Theory for the formation of resonance structure in the spectrum of atmospheric electromagnetic background noise in the range of short-period geomagnetic pulsations

1989 ◽  
Vol 32 (7) ◽  
pp. 594-601 ◽  
Author(s):  
P. P. Belyaev ◽  
S. V. Polyakov ◽  
V. O. Rapoport ◽  
V. Yu. Trakhtengerts
Keyword(s):  
Background Noise ◽  
Resonance Structure ◽  
Geomagnetic Pulsations ◽  
Short Period

scholarly journals Ambient Seismic Noise Analysis Associated with the 2010 Eruption of Merapi Volcano Using Temporal Variations of Randomness and Background Noise

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Afif Rakhman ◽  
Wahyudi ◽  
Agus Budi Santoso ◽  
Hanik Humaida ◽  
Wiwit Suryanto
Keyword(s):  
Background Noise ◽  
Seismic Noise ◽  
Noise Analysis ◽  
Temporal Variations ◽  
Permutation Entropy ◽  
Merapi Volcano ◽  
Frequency Bands ◽  
Volcano Eruption ◽  
Power Spectral ◽  
Short Period

We present the combination of permutation entropy (PE) and power spectral density (PSD) analysis on continuous seismic data recorded by short-period seismic stations during the 2010 Merapi volcano eruption. The calculation of PE aims at characterizing the randomness level in seismic noise, while the PSD parameters use to detect the background noise level in various frequency bands. It was previously observed that a significant reduction of randomness before the volcano eruption could be indicated as one of the short-term precursors due to the lack of high frequencies (>1 Hz) in the noise wave-field caused by high absorption losses as the hot magma uprises to the upper crust. The results show no significant reduction in signal randomness before the eruption series. The characteristic of events during the preeruptive period and the crisis tends to be chaotic (PE in the range 0.9 to 1). Further calculations show that the standard deviation in PE decreased in four days before the first eruption onset on 26 October. PE was stable at the highest values (very close to 1) and gradually returned to the previous fluctuation after the eruption onset. The level of background noise in the low- and high-frequency bands appeared to have the same tendency. The two main eruptions correspond to the two highest peaks of noise levels.

scholarly journals Dispersive changes in magnetic background noise polarization at 0.1 to 6Hz during sunset and sunrise at L=1.3

2004 ◽  
Vol 22 (6) ◽  
pp. 1989-2000 ◽  
Author(s):  
T. Bösinger ◽  
S. L. Shalimov
Keyword(s):  
Background Noise ◽  
Azimuthal Angle ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Major Axis ◽  
Resonance Structure ◽  
Frequency Range ◽  
Ionosphere Model ◽  
F Region ◽  
E Region

Abstract. Polarization properties of the magnetic background noise (MBN) and the spectral resonance structure (SRS) of the ionospheric Alfvén resonator (IAR) below the first Schumann resonance but above 0.1 Hz are measured by a sensitive pulsation magnetometer at the island of Crete (L=1.3) and analyzed using the existing SRS theory by Belyaev et al. (1989b). The focus of the paper is on the systematic changes in the MBN and SRS properties associated with the transition from a sunlit to a dark ionosphere (sunset) and vice versa (sunrise). We are able to pinpoint in observations an E-region and F-region terminator effect and to simulate it by means of a simple ionosphere model, implying the formalism given by Belyaev et al. (1989b). The E-region terminator effect is associated with an apparent control for the SRS presence or absence with no clear frequency dispersion in polarization properties, whereas the F-region terminator effect exhibits strong frequency dispersion, especially in the low frequency range. This yields a change in the ellipticity of MBN, starting as early as 2 to 3h ahead of the "zero-line" of the terminator. In a 24h presentation of the ellipticity versus frequency and time, the sunrise/sunset effect produces a sharp, dispersive boundary between night and day (day and night). Only inside this boundary, during the night hours, is SRS observed, at times accompanied by a large quasi-periodic long period modulation in the azimuthal angle of the major axis of the polarization ellipse. Attention is also paid to peculiarities in the low frequency range (~0.1Hz), where especially large changes in the polarization properties occur in association with the passage of the terminator. The F-region effect is very distinct and well reproduced by our simple model. Changes in the azimuth associated with the E-region terminator effect are of the order of 20&deg.

On the prediction of low‐frequency geomagnetic pulsations for geophysical prospecting

Geophysics ◽  
1989 ◽  
Vol 54 (5) ◽  
pp. 635-642 ◽  
Author(s):  
Hing‐Lan Lam
Keyword(s):  
Background Noise ◽  
Low Frequency ◽  
Field Work ◽  
Magnetic Activity ◽  
Time Of Day ◽  
Virtual Absence ◽  
Long Period ◽  
The Earth ◽  
Short Period ◽  
Geomagnetic Soundings

Pulsations of the earth’s magnetic field due to solar‐terrestrial interaction are used for geomagnetic soundings to study conductive structures in the earth. However, the pulsations are also the unwanted background noise for magnetic exploration surveys. It is, therefore, desirable to conduct the sounding or survey work during geomagnetic conditions optimum for that particular undertaking. This paper relates the pulsational activity to a parameter (the DRX index) which characterizes the magnetic activity for each individual day and which is routinely forecast in Canada. By using the relations established in this study, it is possible to infer the future levels of pulsations from the forecast DRX, and a period of desired pulsational activity can thus be selected for the field work. In the course of a day, the afternoon is appropriate for conducting magnetic surveys because of a generally lower level of pulsational activity and a virtual absence of intense short‐period pulsations, while morning is optimal for carrying out induction soundings because of more intense pulsational activity and a tendency of enhanced long‐period pulsations to recur during that time of day.

Bandpass filtering to reduce noise on seismograms: Is there a better way?

1997 ◽  
Vol 87 (3) ◽  
pp. 770-777
Author(s):  
A. Douglas
Keyword(s):  
Impulse Response ◽  
Background Noise ◽  
Recording System ◽  
Trial And Error ◽  
Signal To Noise ◽  
P Waves ◽  
Noise Component ◽  
Noise Estimate ◽  
A Value ◽  
Short Period

Abstract Short-period (SP) P waves at low signal-to-noise ratios (S/Ns) usually appear as signals of about 1 Hz or higher frequencies riding on background noise with frequencies of 0.5 Hz or less. Often bandpass filtering is used to further attenuate the noise relative to the signal to improve the S/N. However, bandpass filtering introduces significant distortion into the signal. Here the use of optimum filters is described, such filters being constructed using autocorrelation functions of the signal and noise derived from noise and signal models. The autocorrelation of the impulse response of the recording system is used to describe the signal. For the noise, a tapered cosine wave is used that has the frequency of the main noise component. To compute the filter, the relative sizes of the signal and noise correlations should be proportional to the square of the S/N. Now, the noise can be estimated by subtracting the estimated signal from the observed seismogram. This property can be used to decide by trial and error on the S/N. The optimum S/N is found by gradually reducing the trial ratio starting from too high a value, until the noise has the amplitude expected and there is no evidence of significant signal in the noise estimate. Examples are given showing how the method can lift observed signals off the background noise with less distortion to the signal than usually occurs with bandpass filtering.

scholarly journals Preliminary results of simultaneous recording of auroral and geomagnetic pulsations at the ISTP SB RAS station Istok

2019 ◽  
Vol 5 (2) ◽  
pp. 42-48
Author(s):  
Александр Белецкий ◽  
Aleksandr Beletsky ◽  
Равиль Рахматулин ◽  
Ravil Rakhmatulin ◽  
Татьяна Сыренова ◽  
...  
Keyword(s):  
Geomagnetic Field ◽  
Simultaneous Recording ◽  
Activity Level ◽  
High Temporal Resolution ◽  
Distribution Analysis ◽  
Geomagnetic Pulsations ◽  
Silicon Photomultipliers ◽  
Short Period ◽  
Long Time ◽  
Auroral Luminosity

The paper presents the results on first synchronous observations of variations in auroral luminosity and geomagnetic field, made with high temporal resolution at the ISTP SB RAS high-latitude station Istok (70° N, 88° E) in September–December 2018. Auroras were recorded with all-sky camera, pulsations in the auroras were recorded by a photometer in four spectral ranges with silicon photomultipliers. Continuous monitoring of geomagnetic pulsations was performed using a LEMI-30 three-component induction magnetometer. Both synchronous bursts of auroras and magnetic field pulsations, as well as disturbances of auroras, not accompanied by disturbances in the geomagnetic field, were observed. We note that the photometer clearly recorded short-period (~20 min) variations in in auroral luminosity. At the same time, some instability of the photometer signal level occurred at sufficiently long time intervals. In the photometer data, there are powerful signal bursts, probably of a hardware nature. Nevertheless, the temporary distribution analysis of the registration moments (registration frequency) of signal bursts indicates the possible dependence of the burst registration frequency on the geomagnetic activity level.

Sign in / Sign up

Export Citation Format

Share Document