力仪的性能优良,潮汐分析的精度≤0.001.     

利用重复测线校正海空重力仪格值及试验验证

通过分析海空重力测量系统误差的形成机理,我们发现海空重力仪格值标定误差是引起系统性测量偏差的主要因素之一.本文简要介绍了重力仪格值的标定方法,分析论证了格值标定的精度要求,提出了利用东西正反向重复测线检测校正海空重力仪格值的计算模型和补偿方法,分析讨论了该方法的校正精度及其适用条件,利用航空重力实际观测网数据对该方法的合理性和有效性进行了数值验证,证明该方法对消除海空重力测量系统性偏差具有显著作用.     

LaCoste&Romberg航空重力仪K因子的动态标定及其特性研究

摆杆尺度因子(K因子)是反映LaCoste&Romberg航空重力仪线性响应特性的最重要参数.利用基于地面参考数据的外部标定法和基于交叉点不符值的内部标定法分别对其进行了标定,实测数据分析表明,K因子的内、外部标定结果非常一致,且利用新K因子计算的空中重力扰动,其精度较采用出厂值提高了0.2～0.4 mGal.内部标定法具有较好的实际应用价值.研究了K因子与滤波尺度的相关性,表明重力仪可能为一非线性响应系统,即K因子的大小与摆杆速度的变化有关.     

数字重力仪高精度恒温测温系统设计与测试研究

高精度数字重力仪广泛应用于矿产资源勘探领域,由石英弹性系统组成的重力传感器是高精度数字重力仪的核心部件,其对外界环境温度非常敏感,由环境温度变化引起的重力输出变化远远大于仪器本身精度指标,而且不同的数字重力仪具有不同的温度影响特性.若重力传感器的恒温环境得不到保障,或环境温度的微弱变化无法得到准确的测量和补偿,将严重影响重力仪器的测量精度和一致性.本文针对该问题,研究了高精度恒温测温系统的设计方法及关键技术,考虑到数字重力仪器精度高、体积小、功耗低和便携式的特点,对高精度恒温测温系统中的关键器件选型、热结构设计、电路设计、软件设计等进行深入研究,并给出具体的解决措施.并设计了静态试验、高低温试验和石英弹性系统温度系数测定试验三个部分验证高精度恒温测温系统的有效性.试验结果表明：高精度测温系统最小分辨率达到10 μ℃;静态常温时,高精度恒温系统温度变化约为70 μ℃;在-20℃~+45℃的环境温度冲击中高精度恒温系统温度变化小于1 m℃;恒温点微调装置可实现石英弹性系统温度系数的精确测定.该研究为高精度重力测量仪器研制中消除环境温度变化影响提供了一种有效解决方案.     

石英弹簧重力仪温度曲线特征的研究

从大量重力测量资料研究中,发现温度变化对重力测量精度的影响很大,尤其在面积较大的范围中进行重力测量,环境温度差异大,温度对重力仪的影响更为复杂。在目前高精度重力仪数量尚不能满足需要的情况下,提高石英弹簧重力仪的测量精度是十分必要的。为此,我们在1982年与有关厂家协作,制成了一台半导体制冷、制热重力仪温度测试装置,用以模拟野外工作环境温度变化。从1983年7月至1984年4月我们用该装置对列入国家地震局“清理攻关项目”的六台CG-2型,一台ZSM型和十六台Worden型石英弹簧重力仪进行了系统的温度测试。参加测试的仪器型号见下表     

速度传感反馈地震计的参数稳定性分析

从理论上定量分析机械摆和环路滤波等开环诸参数变化对速度传感反馈地震计闭环参数的影响.研究指出,在环路设计中可半自由选取的开环阻尼取值对参数稳定性有重要影响.过大或过小的开环阻尼取值均可能造成参数稳定性急剧变差,影响地震计在只标不调的状况下长期连续稳定工作.     

2016年广西苍梧MS 5.4地震前华南地区连续重力扰动异常分析

收集华南地区8个重力台站gPhone/PET相对重力仪观测原始秒数据,对记录的2016年广西苍梧M_S 5.4地震前4天重力原始秒数据,分别进行原始数据分析、0.01 Hz高通滤波和0.125-0.25 Hz带宽滤波,结果表明,震前4天8个重力台站数据均存在扰动异常,结合地震前后台风活动情况,分析认为,该扰动异常系台风"银河"和"妮妲"活动引起,非地震前兆异常。     

重力测量国际进展

在大地测量、地球物理学、地质学、计量领域中,对精确且可溯源的绝对重力测量的需求不断增加.重力测量的国际组织相继建立,组织国际绝对重力仪比对和区域性比对,推动重力测量的不断发展.本文介绍了历届国际组织的联席会议和国际绝对重力仪比对情况.     

拉科斯特重力仪干扰因素分析

本文根据多年重力监测工作情况，结合拉科斯特重力仪的结构特点，对仪器在观测中的干扰因素进行分析，认为影响仪器观测精度的干扰因素有两类：一类是仪器本身产生的系统误差，如格值误差、零飘及弹性后效等；另一类是外界干扰因素，如振动、温度、人为观测方法不当等，如果在观测中能消除或减小这些干扰因素影响，拉科斯特重力仪就可能达到更高的观测精度。     

The effect of the magnetic field on the accuracy of measurements with Worden and Sharpe gravity meters

Summary The effect of an additional homogeneous magnetic field with an intensity of 0–4.5 Oe on the Worden quartz gravity meter No. 961 and on Sharpe quartz gravity meters Nos 173 and 174 was tested. Whereas no effect was observed with the Worden gravity meter, the magnetic field had a measurable effect on both the Sharpe gravity meters. The largest deviation of the reading beam is caused by the horizontal component of the magnetic field which acts in the plane of oscillation of the gravity-meter arm. The Sharpe gravity meter No. 173 is considerably sensitive; a field of 0.2 Oe intensity, corresponding to the magnitude of the horizontal component of the geomagnetic field in mid-latitudes, causes an error in the measurement of gravity of as much as 0.08 mGal. With a view to the different behaviours of the individual quartz gravity meters of the same type in a magnetic field, it should prove expedient to carry out check measurements with all gravity meters and, with regard to the sensitivity of the gravity meter to the magnetic field and the required accuracy of the gravity determination, take into account this perturbing factor in field measurements, as well as laboratory tests of gravity meters.     

速度传感反馈地震计的环路噪声输出传递特性分析

反馈地震计自身的噪声输出决定了它的动态范围下限.反馈地震计的噪声主要由反馈环内有源器件产生.速度传感反馈地震计的环路参数和滤波类型将会影响环内不同位置的噪声输出传递函数.本文分析了4种一阶环路滤波器和零阶环路滤波器对环内噪声传递函数的影响,开环阻尼D1较小的一阶极点高通、一阶零点高通和双一阶环路滤波在抑制前向通道噪声输出方面具有潜力;一阶极点高通在抑制反向通道低端带外噪声输出方面有较好的性能.     

IMPROVEMENT OF OBSERVATION ACCURACY OF THE LACOSTE-ROMBERG (MODEL D) GRAVITY METER BY SUPPLEMENTARY INSTALLATION OF ELECTRONIC FEEDBACK1

Recent years have seen an increasing need for high-precision gravity meters. A widely used and the most accurate one is the LaCoste-Romberg, model D (LCR-D) meter, equipped with electronic readout. According to the manual the reading accuracy is 5 μGal. A way of reducing most of the instrumental factors limiting the accuracy is the use of an electronic feedback system. We have fitted the LCR-D 34 with a Schnüll-Röder-Wenzel, model D (SRW-D) feedback. After installation the readout voltage was calibrated, the instrumental behaviour tested, and the accuracy of the system determined. By repeat readings in the laboratory without moving the meter, the standard deviation for a single reading is better than 4 μGal in normal mode and better than 1 μGal in feedback mode. The accuracy of gravity differences - this is usually observed in field practice - is the mean value of the repeat errors of several sets of differences observed in a short time to avoid any corrections. This accuracy is better than 9 μGal in normal mode and better than 5 μGal in feedback mode. With this, the accuracy of a single reading becomes more than 6 μGal and more than 3 μGal, respectively. As the described improvement of accuracy was found to be not as good as expected, additional improvements should centre on the use of electronic levels instead of the standard liquid ones.     

CS3301在长周期大地电磁测深仪中的应用研究

大地电磁测深是研究地壳和上地幔构造的一种重要的地球物理探测方法,当前国家正在实施深部探测专项SinoProbe等项目,故需要借助于长周期大地电磁测深仪器.我国没有自己生产的长周期大地电磁测深仪器,只能依靠从乌克兰进口的LEMI-417进行深部探测.在LEMI-417使用中,我们从该仪器提供的数据文件Final.asc中发现它的电场信号测量分辨率为0.01 mV/km,磁场信号测量分辨率为0.01 nT,相对较低,此外,该仪器在无GPS信号时会出现记录紊乱等现象,故需要设计适合课题组需要的长周期大地电磁测深仪器.由于大地电磁测深仪器需要采集的电场、磁场信号为微弱信号,容易淹没于噪声之中,故选用了低噪声、极小总谐波失真率的CS3301作为运算放大器.CS3301提供了4种可选择的信号输入模式和7种可选增益,经分析与测试,测量电场信号时,CS3301设置为输入模式1及×64增益,当极距100 M时,测量精度可达0.001 mV/km,高于LEMI-417的0.01 mV/km;测量磁场信号时,将反馈理论用于测量电路,CS3301设置为输入模式3及×64增益,只对信号的可变部分进行放大,精度可达0.006 nT,高于LEMI-417的0.01 nT.该系统在华南的9005、1005等多个测点以及东北的1600、5105等多个测点进行了测试,并与LEMI-417进行了对比试验,测量结果表明它们的时间序列曲线比较一致,数据处理后,在同一测点得到的大地电磁测深曲线也较一致,说明设计的仪器达到了预期目标.     

RECENT DEVELOPMENTS IN UNDERGROUND GRAVITY SURVEYS1

Underground gravity observations in deep coal mines using the conventional gravity meters Worden (type Master) and LaCoste-Romberg (model D), both of which have been adapted to the fire damp regulations, can be accurate to ± 10 and ± 3 μgal, respectively. For underground determination of the vertical gradient of gravity the LaCoste-Romberg meter is used together with a specially designed measuring tower. Using this euipment an accuracy in tower gradient observations of ± 30 E was obtained. To apply the equipment to precision gravity observations in underground situations an additional correction, i.e. a gallery correction, is needed. High accuracy in correction is achieved by a new method of three-dimensional modelling. The gravity effect is computed for bodies with a surface approximated by triangular elements, which are generated from corner points of the body. The combination of gallery correction with tower gradient data leads to a new method for in situ density determination. It offers the possibility of horizontal instead of vertical density profiling. To demonstrate the effectiveness of the developments in underground observations the localization of a pump room is presented. Microgravity and tower gradient observations were carried out to detect the cavity. The horizontal gradient was also calculated to give a more reliable location.     

固定翼航空电磁系统的线圈姿态及吊舱摆动影响研究与校正

固定翼时间域航空电磁探测系统在实际飞行测量过程中,发射线圈、接收线圈姿态和吊舱摆动状态不断变化,在测量数据中引入如发射磁矩方向、接收分量方向以及系统收发距等参数的误差,影响数据反演成像效果.本文基于固定翼时间域航空电磁正演理论,利用姿态变换,引入发射线圈、接收线圈双旋转矩阵;根据发射、接收线圈相对位置的几何关系,求得摆动格林张量;推导了任意姿态角度以及任意摆动角度情况下的固定翼航空电磁响应三分量计算表达式.通过层状大地模型的仿真计算,分别研究了发射、接收线圈各姿态以及吊舱摆动状态对航空电磁响应的影响,得出发射线圈、接收线圈俯仰旋转和吊舱同向摆动对系统电磁响应影响最强;仿真分析了实际测量中,三种角度同时存在情况下,航空电磁响应的定量变化规律.在此基础上,讨论了响应系数与大地电导率的关系,同时给出基于响应系数的固定翼航空电磁系统线圈姿态和摆动状态校正方法,准二维层状大地模型反演结果表明,校正后数据的反演精度提高了33.1%.     

Magnetic Field Feedback Circuit for Geomagnetic Field Compensation Control

In the current state of geomagnetic instrument testing, some aspects of geomagnetic instrument performance are difficult to test in the laboratory. If laboratory test results are inadequate, the instrument will have multiple problems while operating in the field, where a geomagnetic instrumentation test platform with a stable natural magnetic field is critical. Here, the magnetic field feedback circuit for geomagnetic field compensation control is studied in detail. That is, the magnetic field measured by the feedback magnetic sensor and the required working magnetic field are compared as input to the system, and the electric signal is transmitted to the feedback coil through an analog circuit to form a closed loop control, which provides compensation to control the magnetic field. Compared with the existing magnetic shielding method, the analog control circuit can achieve the realization of any working magnetic field, and it is not limited to a null magnetic field. The experimental result shows that the system compensates the earth''s magnetic field of 10,000nT with an average error of 10.6nT and average compensation error of 0.106%, providing a high compensation accuracy. The system also shows high sensitivity and excellent stability. The feedback circuit has achieved effective compensation control for the earth''s magnetic field.     

Tilt effects on GWR superconducting gravimeters

The superconducting gravimeters (SGs) are the most sensitive and stable gravity sensors currently available. The low drift and high sensitivity of these instruments allow to investigate several geophysical phenomena inducing small- and long-period gravity changes. In order to study such topics, any kind of disturbance of instrumental origin has to be identified and possibly modelled. A critical point in gravity measurement is the alignment of the gravimeter to the local vertical. In fact a tilt of the instrument will lead to an apparent gravity change and can affect the instrumental drift. To avoid these drawbacks, SGs are provided with an “active tilt feedback system” (ATFS) designed to keep the meter aligned to the vertical. We analyse tilt and environmental parameters collected near Strasbourg, France, since 1997 to study the source of the tilt changes and check the capability of the ATFS to compensate them. We also present the outcomes of a calibration test applied to the ATFS output to convert the Tilt Power signals into angles. We find that most of the observed signal has a thermal origin dominated by a strong annual component of about 200 μrad. Nevertheless, our analysis shows that even the tilt due to different geophysical phenomena, other than the thermal ones, can be detected. A clear tidal signal of about 0.05 μrad is detectable thanks to the large data stacking (>11 years). We conclude that (i) the ATFS device compensates the tilt having a thermal origin or coming from any sources and (ii) no significant tilt changes alter the gravity signal, except for the high frequency (>1 mHz) perturbations.     

速度传感反馈地震计的动态范围上限

在开环参数一定的条件下,速度传感反馈地震计中的环路滤波是影响地震计主要技术指标的关键环节之一.本文探讨了一阶极点高通、一阶极点低通、一阶零点高通、双一阶和零阶环路滤波在扩展地震计动态范围上限方面的优缺点.研究指出,对于用闭环反馈直接生成主导二阶极点的速度传感反馈地震计,一阶零点高通环路滤波的优点较多;若允许在环外生成主导二阶极点,则零阶环路滤波也不失为一个较好的方案.