Modelling line of sight availability for high frequency urban radio networks

1999 ◽  
Author(s):  
J.A. Biddiscombe
Keyword(s):  
High Frequency ◽  
Radio Networks ◽  
Line Of Sight

scholarly journals Complementary Bursts, Coronal Inhomogeneities and New Microscopic Spectral Features of Solar Bursts in Type IV Bursts

1980 ◽  
Vol 86 ◽  
pp. 269-271
Author(s):  
H. S. Sawant ◽  
R. V. Bhonsle ◽  
S. S. Degaonkar ◽  
T. Takakura
Keyword(s):  
High Frequency ◽  
High Sensitivity ◽  
Line Of Sight ◽  
Spectral Features ◽  
Frequency Range ◽  
Type Iv ◽  
Linear Extent ◽  
Solar Bursts ◽  
Almost All ◽  
Density Irregularity

Complementary bursts (C.B's) have been observed in the decametric range during noise storms and/or type IV activity. These bursts essentially consist of two components, each component having a duration ~ 1 second. The first component shows weak emission or emission gap over a certain frequency range. The second component is observed after a certain delay. If the bursts are assumed to be generated at the fundamental, and if the radiation corresponding to the gap propagates through an electron density irregularity located close to the source along the line of sight, whose cross-section is less than the linear extent of the source, then almost all properties of the C.B.'s can be explained. High sensitivity, and high frequency and time resolution spectra of type IV bursts at 137 MHz revealed new microscopic spectral features displaying “wave-like” and “fork-like” shapes.

scholarly journals High‐Frequency Communications Response to Solar Activity in September 2017 as Observed by Amateur Radio Networks

Space Weather ◽  
2019 ◽  
Vol 17 (1) ◽  
pp. 118-132 ◽  
Author(s):  
Nathaniel A. Frissell ◽  
Joshua S. Vega ◽  
Evan Markowitz ◽  
Andrew J. Gerrard ◽  
William D. Engelke ◽  
...  
Keyword(s):  
Solar Activity ◽  
High Frequency ◽  
Radio Networks ◽  
Amateur Radio

Along-track analysis of GRACE and GRACE Follow-On KBR and LRI data for new science applications

2020 ◽  
Author(s):  
Shin-Chan Han ◽  
Khosro Ghobadi Far ◽  
Jeanne Sauber ◽  
Christopher Mccullough ◽  
David Wiese ◽  
...  
Keyword(s):  
High Frequency ◽  
Reference Range ◽  
Numerical Differentiation ◽  
Line Of Sight ◽  
Short Term ◽  
Orbital State ◽  
New Science ◽  
Range Rate ◽  
Along Track ◽  
Track Analysis

<p>We present a method of analysing inter-satellite tracking data for detecting short-term (sub-monthly) gravitational changes from GRACE and GRACE Follow-On.  The method is based on the residual range-rate data with respect to the reference range-rate computed with dynamic orbital state vectors.  Then, we apply a numerical differentiation to compute range-acceleration residuals.  We found that the range-acceleration residuals are near-perfectly correlated with the line-of-sight gravity difference (LGD) between two spacecrafts and the transfer (admittance) function between them can be determined regardless of time and space (Ghobadi-Far et al., 2018, JGR-Solid Earth, https://doi.org/10.1029/2018JB016088).  The transfer function, to be applied directly to range-acceleration residuals, enables accurate LGD determination with the error of 0.15 nm/s^2 over the frequency band higher than 1 mHz (5 cycles-per-revolution), whereas the actual GRACE measurement error is several times larger.</p><p>In this presentation, we present two new geophysical applications to examine high-frequency gravitational changes at times scales of significantly less than one month; Gravitational observation of tsunamis triggered by the 2004 Sumatra, 2010 Maule, and 2011 Tohoku earthquakes and transient gravitational changes due to Earth’s free oscillation excited by the 2004 earthquake.  Lastly, we present new results from GRACE Follow-On KBR and LRI inter-satellite ranging data. </p>

scholarly journals Is there a Depolarization Horizon?

2018 ◽  
Author(s):  
A. S. Hill
Keyword(s):  
Interstellar Medium ◽  
Density Distribution ◽  
Electron Density ◽  
High Frequency ◽  
Electron Density Distribution ◽  
Low Frequency ◽  
Line Of Sight ◽  
Low Frequencies ◽  
Ionic Medium ◽  
Spiral Arm

Modern radio spectrometers make measurement of polarized intensity as a function of Faraday depth possible. I investigate the effect of depolarization along a model line of sight. I model sightlines with two components informed by observations: a diffuse interstellar medium with a lognormal electron density distribution and a narrow, denser component simulating a spiral arm or H~{\sc ii} region, all with synchrotron-emitting gas mixed in. I then calculate the polarized intensity from 300-1800 MHz and calculate the resulting Faraday depth spectrum. The idealized synthetic observations show far more Faraday complexity than is observed in Global Magneto-Ionic Medium Survey observations. In a model with a very nearby H~{\sc ii} region observed at low frequencies, most of the effects of a ``depolarization wall'' are evident: the H~{\sc ii} region depolarizes background emission and less (but not zero) information from beyond the H~{\sc ii} region reaches the observer. In other cases, the effects are not so clear, as significant amounts of information reach the observer even through significant depolarization, and it is not clear that low-frequency observations sample largely different volumes of the interstellar medium than high-frequency observations. The observed Faraday depth can be randomized such that it does not always have any correlation with the true Faraday depth.

Instrumentation and Data Acquisition System for an Air-Sea Interaction Buoy

1978 ◽  
Vol 59 (9) ◽  
pp. 1102-1113
Author(s):  
S. SethuRaman ◽  
W. A. Tuthill ◽  
J. McNeil
Keyword(s):  
Data Acquisition ◽  
Data Transmission ◽  
High Frequency ◽  
Fast Rate ◽  
Data Acquisition System ◽  
Acquisition System ◽  
Line Of Sight ◽  
High Frequency Response ◽  
Interaction Experiment ◽  
Future Plans

Instrumentation and data acquisition system for a typical air-sea interaction experiment are described. The experiments were conducted with the help of a stable air-sea interaction buoy anchored 5 km offshore in the Atlantic Ocean near Long Island. Errors due to the tilting motions of the buoy are discussed. The instruments were designed to survive the hostile marine environment and maintain their calibration and relatively high frequency response. A line-of-sight RF telemetry system was used to obtain data at a fast rate. Unique power supply features such as a wind charger and a solar panel were used to extend the life of the batteries. Future plans regarding data transmission through geostationary satellites are presented.

scholarly journals Is There a Polarization Horizon?

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 129 ◽  
Author(s):  
Alex Hill
Keyword(s):  
Interstellar Medium ◽  
Density Distribution ◽  
High Frequency ◽  
Electron Density Distribution ◽  
Low Frequency ◽  
Line Of Sight ◽  
Low Frequencies ◽  
Hii Region ◽  
Warm Ionized Medium ◽  
Spiral Arm

Modern radio spectrometers make measurement of polarized intensity as a function of Faraday depth possible. I investigate the effect of depolarization along a model line of sight. I model sightlines with two components informed by observations: a warm ionized medium with a lognormal electron density distribution and a narrow, denser component simulating a spiral arm or Hii region, all with synchrotron-emitting gas mixed in. I then calculate the polarized intensity from 300–1800 MHz and calculate the resulting Faraday depth spectrum. The idealized synthetic observations show far more Faraday complexity than is observed in Global Magneto-Ionic Medium Survey observations. In a model with a very nearby Hii region observed at low frequencies, most of the effects of a “depolarization wall” are evident: the Hii region depolarizes background emission, and less (but not zero) information from beyond the Hii region reaches the observer. In other cases, the effects are not so clear, as significant amounts of information reach the observer even through significant depolarization, and it is not clear that low-frequency observations sample largely different volumes of the interstellar medium than high-frequency observations. The observed Faraday depth can be randomized such that it does not always have any correlation with the true Faraday depth.

Extra-high frequency line-of-sight propagation for future urban communications

2003 ◽  
Vol 51 (11) ◽  
pp. 3109-3121 ◽  
Author(s):  
S.A. Khan ◽  
A.N. Tawfik ◽  
C.J. Gibbins ◽  
B.C. Gremont
Keyword(s):  
High Frequency ◽  
Line Of Sight ◽  
Line Of Sight Propagation

Apparent Dissociation Between Saccadic Eye Movements and the Firing Patterns of Premotor Neurons and Motoneurons

1999 ◽  
Vol 82 (5) ◽  
pp. 2808-2811 ◽  
Author(s):  
Leo Ling ◽  
Albert F. Fuchs ◽  
James O. Phillips ◽  
Edward G. Freedman
Keyword(s):  
Eye Movements ◽  
Eye Movement ◽  
High Frequency ◽  
Action Potentials ◽  
Saccadic Eye Movements ◽  
Line Of Sight ◽  
Movement Amplitude ◽  
Burst Neurons ◽  
Premotor Neurons ◽  
Motoneuron Activity

Saccadic eye movements result from high-frequency bursts of activity in ocular motoneurons. This phasic activity originates in premotor burst neurons. When the head is restrained, the number of action potentials in the bursts of burst neurons and motoneurons increases linearly with eye movement amplitude. However, when the head is unrestrained, the number of action potentials now increase as a function of the change in the direction of the line of sight during eye movements of relatively similar amplitudes. These data suggest an apparent uncoupling of premotor neuron and motoneuron activity from the resultant eye movement.

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