271 research outputs found

    Mapping Surface Oil Extent From the Deepwater Horizon Oil Spill Using ASCAT Backscatter

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    On the trade-off between enhancement of the spatial resolution and noise amplification in conical-scanning microwave radiometers

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    The ability to enhance the spatial resolution of measurements collected by a conical-scanning microwave radiometer (MWR) is discussed in terms of noise amplification and improvement of the spatial resolution. Simulated (and actual) brightness temperature profiles are analyzed at variance of different intrinsic spatial resolutions and adjacent beams overlapping modeling a simplified 1-D measurement configuration (MC). The actual measurements refer to Special Sensor Microwave Imager (SSM/I) data collected using the 19.35 and the 37.00 GHz channels that match the simulated configurations. The reconstruction of the brightness profile at enhanced spatial resolution is performed using an iterative gradient method which allows a fine tuning of the level of regularization. Objective metrics are introduced to quantify the enhancement of the spatial resolution and noise amplification. Numerical experiments, performed using the simplified 1-D MC, show that the regularized deconvolution results in negligible advantages when dealing with low-overlapping/fine-spatial-resolution configurations. Regularization is a mandatory step when addressing the high-overlapping/low-spatial-resolution case and the spatial resolution can be enhanced up to 2.34 with a noise amplification equal to 1.56. A more stringent requirement on the noise amplification (up to 0.6) results in an improvement of the spatial resolution up to 1.64.Peer ReviewedPostprint (author's final draft

    Improving coherence scanning interferometry signal modelling and topography measurement for complex surfaces

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    This thesis presents work on advanced optical surface metrology methods that enable extending the range of surface slopes that can be reliably measured by optical surface topography measurement instruments, and on investigating the reliability of the current capability. Optical instruments can only capture a limited portion of light scattered from an object’s surface, determined by the instrument’s numerical aperture. As the surface measured becomes steeper, less scatter is captured until all specular scatter is lost, referred to as the specular reflection limit (SRL). While surface measurement of slopes beyond the SRL by modern instruments is possible via the capture and detection of non-specular scatter, the instrument response to these slopes is not well understood. In addition, as the non-specular scatter has a low signal-to-noise ratio, data dropout can occur. Topography measurement of steep and complex surfaces using optical methods can therefore be challenging and have an unknown reliability, and can have significant errors when multiple scattering is present. The instrument modelling and experimental work focussed on coherence scanning interferometry (CSI). Through use of an approximate linear model the instrument response of a CSI instrument to various slope angles and spatial frequencies was described by a three-dimensional (3D) surface transfer function (STF). This theory was experimentally verified by demonstrating that an experimental 3D STF obtained from measurement of microspheres can be used to generate a filter that can compensate for the effect of lens aberration at a fundamental level and consequently reduce errors in the topographies obtained, especially from surface slopes just below the SRL. Second, a rigorous two-dimensional boundary element method (BEM) model of electromagnetic surface scatter was verified through multiple comparisons including an exact analytical Mie scatter solution and through experimental comparison to measurement data from a laser scatterometer, providing evidence of the BEM model’s capability to accurately predict scatter from complex surfaces, including those that linear models cannot accurately model. A CSI model based on this BEM scattering model was then developed and verified, demonstrating the model’s capability to accurately model the CSI signal for complex surfaces which contain steep surfaces, including those that produce multiple scattering. Using this BEM-CSI model and experimental measurement, the capability of optical surface topography measurement methods for measurement of steep surfaces was investigated, illustrated for the first time with both fringe data and the resulting height estimates for a series of surfaces at slopes steeper than the SRL. At high tilt angles it was found that sharp edges with undercuts still provide strong signals which appear as plateaus in the topography data, with a width corresponding to the width of the point spread function of the instrument. While phase information was lost, part of the topography could still be obtained from the non-specular scatter. The BEM-CSI model’s results were accurate even for challenging surfaces beyond the capabilities of linear models, providing a tool for future investigation of other complex surfaces and providing progress towards evaluating the measurement uncertainty of complex surface measurements by optical instruments

    On the Trade-Off Between Enhancement of the Spatial Resolution and Noise Amplification in Conical-Scanning Microwave Radiometers

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    The ability to enhance the spatial resolution of measurements collected by a conical-scanning microwave radiometer (MWR) is discussed in terms of noise amplification and improvement of the spatial resolution. Simulated (and actual) brightness temperature profiles are analyzed at variance of different intrinsic spatial resolutions and adjacent beams overlapping modeling a simplified 1-D measurement configuration (MC). The actual measurements refer to Special Sensor Microwave Imager (SSM/I) data collected using the 19.35 and the 37.00 GHz channels that match the simulated configurations. The reconstruction of the brightness profile at enhanced spatial resolution is performed using an iterative gradient method which allows a fine tuning of the level of regularization. Objective metrics are introduced to quantify the enhancement of the spatial resolution and noise amplification. Numerical experiments, performed using the simplified 1-D MC, show that the regularized deconvolution results in negligible advantages when dealing with low-overlapping/fine-spatial-resolution configurations. Regularization is a mandatory step when addressing the high-overlapping/low-spatial-resolution case and the spatial resolution can be enhanced up to 2.34 with a noise amplification equal to 1.56. A more stringent requirement on the noise amplification (up to 0.6) results in an improvement of the spatial resolution up to 1.64

    Improving coherence scanning interferometry signal modelling and topography measurement for complex surfaces

    Get PDF
    This thesis presents work on advanced optical surface metrology methods that enable extending the range of surface slopes that can be reliably measured by optical surface topography measurement instruments, and on investigating the reliability of the current capability. Optical instruments can only capture a limited portion of light scattered from an object’s surface, determined by the instrument’s numerical aperture. As the surface measured becomes steeper, less scatter is captured until all specular scatter is lost, referred to as the specular reflection limit (SRL). While surface measurement of slopes beyond the SRL by modern instruments is possible via the capture and detection of non-specular scatter, the instrument response to these slopes is not well understood. In addition, as the non-specular scatter has a low signal-to-noise ratio, data dropout can occur. Topography measurement of steep and complex surfaces using optical methods can therefore be challenging and have an unknown reliability, and can have significant errors when multiple scattering is present. The instrument modelling and experimental work focussed on coherence scanning interferometry (CSI). Through use of an approximate linear model the instrument response of a CSI instrument to various slope angles and spatial frequencies was described by a three-dimensional (3D) surface transfer function (STF). This theory was experimentally verified by demonstrating that an experimental 3D STF obtained from measurement of microspheres can be used to generate a filter that can compensate for the effect of lens aberration at a fundamental level and consequently reduce errors in the topographies obtained, especially from surface slopes just below the SRL. Second, a rigorous two-dimensional boundary element method (BEM) model of electromagnetic surface scatter was verified through multiple comparisons including an exact analytical Mie scatter solution and through experimental comparison to measurement data from a laser scatterometer, providing evidence of the BEM model’s capability to accurately predict scatter from complex surfaces, including those that linear models cannot accurately model. A CSI model based on this BEM scattering model was then developed and verified, demonstrating the model’s capability to accurately model the CSI signal for complex surfaces which contain steep surfaces, including those that produce multiple scattering. Using this BEM-CSI model and experimental measurement, the capability of optical surface topography measurement methods for measurement of steep surfaces was investigated, illustrated for the first time with both fringe data and the resulting height estimates for a series of surfaces at slopes steeper than the SRL. At high tilt angles it was found that sharp edges with undercuts still provide strong signals which appear as plateaus in the topography data, with a width corresponding to the width of the point spread function of the instrument. While phase information was lost, part of the topography could still be obtained from the non-specular scatter. The BEM-CSI model’s results were accurate even for challenging surfaces beyond the capabilities of linear models, providing a tool for future investigation of other complex surfaces and providing progress towards evaluating the measurement uncertainty of complex surface measurements by optical instruments

     Ocean Remote Sensing with Synthetic Aperture Radar

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    The ocean covers approximately 71% of the Earth’s surface, 90% of the biosphere and contains 97% of Earth’s water. The Synthetic Aperture Radar (SAR) can image the ocean surface in all weather conditions and day or night. SAR remote sensing on ocean and coastal monitoring has become a research hotspot in geoscience and remote sensing. This book—Progress in SAR Oceanography—provides an update of the current state of the science on ocean remote sensing with SAR. Overall, the book presents a variety of marine applications, such as, oceanic surface and internal waves, wind, bathymetry, oil spill, coastline and intertidal zone classification, ship and other man-made objects’ detection, as well as remotely sensed data assimilation. The book is aimed at a wide audience, ranging from graduate students, university teachers and working scientists to policy makers and managers. Efforts have been made to highlight general principles as well as the state-of-the-art technologies in the field of SAR Oceanography

    Analyses of stone surfaces by optical methods

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    Ornamental stone products are generally used for decorative cladding. A major quality parameter is their aesthetical appearance, which directly impacts their commercial value. The surface quality of stone products depends on the presence of defects both due to the unpredictability of natural materials and to the actual manufacturing process. This work starts reviewing the literature about optical methods for stone surface inspection. A classification is then proposed focusing on their industrial applicability in order to provide a guideline for future investigations. Three innovative systems are proposed and described in details: a vision system, an optical profilometer and a reflectometer for the inspection of polished, bush-hammered, sand-blasted, flame-finished, waterjet processed, and laser engraved surfaces
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