471,886 research outputs found
GEOCHEMISTRY OF METALS AND NUTRIENTS IN FINE-SEDIMENT PORE WATER IN BLACKTAIL AND SILVER BOW CREEKS, BUTTE, MONTANA
Historical mining in Butte, Montana has impacted surface and groundwater in the area. Although most of the known sources of contaminants of concern have been removed or remediated, metal loading continues to occur in lower Blacktail Creek and upper Silver Bow Creek. Possible sources of metals include upwelling groundwater and interaction between the stream and metal-rich sediment in the stream bed. To assess the importance of fine sediment as a source (or sink) for metals, this investigation used sediment pore water diffusion samplers (“peepers”). Peepers are ideal for capturing cm-scale vertical gradients in pore water chemistry across the sediment-water interface. Eight peepers were deployed in Blacktail Creek, six in Silver Bow Creek, one in Grove Gulch, and two in shallow ponds south of lower Blacktail Creek. Four piezometers were also installed in the ponds. Pore-water samples extracted from the peepers and piezometers were analyzed for dissolved trace metals, major ions, alkalinity, and selected nutrients. Sediment samples collected at some peeper sites were analyzed by X-ray diffraction and handheld X-ray fluorescence. Dissolved Fe, Mn, As, PO43-, and HCO3- ions generally increased with depth below the sediment-water interface. Pore-water concentrations of up to 609 mg/L Fe, 55 mg/L Mn, and 1.0 mg/L As were measured at depth. These increases in concentration were attributed to reductive dissolution of Fe- and Mn-oxides, coupled to organic matter decay, in the anoxic environment of the fine-grained sediment. Dissolved Fe2+ could then reprecipitate as Fe-oxides once it reached an aerobic environment and potentially reabsorb dissolved As. PO43- and HCO3- concentrations could also be influenced by sulfate reducing bacteria and oxidation of organic matter. Copper, lead, and zinc behaved differently, and generally had very low concentrations in the deeper samples. Bacterial sulfate reduction was indicated by trace levels of H2S, enough to precipitate Cu, Pb and Zn as sulfide minerals. In some cases, there was a zone where dissolved Cu and Zn concentrations increased sharply in the top 2–6 cm of the sediment column. This could indicate oxidation of fine-grained sulfide minerals in the near-surface pore water. Fick’s first law was used to quantify the diffusive flux of dissolved arsenic from the sediment pore water into Silver Bow and Blacktail Creeks. The same approach was use to estimate downwards diffusion of dissolved Zn from Grove Gulch into its own sediment. The calculated fluxes are negligible for the streams due to the short residence time of water passing through Lower Area One. However, upwards diffusion of As into the shallow ponds could lead to a build-up in dissolved As over time. Although the stream sediments act as a temporary metal sink, the fine sediments are eventually dispersed back into the main stream during periods of high streamflow and bioturbation. Periodic removal of these fine-grained sediments from the stream channels would reduce the total load of metals flowing down Silver Bow Creek
Annual report RUAF - Cities farming for the future, South and South East Asia Region, 2008
Urban agriculture / Training / Development projects / India / Sri Lanka
Methods for verifying the accuracy of wind profiles
Comparisons of radar-measured winds have been made with several types of measurements not only to verify radar data but also to seek a satisfactory comparison method. Three of the comparisons that have been made with Colorado Profiler radars are summarized. Radar measurements were compared with radiosonde measurements. Infrared lidar and 915 MHz radar were compared with radiosondes. A brief radar/radar comparison was made using the 50-MHz radar and a 3-cm wavelength meteorological Doppler radar during precipitation
Properties of the MIMO radar ambiguity function
MIMO (multiple-input multiple-output) radar is an emerging technology which has drawn considerable attention. Unlike the traditional SIMO (single-input multiple-output) radar, which transmits scaled versions of a single waveform in the antenna elements, the MIMO radar transmits independent waveforms in each of the antenna elements. It has been shown that MIMO radar systems have many advantages such as high spatial resolution, improved parameter identifiability, and enhanced flexibility for transmit beampattern design. In the traditional SIMO radar, the range and Doppler resolutions can be characterized by the radar ambiguity function. It is a major tool for studying and analyzing radar signals. Recently, the ambiguity function has been extended to the MIMO radar case. In this paper, some mathematical properties of the MIMO radar ambiguity function are derived. These properties provide insights into the MIMO radar waveform design
Constant Amplitude Doppler Producing Radar Reflector
A constant amplitude Doppler producing radar reflector for simulating a moving target. A plurality of dihedral reflectors having equal radar cross sections are rotated axially at equal rotational speeds. The dihedral reflectors are separated laterally and in the direction towards the illuminating radar by a distance which keeps the radar returns from the two reflectors in phase quadrature. With the radar cross sections of the reflectors being equal, the return signals to a linearly polarized radar maintains constant amplitude as the dihedral reflectors rotate.Georgia Tech Research Corporatio
Numerical study on signatures of atmospheric convective cells in radar images of the ocean
Current and wind variations at the ocean surface can give rise to a modulation of the sea surface roughness and thus become visible in radar images. The discrimination between radar signatures of oceanic and atmospheric phenomena can be quite difficult, since signatures of different origin can have very similar shapes and magnitudes and are often superimposed upon each other. In this work we employ a numerical radar imaging model for an investigation of typical properties of radar signatures of atmospheric convective cells and of theoretical differences between such atmospherically induced radar signatures and those of oceanic phenomena. We show that main characteristics of observed multifrequency/multipolarization radar signatures of atmospheric convective cells over the Gulf Stream are reproduced quite well by the proposed model. This encourages us to vary wind and radar parameters systematically in order to get a general overview of the dependency of atmospherically induced radar signatures on these parameters. Finally, we compare typical characteristics of radar signatures of atmospheric and oceanic phenomena, and we present simulated radar images of a scenario of superimposed atmospheric convective cells and oceanic internal waves. We show that the proposed model supports the experimental finding that radar signatures of oceanic phenomena are stronger at horizontal (HH) than at vertical (VV) polarization, while atmospherically induced radar signatures are better visible at VV polarization
The Fundamentals of Radar with Applications to Autonomous Vehicles
Radar systems can be extremely useful for applications in autonomous vehicles. This paper seeks to show how radar systems function and how they can apply to improve autonomous vehicles. First, the basics of radar systems are presented to introduce the basic terminology involved with radar. Then, the topic of phased arrays is presented because of their application to autonomous vehicles. The topic of digital signal processing is also discussed because of its importance for all modern radar systems. Finally, examples of radar systems based on the presented knowledge are discussed to illustrate the effectiveness of radar systems in autonomous vehicles
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