Magnetic observations

In 2008, like in the previous years, the geomagnetic recording was carried out by means of two recording sets. Recording set I is the basis ones, while set II is auxiliary. In this sets there operate PSM-type portable torsion photoelectric magnetometers, recording variations of components X, Y and Z of the Earth's magnetic field vector.

The Torsion Photoelectric Magnetometers, based on Bobrow-system quartz variometers, have been constructed at Belsk since 1977. In these magnetometers, angular deflections of variometer magnet's mirrors are converted, by means of photoelectric converters, into electric voltage changes, in a system with a strong negative feedback. The recording is made by two independent sets, which in practice ensures a 100 percent continuity of magnetic data at Hel Observatory.

The absolute measurements from which the bases of X, Y, Z and F are being determined are made with DI-fluxgate and proton magnetometers. The ELSEC DI-fluxgate magnetometer, whose sensor is munted on a non-magnetic theodolite THEO 010B produced by CARL Zeiss, serves to measure angles of magnetic declination D and inclination I. The PMP-7 proton magnetometer is used to make measurements of vector F. With this magnetometer, whose sensor is installed some 50 m away from the absolute pavilion, there is also made a continuous recording of vector F at the observatory. At Hel the absolute measurements are made, on the average, twice a week.

Digital loggers DR-02 were designed by the EL-LAB company especially for making incessant digital recording. They contain 15-bit binary A/D converters, 1 MB internal memory with back-up battery (when the mains is disconnected), real time clock, and a RS-232 interface with optoisolation to connect the logger to a computer. At Hel Observatory these loggers record the magnetic field changes with scale values of about 0.06 nT/bit and sampling period of 5 s.

The "time service" employs DCF-77 radioclocks installed in various houses and rooms of the observatory. The magnetometers, loggers, radioclocks and the IBM-PC computer which collects and processes magnetic data, are provided with a device ensuring their many-hour powering from batteries, in case the mains fails. This ensures the practically 100 percent continuity of magnetic data, regardless of possible breaks in the 220 V power, which sometime happen to occur at Hel, notably in the fall-winter season.

The data from loggers are being automatically sent to the IBM-PC computer once daily. The computer converts the data to the format used in the INTERMAGNET network (IMFV1.23), taking into account base values, scale coefficients and thermal coefficients. Following the INTERMAGNET recomendation, these data are also filtered digitally by means of a 9-degree Gauss filter. The conversion is made for data from both sets.

The basic set is set I, while set II is auxiliary and it is ised in case set I fails. If in the set I data happen to occur gaps, they are also automatically filled with the set II data. The file thus prepared, containing data from the 24 hours, is at night automatically (with no operator involved) sent via Internet to the data centers (GIN) in Edinburgh and Paris.