地电阻率交流观测方法中存在电感性耦合效应,会影响观测值的准确性.理论研究表明电感性耦合效应与供电信号频率、供电线与测量线间距离以及线路间平行走线的长度等条件相关.为了探讨理论研究与实际观测的一致性,在江苏省高邮地电台进行电感性耦合效应对地电阻率交流观测影响研究的实验,实验通过改变观测电极间的布线,分析上述条件对地电阻率交流观测结果的影响.实验结果表明,减小平行长度、增大线间距离、减小供电信号频率均能够减小电感性耦合效应,此结果与理论分析一致.当供电信号频率低于0.5 Hz时,平行长度与线间距离的变化对电感性耦合效应的影响较小,可忽略不计;当供电信号频率大于1 Hz时,为降低电感性耦合效应的影响,需要随供电信号频率增加,减小线间平行长度或增大线间距离.

The AC (Alternating Current) observation method of geoelectrical resistivity can effectively suppress the interference of stray current in the measurement area, such as the subway, light rail and other urban rail transit interference. The inductive coupling effect is a common problem to be solved in the AC observation method. It is caused by the magnetic field interaction between the current circuit and the potential circuit of the observation system and then affects the accuracy of observation. In order to explore the characteristics of inductive coupling effect, an inductive coupling model for AC geoelectrical resistivity observation is built, and the mutual inductance is calculated. On this basis, the effects of electrical frequency, geoelectrical resistivity, distance between circuits, and the length of the parallel segments of two circuits is discussed. The results show that the inductive coupling effect is positively related to electrical frequency and the length of parallel lines. On the contrary, the inductive coupling effect becomes weak as the distance between circuits increases. Besides, there is a peak of the inductive coupling effect as a function of the geoelectrical resistivity. Furthermore, the predicted and observed value of geoelectrical resistivity are compared to verify the model. The model can be used as a theoretical basic to eliminate the inductive coupling effect in practical observations. The conclusion can provide reference for the design and construction of geoelectrical resistivity AC observation system.

在对地铁杂散电流产生机理的讨论的基础上,定量计算了地铁运行时杂散电流在地电阻率观测中所呈现的影响幅度,结果表明地铁杂散电流传播范围可以达到几十甚至上百千米.通过对城市周边的北京通州、天津青光、宝坻、塘沽、江苏江宁和辽宁新城子等六个地电阻率观测台站观测到的该类信号的研究,分析了其幅值、主要频率范围以及空间分布特征,结果表明该类信号的幅值从几mV至几十mV不等,与源距关系密切,周期主要集中在50—200 s范围内,在分析地震异常前兆信号时该类信号可使信噪比降低10—30 dB左右,其相对方差最大超出标准20倍左右.根据地铁运行时杂散电流传播的特征,本文提出了几种压制该类信号的措施,为识别地震前地电阻率异常信息及排除噪声提供依据.

为了更好地开展地震电离层扰动监测和异常信息提取研究,基于空间电离层环境层析成像测量仪研制了地震电离层扰动监测系统,包括小区域监测站网和监测软件系统.?该监测系统产出空间分辨率1°×1°的电离层总电子含量(TEC)、F2层最大电子密度(NmF2)和F2层峰值电子密度对应高度(hmF2)二维分布图,对扰动异常超过10％的事件进行报警提示.?实现了空间电离层层析成像测量仪在地震电离层监测领域的示范应用,并为其进一步推广应用提供了技术基础.

当地电场和地电阻率同场地观测时,地电场观测会受到地电阻率观测的供电干扰,这类干扰时间短、干扰形态和出现时间固定,影响了地电场观测数据的正常变化形态,给数据分析和地震科学研究造成困难。为解决这一干扰问题,本文在比较分形插值方法与传统插值方法优劣的基础上,采用分形插值方法对受干扰的地电场观测数据进行重建,以提高信号重建的精度。结果表明,采用该方法重建的数据是对原数据很好的近似,可有效地恢复观测数据信息,保持观测数据原有的变化趋势。

Using magnetic field data from the China Seismo-Electromagnetic Satellite (CSES) mission, we derive a global geomagnetic field model, which we call the CSES Global Geomagnetic Field Model (CGGM). This model describes the Earth’s magnetic main field and its linear temporal evolution over the time period between March 2018 and September 2019. As the CSES mission was not originally designed for main field modelling, we carefully assess the ability of the CSES orbits and data to provide relevant data for such a purpose. A number of issues are identified, and an appropriate modelling approach is found to mitigate these. The resulting CGGM model appears to be of high enough quality, and it is next used as a parent model to produce a main field model extrapolated to epoch 2020.0, which was eventually submitted on October 1, 2019 as one of the IGRF-13 2020 candidate models. This CGGM candidate model, the first ever produced by a Chinese-led team, is also the only one relying on a data set completely independent from that used by all other candidate models. A successful validation of this candidate model is performed by comparison with the final (now published) IGRF-13 2020 model and all other candidate models. Comparisons of the secular variation predicted by the CGGM parent model with the final IGRF-13 2020–2025 predictive secular variation also reveal a remarkable agreement. This shows that, despite their current limitations, CSES magnetic data can already be used to produce useful IGRF 2020 and 2020–2025 secular variation candidate models to contribute to the official IGRF-13 2020 and predictive secular variation models for the coming 2020–2025 time period. These very encouraging results show that additional efforts to improve the CSES magnetic data quality could make these data very useful for long-term monitoring of the main field and possibly other magnetic field sources, in complement to the data provided by missions such as the ESA Swarm mission.

井下地电阻率观测方法能有效减小和抑制地表干扰因素影响,提高观测精度.近年来,该方法在国内得到了快速发展.但也存在一些需要解决的问题,其中观测装置稳定性就是很重要的一个问题,影响装置稳定性最重要的因素就是外线路绝缘性能.外线路埋设在上百米深的地下,其绝缘性能在长期的观测中可能出现变化,对观测结果造成影响.本文通过理论分析计算,定量给出了井下地电阻率观测中线路绝缘性能对观测结果影响,并据此提出了外线路绝缘的技术要求,为该类台站的设计、建设和运行提供了技术依据.

The correlation and synchronization between ground-based and space-based electric field in calm period, is the basis for a comprehensive study of earthquake monitoring. However, it is difficult to study their relevance because of large dissimilarities on data records. The DC-ULF electric field recorded by the DEMETER satellite and the geo-electric field observed in ground-based stations in China were comprehensively analyzed in this paper. The results show that the ionospheric electric field after removing the additional electric field caused by the satellite motion in the magnetic field has a stable annual variation trend; both the annual variation trend and the amplitude of ionospheric electric field above different locations in China are similar. The synchronous, corresponding and similar significant annual variation trends of both ionospheric electric field and geo-electric field in the same direction and with same frequency were found above some locations. The trend displays higher value in summer and lower value in winter. The Sq (Solar quiet) current system is the main source for these phenomena. It is noticed that the shapes and amplitude of geo-electric field for different stations are different, largely due to their individual underground layer conductivity, water level and so on. It is of great significance to explore the correlation and consistency between ground-based and space-based data in order to recognize the anomalies related to the seismic activity and to understand the LAI (Lithosphere-Atmosphere-Ionosphere) coupling mechanism.

介绍地震地电阻率交流观测的原理及方法、观测系统的要求及主要技术指标,并在受地铁干扰严重的江宁台进行实验观测.初步观测结果表明,该系统观测结果与直流观测结果相当,能满足台站实际观测需求,同时达到抗干扰目的.证明采用交流供电方法进行地电阻率观测,能够在较强干扰背景下获取较高的信噪比,很好地抑制城市地铁、轻轨以及其他因素引起的电磁干扰.

利用2005年1月-2009年12月DEMETER卫星观测的极低频/甚低频(ELF/VLF)40 Hz～6 kHz频段的电场功率谱密度数据,对空间天气平静期间(Dst＞-30 nT,Kp＜3)东北亚地区(105°E-145°E;38°N-58°N)电离层电场背景场变化特征进行统计研究.研究发现夜侧不同年份的相同月份、相同频段的电场分布特征有较高相似度,昼侧相似度不如夜侧;不同年份的相同月份、相同频段昼侧背景场和夜侧背景场强度变化范围均较为一致,从2005年开始东北亚地区的ELF/VLF频段的电场强度呈现逐年递减的趋势;夜侧电场背景场具有季节变化特征:背景场强度变化从强到弱分别是夏季、冬季、春季和秋季,昼侧电场季节变化规律则不明显;电场背景场除371～ 879Hz这个频段外,其他频段夜侧强度均强于昼侧强度.

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The China Seismo-Electromagnetic Satellite (CSES) mission was proposed in 2003 and approved in 2013 after ten years' scientific and engineering demonstrations. To meet the requirement of scientific objectives, the satellite is designed to be in a sunsynchronous orbit with an altitude of 507 km and descending node time of 14:00 LT. The CSES satellite carries 8 instruments, including search-coil magnetometer (SCM), electric field detector (EFD), high precision magnetometer (HPM), GNSS occultation receiver (GOR), plasma analyzer package (PAP), langmuir probe (LAP), high energetic particle package (HEPP) and detector (HEPD), and tri-band beacon (TBB), among which HEPD is provided by Italian Space Agency. The CSES satellite was launched successfully on February 2, 2018, and is planned to operate for 5 years. The CSES mission is the first satellite in China to measure geophysical fields, which will have a lot of application prospects in the study of seismology, geophysics, space sciences, and so on.

With the increased number of low Earth orbit (LEO) satellites equipped with global navigation satellite system (GNSS) receiver, the LEO based GNSS slant total electron content (TEC) and electron density profile (EDP) data play an increasingly important role in space weather and ionospheric research due to improved global coverage. China Seismo-Electromagnetic Satellite (CSES), which was launched in February 2018, is equipped with GNSS receiver for either precise orbit determination (POD) and ionospheric inversion. The purpose of the present paper is to validate CSES GNSS ionospheric inversion technique based on the real observations and verify the accuracy of TEC and EDP retrieval based on the simulated data. The following conclusions can be drawn: the epoch difference inversion (EDI) derived from CSES can successfully retrieve the EDPs without non-occultation side measurements; the technique of EDI and the calibrated TEC inversion (CTI) have similar behaviors in inversion errors, however, the retrieved NmF2 and hmF2 have a larger systematic error surrounding the equatorial ionization anomaly (EIA) where the assumption of spherical symmetry is often invalid; the precision and accuracy of retrieved TEC have been investigated in the paper based on the simulated data, and it is found that the accuracy of the retrieved TEC is relative to solar activity: the lower the F10.7 index, the higher the accuracy of retrieved TEC.

In this paper, we report significant evidence for preseismic ionospheric anomalies in total electron content (TEC) of the global ionosphere map (GIM) and plasma density appearing on day 2 before the 17 July 2006 M7.7 south of Java earthquake. After distinguishing other anomalies related to the geomagnetic activities, we found a temporal precursor around the epicenter on day 2 before the earthquake (15 July 2006), which agrees well with the spatial variations in latitude–longitude–time (LLT) maps. Meanwhile, the sequences of latitude–time–TEC (LTT) plots reveal that the TECs on epicenter side anomalously decrease and lead to an anomalous asymmetric structure with respect to the magnetic equator in the daytime from day 2 before the earthquake. This anomalous asymmetric structure disappears after the earthquake. To further confirm these anomalies, we studied the plasma data from DEMETER satellite in the earthquake preparation zone (2046.4 km in radius) during the period from day 45 before to day 10 after the earthquake, and also found that the densities of both electron and total ion in the daytime significantly increase on day 2 before the earthquake. Very interestingly, O+ density increases significantly and H+ density decreases, while He+ remains relatively stable. These results indicate that there exists a distinct preseismic signal (preseismic ionospheric anomaly) over the epicenter.

Langmuir probe (LP) is a plasma environment detection technology,which is used in a wide range of space-based detection.The LP,as a payload of the China seismo-electromagnetic satellite (CSES),has been designed for in situ measurement of the ionosphere plasma parameters.In this paper,we presented a simplified inversion method of Langmuir probe observation data in the plasma environment,basing on the observation principle of Langmuir probe and the approximate theoretical formula proposed by Irving Langmuir et al.Langmuir probe data tested in plasma chamber is used to verify the method.The results show that the data inversion method is effective and can be used as a basic inversion method of Langmuir probe observation data,which would provide the technical basis for subsequent data processing.

This paper proposes a surface dipole interference model and a location method by dynamic enumeration.This location method adopts interference amplitude and location of different measuring electrodes to calculate location of the dipole source based on a uniform current field and a point source model.And then some simulation results are also presented.Furthermore,taking the test data of artificial interference sources experiment in Gaoyou seismic station as an example,the interference sources are located within 30 meters by this method,verifying the validity and feasibility of the model and the algorithm.The present research will provide an effective method for locating the leakage interference sources around geo-electric observation stations.

Based on the previous research results,we used some statistical methods such as scatter plot,trend line,correlation coefficient and deviation to process the peak electron density (NmF2) data received by COSMIC satellite and SPIDR ground ionosonde.Both total data statistics and classified data statistics by season,local time and latitude are employed in order to carry out the research on quantitative verification on ionospheric structure parameters.The results show that the NmF2 of COSMIC satellite is consistent with the measured value of ionosonde with correlation coefficient 0.95 and average relative difference-3.38％,along with the standard deviation 19.54％.Based on the study,the verification method of NmF2 observed by satellite is given,and the qualitative and quantitative criteria are also provided,which will ensure the quality of NmF2 observed by China Seismo-Electromagnetic Satellite (CSES).