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1

Analysis and usage of linear relationships between the magnetic field components recorded by INTERMAGNET

Nowożyński K., Ślęzak K.

Acta Geophysica

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2013

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Vol. 61, no. 3

511--534

EN

An analysis of linear relationships between the ground-level components of the Earth’s magnetic field measured at different sites is a relatively new topic compared to the analysis of data at a single location. The data collected by the INTERMAGNET observation network provide perfect set of data to which this analysis can be used. An important tool in this analysis may be developing a method of determination of the impulse response for linear systems in the time domain. An advantage of calculations in the time domain over the generally known and applied methods in the frequency domain is the possibility of determining prediction of output signals. By that, simultaneously with the analysis of linear relationships, a tool for recovering missing records in incomplete observation data is obtained. Filling-in the missing data may increase interest and possibility of using the observational data by researchers experimenting with the analysis in the frequency domain where gaps in data records are a significant limitation.

2

New induction sounding tested in Central Europe

Semenov V., Ladanivskyy B., Nowożyński K.

Acta Geophysica

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2011

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Vol. 59, no. 5

815-832

EN

The hourly data of nine geomagnetic observatories situated in Central Europe have been analyzed using the generalized magnetovariation (GMV) method designed recently for induction soundings of inhomogeneous media. In this method, impedance is one of transfer functions in the differential relation between spectra of the magnetic components and their derivatives. The peculiarity of this impedance is its correspondence to the magnetotelluric one estimated from the linear relations. Three transfer functions have been estimated simultaneously for data of geomagnetic observatories, using three different routines working in the period range from three hours up to two days. Noises in the source field components have been compared with noise in the estimated plane field divergence. The multivariate errorsin-variables method was used to extract spatially and temporally coherent geomagnetic field structure from the partially incoherent geomagnetic variations. This method allows estimating reliably impedances and gradient tippers for each observatory, taking into consideration the Earth’s sphericity. The obtained responses have been used for induction soundings and for detecting a deep inhomogeneity in the region.

3

A new magnetic index based on the external part of vertical geomagnetic variations

Ernst T., Jankowski J., Nowożyński K.

Acta Geophysica

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2010

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Vol. 58, no. 6

963-972

EN

Variations of geomagnetic components X, Y, and Z recorded in 19 Intermagnet European observatories in 2004 were analysed. The original data from all observatories were preliminarily processed. In the first step, periods longer than three hours were filtered out. In the second step, variations of vertical geomagnetic component Z were separated into external and internal parts. We introduced a non-dimensional index η defined as the square root of a ratio of the energy of the external part of the vertical component to that of the horizontal components. Maps of the surface distribution of a new magnetic index η for the area of Europe at selected time periods were created, and their time changes are presented. The time changes of η for selected observatories are also shown. Moreover, we discuss a very interesting phenomenon we discovered, that has never been described in geophysical literature. Namely, in the recordings of all the observatories we noticed the presence of very regular variations, observed almost exclusively in the vertical component Z, which is quite unusual. These regular variations occur in the form of sinusoidal "wave packets". The amplitudes of these variations do not depend on the geomagnetic latitude and appear in the records of all the observatories we analyzed. They occur in quiet days, which suggests that their source is in the ionosphere.

4

Time-domain filtering of seismic rotation waves

Nowożyński K., Teisseyre K.

Acta Geophysica Polonica

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2003

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Vol. 51, nr 1

51-61

EN

Rotational parts of seismic waves are extracted from recordings of differential seismic signals. Thus, all differences in responses of the seismometers cause disturbances which obscure these hidden components. The method of removing great part of these disturbances is developed, based on the time-domain filtering and using the data collected over a selected period of seismic monitoring called the test phase. Examples of seismic rotation components for some events registered in the Ojców observatory are shown, together with results of checking the adequacy of the presented method.

5

Determination of transfer function through solution in time domain

Wielądek R., Nowożyński K.

Acta Geophysica Polonica

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2001

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Vol. 49, nr 1

131-142

EN

A new method of transfer function determination through solution in time domain is presented. As compared to the linear problem the proposed new formulation of the problem employs five instead of three sequences of unknowns. This makes it possible to bring the errors of adjusted observations closer to white noise and to improve the accuracy of transfer function approximation. In this formulation, however, the problem looses its linearity and one must use a nonlinear instead of linear method of least-squares. The authors propose an economical algorithm of the method of successive approximations. For finding the initial approximation, the use is made of the linear problem solution.

6

Determination and processing of measuring equipment responses

Nowożyński K.

Acta Geophysica Polonica

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2001

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Vol. 49, nr 3

389-413

EN

The aim of this paper is to present algorithms useful in determination of measuring equipment responses. It shows how the phase and amplitude response of a device can be determined. Taking benefit of a digital FIR filter equivalent to the device, the paper discusses different ways of finding such filters as to eliminate or modify the effect of the device on the recorded data. Determination of equipment response is understood to be both the determination of response in the frequency domain and finding the coefficients of a filter equivalent to the device.