959 resultados para Imaging and optical processing
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Otto-von-Guericke-Universität Magdeburg, Fakultät für Naturwissenschaften, Dissertation, 2016
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Identifying cloud interference in satellite-derived data is a critical step toward developing useful remotely sensed products. Most MODIS land products use a combination of the MODIS (MOD35) cloud mask and the 'internal' cloud mask of the surface reflectance product (MOD09) to mask clouds, but there has been little discussion of how these masks differ globally. We calculated global mean cloud frequency for both products, for 2009, and found that inflated proportions of observations were flagged as cloudy in the Collection 5 MOD35 product. These erroneously categorized areas were spatially and environmentally non-random and usually occurred over high-albedo land-cover types (such as grassland and savanna) in several regions around the world. Additionally, we found that spatial variability in the processing path applied in the Collection 5 MOD35 algorithm affects the likelihood of a cloudy observation by up to 20% in some areas. These factors result in abrupt transitions in recorded cloud frequency across landcover and processing-path boundaries impeding their use for fine-scale spatially contiguous modeling applications. We show that together, these artifacts have resulted in significantly decreased and spatially biased data availability for Collection 5 MOD35-derived composite MODIS land products such as land surface temperature (MOD11) and net primary productivity (MOD17). Finally, we compare our results to mean cloud frequency in the new Collection 6 MOD35 product, and find that landcover artifacts have been reduced but not eliminated. Collection 6 thus increases data availability for some regions and land cover types in MOD35-derived products but practitioners need to consider how the remaining artifacts might affect their analysis.
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PURPOSE The purpose of this study was to identify SD-OCT changes that correspond to leakage on fluorescein (FA) and indocyanine angiography (ICGA) and evaluate effect of half-fluence photodynamic therapy (PDT) on choroidal volume in chronic central serous choroidoretinopathy (CSC). METHODS Retrospective analysis of patients with chronic CSC who had undergone PDT. Baseline FA and ICGA images were overlaid on SD-OCT to identify OCT correlates of FA or ICGA hyperfluorescence. Choroidal volume was evaluated in a subgroup of eyes before and after PDT. RESULTS Twenty eyes were evaluated at baseline, of which seven eyes had choroidal volume evaluations at baseline and 3 months following PDT. SD-OCT changes corresponding to FA hyperfluorescence were subretinal fluid (73%), RPE microrip (50%), RPE double-layer sign (31%), RPE detachment (15%), and RPE thickening (8%). ICGA hyperfluoresence was correlated in 93% with hyperreflective spots in the superficial choroid. Choroidal volume decreased from 9.35 ± 1.99 to 8.52 ± 1.92 and 8.04 ± 1.7 mm(3) (at 1 and 3 months post PDT, respectively, p ≤ 0.001). CONCLUSIONS We identified specific OCT findings that correlate with FA and ICGA leakage sites. SD-OCT is a valuable tool to localize CSC lesions and may be useful to guide PDT treatment. Generalized choroidal volume decrease occurs following PDT and extends beyond PDT treatment site.
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National Highway Traffic Safety Administration, Washington, D.C.
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National Highway Traffic Safety Administration, Washington, D.C.
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"EDL# 13980"--P. [4] of cover.
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"UIUCDCS-R-74-630"
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"2 August 1957."
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Mode of access: Internet.