scholarly journals Magnetospheric lion roars

2000 ◽  
Vol 18 (4) ◽  
pp. 406-410 ◽  
Author(s):  
W. Baumjohann ◽  
E. Georgescu ◽  
K.-H. Fornacon ◽  
H. U. Auster ◽  
R. A. Treumann ◽  
...  
Keyword(s):  
Sampling Rate ◽  
Cone Angle ◽  
Mhd Waves ◽  
Lower Hybrid ◽  
High Sampling Rate ◽  
Polarized Waves ◽  
Magnetospheric Configuration And Dynamics ◽  
Mhd Waves And Instabilities ◽  
Electron Gyrofrequency ◽  
First Time

Abstract. The Equator-S magnetometer is very sensitive and has a sampling rate normally of 128 Hz. The high sampling rate for the first time allows detection of ELF waves between the ion cyclotron and the lower hybrid frequencies in the equatorial dawnside magnetosphere. The characteristics of these waves are virtually identical to the lion roars typically seen at the bottom of the magnetic troughs of magnetosheath mirror waves. The magnetospheric lion roars are near-monochromatic packets of electron whistler waves lasting for a few wave cycles only, typically 0.2 s. They are right-hand circularly polarized waves with typical amplitudes of 0.5 nT at around one tenth of the electron gyrofrequency. The cone angle between wave vector and ambient field is nearly always smaller than 1°.Key words: Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma waves and instabilities)

scholarly journals Waveform and packet structure of lion roars

1999 ◽  
Vol 17 (12) ◽  
pp. 1528-1534 ◽  
Author(s):  
W. Baumjohann ◽  
R. A. Treumann ◽  
E. Georgescu ◽  
G. Haerendel ◽  
K.-H. Fornacon ◽  
...  
Keyword(s):  
Sampling Rate ◽  
Cone Angle ◽  
Mhd Waves ◽  
Lower Hybrid ◽  
Fluxgate Magnetometer ◽  
High Sampling Rate ◽  
Polarized Waves ◽  
Interplanetary Physics ◽  
Electron Gyrofrequency ◽  
First Time

Abstract. The Equator-S magnetometer is very sensitive and has a sampling rate of normally 128 Hz. The high sampling rate allows for the first time fluxgate magnetometer measurements of ELF waves between the ion cyclotron and the lower hybrid frequencies in the equatorial dayside magnetosheath. The so-called lion roars, typically seen by the Equator-S magnetometer at the bottom of the magnetic troughs of magnetosheath mirror waves, are near-monochromatic packets of electron whistler waves lasting for a few wave cycles only, typically 0.25 s. They are right-hand circularly polarized waves with typical amplitudes of 0.5–1 nT at around one tenth of the electron gyrofrequency. The cone angle between wave vector and ambient field is usually smaller than 1.5°.Key words. Interplanetary physics (MHD waves and turbulence; plasma waves and turbulence)

scholarly journals Akinetic Swept-Source Master–Slave-Enhanced Optical Coherence Tomography

Photonics ◽  
2021 ◽  
Vol 8 (5) ◽  
pp. 141
Author(s):  
Manuel J. Marques ◽  
Ramona Cernat ◽  
Jason Ensher ◽  
Adrian Bradu ◽  
Adrian Podoleanu
Keyword(s):  
Optical Coherence Tomography ◽  
Sampling Rate ◽  
Calibration Procedure ◽  
Depth Information ◽  
Optical Coherence ◽  
Time Intervals ◽  
Swept Source ◽  
High Sampling Rate ◽  
First Time ◽  
Down Conversion

This paper presents a different approach for processing the signal from interferometers driven by swept sources that exhibit non-linear tuning during stable time intervals. Such sources are, for example, those commercialised by Insight, which are electrically tunable and akinetic. These Insight sources use a calibration procedure to skip frequencies already included in a spectral sweep, i.e., a process of “clearing the spectrum”. For the first time, the suitability of the Master–Slave (MS) procedure is evaluated as an alternative to the conventional calibration procedure for such sources. Here, the MS process is applied to the intact, raw interferogram spectrum delivered by an optical coherence tomography (OCT) system. Two modalities are investigated to implement the MS processing, based on (i) digital generation of the Master signals using the OCT interferometer and (ii) down-conversion using a second interferometer driven by the same swept source. The latter allows near-coherence-limited operation at a large axial range (>80 mm), without the need for a high sampling rate digitiser card to cope with the large frequency spectrum generated, which can exceed several GHz. In both cases, the depth information is recovered with some limitations as described in the text.

scholarly journals Compressional Pc5 type pulsations in the morningside plasma sheet

2001 ◽  
Vol 19 (3) ◽  
pp. 311-320 ◽  
Author(s):  
A. Vaivads ◽  
W. Baumjohann ◽  
G. Haerendel ◽  
R. Nakamura ◽  
H. Kucharek ◽  
...  
Keyword(s):  
Phase Velocity ◽  
Plasma Sheet ◽  
Mhd Waves ◽  
Plasma Velocity ◽  
Frequency Range ◽  
Magnetospheric Configuration And Dynamics ◽  
Substorm Activity ◽  
Mhd Waves And Instabilities ◽  
Magnetospheric Configuration ◽  
Generation Mechanisms

Abstract. We study compressional pulsations in Pc5 frequency range observed in the dawn-side at distances of about 10 RE , close to the magnetic equator. We use data obtained during two events of conjunctions between Equator-S and Geotail: 1000–1700 UT on 9 March 1998, and 0200–0600 UT on 25 April 1998. In both events, pulsations are observed after substorm activity. The pulsations are antisymmetric with respect to the equatorial plane (even mode), and move eastward with phase velocity close to plasma velocity. The pulsations tend to be pressure balanced. We also discuss possible generation mechanisms of the pulsations.Key words. Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma sheet)

scholarly journals Cluster as a wave telescope – first results from the fluxgate magnetometer

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1439-1447 ◽  
Author(s):  
K.-H. Glassmeier ◽  
U. Motschmann ◽  
M. Dunlop ◽  
A. Balogh ◽  
M. H. Acuña ◽  
...  
Keyword(s):  
Wave Vector ◽  
Low Frequency ◽  
Plasma Waves ◽  
Minimum Variance ◽  
Mhd Waves ◽  
Fluxgate Magnetometer ◽  
Propagating Waves ◽  
First Results ◽  
Mhd Waves And Instabilities ◽  
First Time

Abstract. The four Cluster spacecraft provide an excellent opportunity to study spatial structures in the magnetosphere and adjacent regions. Propagating waves are amongst the interesting structures and for the first time, Cluster will allow one to measure the wave vector of low-frequency fluctuations in a space plasma. Based on a generalized minimum variance analysis wave vector estimates will be determined in the terrestrial magnetosheath and the near-Earth solar wind. The virtue and weakness of the wave telescope technique used is discussed in detail.Key words. Electromagnetics (wave propagation) – Magnetospheric physics (MHD waves and instabilities; plasma waves and instabilities)

scholarly journals Connections between whistlers and pulsation activity

2000 ◽  
Vol 18 (8) ◽  
pp. 866-873 ◽  
Author(s):  
J. Verö ◽  
B. Zieger ◽  
J. Szendröi ◽  
M. Vellante ◽  
J. Střesğtik ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Time Scales ◽  
Geomagnetic Pulsation ◽  
Lower Latitude ◽  
Mhd Waves ◽  
Magnetospheric Configuration And Dynamics ◽  
Mhd Waves And Instabilities ◽  
L Value ◽  
Magnetospheric Configuration ◽  
Pulsation Activity

Abstract. Simultaneous whistler records of one station and geomagnetic pulsation (Pc3) records at three stations were compared. In a previous study correlation was found between occurrence and L value of propagation/excitation for the two phenomena. The recently investigated simultaneous records have shown that the correlation is better on longer time scales (days) than on shorter ones (minutes), but the L values of the propagation of whistlers/excitation of pulsations are correlated, i.e. if whistlers propagate in higher latitude ducts, pulsations have periods longer than in the case when whistlers propagate in lower latitude ducts.Key words: Electromagnetics (wave propagation) - Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities)

scholarly journals Location of Pc 1–2 waves relative to the magnetopause

2002 ◽  
Vol 20 (11) ◽  
pp. 1763-1767 ◽  
Author(s):  
R. E. Denton ◽  
J. LaBelle ◽  
X. Zhu
Keyword(s):  
Plasma Waves ◽  
Mhd Waves ◽  
Temperature Anisotropy ◽  
Period Range ◽  
Limited Region ◽  
Ion Cyclotron Waves ◽  
Magnetospheric Configuration And Dynamics ◽  
Mhd Waves And Instabilities ◽  
L Value ◽  
Electromagnetic Ion Cyclotron Waves

Abstract. Spacecraft-borne and ground-based magnetometers frequently detect magnetospheric micropulsations in the period range 0.2–10 s, termed Pc 1–2, and attributed to electromagnetic ion cyclotron waves driven by temperature anisotropy (T^ > T ||). Previous surveys of Pc 1 occurrence locations have been limited to L <  9. We present AMPTE/IRM observations of the distribution of Pc 1 waves out to the magnetopause, for a limited region of MLT = 10–14. The probability of wave occurrence Pwav is large (> 0.15) between L = 7–12, peaking at L = 8–10 (Pwav ~ 0.25). When the L-value is normalized to the magnetopause position Lmp, however, the highest probabilities of Pc 1 wave occurrence are close to the magnetopause, with Pwav ~0.25 for Lnorm = L/Lmp = 0.8–1.0. These results are consistent with increased convective growth rate at large L and with the greater effect of magnetosphere compression close to the magnetopause. On the other hand, we only directly observe magnetic field compression for at most about 25% of the wave events.Key words. Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma waves and instabilities)

Intelligent Displacement Measuring System for Rock Stratum

2011 ◽  
Vol 103 ◽  
pp. 583-586
Author(s):  
Feng Ling Li ◽  
Jian Hua Rong ◽  
Yu Ping Zhang
Keyword(s):  
Civil Engineer ◽  
Real Time ◽  
Sampling Rate ◽  
Measuring System ◽  
Displacement Sensor ◽  
Rock Stratum ◽  
Baud Rate ◽  
Real Time Clock ◽  
High Sampling Rate ◽  
Displacement System

Measuring rock stratum displacement in dam grouting process is very important. A new displacement system is designed, comprising a programmable microcontroller Atmega16, a new grating capacitive displacement sensor(GCDS), DS1302 real time clock chip and announciator etc. The system has high sampling rate of 9600 baud rate and can trap the displacement equal to 0.001 millimeter in one second. Equipped with mechanical conveyance system, the system can be applied to the civil engineer. The experiment results show the instrument can measure accurately the displacement value and alarm geologic disaster in time, which can conduct continuous and accurate monitoring and provide operation decisions for dam engineers.

scholarly journals An Automatic Method for Detection and Update of Additive Changes in Road Network with GPS Trajectory Data

2019 ◽  
Vol 8 (9) ◽  
pp. 411 ◽  
Author(s):  
Tang ◽  
Deng ◽  
Huang ◽  
Liu ◽  
Chen
Keyword(s):  
Road Network ◽  
Sampling Rate ◽  
Quality Data ◽  
Automatic Method ◽  
Trajectory Data ◽  
The Road ◽  
High Sampling Rate ◽  
Map Generation ◽  
Gps Trajectory Data ◽  
Gps Trajectory

Ubiquitous trajectory data provides new opportunities for production and update of the road network. A number of methods have been proposed for road network construction and update based on trajectory data. However, existing methods were mainly focused on reconstruction of the existing road network, and the update of newly added roads was not given much attention. Besides, most of existing methods were designed for high sampling rate trajectory data, while the commonly available GPS trajectory data are usually low-quality data with noise, low sampling rates, and uneven spatial distributions. In this paper, we present an automatic method for detection and update of newly added roads based on the common low-quality trajectory data. First, additive changes (i.e., newly added roads) are detected using a point-to-segment matching algorithm. Then, the geometric structures of new roads are constructed based on a newly developed decomposition-combination map generation algorithm. Finally, the detected new roads are refined and combined with the original road network. Seven trajectory data were used to test the proposed method. Experiments show that the proposed method can successfully detect the additive changes and generate a road network which updates efficiently.

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