500 research outputs found
Opto-Mechanical Design of a Chromotomographic Imager Direct-Vision Prism Element
Chromotomographic Imaging (CTI) offers advantages in remote sensing by resolving intensity distribution spatially, spectrally, and temporally. The Chromotomography Experiment (CTEx) at the Air Force Institute of Technology (AFIT) explores the application of CTI as a space-based observer. Previous work in instrument development has revealed many of the intricacies of component fabrication and how they impact the resolving of image data. The proposed CTEx instrument has as its chromatic dispersion element a direct-vision prism (DVP) that is made to rotate in order to achieve multiple projection angles. Analysis of previous research established the need for a more accurate characterization of the DVP than has been achieved to date. Research herein presents an investigation into precise characterization of a DVP and a proposed mechanical design of the DVP hardware. The findings of this investigation provide the tools to specify fabrication tolerances for the DVP and advance the research effort
Applications of remote sensing to estuarine management
Projects for sewage outfall siting for pollution control in the lower Chesapeake Bay wetlands are reported. A dye-buoy/photogrammetry and remote sensing technique was employed to gather circulation data used in outfall siting. This technique is greatly favored over alternate methods because it is inexpensive, produces results quickly, and reveals Lagrangian current paths which are preferred in making siting decisions. Wetlands data were obtained by interpretation of color and color infrared photographic imagery from several altitudes. Historical sequences of photographs are shown that were used to document wetlands changes. Sequential infrared photography of inlet basins was employed to determine tidal prisms, which were input to mathematical models to be used by state agencies in pollution control. A direct and crucial link between remote sensing and management decisions was demonstrated in the various projects
SPHERE: the exoplanet imager for the Very Large Telescope
Observations of circumstellar environments to look for the direct signal of
exoplanets and the scattered light from disks has significant instrumental
implications. In the past 15 years, major developments in adaptive optics,
coronagraphy, optical manufacturing, wavefront sensing and data processing,
together with a consistent global system analysis have enabled a new generation
of high-contrast imagers and spectrographs on large ground-based telescopes
with much better performance. One of the most productive is the
Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE)
designed and built for the ESO Very Large Telescope (VLT) in Chile. SPHERE
includes an extreme adaptive optics system, a highly stable common path
interface, several types of coronagraphs and three science instruments. Two of
them, the Integral Field Spectrograph (IFS) and the Infra-Red Dual-band Imager
and Spectrograph (IRDIS), are designed to efficiently cover the near-infrared
(NIR) range in a single observation for efficient young planet search. The
third one, ZIMPOL, is designed for visible (VIR) polarimetric observation to
look for the reflected light of exoplanets and the light scattered by debris
disks. This suite of three science instruments enables to study circumstellar
environments at unprecedented angular resolution both in the visible and the
near-infrared. In this work, we present the complete instrument and its on-sky
performance after 4 years of operations at the VLT.Comment: Final version accepted for publication in A&
Modern optical astronomy: technology and impact of interferometry
The present `state of the art' and the path to future progress in high
spatial resolution imaging interferometry is reviewed. The review begins with a
treatment of the fundamentals of stellar optical interferometry, the origin,
properties, optical effects of turbulence in the Earth's atmosphere, the
passive methods that are applied on a single telescope to overcome atmospheric
image degradation such as speckle interferometry, and various other techniques.
These topics include differential speckle interferometry, speckle spectroscopy
and polarimetry, phase diversity, wavefront shearing interferometry,
phase-closure methods, dark speckle imaging, as well as the limitations imposed
by the detectors on the performance of speckle imaging. A brief account is
given of the technological innovation of adaptive-optics (AO) to compensate
such atmospheric effects on the image in real time. A major advancement
involves the transition from single-aperture to the dilute-aperture
interferometry using multiple telescopes. Therefore, the review deals with
recent developments involving ground-based, and space-based optical arrays.
Emphasis is placed on the problems specific to delay-lines, beam recombination,
polarization, dispersion, fringe-tracking, bootstrapping, coherencing and
cophasing, and recovery of the visibility functions. The role of AO in
enhancing visibilities is also discussed. The applications of interferometry,
such as imaging, astrometry, and nulling are described. The mathematical
intricacies of the various `post-detection' image-processing techniques are
examined critically. The review concludes with a discussion of the
astrophysical importance and the perspectives of interferometry.Comment: 65 pages LaTeX file including 23 figures. Reviews of Modern Physics,
2002, to appear in April issu
Volume based texture mapping
Ankara : The Department of Computer Engineering and Information Science and the Institute of Engineering and Science of Bilkent Univ., 1995.Thesis (Master's) -- -Bilkent University, 1995.Includes bibliographical references leaves 52-55.'I'he most realistic and attractive computer generated images are usually those
that contain a large arnount of visual complexity and detail. Texturing is a
widely used way of adding visual complexity and detail to computer generated
iniciges. Traditionally surface texturing was only used to simulate surface
detail. In this thesis we generate textures dehiuid throughout a region of
three-dimensional space and map those textures together with their geometric
definition onto complex objects. The textured object is rendered volume based
with a. backward mapping algorithm (ray tracing). Hence the texture aJfects
the definition and the realism of the object. In rendering tlie scene, natural
phenomena such cis dispersion and absorption of light is also incorporated.Salk, GĂŒrkanM.S
Multispectral photography for earth resources
A guide for producing accurate multispectral results for earth resource applications is presented along with theoretical and analytical concepts of color and multispectral photography. Topics discussed include: capabilities and limitations of color and color infrared films; image color measurements; methods of relating ground phenomena to film density and color measurement; sensitometry; considerations in the selection of multispectral cameras and components; and mission planning
Examining the relationship of variables related to litigation regarding students with significant cognitive disabilities
Non-null interferometry offers a viable alternative to traditional interferometric testing of aspheric micro-lenses since computer generated holograms or null optics whose fabrication and testing are very expensive, are not required. However, due to the violation of the Nyquist sampling theorem these non-null tests provide limited dynamic range. The dynamic range of these non-null tests can be extended by implementing an index liquid which allows the measurement of micro-lenses with several microns of departure from a sphere. The first objective of this dissertation was to test important micro-lens properties such as the sag, radius of curvature and form errors for a micro-lens by using an index liquid. The results compared favorably to measurements taken on a Twyman-Green interferometer, a contact profilometer and an optical non-contact profilometer. Also, retrace errors, which are aberrations caused by altered ray paths of the test beam through a micro-lens were investigated. Reverse ray-trace and reverse optimization techniques are typically used to calibrate retrace errors, but in depth knowledge of the interferometer optics is assumed, and hence cannot be used for systems containing commercial optics. In this dissertation, re-trace errors are quantified and a novel calibration procedure derived to experimentally compensate for these errors. This retrace error calibration led to agreement of within 1% for the sag values between the index liquid technique and a profilometer. The second objective of this dissertation was to enable measurements of arbitrary geometries and to reduce testing time compared to profilometry. The index liquid technique was applied to faceted microstructured optical products which are becoming more widespread due to advances in manufacturing. Many of these structures contain faceted surfaces with steep slopes. Adequate metrology for such surfaces is lacking. The use of the index liquid technique achieved high quality, high speed measurements of such faceted microstructures. Refraction is accounted for at the interfaces, rather than consider only optical path length changes due to the index liquid, and this significantly improves the facet angle measurement. The technique is demonstrated with the measurement of an array of micro-pyramids and show that our results are in good agreement with measurements taken on a contact profilometer. The index liquid measurements took approximately five seconds to complete compared to a measurement time of six hours for the contact profilometer. The technique was also extended to measure opaque micro-corner cubes by implementing an intermediate replication step. This allowed a measurement of the angle between facets of a nickel micro-corner cube hexagonal array, a combination not previously demonstrated in the literature. A first order uncertainty analysis was carried out on the index liquid technique to determine any limiting factors that need to be taken into account when assessing such parameters as the sag and facet angle. The uncertainties in the sag and facet angle were found to be well below 1%. Lastly secondary factors such interferometer bias, refraction, masking effects and pixel calibration were investigated to understand the possible
implications on the sag and facet angle calculation
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