RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 10, ES3007, doi:10.2205/2007ES000227, 2008

Geophysical Observations in Borok Geophysical Observatory

Geomagnetic Field Observations

[13]  One of the most advanced directions of geophysical researches is observation of the Earth magnetic field. The geophysical observatory can be considered like magnetic if there are carried out long-term continuous observations of geomagnetic field variations, regular absolute measurements, processing and analysis of raw data. Continuous digital registration of geomagnetic field in the wide frequency range with data presentation in absolute physical scales and exact absolute time is carried out on modern magnetic observatories. Daily files of geomagnetic field variations, presented as digital amplitude-time series adjusted by the results of absolute measurements, are formed. The modern level of measuring equipment, digital technologies and satellite systems of global positioning allows making accuracy of the main geomagnetic field measurement about 1 nT.

[14]  The middle-latitude Borok Geophysical Observatory observations include digital registration of three components of geomagnetic field, absolute measurements, geomagnetic field variations, ultra low frequency geomagnetic pulsations. The geographic location of the observatory, the geomagnetic field registration received continuously within several decades, a low level of electromagnetic noise result in geomagnetic data usage by Russian and foreign geophysicists.

[15]  Geomagnetic field on Borok Geophysical Observatory are registered within the framework of international program INTERMAGNET (http//www.intermagnet.org). The observatory acts in the global network of digital magnetic observatories INTERMAGNET according to rules and standards of global network of geomagnetic observations [St-Louis, 2007]. The measuring equipment includes scalar and vector magnetometers and devices for absolute measurements, including the precision proton magnetometer and Declination/Inclination fluxgate-magnetometer.

[16]  Scalar proton magnetometer SM-90R (produced by GEOMAG, France) measures total magnetic field and has the following basic characteristics:

[17]  Vector three-component fluxgate-magnetometer VM-391 (produced by IPGP, France) measures three components of magnetic field and has the following basic characteristics:

[18]  Absolute measurements of a geomagnetic field are carried out by portable single-axis fluxgate vector magnetometer, type Mag-01H, installed on the steel-free Zeiss theodolite. Magnetometer Mag-01H (produced by Bartington Instruments), provides precision measurements of the direction and intensity of static and slowly varying magnetic fields from 0.1 nT to 2 mT with 0.1 nT resolution.

[19]  The geomagnetic field variations are registered by the fluxgate-magnetometer of SAMNET network (http://www.dcs.lancs.ac.uk/iono/samnet/). The fluxgate-magnetometer measures three components of magnetic field with 1 s sampling rate and 0.1 nT resolution.

[20]  Ultralow-frequency geomagnetic field pulsations are registered by the induction magnetometers, produced in the Geoelectromagnetic Monitoring Laboratory of Borok Geophysical Observatory (http://borok.adm.yar.ru/gemm/index.html).

[21]  The magnetometers include induction sensors with permalloy cores, measuring amplifiers and blocks of filters. The linear frequency characteristic of magnetic sensors allows expanding a dynamic range of measurements owing to indemnification of spectral heterogeneity and a wide range of changes of amplitudes of geomagnetic pulsations. Transfer factor of the active induction sensor is about 1 V/(nT Hz) with the built-in amplifier. The basic characteristics of induction magnetometers are

Telluric and Air Electricity Measurements

[22]  Measurements of telluric currents are necessary to study the structure of ULF geomagnetic pulsations, to produce remote diagnostics of magnetosphere plasmas, to research magnetosphere resonant features, to design the methods for the electromagnetic forecast of the abnormal geophysical phenomena, to develop methods of magneto-telluric sounding. High-sensitive, precision and noise stable equipment is used to measure the telluric currents.

[23]  Variable part of the potential difference between the fixed points of ground surface is measured by pairs of lead electrodes, located along the magnetic meridian, along the magnetic parallel and vertically. Observable components of telluric electric field are determined from the potential difference between the corresponding pair of the electrodes referred to the fixed distance between them.

[24]  The main difficulty of registration of telluric currents consists in maintenance of the high noise stability of the equipment. Authentic results are guaranteed by installation of electrodes in region with a very small industrial electromagnetic noise level, far from power plants, the mass transit electrified lines and large towns. Thus the magneto-telluric measuring complex should be installed in areas with a homogeneous geological and geoelectric structure, and also with a quiet relief. The territory near location of Borok Geophysical Observatory completely meets the specified requirements.

[25]  The lead sheets, used as electrodes for measurement of telluric current horizontal components, are buried on depth 1.0 m with distance between electrodes 300 m. Electrodes for measurement of telluric current vertical component are located in the vertical hole with 400 m depth.

[26]  To suppress the in phase noise in the measuring channel of telluric currents the symmetric circuit with a differential input is used. Technical parameters of the measuring equipment are

[27]  The atmospheric electric field is measured by electrostatic fluxmeter (field-mill), convert constant or slowly varying electric field to the variable one by means of periodic screening of measuring electrodes by rotated and grounded screen. The field-mill, installed in the observatory measuring complex, has been designed specially for long continuous observations. The field-mill design provides the constant exposed area of measuring electrode and allows increasing sensitivity by the differential measurement method. The basic characteristics of field-mill are

[28]  The density of an atmosphere vertical electric current of is measured by means of "current collector''. The basic part of installation is the ring wire antenna with 300 m diameter. The effective height of the antenna is 4.5 m, the effective area is about 2500 m2.

[29]  The regular error of the antenna effective area calculation does not exceed other random errors of air electric measurements and makes ~10%. For working antennas the calculation of the effective area can be adjusted by measurement of real antenna capacity. Thus the dynamic and static effective areas are considered to be approximately equal, that is true for the advanced turbulent electrode effect, influenced up to the effective height of the antenna.

[30]  The vertical electric current density of an atmosphere is measured by the methods of voltage decreasing on the fixed stable resistance. The block of filters in the channel of an atmospheric current density measurement is similar to those, used in the measuring complex for registration of other stationary geophysical fields. The basic characteristics of the measuring equipment are

Doppler Radio Sounding of the Ionosphere

[31]  High-frequency Doppler method for ionosphere researches is based on observation of frequency variations of the radio wave reflected from ionosphere inhomogeneities, changing in time and in space. Thus changes of an ionosphere state can be caused by solar geophysical factors as well as by atmosphere and seismic events from natural and artificial origins. Propagation of the radio wave is accompanied by frequency deviation caused by changes in physical properties of media and in the geometric trajectory or an altitude of reflection.

[32]  The high-frequency Doppler method consists in comparison between the frequency of the continuous radio signal, reflected by the ionosphere, and the frequency of the stable basic generator. Usage of the basic source enables to apply the device both for vertical and inclined sounding. The basic generator frequency is shifted on some hertz from the transmitter frequency to detect Doppler shift.

[33]  The equipment resolution, or its sensitivity, depends on the frequency stability of the heterodyne receiver and carrier wave of the radio transmitter. The highly stable broadcasting radio station working in a short wave range is used as radio transmitter. The radio receiver basic generator is the quartz generator with proportional thermostat system of the resonator, providing the frequency stability about 10 -8. So the resolution of the measuring complex on frequencies about 10 MHz is provided at 0.1 Hz level. With decreasing of a radio frequency this value decreases proportionally. Main parameters of the measuring are

Meteorological Measurements

[34]  Meteorological measurements on modern observatories are carried out by the digital meteorological stations. The professional digital meteorological station WS-2500, providing continuous measurements of air temperature and humidity, wind direction and velocity, atmospheric pressure and precipitation, is included into the measuring complex of Borok Geophysical Observatory. Meteorological station WS-2500 consists of the base station, equipped with the power adapter and the cable (5 m) to communicate with the personal computer, set of temperature and humidity sensors (up to 9), the wind sensor and the precipitation sensor. The station is equipped with the display and to transfer the measured parameters to the personal computer via COM-port in RS-232 format. Power supply of the meteorological station is carried out via the power adapter. Power supply of the sensors is carried out from solar batteries. The obtained data are transferred from sensors to base station by the radio channel on frequency of 433 MHz.

[35]  The digital ultrasonic meteorological stations, using contactless methods to measure wind velocity and air temperature, are applied in the atmosphere physics researches, including atmosphere dynamics. In measuring complex of Borok Geophysical Observatory this kind of meteorological stations is presented by the automatic ultrasonic complex "Meteo-2'', produced by Institute of Atmosphere Optics of the Russian Academy of Science. The complex measures temperature, velocity and direction of the wind (air streams), relative humidity, atmosphere pressure. The complex allows to estimate also parameters of air turbulence. The raw data are transferred to the personal computer via the cable as a digital code in RS-232 format.

[36]  The complex "Meteo-2'' includes the ultrasonic measuring block, the block of humidity and pressure sensor, the power unit and personal computer (operation system Windows 95/98/2000/NT) with the special software. Both measuring blocks are placed directly in the air media. They can be installed on a mast for measurements in a free atmosphere. The power unit is installed near a computer.

[37]  The ultrasonic measuring block includes ultrasonic system and the electronic module to convert measured values to a digital format and to transfer them to the computer. The ultrasonic system is designed as two tubular metal rings, installed vertically and orthogonal to each other, with 8 ultrasonic sensors fixed on the rings. The measurements of air temperature and three orthogonal component of wind velocity are based on functional dependence of sound group velocity from the specified meteorological parameters. The software calculates sound wave group velocities for four directions of its propagation and then meteorological values are calculated.

[38]  The humidity sensor sensitive element is serial sorption-capacitor element with the sensitive layer dielectric permeability depending on air humidity. The atmosphere pressure sensor is electric strain gage, with the output voltage depending on atmospheric pressure. So the ultrasonic complex "Meteo-2'' allows to measure:

[39]  For continuous measurements of infrasonic variations of atmosphere pressure the high-sensitivity liquid microbarograph, designed and produced by Institute of atmosphere physics of the Russian Academy of Science, is used. The microbarograph basic characteristics are


RJES

Citation: Anisimov, S. V., A. Chulliat, and E. M. Dmitriev (2008), Information-measuring complex and database of mid-latitude Borok Geophysical Observatory, Russ. J. Earth Sci., 10, ES3007, doi:10.2205/2007ES000227.


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