scholarly journals Observation of 2nd Schumann eigenmode on Titan's surface

2013 ◽  
Vol 3 (1) ◽  
pp. 157-192 ◽  
Author(s):  
C. Béghin ◽  
G. Wattieaux ◽  
R. Grard ◽  
M. Hamelin ◽  
J. P. Lebreton
Keyword(s):  
Electromagnetic Waves ◽  
Low Frequency ◽  
Amplitude Distribution ◽  
Data Conversion ◽  
Schumann Resonance ◽  
Huygens Probe ◽  
Atmospheric Structure ◽  
The Impact ◽  
Space Wave ◽  
Expected Signal

Abstract. This works presents the results obtained from an updated data analysis of the observations of Extremely Low Frequency (ELF) electromagnetic waves performed with the HASI-PWA (Huygens Atmospheric Structure and Permittivity, Wave and Altimetry) instrumentation after Huygens Probe landing on Titan surface in January 2005. The most significant signals observed at around 36 Hz throughout the descent in the atmosphere have been extensively analyzed for several years, and subsequently interpreted as the signature of a Schumann resonance, although the latter exhibits atypical peculiarities compared with those known on Earth. The usual depicting methods of space wave data used so far could not allow retrieving the presence of weak signals when Huygens was at rest for 32 min on Titan's surface. Whereas the expected signal seems hidden within the instrumental noise, we show that a careful statistical analysis of the amplitude distribution of the 418 spectral density samples of the 36 Hz line reveals abnormal characteristics compared to other frequencies. This behavior is shown to occur under propitious circumstances due to the characteristics of the onboard data conversion processes into digital telemetry counts, namely 8-bit dynamic after logarithm compression of the DFT (Discrete Fourier Transform) of ELF waveforms. Since this phenomenon is observed only at the frequency bin around 36 Hz, we demonstrate that the Schumann resonance, seen in the atmosphere within the same band, is still present on the surface, albeit with a much smaller amplitude compared to that measured before and a few seconds after the impact, because the electric dipole is thought to have been stabilized ten seconds later almost horizontally until the end of the measurements.

scholarly journals Observation of 2nd Schumann eigenmode on Titan's surface

2013 ◽  
Vol 2 (2) ◽  
pp. 237-248 ◽  
Author(s):  
C. Béghin ◽  
G. Wattieaux ◽  
R. Grard ◽  
M. Hamelin ◽  
J. P. Lebreton
Keyword(s):  
Electromagnetic Waves ◽  
Low Frequency ◽  
Amplitude Distribution ◽  
Data Conversion ◽  
Schumann Resonance ◽  
Huygens Probe ◽  
Atmospheric Structure ◽  
The Impact ◽  
Space Wave ◽  
Expected Signal

Abstract. This work presents the results obtained from an updated data analysis of the observations of extremely low frequency (ELF) electromagnetic waves performed with the HASI-PWA (Huygens Atmospheric Structure and Permittivity, Wave and Altimetry) instrumentation after Huygens Probe landing on Titan's surface in January 2005. The most significant signals observed at around 36 Hz throughout the descent in the atmosphere have been extensively analyzed for several years, and subsequently interpreted as the signature of a Schumann resonance, although the latter exhibits atypical peculiarities compared with those known on Earth. The usual depicting methods of space wave data used so far could not allow for retrieving the presence of weak signals when Huygens was at rest for 32 min on Titan's surface. Whereas the expected signal seems hidden within the instrumental noise, we show that a careful statistical analysis of the amplitude distribution of the 418 spectral density samples of the 36 Hz line reveals abnormal characteristics compared to other frequencies. This behavior is shown to occur under propitious circumstances due to the characteristics of the onboard data conversion processes into digital telemetry counts, namely 8-bit dynamic after logarithm compression of the DFT (Discrete Fourier Transform) of ELF waveforms. Since this phenomenon is observed only at the frequency bin around 36 Hz, we demonstrate that the Schumann resonance, seen in the atmosphere within the same band is still present on the surface, albeit with a much smaller amplitude compared to that measured before and a few seconds after the impact, because the electric dipole is thought to have been stabilized ten seconds later almost horizontally until the end of the measurements.

scholarly journals Monitoring the Impact of Electromagnetic Waves on Yield and Quality in Maize

2011 ◽  
Vol 68 (1) ◽  
Author(s):  
Florin IMBREA ◽  
Branko MARINCOVIC ◽  
Valeriu TABĂRĂ ◽  
PAUL PÎRŞAN ◽  
Gheorghe DAVID ◽  
...  
Keyword(s):  
Protein Content ◽  
Quality Indicators ◽  
Electromagnetic Waves ◽  
Starch Content ◽  
New Technology ◽  
Low Frequency ◽  
Cultivation Method ◽  
Yield And Quality ◽  
The Impact ◽  
Starch Yield

Experimenting new technology of cultivating maize is an important step forward in order to optimise the yielding capacity if a crop that ranks second among crops cultivated worldwide and first among crops cultivated in Romania. Using low frequency radiations to stimulate yield and quality in maize allows increases in yield between 10 and 15% compared to the classical cultivation method and an improvement of the quality indicators (protein content increased with 6-11% determining an increase of the protein yield per ha; starch content increased with 7-14%, which also determined an increase of the starch yield per ha; while fat content, another indicator we monitored, increased with 2-6%).

scholarly journals Calibration and 21-cm power spectrum estimation in the presence of antenna beam variations

2019 ◽  
Vol 492 (2) ◽  
pp. 2017-2028 ◽  
Author(s):  
Ronniy C Joseph ◽  
C M Trott ◽  
R B Wayth ◽  
A Nasirudin
Keyword(s):  
Data Analysis ◽  
Power Spectrum ◽  
Low Frequency ◽  
Analytic Description ◽  
Spectral Features ◽  
Spectrum Estimation ◽  
Power Spectrum Estimation ◽  
Murchison Widefield Array ◽  
The Impact ◽  
Expected Signal

ABSTRACT Detecting a signal from the Epoch of Reionization (EoR) requires an exquisite understanding of Galactic and extragalactic foregrounds, low-frequency radio instruments, instrumental calibration, and data analysis pipelines. In this work, we build upon existing work that aims to understand the impact of calibration errors on 21-cm power spectrum (PS) measurements. It is well established that calibration errors have the potential to inhibit EoR detections by introducing additional spectral features that mimic the structure of EoR signals. We present a straightforward way to estimate the impact of a wide variety of modelling residuals in EoR PS estimation. We apply this framework to the specific case of broken dipoles in Murchison Widefield Array (MWA) to understand its effect and estimate its impact on PS estimation. Combining an estimate of the percentage of MWA tiles that have at least one broken dipole (15–40 per cent) with an analytic description of beam errors induced by such dipoles, we compute the residuals of the foregrounds after calibration and source subtraction. We find that that incorrect beam modelling introduces bias in the 2D-PS on the order of $\sim 10^3\, \mathrm{mK}^2 \, h^{-3}\, \mathrm{Mpc}^{3}$. Although this is three orders of magnitude lower than current lowest limits, it is two orders of magnitude higher than the expected signal. Determining the accuracy of both current beam models and direction-dependent calibration pipelines is therefore crucial in our search for an EoR signal.

Schumann Resonance Measurement Based on Nonlinear Interaction

2010 ◽  
Vol 439-440 ◽  
pp. 1294-1299
Author(s):  
Bing Xia Cao ◽  
Xiao Lin Qiao
Keyword(s):  
High Frequency ◽  
Electromagnetic Waves ◽  
Low Frequency ◽  
Middle Latitude ◽  
Schumann Resonance ◽  
Short Term ◽  
Time Service ◽  
Resonance Measurement ◽  
Modulation Model ◽  
Nonlinear Modulation

Schumann Resonance relates with global temperature variations, new geophysics phenomena in the low ionosphere and short-term earthquake prediction etc. In this paper based on the nonlinear modulation model of high frequency and extreme-low frequency electromagnetic waves in low ionosphere, the Schumann Resonance observing is researched. Taking the fair weather electric field in account, the cross modulation index was 4.2×10-4. At the first Schumann Resonance observatory of China, the first 4 peaks of Schumann Resonance respectively at 7, 14, 20, 26Hz were obtained in demodulation spectra of the high frequency time service signals. The parameter characteristics of Schumann Resonance in the low ionosphere were analyzed under the geographical condition of middle latitude area. The feasibility of Schumann Resonance measurement by demodulating the spectra of HF has been verified. The non-linearity between Schumann Resonance and very low frequency signals also was discussed.

USING FIELD DATA FOR THE EVALUATION OF THE IMPACT OF ULTRA-LOW FREQUENCY MOTIONS ON THE FATIGUE OF MOORING LINES

2019 ◽  
Author(s):  
Guilherme Borzacchiello ◽  
Carl Albrecht ◽  
Fabricio N Correa ◽  
Breno Jacob ◽  
Guilherme da Silva Leal
Keyword(s):  
Field Data ◽  
Low Frequency ◽  
Mooring Lines ◽  
The Impact

scholarly journals Evaluation of P-Band SAR Tomography for Mapping Tropical Forest Vertical Backscatter and Tree Height

2021 ◽  
Vol 13 (8) ◽  
pp. 1485
Author(s):  
Naveen Ramachandran ◽  
Sassan Saatchi ◽  
Stefano Tebaldini ◽  
Mauro Mariotti d’Alessandro ◽  
Onkar Dikshit
Keyword(s):  
Tropical Forest ◽  
Vertical Profile ◽  
Mean Squared Error ◽  
Low Frequency ◽  
Tree Height ◽  
Canopy Layer ◽  
Local Maxima ◽  
Slope Correction ◽  
Compensation Approach ◽  
The Impact

Low-frequency tomographic synthetic aperture radar (TomoSAR) techniques provide an opportunity for quantifying the dynamics of dense tropical forest vertical structures. Here, we compare the performance of different TomoSAR processing, Back-projection (BP), Capon beamforming (CB), and MUltiple SIgnal Classification (MUSIC), and compensation techniques for estimating forest height (FH) and forest vertical profile from the backscattered echoes. The study also examines how polarimetric measurements in linear, compact, hybrid, and dual circular modes influence parameter estimation. The tomographic analysis was carried out using P-band data acquired over the Paracou study site in French Guiana, and the quantitative evaluation was performed using LiDAR-based canopy height measurements taken during the 2009 TropiSAR campaign. Our results show that the relative root mean squared error (RMSE) of height was less than 10%, with negligible systematic errors across the range, with Capon and MUSIC performing better for height estimates. Radiometric compensation, such as slope correction, does not improve tree height estimation. Further, we compare and analyze the impact of the compensation approach on forest vertical profiles and tomographic metrics and the integrated backscattered power. It is observed that radiometric compensation increases the backscatter values of the vertical profile with a slight shift in local maxima of the canopy layer for both the Capon and the MUSIC estimators. Our results suggest that applying the proper processing and compensation techniques on P-band TomoSAR observations from space will allow the monitoring of forest vertical structure and biomass dynamics.

scholarly journals Shift Detection in Hydrological Regimes and Pluriannual Low-Frequency Streamflow Forecasting Using the Hidden Markov Model

Water ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 2058 ◽  
Author(s):  
Larissa Rolim ◽  
Francisco de Souza Filho
Keyword(s):  
Time Series ◽  
Markov Model ◽  
Hidden Markov Model ◽  
Extreme Events ◽  
Hidden Markov ◽  
Low Frequency ◽  
Streamflow Forecasting ◽  
Hydrologic Time Series ◽  
Low Frequency Variability ◽  
The Impact

Improved water resource management relies on accurate analyses of the past dynamics of hydrological variables. The presence of low-frequency structures in hydrologic time series is an important feature. It can modify the probability of extreme events occurring in different time scales, which makes the risk associated with extreme events dynamic, changing from one decade to another. This article proposes a methodology capable of dynamically detecting and predicting low-frequency streamflow (16–32 years), which presented significance in the wavelet power spectrum. The Standardized Runoff Index (SRI), the Pruned Exact Linear Time (PELT) algorithm, the breaks for additive seasonal and trend (BFAST) method, and the hidden Markov model (HMM) were used to identify the shifts in low frequency. The HMM was also used to forecast the low frequency. As part of the results, the regime shifts detected by the BFAST approach are not entirely consistent with results from the other methods. A common shift occurs in the mid-1980s and can be attributed to the construction of the reservoir. Climate variability modulates the streamflow low-frequency variability, and anthropogenic activities and climate change can modify this modulation. The identification of shifts reveals the impact of low frequency in the streamflow time series, showing that the low-frequency variability conditions the flows of a given year.

CORRELATION OF LOCAL LIGHTNING ACTIVITY WITH EXTRA LOW FREQUENCY DETECTOR FOR SCHUMANN RESONANCE MEASUREMENTS

2021 ◽  
pp. 147671
Author(s):  
G. Tatsis ◽  
A. Sakkas ◽  
V. Christofilakis ◽  
G. Baldoumas ◽  
S.K. Chronopoulos ◽  
...  
Keyword(s):  
Low Frequency ◽  
Lightning Activity ◽  
Schumann Resonance ◽  
Frequency Detector

Scattering of electromagnetic waves by hybrid waves in a two-electron-temperature plasma

1991 ◽  
Vol 46 (1) ◽  
pp. 99-106 ◽  
Author(s):  
S. K. Sharma ◽  
A. Sudarshan
Keyword(s):  
Growth Rate ◽  
Electron Temperature ◽  
High Frequency ◽  
Electromagnetic Waves ◽  
Low Frequency ◽  
Lower Hybrid ◽  
Stimulated Scattering ◽  
Coupled Modes ◽  
Temperature Plasma ◽  
Electrostatic Perturbation

In this paper, we use the hydrodynamic approach to study the stimulated scattering of high-frequency electromagnetic waves by a low-frequency electrostatic perturbation that is either an upper- or lower-hybrid wave in a two-electron-temperature plasma. Considering the four-wave interaction between a strong high-frequency pump and the low-frequency electrostatic perturbation (LHW or UHW), we obtain the dispersion relation for the scattered wave, which is then solved to obtain an explicit expression for the growth rate of the coupled modes. For a typical Q-machine plasma, results show that in both cases the growth rate increases with noh/noc. This is in contrast with the results of Guha & Asthana (1989), who predicted that, for scattering by a UHW perturbation, the growth rate should decrease with increasing noh/noc.

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