10 research outputs found
Recommended from our members
Huygens-Fresnel Wave-Optics Simulation of Atmospheric Optical Turbulence and Reflective Speckle in CO
The measurement sensitivity of CO{sub 2} differential absorption LIDAR (DIAL) can be affected by a number of different processes. Two of these processes are atmospheric optical turbulence and reflective speckle. Atmospheric optical turbulence affects the beam distribution of energy and phase on target. The effects of this phenomenon include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has been shown to have a major impact on the sensitivity of CO{sub 2} DIAL. The authors have previously developed a Huygens-Fresnel wave optics propagation code to separately simulate the effects of these two processes. However, in real DIAL systems it is a combination of these phenomena, the interaction of atmospheric optical turbulence and reflective speckle, that influences the results. In this work, the authors briefly review a description of the model including the limitations along with a brief summary of previous simulations of individual effects. The performance of the modified code with respect to experimental measurements affected by atmospheric optical turbulence and reflective speckle is examined. The results of computer simulations are directly compared with lidar measurements and show good agreement. In addition, simulation studies have been performed to demonstrate the utility and limitations of the model. Examples presented include assessing the effects for different array sizes on model limitations and effects of varying propagation step sizes on intensity enhancements and intensity probability distributions in the receiver plane
Recommended from our members
Measurement of H zero excited states produced by foil stripping of 800-MeV H[sup [minus]] ions
Foil stripping of H[sup [minus]] directly to H[sup +] is being considered for proton injection in the next generation of high-current proton storage rings. This technique can result in significant losses because excited states of HO, which are also produced in the foil, are field stripped in the downstream bending magnets. Without due care in the injection system design, many of the resulting protons will be outside the acceptance of the storage ring and will be quickly lost. We measured the production of such H[sup 0] excited states at the LAMPF High Resolution Atomic Beam Facility. An 800-MeV H[sup [minus]] beam was passed through carbon foils of thicknesses 70, 100, 200, and 300 [mu]g/cm[sup 2], and the excited states were analyzed by a special magnet downstream of the foil. The magnet had a linear field gradient so that the trajectories of the outgoing protons could be used to reconstruct the field values at which the various H[sup 0] stripped. We found that about 1% of the H[sup 0] emerge in excited states which can be stripped to protons by ring-bending magnets
Tempo de uso em pastagens e volume dos macroporos do solo na Amazônia Central
Soil quality under usage through time, and within agroecosystems, is an important aspect in order to improve soil usage sustainability in tropical regions. In this scenario, quantifying the effects of time of usage in pastures under the different soil components (macropores) is important to determine the management planning and reclamation most adequate for such areas. The objective of this study was to evaluate the time effect in pastures (4, 5 and 8 years) on macropore volume after ten years of abandonment and nine of reclamation through Capoeira and agroecosystems. Macropore volume was measured in three different depths (0-5; 5-10 and 10-15 cm) in 100 cm3 steel cylinders. Macropore volume dropped significantly with the raise in time usage of the areas as pasture, which in turn makes time usage evident in pastures over macropore volume of soil ≥ 50μ μm, mainly in the first soil layer (0-5 cm), directly affected by animal impact. Therefore, it is suggested that time of soil reclamation should be longer than ten years so that the soil characteristics can be recovered