Test Method for Determining the Thickness of Bound Pavement Layers Using Short-Pulse Radar

AbstractThe ice-thickness profiling performance of a helicopter-mounted short-pulse radar operating at approximate center frequencies of 600 and 900 MHz was assessed. The antenna packages were mounted 1.2 m off the skid of a small helicopter whose speed and altitude were varied from about 1.8 to 9 m/s and 3 to 12 m. Clutter from the helicopter offered minimal interference with the ice data. Data were acquired in Alaska over lakes (as a proving exercise) and two rivers, whose conditions varied from open water to over 1.5 m of solid ice with numerous frazil-ice formations. The most readily interpretable data were acquired when the ice or snow surface was smooth. Detailed surface investigations on the Tanana River revealed good correlations of echo delay with solid ice depth, but an insensitivity to frazil-ice depth due to its high water content. On the Yukon River, coinciding temporally coherent surface and bottom reflections were associated with solid ice and smooth surfaces. All cases of incoherent surface returns (scatter) occurred over ice rubble. Rough-surface scattering was always followed by the appearance of bottom scattering but, in many cases, including a hanging-wall formation of solid frazil ice, bottom scattering occurred beneath coherent, smooth-surface reflections. Areas of incoherent bottom scattering investigated by drilling revealed highly variable ice conditions, including frazil ice. The minimum ice thickness that could be resolved from the raw data was about 0.2 m with the 600 MHz antenna and less than 0.15 m with the 900 MHz antenna.

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Comparative Research on the Quality of Micro Hole in Superalloy GH2135 and Stainless Steel 420J1 by Laser Processing

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.703.27 ◽

2016 ◽

Vol 703 ◽

pp. 27-33

Author(s):

Liang Wang ◽

Nai Fei Ren ◽

Yun Long Wang ◽

Lin Zhong Zhu

Keyword(s):

Stainless Steel ◽

Pulse Energy ◽

Laser Processing ◽

Pulse Width ◽

Laser Scanning ◽

Short Pulse ◽

Test Method ◽

Repetition Frequency ◽

Orifice Diameter

Both superalloy GH2135 and stainless steel 420J1 were used as test materials to be processed by LASERTEC 80 PowerDrill three-dimensional solid laser processing center. The microstructure of the hole was investigated by super depth of field microscope and laser scanning microscope. The front and back orifice diameter, orifice deposits and thermal effect of accumulation zone were studied. The single factor test method was used to study the influence of pulse energy, pulse width and repetition frequency on the quality of micro holes. The results showed that the front and back diameter of the holes all increase with the increase of pulse energy from 0.4J-3.9J. And the front and back aperture are increase with the increase of pulse width from 0.9ms-1.9ms. Meanwhile, the variation of the aperture and pore taper is more noticeable with the repetition frequency changed from 10Hz-60Hz. The results revealed that pulse energy is one of the biggest influence factors, large pulse energy can lead to small hole taper within a certain range, and short pulse width can reduce orifice debris and splash. Both the recast layer and microcrack were existed in the two kinds of metal materials. The quality of holes drilling in GH2135 is better than 420J1.

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Stratigraphic continuity in 400MHz short-pulse radar profiles of firn in West Antarctica

Annals of Glaciology ◽

10.3189/172756404781813925 ◽

2004 ◽

Vol 39 ◽

pp. 195-200 ◽

Cited By ~ 43

Author(s):

Steven A. Arcone ◽

Vandy B. Spikes ◽

Gordon S. Hamilton ◽

Paul A. Mayewski

Keyword(s):

Short Pulse ◽

Accumulation Rate ◽

High Density ◽

Thin Layers ◽

East Antarctica ◽

Relative Amplitude ◽

Accumulation Rates ◽

West Antarctica ◽

Constructive Interference ◽

Pulse Radar

AbstractWe track dated firn horizons within 400 MHz short-pulse radar profiles to find the continuous extent over which they can be used as historical benchmarks to study past accumulation rates in West Antarctica. The 30–40cm pulse resolution compares with the accumulation rates of most areas. We tracked a particular set that varied from 30 to 90 m in depth over a distance of 600 km. The main limitations to continuity are fading at depth, pinching associated with accumulation rate differences within hills and valleys, and artificial fading caused by stacking along dips. The latter two may be overcome through multi-kilometer distances by matching the relative amplitude and spacing of several close horizons, along with their pulse forms and phases. Modeling of reflections from thin layers suggests that the – 37 to – 50 dB range of reflectivity and the pulse waveforms we observed are caused by the numerous thin ice layers observed in core stratigraphy. Constructive interference between reflections from these close, high-density layers can explain the maintenance of reflective strength throughout the depth of the firn despite the effects of compaction. The continuity suggests that these layers formed throughout West Antarctica and possibly into East Antarctica as well.

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