地磁台网秒采样数据噪声分析及降低方法

中国地震局国家地磁台网共有111套秒采样仪器装备在50个地磁台站以及甘肃天祝、四川西昌、重庆三峡3个磁通门台阵上,主要包括FHDZ-M15地磁总场和分量组合观测系统28套,GM4/GM3型磁通门磁力仪观测系统78套,FGE型磁通门磁力仪观测系统2套,GSM-19FD型磁力仪3套.     

磁通门磁力仪和探头研制的最新进展

磁通门磁力仪重量轻、体积小、电路简单、功耗低、温度范围宽、灵敏度高、稳定性好,可连续读数,可进行任意方向测量,尤其适合在零磁场和弱磁场下应用．所以,磁通门磁力仪在星际磁测、磁法勘探、地磁观测等领域得到了广泛的应用．本文对经典式探头和三端式探头做了深入浅出的论述．     

喀什地磁台数字观测系统性能分析

喀什地磁台目前已配备了两套相对记录仪器与两套绝对观测仪器.为了解不同仪器观测精度的异同,以确定合理的仪器组合方式,本文对比了两套记录仪器观测到的日变形态和极值时间,以及两套绝对观测仪器对相同的相对记录仪器测定的基线值.分析结果表明,FGE磁力仪和Mingeo DIM磁力仪精度较高,可作为第一观测组合,另两套仪器町作为喀什地磁台的第二观测组合.     

磁通门磁力仪探头定向角度与准确度标定分析

乌鲁木齐地震台迁往呼图壁,采用传统方法对地磁仪进行安装调试,对探头不同定向角度下日变化进行准确度标定,每个角度观测一天,持续9小时。因对仪器系统零场漂移值估计不足,探头定向角度范围偏小,建议取值范围±500 nT(约±1°),受绝对观测精度及磁通门磁力仪影响因素的制约,取100 nT作为步长较好。实验认为,定向角度与日变化准确度标定精度无明显统计关系,认为影响磁通门磁力仪数据质量的主要因素是人为影响和仪器自身零场漂移过大。     

氦光泵磁力仪探头设计和环路数字化研究

磁法勘探是一种常用的地球物理勘探方法,其中光泵磁力仪是国内外应用于航空和地面磁法测量最多的磁力仪器.为满足深部矿产资源勘查对高精度磁测设备的需求,本文开展了低噪声、宽量程的高性能数字氦光泵磁力仪关键技术研究,主要包括磁传感器探头优化设计和新型数字化环路设计两方面.首先通过深入分析影响氦光泵磁力仪灵敏度的主要决定因素,对磁传感器关键部件氦灯、氦室进行小型化技术研究,解决高性能氦泵源和原子气室等关键件的制作工艺,提高氦灯效率和氦吸收室的磁共振信号输出强度,制作出高性能、低噪声的小型化氦光泵探头.然后,针对常规模拟跟踪环路的局限性,通过数字化技术研究,采用FPGA、DSP、DDS、环路跟踪算法和信号处理软件等技术构成新型数字环路,弥补现有基于模拟跟踪环路技术的模拟式氦光泵磁力仪的不足,该数字环路降低了氦光泵磁力仪的电路噪声,增强了抗电磁干扰能力,并扩展了磁力仪的量程.本文通过小型探头和数字环路的技术设计,研制出高精度大量程的地面数字氦光泵磁力仪,并用于第三方测试.通过第三方测试证明：实测仪器的静态噪声小于4 pT,磁场测量范围为20000~100000 nT,梯度容限大于10000 nT/m.     

天水台CZM-2型质子磁力仪探头支架的改装实验(摘要)

天水地磁台1986年购置了一台 CZM-2型质子磁力仪,该仪器抗干扰性能好,测程在32,000-70,000nT。他们将该仪器探头用于天水台核旋仪的分量线圈下。因此,对探头支架进行了改装。由于 CZM-2型质子磁力仪的探头外形尺寸为φ112×95mm,重量为2.5kg。CHD-6型核旋分量仪的探头外形尺寸为φ76×85mm,重量为1.1kg。二者相比,CZM-2型质子磁力仪的探头远比核旋分量仪的探头大的多,也重的多,为防止探头支架的底板长期受压变形,而影响     

肇庆地磁台磁通门磁力仪对比分析

对2003年肇庆地磁台GM3和Flare-plus磁通门磁力仪的H、D、Z分量观测数据.进行了趋势变化、均值、方差一致性检验以及基线值分析,认为两台磁力仪的观测数据具有同等观测精度和一致的变化趋势,仅均值存在较小的差别,已达到了国内高精度地磁观测的水平.与英国产的Flare-plus磁力仪相比,国产GM3磁力仪的观测精度和稳定性部分性能已达到世界上高精度数字地磁观测仪器的水平,但仪器的总体稳定性,传感器探头受温度影响的程度、仪器零漂等指标还需进一步提高.     

云南澜沧、耿马地震前地磁变化异常

1988年8月底至9月底,横跨红河断裂布设8个测点进行三分量地磁短周期变化的同步连续观测。测点分布见图1.8个测点是:昆明、玉溪、峨山、杨武、元江、墨江、思茅、景洪。昆明及玉溪测点使用MFM-3磁饱和磁力仪,其它测点使用GM-1磁饱和磁力仪。MFM-3和GM-1仪的仪器噪声水平分别为0.02nT和0.05nT,温度系数均为0.5nT/℃。为了减少温度变化对观测的影响,观测时将仪器探头埋于地下。采取可见曲线记录仪记录地磁变化。H和D变化的记录灵敏度为1.333nT/mm,Z变化的记录灵     

感应式磁探头及数据采集系统的设计

感应式磁力仪是观测变化磁场,特别是地磁脉动的有力工具。它的探头由高导磁合金棒、长螺线管线圈及铝屏蔽筒构成。本文记述了探头的设计,并提出了一种新的标定探头绝对灵敏度的简单方法。此外,本文还将介绍数字化感应仪——智能地磁数据采集装置的研制工作。     

环形芯磁通门磁力仪探头的灵敏度

由高导磁系数的玻莫合金材料做成的环形芯磁通门磁力仪探头,由于它需要的激励功率小,对称性好是一种较理想的探头结构形式。本文从求在外磁场中均匀磁化的球形壳体的内部轨場出发导小了环形芯磁通门磁力仪最大灵敏度公式, Es/H_0=6(2~(1/2)πkNf_Db~2·10~(-8) (伏/奥斯特) 由该公式计算出来的环形芯探头的灵敏度与实验结果进行对比符合较好。由于在公式推导过程中采用了很多近似方法,因而该灵敏度公式只能是一个近似公式。     

磁通门经纬仪磁传感器的研制

结合磁通门地磁经纬仪的观测特点,对磁通门传感器模型进行理论分析,选择具有高磁导率的1J86坡莫合金,和具有相同热膨胀系数、高塑性、较高持久蠕变强度的GH128合金,分别作为磁芯和骨架材料,采用跑道形磁芯结构作为设计磁通门传感器的核心部分.对设计的磁通门传感器进行技术指标测试,结果表明,实验磁通门传感器优于设计要求.     

On-site calibration of air-coil sensor for transient electromagnetic exploration

This paper proposes a time-domain fitting method for on-site calibration of the air-coil sensor. The air-coil sensor has been widely used in transient electromagnetic exploration. Due to limited bandwidth of the coil, the output signal is distorted, causing a phenomenon known as the transition process. To accurately measure the magnetic field from the output signals, the relationship between the coil induced electromotive force and the output voltage must be confirmed by on-site calibration, which requires high calibration accuracy and demands simple operation, portable equipment, and adaptability to the environment. Conventional frequency response methods, however, requires a uniform magnetic field with various frequencies to obtain the frequency response curve of the air-coil sensor. The time to acquire the signal correlates with the number of test frequencies, and the equipment used to generate a uniform magnetic field must be tailored to the shape of the air-coil sensor under test. This paper constructs a relationship between the calibration file and the zero-input response of the air-coil sensor and designs an optimization algorithm to suppress the soil eddy current effect. This on-site calibration method lifts the dependence on the uniform calibration field and reduces significantly the time required for calibration. The calibration source can be generated by cutting off the voltage source in parallel to the calibration coil, which greatly reduces the cost of the signal generator and provides a better solution for realizing the embedded self-test devices. Experimental results show that the proposed method effectively improves the calculation accuracy of the apparent resistivity.     

三轴磁通门探头球型反馈线圈的设计方法研究

长周期大地电磁测量要求三轴磁通门传感器具有低的噪声水平及高稳定性,根据实际需求设计一个尺寸合适的球型反馈线圈可以有效提高反馈磁场的均匀性,进而降低磁通门传感器的噪声水平.本文首先分析了非均匀反馈磁场引入磁通门噪声的机理,然后根据毕奥-萨伐尔定律和矢量叠加原理,以等间距多个单匝线圈构成单轴绕组的形式,建立了球型反馈线圈轴线上的轴向磁场分布及磁场均匀度数学模型,在给定磁场均匀度和球型反馈线圈直径的条件下,运用控制变量法确定了球型反馈线圈的单匝线圈数量和间距等关键结构参数.我们把设计的结构参数代入球型空间磁场分布数学模型,验证了本设计方法的正确性.最后,按照设计的结构参数制作了基于球型反馈线圈磁通门探头的三轴磁通门传感器,通过与体积相近的基于亥姆霍兹型反馈线圈磁通门探头的三轴磁通门传感器对比测试噪声水平,结果表明球型反馈线圈磁通门探头能够使得三轴磁通门传感器具有更稳定和较低的噪声水平.     

基于磁弹效应的索力传感器研究

本文介绍了一种建立在磁弹效应原理基础上的可用来测量钢索轴向拉力的传感器。文中详细阐述了其基本原理,设计了单路磁循环的磁路结构,进行了磁路分析并提出一种电脉冲磁化法的实验装置,给出实验结果。实验结果与理论设计相符,系统稳定可靠。该装置具有可由电池供电、体积小、造价低廉、便于携带的特点。     

Impact of sensor measurement error on sensor positioning in water quality monitoring networks

This paper studies the impact of sensor measurement error on designing a water quality monitoring network for a river system, and shows that robust sensor locations can be obtained when an optimization algorithm is combined with a statistical process control (SPC) method. Specifically, we develop a possible probabilistic model of sensor measurement error and the measurement error model is embedded into a simulation model of a river system. An optimization algorithm is used to find the optimal sensor locations that minimize the expected time until a spill detection in the presence of a constraint on the probability of detecting a spill. The experimental results show that the optimal sensor locations are highly sensitive to the variability of measurement error and false alarm rates are often unacceptably high. An SPC method is useful in finding thresholds that guarantee a false alarm rate no more than a pre-specified target level, and an optimization algorithm combined with the thresholds finds a robust sensor network.     

山区乡村房屋模型洪水冲击试验研究

洪水对山区乡村房屋冲击作用的试验研究成果,可为山区乡村房屋的抗洪设计和抗洪能力评价提供依据。试验主要研究到溃口不同距离处的乡村房屋所受的洪水冲击作用。采用3种开洞率模型进行试验,研究洪水在不同距离、不同开洞率的情况下对房屋结构的冲击荷载分布、冲击力大小以及冲击弯矩的影响,得出了荷载分布规律和冲击力、冲击弯矩的变化规律。研究结果表明,迎水面冲击荷载沿水平方向的变化无明显规律,沿竖直方向随着高度的增大而逐渐减小;冲击力随着房屋到溃口距离的增大而增大,而开洞率对其影响不明显;冲击弯矩、冲击作用力随着距离的增大而增大,随着开洞率的增大而减小。     

三轴磁通门传感器水平和定向对地磁日变化观测数据的影响

针对多套三轴磁通门传感器在同一观测环境下,日变化观测曲线不是完全重合,存在观测数据的不一致性问题,通过理论计算和地磁台站测试实验,分析仪器的定向、底座水平与地磁各分量观测数据之间的变化规律并给出其定量关系.实验结果表明:若存在定向误差角α,则表现为D分量的观测曲线中包含了一定比例的H分量;在水平面内,若存在磁传感器以H分量为轴在ZOD平面内的旋转夹角φ,则表现为D分量的观测曲线中包含了一定比例的Z分量;若存在磁传感器以D分量为轴在ZOH平面内的旋转夹角θ,则表现为H和Z两分量的记录数据中分别包含了一定比例的对方分量成分.      

Coaxial coil towed EMI sensor array for UXO detection and characterization

A new broadband electromagnetic induction (EMI) array sensor, GEM-5, for detecting and characterizing Unexploded Ordnance (UXO) has been developed in order to provide high production rates for EMI surveys. The sensor consists of a single rectangular loop transmitter around a linear array of seven pairs of coaxial receiver coils, with each coil in a pair located at the same vertical distance above and below the loop transmitter. The coil pairs are wired in an inverted series so that the signal consists of the difference between the voltage induced in the upper and lower coils. This particular configuration provides a high degree of primary field cancellation, dense spatial sampling rate due to simultaneous and continuous operation of all sensors, suppression of motion-induced and environmental noise, and strong source fields at typical UXO burial depths providing deep detection range. Our prototype tests indicate that the array yields a lower static and motion-induced noise over the critical low frequencies than that of existing sensors, and in particular, the signal-to-noise ratio at 90 Hz is 32 dB higher. Environmental noise can be largely removed from the difference measurements. The field test results from UXO test sites show that the prototype sensor has smoother background and appears to detect more seeded targets than the GEM-3 concentric sensor, however some of that gain can be attributed to higher power transmitter electronics.     

Portable magnetometer theodolite with fluxgate sensor for earth's magnetic field component measurements

A new portable magnetometer theodolite with fluxgate sensor has been developed for measuring the components of the earth's magnetic field. With this instrument, used as a null detector, it is possible to make absolute measurements of declination (D) and inclination (I). The compensation of the main magnetic field allows direct intensity measurements (H, X, Y, Z components); in this case the calibration is made by reference to a proton magnetometer.The observation procedure is particularly easy and quick. The accuracy is better than 5 sec of arc forD andI and better than 1 nT for direct intensity measurements.     

A theory of pressure sensor performance in snow

A theory of pressure sensor response in snow is derived and used to examine the sources of measurement errors in snow water equivalent (SWE) pressure sensors. Measurement errors in SWE are caused by differences in the compressibility of the pressure sensor and the adjacent snow layer, which produces a shear stress along the perimeter of the sensor. When the temperature at the base of the snow cover equals 0 °C, differences in the snowmelt rate between the snow–SWE sensor interface and the adjacent snow–soil interface may also produce a shear stress along the sensor's perimeter. This shear stress perturbs the pressure field over the sensor, producing SWE measurement errors. Snow creep acts to reduce shear stresses along the SWE sensor's perimeter at a rate that is inversely proportional to the snow viscosity. For sustained periods of differential snowmelt, a difference in the mass of snow over the sensor compared with the surrounding soil will develop, producing additional permanent errors in SWE measurements. The theory indicates that SWE pressure sensor performance can be improved by designing a sensor with a high Young's modulus (low compressibility), low aspect ratio, large diameter and thermal properties that match those of the surrounding soil. Simulations of SWE pressure sensor errors using the theory are in close agreement with observed errors and may provide a means to correct historical SWE measurements for use in hydrological hindcast or climate studies. Published in 2003 by John Wiley & Sons, Ltd.