MICROWAVE BRIGHTNESS SPECTRA OF LAYERED MEDIA

Geophysics ◽  
1977 ◽  
Vol 42 (3) ◽  
pp. 514-521 ◽  
Author(s):  
A. W. England ◽  
G. R. Johnson
Keyword(s):  
Layer Thickness ◽  
Spectral Resolution ◽  
Free Space ◽  
Wave Length ◽  
Layered Media ◽  
Frozen Soil ◽  
Diffuse Interface ◽  
Water Ice ◽  
Space Wave ◽  
Natural Media

Many natural media are layered at the scale of microwaves. Examples include frozen soil over moist soil, ice over water, and snow over soil. The microwave brightness spectra of such media may exhibit interference patterns. Such patterns have been observed for emission from fresh‐water ice but not for emission from snow or from seasonally frozen soil. Three factors which determine whether interference is detectable are the spectral resolution of the radiometer, the uniformity of layer thickness, and the distinctness of interfaces between layers. Analyses of these factors show that: (1) The radiobrightnesses of layered media vary sufficiently slowly with wave‐length that radiometers designed for the radio‐astronomy bands provide adequate spectral resolution; (2) a variability of layer thickness greater than 15 percent of the free‐space wavelength in the area viewed by the radiometer will effectively eliminate an interference pattern; and (3) a diffuse interface, whose thickness is 15 percent of the free‐space wave‐length, is transparent to microwaves so that effects of the interface will not appear in the radiobrightness spectrum.

Determination of the velocity of short electromagnetic waves by interferometry

1952 ◽  
Vol 213 (1112) ◽  
pp. 123-141 ◽  
Keyword(s):  
Phase Velocity ◽  
Electromagnetic Radiation ◽  
Free Space ◽  
Electromagnetic Waves ◽  
Wave Beam ◽  
Wave Length ◽  
Wave Frequency ◽  
Space Wave

A new measurement of the velocity of electromagnetic radiation is described. The result has been obtained, using micro-waves at a frequency of 24005 Mc/s ( λ = 1∙25 cm), with a form of interferometer which enables the free-space wave-length to be evaluated. Since the micro-wave frequency can also be ascertained, phase velocity is calculated from the product of frequency and wave-length. The most important aspect of the experiment is the application to the measured wave-length of a correction which arises from diffraction of the micro-wave beam. This correction is new to interferometry and is discussed in detail. The result obtained for the velocity, reduced to vacuum conditions, is c 0 = 299792∙6 ± 0∙7 km/s.

SECOND-ORDER BEAMS OF SLOTTED WAVE GUIDE ARRAYS

1953 ◽  
Vol 31 (1) ◽  
pp. 55-69 ◽  
Author(s):  
H. Gruenberg
Keyword(s):  
Radiation Pattern ◽  
Free Space ◽  
Wave Length ◽  
Second Order ◽  
Wave Guide ◽  
Main Beam ◽  
Space Wave

It is shown that the radiation pattern of slotted wave guide arrays may contain small second-order beams even for slot spacings less than a free-space wave length. These beams are usually split with a minimum or even a null in the plane containing the array and main beam. Since patterns are normally taken in this plane, the second-order beams have until now escaped attention, as far as the writer is aware. Methods of suppressing these beams are discussed.

scholarly journals Melt-layer thickness measurements during crushing experiments on fresh-water ice

1994 ◽  
Vol 40 (134) ◽  
pp. 119-124
Author(s):  
R.E. Gagnon
Keyword(s):  
High Pressure ◽  
Layer Thickness ◽  
Fresh Water ◽  
Contact Zone ◽  
Pressure Sensor ◽  
Front Face ◽  
Total Load ◽  
Water Ice ◽  
The Face ◽  
Electrical Conductors

AbstractA stainless-steel platen, with a centrally located pressure sensor on the front face, has been used to crush mono-crystalline, bubble-free fresh-water ice samples. Two electrical conductors, located on the face of the pressure sensor, were connected to a bridge circuit so that the presence of liquid between the two conductors could be detected and its thickness measured. Video records of the ice/ steel contact zone during crushing were obtained by mounting samples on a thick Plexiglas plate which permitted viewing through the specimen to the ice/steel interface. Total load and pressure records exhibited a sawtooth pattern due to the compliance of the ice and the testing apparatus, and spalling of ice from the contact zone. When the region of contact was in the vicinity of the pressure transducer, liquid was detected and peaks occurred in the liquid sensor output when load drops occurred. Contact between the platen and the ice consisted of low pressure zones of highly damaged crushed and/or refrozen ice, opaque in appearance, and transparent, high-pressure regions of relatively undamaged ice. Upper limits for the liquid-layer thickness on the high-pressure undamaged ice were ~3 µm on the ascending sides of the sawteeth in the load records and ~ 21 µ on the sharp descending sides.

Modeling Energy Deposition in Very Thin Layered Media by Monte Carlo Simulation

2007 ◽  
Author(s):  
Reginald Eze ◽  
Anisur Rahman ◽  
Sunil Kumar
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Thin Layer ◽  
Layer Thickness ◽  
Path Length ◽  
Energy Deposition ◽  
Radiation Transport ◽  
Monte Carlo Model ◽  
Layered Media ◽  
Thin Layers

A Monte Carlo model with special features for modeling of radiation transport through very thin layers has been presented. Over the decades traditional Monte Carlo model has been used to model highly scattering thin layers in skin and may inaccurately capture the effect of thin layers since their interfaces are not perfectly planar and thicknesses non-uniform. If the Monte Carlo model is implemented without special features then the results of the simulation would show no effect of the outer thin layer since the path length of most photons would be significantly larger than the layer thickness and the resulting predicted photon travel would simply not notice the presence of the layer. Examples of multi-layered media are considered where the effect of a very thin absorbing layers is systematically examined using both the traditional Monte Carlo and that with new features incorporated. The results have profound implications in the diagnostic and therapeutic applications of laser in biomedicine and surgery.

scholarly journals Melt-layer thickness measurements during crushing experiments on fresh-water ice

1994 ◽  
Vol 40 (134) ◽  
pp. 119-124 ◽  
Author(s):  
R.E. Gagnon
Keyword(s):  
High Pressure ◽  
Layer Thickness ◽  
Fresh Water ◽  
Contact Zone ◽  
Pressure Sensor ◽  
Front Face ◽  
Total Load ◽  
Water Ice ◽  
The Face ◽  
Electrical Conductors

AbstractA stainless-steel platen, with a centrally located pressure sensor on the front face, has been used to crush mono-crystalline, bubble-free fresh-water ice samples. Two electrical conductors, located on the face of the pressure sensor, were connected to a bridge circuit so that the presence of liquid between the two conductors could be detected and its thickness measured. Video records of the ice/ steel contact zone during crushing were obtained by mounting samples on a thick Plexiglas plate which permitted viewing through the specimen to the ice/steel interface. Total load and pressure records exhibited a sawtooth pattern due to the compliance of the ice and the testing apparatus, and spalling of ice from the contact zone. When the region of contact was in the vicinity of the pressure transducer, liquid was detected and peaks occurred in the liquid sensor output when load drops occurred. Contact between the platen and the ice consisted of low pressure zones of highly damaged crushed and/or refrozen ice, opaque in appearance, and transparent, high-pressure regions of relatively undamaged ice. Upper limits for the liquid-layer thickness on the high-pressure undamaged ice were ~3 µm on the ascending sides of the sawteeth in the load records and ~ 21 µ on the sharp descending sides.

scholarly journals First Results and Discoveries with the ISO Short-Wavelength Spectrometer

1998 ◽  
Vol 11 (2) ◽  
pp. 1113-1115
Author(s):  
Thijs De Graauw
Keyword(s):  
Spectral Resolution ◽  
Short Wavelength ◽  
Wave Length ◽  
Space Observatory ◽  
Infrared Space Observatory ◽  
Length Range ◽  
First Results ◽  
Scientific Results

AbstractThe Short-Wavelength Spectrometer(SWS) is one of the four instruments on-board of ESA’s Infrared Space Observatory(ISO), launched on 15 Nov. 1995. It covers the wave-length range of 2.38-45.2μm with a spectral resolution ranging from 1000-2000. An overview is given of the in-orbit performance and a summary of the main scientific results and discoveries obtained in the first 18 months of operation of the ISO-SWS.

Sign in / Sign up

Export Citation Format

Share Document