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Abstract: Beijing Ming Tombs station is located at the northeast of Deshengkou Village, Ming Tombs Town, Changping District, Beijing. It belongs to Space Environment Exploration Laboratory, Institute of Geology and Geophysics, Chinese Academy of Sciences, and is a member of INTERMAGNET. This dataset contains geomagnetic data observed by the Beijing Ming Tombs station from 1991 to 2001, covering such aspects as magnetic declination, horizontal intensity and vertical intensity. It can be used in research on, for example, geomagnetism, space environment and the interactions between various layers of the Earth.
Keywords: Beijing Ming Tombs; geomagnetic data; magnetic declination; minutely value
|English title||The geomagnetic dataset of Beijing Ming Tombs station (1991 – 2001)|
|Corresponding author||Zhao Xiukuan (email@example.com)|
|Data authors||Zhao Xiukuan, Wu Baoyuan, Ning Baiqi|
|Time range||1991 – 2001|
|Geographical scope||Geographic longitude (116.2°E), Geographic latitude (40.3°N), Geomagnetic latitude (29.5°N), Altitude (183m)|
|Data format||*.MIN||Data volume||401 MB|
|Data service system||<http://www.sciencedb.cn/dataSet/handle/126>|
|Sources of funding||National Natural Science Foundation of China (No. 41374164) and the CAS Key Technology Talent Program|
|Dataset composition||The dataset consists of 11 subsets in total. One .zip file corresponds to one-year data. There are 365 (or 366) data files in each zip file. The size of each file is approximately 103 KB.|
Like air and water, geomagnetic field is one of the indispensable environmental conditions for human survival. Like a natural barrier, the geomagnetic field surrounding the Earth protects the life on Earth from the threat of high temperature, high speed solar winds and the bombardment of cosmic high-energy particles. The geomagnetic field originates from the magnetic fluid process of the outer core of the Earth and the current system of the solar system, so the geomagnetic field carries rich information about the inner and outer spaces of the Earth.1–2
Development of geomagnetism depends on the long-term accumulation of data. Geomagnetism is closely related to national economy and national defense construction. The research outcomes of geomagnetism directly or indirectly serve many fields, including navigation, communication, space environment monitoring, the forecast of natural disasters and climate changes, the exploration of energy and mineral resources, and so forth. A complete high-precision geomagnetic data set not only serves geomagnetism itself, but also provides the basis for research on, for example, seismics, geological structure, deep earth exploration and mineral exploration.3–5
In the study of geomagnetics and geospatial environments, ground station observation plays an important role. Study of the spatial distribution and long-term variation of the main magnetic field of the Earth mainly relies on data from geomagnetic station and geomagnetic complex points. In the study of geomagnetic origin and long-term variations of the main magnetic field, satellite magnetic data still cannot replace ground data. Indeed, studies of the origin of magnetic fields and the internal processes of the Earth have been drawing basic data from over-100-year station observation data, as well as hundreds-of-year sea magnetic data.6–8 With a large number of high-temporal resolution and high-precision geomagnetic data, scientists have made significant progress in sub-storm current systems, ionospheric-magnetospheric coupling and spatial weather forecasting. The long-term historical observation data provide a solid foundation for these studies.8–10 After decades of efforts, China has basically completed a nationwide digital geomagnetic observation network composed by 160 observation stations, which achieved the quasi-real-time transmission and automatic collection of observation data, and a large number of observation data have been accumulated since then.11
Beijing Ming Tombs station (BMT) was established in October 1985 and completed in August 1990. The station belongs to the Institute of Geology and Geophysics, Chinese Academy of Sciences. It is the first observation station entering the International Real-time Magnetic Observatory Network (INTERMAGNET). The station is located at about 600 meters northeast of Deshengkou Village, Changping District, Beijing. The geological base of this station is quartzite and gray matter rock. The magnetic background has a small local anomaly. After the land leveling and reconstruction, the distribution of the geomagnetic field has improved, in which the gradient of the total intensity of the magnetic field in the recording room and its surrounding area is less than 1 nT/m.
The geomagnetic observation room was built above ground. To ensure a stable instrument base, the foundation of external walls and 13 indoor white marble instrument frusta was built using limestone from 4 meters deep. There are three permanent signs in the southwest of the observation room, of which the commonly used standard sign No. 2 is about 700 meters from the observation room and has an azimuth angle of 207º31'50". The geomagnetic recording room is a semi-underground building. Its indoor temperature difference is less than 0.5℃, annual temperature difference about 12℃, and relative humidity less than 70%.12
Raw data observed by the Beijing Ming Tombs station are transmitted to the Data Center of the Space Environment Exploration Laboratory, Institute of Geology and Geophysics, Chinese Academy of Sciences. Based on the raw data, the curves are drawn on server of the Data Center to illustrate the changes of geomagnetic components. The real-time curves are published online by the website of the laboratory (http://space.iggcas.ac.cn). At the beginning of the second year, the automatic observation data of the previous year are processed manually by the laboratory personnel. The processing includes to compare and correct a variety of instrument data, and to calculate the baseline value and scale value using artificial observation data as well. Finally, the IAGA2002 format data are generated and published online through the website of WDC for Geophysics, Beijing (http://wdc.geophys.ac.cn). The flow chart of geomagnetic data processing is shown in Figure 1.
2.1 Data observation
The automatic observation system consists of two sets of quartz photoelectric magnetometers (Figure 2a)① linking to two sets of digital acquisition and recording systems (MD1 and MD2). Three components of geomagnetic ﬁeld D, H, Z are recorded automatically. The manual observation system uses Declination and Inclination Magnetometer (Figure 2b) to measure declination angle D and inclination angle I. The total intensity of geomagnetic field, F, is measured by the Proton Precession Magnetometer.
2.2 Data transmission
Data observed by the Beijing Ming Tombs station are received and stored by the server in the Institute of Geology and Geophysics, CAS.
2.3 Data processing
(1) Baseline value
The absolute values of the three components of geomagnetic ﬁeld D, I, F are observed twice a week. Two groups of data are observed each time, using Declination and Inclination Magnetometer and Proton Precession Magnetometer. The components of geomagnetic ﬁeld H, Z are obtained by the measured value. The baseline value of each component is ascertained by smoothing curve method. Temperature correction is not needed since the baseline value has already considered the impact of temperature on the magnetometer-recorded data.
(2) Scale value
The scale value of each component calibrates plus or minus 30 seconds. The scale value of each component is also ascertained by smoothing curve method.
(3) Final processing
The processing is mainly completed by computer programs. All the data are converted to the standard sign No. 2 at the Beijing Ming Tombs station.
2.4 Data publishing
The real-time curves are published online through the website of the laboratory (http://space.iggcas.ac.cn). At the beginning of the second year, the automatic observation data of the previous year are processed manually by the laboratory personnel. Finally, the IAGA2002 format data are generated and published online through the website of WDC for Geophysics, Beijing (http://wdc.geophys.ac.cn).
3.1 Format description
This dataset uses IAGA2002 format, which is an international data exchange format for geomagnetic data.13 The format is described as follows.
(1) The 12 mandatory file header records: Mandatory header records begin with a space character in Column 1 and end with the vertical bar | (ASCII 124) in Column 70. Content labels begin in Column 2 and descriptions begin in Column 25.
(2) The optional annotation records: Annotation is for recording important information not contained in the defined fields.
(3) The mandatory data header record: The mandatory data-header record contains column headers useful for multi-station analysis. Both the type and order of geomagnetic elements are indicated in the file-header field “Reported”.
(4) The data records: The data records contain the date, time, and magnetic field elements reported. Indicate missing data with 99999 to the corresponding accuracy for a given component (e.g., 99999.0 or 99999.00). If an element is not observed, record 88888 (to the corresponding accuracy) in that field. The format for field elements is 4(1X, F9.2). Each record is exactly 70 characters long plus the machine-dependent carriage return / line feed.
(5) Nomenclature: To facilitate data exchange and recognition, IAGA recommends the following guidelines and style for naming files containing magnetic observatory data. The recommendations closely follow the current International Standards Organization (ISO) Level II recommendations, and are fully compliant with both the Joliette extension to Level II and to the proposed modifications for the ISO standard. These recommendations are for data exchange and do not necessarily apply to data archiving.
3.2 Sample description
The dataset is observed by the Beijing Ming Tombs station. It is consisted by minute values of the three geomagnetic components: declination angle D, horizontal intensity H, and vertical intensity Z. Total intensity F was not observed and its value was set to 88888.00. The missing data recorded 99999.00 to a given component. Figure 3 shows some data samples. Components H, Z and F are in unit of nT, and component D is in unit of minute. Figure 4 shows the changes of the geomagnetic components of this dataset.
Data collection is mainly operated by computer programs automatically, which have been running stably since 1991. To ensure the reliability of the data, the following measures are adopted for quality control.
(1) In order to ensure the time accuracy of the system, the clock of the acquisition system is manually adjusted periodically.
(2) In order to ensure the reliability of data transmission, all uploaded data files are validated against the raw data, and erroneous data are retransmitted.
(3) In order to ensure the quality of data, we use multiple sets of instruments to record, and through the comparison, to eliminate invalid data.
This dataset can be used to study geomagnetic field, space environment and the coupling relationship among various Earth systems. The data set contains minute values whereas the observed raw data contains second values. Raw data can be obtained by contacting the authors.
We would like to thank Chang Shoumin, Xu Tao, Hao Xiqing and Xie Haiyong for their hard work to handle the data.
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Zhao X, Wu B & Ning B. The geomagnetic dataset of Beijing Ming Tombs station (1991 – 2001). Science Data Bank. DOI: 10.11922/sciencedb.126
How to cite this article
Zhao X, Wu B & Ning B. The geomagnetic dataset of Beijing Ming Tombs station (1991 – 2001). China Scientific Data 2 (2017), DOI: 10.11922csdata.170.2016.0074