scholarly journals Radio-Echo Sounding on South Cascade Glacier, Washington, using A Long-Wavelength, Mono-Pulse Source

1975 ◽  
Vol 15 (73) ◽  
pp. 459-461 ◽  
Author(s):  
Raymond D. Watts ◽  
Anthony W. England ◽  
Roger S. Vickers ◽  
Mark F. Meier
Keyword(s):  
Prior Knowledge ◽  
Short Pulse ◽  
Acute Angle ◽  
Center Frequency ◽  
Wire Antenna ◽  
Pulse Source ◽  
Long Wavelength ◽  
Radio Echo Sounding ◽  
Polaroid Camera ◽  
Lumped Resistors

A short-pulse, long-wavelength radio-echo sounder has successfully measured the ice depth on the South Cascade Glacier. Depths up to 250 m were determined with resolution of about 5%. Bottom returns were clear and almost never ambiguous. Their accuracy was confirmed by comparison with hot-point drilling results. The secret for successful sounding in temperate glaciers is the use of a sufficiently low center frequency. Five megahertz was most successful. Tests at 15 MHz indicated an increase in coherent clutter which rendered the bottom return observable only with prior knowledge of its location. The cause of the clutter is probably water-filled voids in the ice which behave as Rayleigh scatterers.The sounding system consists of an avalanche-transistor transmitter, which delivers a pulse to an acute-angle crossed-wire antenna. The pulse is shaped and given its center-frequency characteristics by the resonant properties of the antenna. The transmitting and receiving antennas are identical, consisting of wires and lumped resistors. The resistors reduce antennas ringing, thereby maintaining as short a pulse as possible. The receiver consists of an oscilloscope and a Polaroid camera. No preamplification is required for depths up to 250 m, but may be necessary for deeper glaciers.

scholarly journals Radio-Echo Sounding on South Cascade Glacier, Washington, using A Long-Wavelength, Mono-Pulse Source

1975 ◽  
Vol 15 (73) ◽  
pp. 459-461 ◽  
Author(s):  
Raymond D. Watts ◽  
Anthony W. England ◽  
Roger S. Vickers ◽  
Mark F. Meier
Keyword(s):  
Prior Knowledge ◽  
Short Pulse ◽  
Acute Angle ◽  
Center Frequency ◽  
Wire Antenna ◽  
Pulse Source ◽  
Long Wavelength ◽  
Radio Echo Sounding ◽  
Polaroid Camera ◽  
Lumped Resistors

A short-pulse, long-wavelength radio-echo sounder has successfully measured the ice depth on the South Cascade Glacier. Depths up to 250 m were determined with resolution of about 5%. Bottom returns were clear and almost never ambiguous. Their accuracy was confirmed by comparison with hot-point drilling results. The secret for successful sounding in temperate glaciers is the use of a sufficiently low center frequency. Five megahertz was most successful. Tests at 15 MHz indicated an increase in coherent clutter which rendered the bottom return observable only with prior knowledge of its location. The cause of the clutter is probably water-filled voids in the ice which behave as Rayleigh scatterers.The sounding system consists of an avalanche-transistor transmitter, which delivers a pulse to an acute-angle crossed-wire antenna. The pulse is shaped and given its center-frequency characteristics by the resonant properties of the antenna. The transmitting and receiving antennas are identical, consisting of wires and lumped resistors. The resistors reduce antennas ringing, thereby maintaining as short a pulse as possible. The receiver consists of an oscilloscope and a Polaroid camera. No preamplification is required for depths up to 250 m, but may be necessary for deeper glaciers.

10 Gb/s multiple wavelength, coherent short pulse source based on spectral carving of supercontinuum generated in fibers

2000 ◽  
Vol 18 (12) ◽  
pp. 2167-2175 ◽  
Author(s):  
O. Boyraz ◽  
J. Kim ◽  
M.N. Islam ◽  
E. Coppinger ◽  
B. Jalali
Keyword(s):  
Short Pulse ◽  
Pulse Source ◽  
Multiple Wavelength

The performance of ESS spectrometers in comparison with instruments at a short-pulse source

2020 ◽  
Vol 22 (1) ◽  
pp. 71-85
Author(s):  
Masatoshi Arai ◽  
Luca Zanini ◽  
Ken H. Andersen ◽  
Esben Klinkby ◽  
Félix J. Villacorta ◽  
...  
Keyword(s):  
Short Pulse ◽  
Pulse Source

scholarly journals Radio Echo Sounding On Temperate Glaciers

1975 ◽  
Vol 14 (70) ◽  
pp. 57-69 ◽  
Author(s):  
R. H. Goodman
Keyword(s):  
Short Pulse ◽  
Pulse Length ◽  
Beam Width ◽  
Field Trials ◽  
Water Levels ◽  
Quality Data ◽  
Real Time Analysis ◽  
Radio Echo Sounding ◽  
Excellent Spatial Resolution ◽  
Echo Sounder

A high-resolution radio echo sounder operating at a frequency of 620 MHz has been developed for studies of temperate glaciers. Excellent spatial resolution is obtained through the use of a short pulse length (70 ns) and an antenna beam width of 5.2°. Large amounts of high-quality data may be rapidly collected since the sounder incorporates an automatic positioning system and an on-line computer. Real time analysis of the echoes facilitates the understanding of complex reflecting horizons observed in temperate glaciers.Results obtained during field trials of the echo sounder on both the Wapta Icefield and Athabasca Glacier are given. Intraglacial structures which may be due to water levels within the ice have been detected.

Radar signature of a 2.5-D tunnel

Geophysics ◽  
1993 ◽  
Vol 58 (11) ◽  
pp. 1573-1587 ◽  
Author(s):  
Mark L. Moran ◽  
Roy J. Greenfield
Keyword(s):  
Fourier Transform ◽  
Green’S Function ◽  
Green's Function ◽  
Electric Dipole ◽  
Short Pulse ◽  
Three Dimensional ◽  
Acute Angle ◽  
Peak Power Output ◽  
Early Arrival ◽  
Low Amplitude

The effects of an infinitely long cylindrical void on short‐pulse cross‐borehole radar waveforms are modeled and analyzed. Pulsed electromagnetic sensing system (PEMSS) data are of particular interest. The PEMSS system developed by the Southwest Research Institute uses a vertically oriented electric dipole that emits a short electromagnetic pulse with peak power output centered around 30 MHz, which gives wavelengths of roughly 1.5 cavity diameters. The transmitter and receiver are typically located in boreholes separated by approximately 30 m. The model is based on field solutions for a vertically oriented point‐source electric dipole. A three‐dimensional (3-D) analytical frequency domain derivation of the Green’s function is found using a spatial Fourier transform over the cylinder axis. The resulting wavenumber integral is evaluated by a numerical integration over wavenumber. Time‐domain waveforms are produced by applying a Fourier transform to a 7-80 MHz band of frequencies in the Green’s function spectrum. Model results agree well with PEMSS field data sets. Further modeling examines the effects on waveforms for a wide variety of cases in which the raypath is not orthogonal to the tunnel axis, including the effect of tunnel dip. An air‐filled tunnel with a radius greater than 1.0 m produces a low amplitude shadow zone along its entire length. A low amplitude early arrival is observed in simulations with air‐filled tunnels in which the source to receiver path forms an acute angle larger than 45 degrees with the tunnel axis. This arrival is interpreted as propagation through the tunnel. When this angle is smaller than 45 degree the tunnel is effectively an opaque object and only the energy diffracted around the cylindrical void is observed. Waveform behavior gradually transitions from propagation through the tunnel in the vicinity of 45 degrees.

scholarly journals Modulational instability in the beat-wave generation

1988 ◽  
Vol 6 (2) ◽  
pp. 199-210 ◽  
Author(s):  
D. Pesme ◽  
S. J. Karttunen ◽  
R. R. E. Salomaa ◽  
G. Laval ◽  
N. Silvestre
Keyword(s):  
Dispersion Relation ◽  
Acoustic Waves ◽  
Wave Process ◽  
Short Pulse ◽  
Modulational Instability ◽  
Ion Acoustic Waves ◽  
Long Wavelength ◽  
Ion Acoustic ◽  
Large Growth ◽  
General Dispersion

The coupling of a large amplitude plasmon, generated by the beat-wave process, to ion acoustic waves may lead to modulational or decay instabilities, which are investigated here. A general dispersion relation obtainable from Zakharov equations predicts large growth rates (∼ωpi) for short wavelength modulations. To avoid these, extremely short pulse lengths are required in the beat-wave experiments. Due to the very long wavelength of the beat-plasmon, the decay instability is not likely below the ke V-temperatures.

scholarly journals Radio Echo-Sounding Studies of Englacial Water Movement in Variegated Glacier, Alaska

1984 ◽  
Vol 30 (104) ◽  
pp. 22-29 ◽  
Author(s):  
Robert Jacobel ◽  
Charles Raymond
Keyword(s):  
Magnetic Tape ◽  
Water Movement ◽  
Water Pressure ◽  
Center Frequency ◽  
Phase Information ◽  
Glacier Surface ◽  
Radio Echo Sounding ◽  
Surface Melt ◽  
Glacier Velocity ◽  
Increased Pressure

AbstractRadio-echo returns from internal reflectors were monitored for three weeks during surge motion on Variegated Glacier, Alaska in July 1982. A monopulse transmitter with 3 MHz center frequency was fixed on the glacier surface near the equilibrium line. Data were recorded on magnetic tape approximately three times daily and contain both amplitude and phase information. The frequency spectrum of returned radiation from englacial scatterers shows peaks in the 12 to 30 MHz range which places constraints on the size and geometry of the scatterers. Timing of variations in the amplitude and frequency of returned radiation were found to coincide with changes in glacier velocity, basal water pressure, and surface melt rate. These changes in the echo pattern are interpreted in terms of the redistribution of water in englacial channels and cavities connected to the bed some distance down-glacier. This connection has large hydraulic resistance compared to a bore hole connected vertically to the bed. The inflow of water to the cavities from surface melt and rain and the drainage are generally in equilibrium except in times of changed surface input and during surge pulses. In the latter case, water may fill these cavities due to increased pressure at the bed associated with the motion pulse. The information obtained is therefore complementary to bore-hole water pressure levels but cannot duplicate it. This is apparently due to fundamental differences in the hydraulics of the natural cavity and conduit system, and a bore hole connected vertically to the bed.

Optical comb generator as an efficient short-pulse source

1996 ◽  
Vol 21 (7) ◽  
pp. 534 ◽  
Author(s):  
G. M. Macfarlane ◽  
A. S. Bell ◽  
E. Riis ◽  
A. I. Ferguson
Keyword(s):  
Short Pulse ◽  
Pulse Source
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