The Geophysical monitoring laboratory is equipped by the experimental complex (see chart) for the field digital recording of the wide class of geophysical fields. The experimental complex comprises the set of sensors, amplifiers, analog filters, time system and data logging network. It gives the possibility to record some variations in the wide frequency range of the following geophysical parameters:
- geomagnetic field by the Intermagnet geomagnetic station;
- 3-component of magnetic field variations by the fluxgate magnetometer;
- 3-component of ULF magnetic field by induction magnetometers;
- 3-component of telluric currents;
- atmospheric electric field with the help of electrostatic fluxmeter (“field mill”);
- vertical atmospheric electric current by the current collector;
- atmospheric pressure variations by the microbarograph;
- meteorological parameters by the digital meteorological station “WS2500” and ultrasonic meteorological station “Meteo-2M”;
- volumetric activity of 222Rn and 220Rn by the seismic radon station “SRS-05”;
- solar radiation flux density by the pyranometer “CMP-3”;
- altitude profiles of wind velocity by the meteorological acoustic Doppler locator (sodar) “Volna-3”.
The automatic magnetic station the International network of geomagnetic observatories Intermagnet measures three components of a geomagnetic field, using three-componental flaxgate-magnetometer, and full geomagnetic field value by the scalar proton magnetometer.
Vector three-componental magnetometer has the following basic characteristics
- sensitivity is 0.1 nT;
- dynamic range is 2000 nT;
- passband is 0− 1 Hz;
- temperature stability is 0.25 nT/gradC;
- long-term stability is 5 nT/Year.
Scalar proton magnetometer has the following basic characteristics
- sensitivity is 0.1 nT;
- accuracy is 1 nT.
The fluxgate magnetometer is the sensor of magnetic field variations. Some technical data of magnetometer are
- 3 measured components of the Earth's magnetic field;
- sampling interval is 1 s;
- resolution is 0.1 nT.
The induction magnetometers have been developed for recording the ULF magnetic field. The linear frequency response of the magnetic sensors allows compensation for the spectral inhomogeneity and large dynamic range of magnetic pulsation intensity. The transformation coefficient of the induction sensor with preamplifier is about 1 V/(nT Hz). Some technical data of magnetometer are
- frequency range is 10-3−3 Hz;
- magnetic field noise is 0.5 pT/Hz1/2for frequency f=1 Hz;
- power supply is ±12 V, 0.25 W.
The telluric currents. The method of differential measuring is used for telluric current observation. 3 components of telluric current are measured, using 300m baseline between lead electrodes and 400m borehole.
- Threshold sensitivity of geovoltmeter is ~0.0 mkV/m;
- passband is 0.001−5 Hz.
The electrostatic fluxmeter. For precise measurements of the atmospheric electric field, an electrostatic generator is used as a sensor. A quasi-static electric field is transformed into AC signals by means of periodic screening/unscreening of the sensor-based electrodes during rotation of the grounded plate. The electrostatic fluxmeter is designed according to the principle of a constant area of the sensor-based electrode. The construction enables increasing of sensitivity by a differential method of the measurement. For calibration of the device, a calibrating plate is used, which is mounted at a fixed distance from the sensor-based electrodes. Main technical parameters are
- dynamic range for DC electric field is ~80 db;
- electric field noise is 0.1 V/Hz1/2 for frequency f=1 Hz;
- power supply is ~220 V, 50 W.
The current collector. The vertical current in the near-surface atmosphere is measured using the method of voltage difference at a given stable resistor, connecting the sensor with the ground. The device comprises a current-collecting sensor, amplifier and a block of band-pass filters. Technical data are
- sensitivity is ~10-13 A/m;
- dynamic range is ~10-13−10-9 A/m.
The liquid microbarograph is suitable for the long-term recording of infrasound pressure variations with high sensitivity. The microbarograph consists of 2 chambers with a measuring condenser. The pressure difference in chambers results the difference in liquid levels and, consequently, in the imbalance between capacities of measuring condensers. While recording of infrasound pulsations, one chamber is connected with the atmosphere and the other is connected with the air some volume.
- Output sensitivity is ~15 mV/(dyne/cm2).
Digital meteorological station “WS2500” is designed to measure wind direction, wind velocity, temperature, pressure, humidity, dew point, amount of precipitations. Meteorological station “WS2500” includes the main unit communicated with the personal computer, a set of termo-gigro-sensors (up to 9 pieces), the wind sensor, the precipitation sensor.
The station is equipped with the liquid-crystal display. Measured parameters are transferred to the personal computer through COM-port. Power supply of meteorological station is carried out by the network adapter. A power supply of sensors is carried out by solar batteries. The measurement data are transferred from gages to the main unit throug a radio channel on frequency 433 MHz.
Ultrasonic meteorological station “Meteo-2M” is designed to measure fast variations of temperature, pressure, humidity, wind direction and wind velocity. Meteorological station includes an ultrasonic head, the unit of humidity and pressure sensors, the power supply unit. Measured parameters are transferred to the personal computer through COM-port. Data logging frequency is ~10 Hz. Instrument ranges are presented below.
- air temperature is measured from −40 to +50°C;
- horizontal wind velocity is measured from 0.2 to 30 m/s;
- horizontal wind direction is measured from 0 to 360°;
- relative air humidity is measured from 10 to 98%;
- air pressure is measured from 600 to 800 mm Hg.
Seismic radon station “SRS-05” is designed to measure volume activity of radon (222Rn) and thoron (220Rn) in ground air as well as air temperature, humidity and pressure. Instrument ranges are presented below.
- volumetric activity of 222Rn and 220Rn are measured from 20 to 2.0×104 Bq/m3;
- air temperature is measured from 5 to 50°C;
- relative air humidity is measured from 30 to 90%;
- air pressure is measured from 700 to 820 mm Hg.
The rugged pyranometer “CMP-3“ is manufactured by Kipp & Zonen. It measures solar radiation with a high-quality blackened thermopile protected by a dome. The blackened thermopile provides a flat spectral response for the full solar spectrum range. This allows the CMP3 to be used under plant canopies or lamps, when the sky is cloudy, and for reflected radiation measurements.
Main technical parameters are
- response time (95%) is 18 s;
- instability is ±1%;
- nonlinearity (0 − 1000 W/m2) is ±2,5%;
- sensitivity is 5 − 15 μV/W/m2;
- temperature dependence is ±6% (−10 − +40°C);
- temperature range is −40 − +80°C;
- measurement waveband is 305 − 2800 nm;
- maximum irradiance is 2000 W/m2.
Meteorological acoustic Doppler locator (sodar) “Volna-3” consists of three parabolic aerials protected against ambient noise by conic screens, an electronic unit for outgoing pulse shaping and amplification of received signals, and a PC-based system control block.
Main technical parameters are
- Sounding range is from 20 up to 800 m;
- Height resolution in wind measurements is 12 − 25 m;
- Reception period for one profile is 15 − 17 s;
- Measured wind velocity range is from 1 up to 20 m/s;
- Measurement accuracy for velocity and direction of variable wind is ±0,2 m/s.
The data logging network
The local data logging network provides continuous logging and processing of the geophysical data, supporting of the observatory databases in a near real time mode. The data logging network includes
- the main data logging system equipped with a analog-digital converter to process the data from sensors of geophysical fields;
- the data logging system to the fluxgate magnetometer;
- the data logging computer to the automatic geomagnetic observatory Intermagnet;
- the data logging computer to the digital meteorological station WS2500 measuring meteorological parameters;
- the data processing computer to process the primary data from all data logging computers, including data formatting, averaging abd transformation into physical values;
- the database server are providing maintenance of the database and access to the data from the Internet via a local access network of Borok Geophysical Observatory;
- the archiving computer on which monthly primary data are transferred to the CD-ROMs.
Connection between computers the data logging network is carried out via the switchboard functioning separately from a local access network and a server of Borok Geophysical Observatory.