Results 1 - 10 of 2837
Results 1 - 10 of 2837. Search took: 0.024 seconds
|Sort by: date | relevance|
[en] Simulations from the University of Wisconsin Non-Hydrostatic Modeling System (UW-NMS) along with those from other models indicate a strong tendency to overproduce ice, resulting in a decimation of the liquid portion of mixed-phase stratus through the Bergeron-Findeissen process. Immersion freezing was illustrated to be a major contributor to ice production within these cloud layers, and aerosol properties were illustrated to be an important consideration in the simulation of this process. In particular, the soluble mass fraction and aerosol insoluble mass type were demonstrated to influence simulation of the immersion freezing process, Data collected by the Arctic High Spectral Resolution Lidar and Millimeter Cloud Radar during the M-PACE period was analyzed in order to provide a statistical dataset for validation of simulations of mixed-phase stratus. 270 hours of single-layer cases were reviewed, and mean values for cloud base height, cloud thickness, cloud optical thickness, cloud temperature, wind direction, and liquid and ice particle size, particle number density, and water content were derived.
[en] Ground Penetrating Radar (GPR) uses electromagnetic microwave that is similar to sound in an ultrasonic pulse-echo methods. It is based on the propagation of electromagnetic energy through materials of different dielectric constants (similar to acoustic impedance in sound). The greater the difference between dielectric constants at an interface between two materials, the greater the amount of electromagnetic energy reflected at the interface. This paper discuss about the study of GPR signal pattern reflected from anomalies underground. The equipment used is MALA Geoscience RAMAC utilizing 250 MHz antenna. The subject of interest is remains of graves that dated back 50 years of age. Scanning was performed from the top surface of the grave. Then, the remains were exhumed and the reflector are identified. Post processing using Matlab are performed for signal pattern analysis and compared with actual reflector contain in each individual grave. (author)
[en] The objective of this applied research and development project is to develop a system known as '3-D SISAR'. This system consists of a ground penetrating radar with software algorithms designed for the detection, location, and identification of buried objects in the underground hazardous waste environments found at DOE storage sites. Three-dimensional maps of the object locations will be produced which can assist the development of remediation strategies and the characterization of the digface during remediation operations. It is expected that the 3-D SISAR will also prove useful for monitoring hydrocarbon based contaminant migration after remediation. The underground imaging technique being developed under this contract utilizes a spotlight mode Synthetic Aperture Radar (SAR) approach which, due to its inherent stand-off capability, will permit the rapid survey of a site and achieve a high degree of productivity over large areas. When deployed from an airborne platform, the stand-off techniques is also seen as a way to overcome practical survey limitations encountered at vegetated sites
[en] In this paper, we compare statistical methods for analyzing pass/fail data collected over time; some methods are traditional and one (the RADAR or Rationale for Assessing Degradation Arriving at Random) was recently developed. These methods are used to provide uncertainty bounds on reliability. We make observations about the methods' assumptions and properties. Finally, we illustrate the differences between two traditional methods, logistic regression and Weibull failure time analysis, and the RADAR method using a numerical example.
[en] In this paper we discuss the edge-preserving regularization method in the reconstruction of physical parameters from geophysical data such as seismic and ground-penetrating radar data. In the regularization method a potential function of model parameters and its corresponding functions are introduced. This method is stable and able to preserve boundaries, and protect resolution. The effect of regularization depends to a great extent on the suitable choice of regularization parameters. The influence of the edge-preserving parameters on the reconstruction results is investigated and the relationship between the regularization parameters and the error of data is described.
[en] Comets rarely come close enough to be studied intensively with Earth-based radar. The most recent such occurrence was when Comet 103P/Hartley 2 passed within 0.12 AU in late 2010 October, less than two weeks before the EPOXI flyby. This offered a unique opportunity to improve pre-encounter trajectory knowledge and obtain complementary physical data for a spacecraft-targeted comet. 103P/Hartley 2 is only the fourth comet nucleus to be imaged with radar and already the second to be identified as an elongated, bilobate object based on its delay-Doppler signature. The images show the dominant spin mode to be a rotation about the short axis with a period of 18.2 hr. The nucleus has a low radar albedo consistent with a surface density of 0.5-1.0 g cm-3. A separate echo component was detected from large (>cm) grains ejected anisotropically with velocities of several to tens of meters per second. Radar shows that, in terms of large-grain production, 103P/Hartley 2 is an unusually active comet for its size.
[en] Experimental results of multifrequency HF Doppler radar studies during electromagnetic pumping of the ionosphere from the ground are reported. The Doppler shifts of the radar waves after turn-on of the vertically injected HF pump wave depend on the pump frequency and exhibit, at relatively large reflection altitudes, opposite signs for pump frequencies above or below an electron gyroharmonic. The results are interpreted in terms of pump-induced plasma expulsion and enhanced ionization. For pump frequencies at a gyroharmonic, a minimum of plasma perturbation is detected with the radars. copyright 1997 The American Physical Society
[en] Complete text of publication follows. A major new research infrastructure is being planned to be constructed in Northern Scandinavia. The new EISCAT 3D radar system has a design goal of ten times higher temporal and spatial resolution than the present radars. The modular construction is aimed at a final configuration consisting of several very large phased-array transmitters/ receivers with multiple receiver arrays. Some arrays are very large, up to the scale of 30000 individual antenna elements. The receiver arrays will be located at 50-150 km distance from the illuminators, so that the total system will comprise in the order of 100 000 elements. The volumetric radar imaging capability in an extended spatial area with simultaneous full-vector drift velocities, continuous operation modes, built-in short baseline interferometry capability for imaging sub-beam width scales, real-time data access for applications and extensive data archiving and analysis solutions will provide an unprecedented science and technology application opportunity, well beyond the traditional ground-based ionospheric remote sensing role of the old incoherent scatter radars. EISCAT 3D was accepted on the European Roadmap for Research Infrastructures by the European Strategy Forum on Research Infrastructures in December 2008. The facility will be constructed as a modular concept by year 2015. The first design study of the facility was conducted recently, during 2005-2009 by EISCAT Scientific Association, University of Tromso, Lulea University of Technology, Swedish Institute of Space Physics, Rutherford Appleton Laboratory, and supported by EU FP6 funding. EISCAT Scientific Association operates currently three incoherent scatter radars in Northern Scandinavia on behalf of its associate members in Finland, China, Germany, Japan, Norway, Sweden and United Kingdom, as well as currently supporting partners in France, Russia and Ukraine.
[en] When a spill of radioactive waste occurs, one of the main concerns is the flow pattern of ground water in the area of the spill. Ground probing radar is a relatively new geophysical technique which can provide high resolution data on the surficial geology and water distribution. The results of some preliminary radar experiments conducted at Chalk River Nuclear Laboratories (CRNL) of the Atomic Energy of Canada Limited (AECL), Chalk River, Ontario are presented. (auth)