Judit Szendrői

On spectral methods in Schumann resonance data processing

Our experience in the processing of time series stems from the processing of magnetotelluric and geomagnetic pulsation data where conditions and aims are different from the processing of Schumann resonances. Nevertheless, several points are common in each of these fields. The major problem when processing time series is mostly the correct selection of the time/frequency resolutions. If one of them is increased, the other decreases. In the case of the Fourier transform, both resolutions are determined — in terms of a dynamic spectrum — by the time dimension of the time/frequency box within which the actual computations are made. In case of convolution filtering (especially if both components of complex vectors are computed), the selection is more versatile. The step in frequency can be freely selected, the independence, however, of the filtered series is only ensured if filters have sufficient length in time what means a corresponding time resolution. If time resolution is to be increased, then the frequency step most be increased (frequency resolution decreased) to get independent time series. Convolution filtering has the advantage that disturbed sections can be easily cut from the filtered series without disturbing other sections, thus the reduction of noise is more effective. Moreover “momentary” spectra can be found in any moment or section. Additionally, an impulsive event can also be resolved independently of possible other impulses in arbitrary position outside of the length of the filter. The same method of convolution filtering can also be used for the complex demodulation of time series, resulting in high precision frequency determination.

Modelling of the Propagation of Radio Waves Transmitted by GPS Satellites in an Ionosphere with Irregularities

The results concerning the modelling of the propagation of radio waves transmitted by GPS satellites in the presence of sporadic E layers are described. The greatest deviations of the difference between the true path and the geometrical path found for the higher frequency from the difference true path-geometrical path obtained for the lower frequency attain values of the order of 26 cm at the zenith angle 75° of the satellite in the N-S direction (summer, night and low solar activity conditions) and about 7 cm in the W-E direction (summer and winter night, as well as low solar activity conditions).

50 years, thousands of papers, a changing future

As it was announced at the beginning of 2015 Acta Geodaetica et Geophysica (AGG) is celebrating the 50 years anniversary of its foundation. It is an exceptional occasion to look back to the evolution, to evaluate the present status and also to assess future tasks and challenges that we are facing. The predecessor of AGG, Acta Geodaetica Geophysica et Montanistica Academiae ScientiarumHungaricaewas founded by the Hungarian Academy of Sciences in the frame of the academic mission of propagating domestic scientific results abroad and promotion of international connections of the Hungarian scientists. Thanks to the exceptional international character of the disciplines of geodesy and geophysics and also to the right propagation policy—namely providing exchange copies for many universities, libraries and research institutes for many years—the journal has been well-known from an early stage. It attracted many of the most prominent contemporary scientists worldwide and became a relevant international forum on geodesy especially research related to figure of the Earth, on geomagnetism and on electromagnetic investigation of the Earth’s interior. Author names like Ledersteger, Barvir, Rinner, Wolf, Meissl, Isotov, Hristov, Bossolasco, Böhm, Fanselau, Korschunow, Le Minh Triet, Bouska, Troitskaya, Porstendorfer, Fournier, Berdichevsky, Lipskaya, Kovtun, Hutton clearly demonstrate the historical internationality. However a