A dark field illumination probe linked to Raman spectroscopy for non-invasivety determination of ocular biomarkers

For early and effective diagnosis of eye diseases, acquiring biochemical information in the eye is preferred. However, it is obtained by performing a biopsy of the eye tissue. This poses a risk to the integrity of the eye and cannot be performed on a regular basis. Raman spectrometry is a potential and powerful tool for the non-invasive investigation of biochemical information. The challenge to use it in an ophthalmic application is the essential of a high-power laser direct shining through the eye, which raises safety concerns for potential retinal damage .In this thesis, biomedical applications of Raman spectroscopy are explored for eye disease biomarkers and ocular drug measurements in ex vitro, in vitro and in vivo. To ensure a safety measurement by projecting a laser in the eye, two types of dark-field illumination probes are designed, manufactured and validated in conjunction with confocal Raman spectroscopy (CRS) to avoid light damage of the retina. Furthermore, a non-contact dark-field illumination method for the same purpose is proposed and theoretically validated

Comparison of methods for generation of absolute reflectance factor measurements for BRDF studies

For remote sensing applications, there is a need for knowledge concerning the reflectance properties of natural and man-made materials as a function of measurement geometry and wavelength. This information is used to determine the so-called bidirectional reflectance distribution function (BRDF). This study is intended to generate an absolute bidirectional reflectance factor for BRDF studies. This is accomplished by development of a goniospectroradiometer which can simulate any source-sensor-target geometry. The spectral range is from visible to near- infrared (2500 nm) with a spectral resolution of 10 nm. The study involves both theoretical and experimental work for calibration of BRDF by: (1) the directional hemispherical reflectance and (2) a NIST calibrated standard reflectance tile. A PTFE sample is calibrated using both methods, and a comparison test was conducted to verify the accuracy. This PTFE sample can be used as a reference standard material to transfer reflectance factor scale to all source-target-sensor geometries in the visible and infrared regions (400 nm to 2500 nm) of the spectrum

BRDF representation and acquisition

Photorealistic rendering of real world environments is important in a range of different areas; including Visual Special effects, Interior/Exterior Modelling, Architectural Modelling, Cultural Heritage, Computer Games and Automotive Design. Currently, rendering systems are able to produce photorealistic simulations of the appearance of many real-world materials. In the real world, viewer perception of objects depends on the lighting and object/material/surface characteristics, the way a surface interacts with the light and on how the light is reflected, scattered, absorbed by the surface and the impact these characteristics have on material appearance. In order to re-produce this, it is necessary to understand how materials interact with light. Thus the representation and acquisition of material models has become such an active research area. This survey of the state-of-the-art of BRDF Representation and Acquisition presents an overview of BRDF (Bidirectional Reflectance Distribution Function) models used to represent surface/material reflection characteristics, and describes current acquisition methods for the capture and rendering of photorealistic materials

Early Detection of Forest Drought Stress with Very High Resolution Stereo and Hyperspectral Imagery

The project ‘Application of remote sensing for the early detection of drought stress at vulnerable forest sites (ForDroughtDet)’ is funded by the German Federal Agency of Agriculture and Food and aims to detect drought stress in an early phase using remote sensing techniques. In this project, three test sites in the south and middle part of Germany are selected. Three levels of observation and analyses are performed. In the first level, close-range stereo images and spectral information are captured with a research crane in Kranzberg forest. In the second level, three study sites are imaged twice in three years by airborne hyperspectral and stereo cameras. In the third level, the drought stress detection approach will be transferred to regional scale by satellite image. In this paper, we will briefly report our results from the first and second levels. In the first level, 3D models of the forest canopies are generated with the MC-CNN based dense matching approaches, with which the 3D shapes of the stressed and healthy trees are analysed. In addition, for the spectral analyses, different chlorophyll-sensitive indices are calculated and compared for the stressed and healthy trees. In order to further analyse the tree drought stress in the second level, a novel individual tree crown (ITC) segmentation approach is proposed and tested on the airborne stereo dataset

BRDF Representation and Acquisition

Photorealistic rendering of real world environments is important in a range of different areas; including Visual Special effects, Interior/Exterior Modelling, Architectural Modelling, Cultural Heritage, Computer Games and Automotive Design. Currently, rendering systems are able to produce photorealistic simulations of the appearance of many real-world materials. In the real world, viewer perception of objects depends on the lighting and object/material/surface characteristics, the way a surface interacts with the light and on how the light is reflected, scattered, absorbed by the surface and the impact these characteristics have on material appearance. In order to re-produce this, it is necessary to understand how materials interact with light. Thus the representation and acquisition of material models has become such an active research area. This survey of the state-of-the-art of BRDF Representation and Acquisition presents an overview of BRDF (Bidirectional Reflectance Distribution Function) models used to represent surface/material reflection characteristics, and describes current acquisition methods for the capture and rendering of photorealistic materials

Goniophotometry and assessment of bidirectional photometric properties of complex fenestration systems

This paper seeks to provide an overview of the currently available assessment tools for bidirectional transmission or reflection distribution functions (BTDFs and BRDFs) of complex fenestration systems (CFS). In the first part of the paper, the existing experimental devices (goniophotometers) developed specifically for CFS measurement are described. All but two are based on a scanning process to investigate the emerging light flux distribution, the alternative approach being based on digital imaging techniques. A critical analysis of their advantages and shortcomings is proposed to provide both researchers interested in replicating them and more generally potential users of BTDF or BRDF data with a lucid idea of the available options

3D Shape Measurement of Objects in Motion and Objects with Complex Surfaces

This thesis aims to address the issues caused by high reflective surface and object with motion in the three dimensional (3D) shape measurement based on phase shifting profilometry (PSP). Firstly, the influence of the reflectivity of the object surface on the fringe patterns is analysed. One of the essential factors related to phase precision is modulation index, which has a direct relationship with the surface reflectivity. A comparative study focusing on the modulation index of different materials is presented. The distribution of modulation index for different material samples is statistically analysed, which leads to the conclusion that the modulation index is determined by the diffuse reflectivity. Then the method based on optimized combination of multiple reflected image patterns is proposed to address the saturation issue and improve the accuracy for the reconstruction of object with high reflectivity.A set of phase shifted sinusoidal fringe patterns with different exposure time are projected to the object and then captured by camera. Then a set of masks are generated to select the data for the compositing. Maximalsignal-to-noise ratio combining model is employed to form the composite images pattern. The composite images are then used to phase mapping.Comparing to the method only using the highest intensity of pixels for compositing image, the signal noise ratio (SNR) of composite image is increased due to more efficient use of information carried by the images

Influence of snow properties on directional surface reflectance in Antarctica

The significance of the polar regions for the Earth’s climate system and their observed amplified response to climate change indicate the necessity for high temporal and spatial coverage for the monitoring of the reflective properties of snow surfaces and their influencing factors. Therefore, the specific surface area (SSA, as a proxy for snow grain size) and the hemispherical directional reflectance factor (HDRF) of snow were measured for a 2-month period in central Antarctica (Kohnen research station) during austral summer 2013/14. The SSA data were retrieved on the basis of ground-based spectral surface albedo measurements collected by the COmpact RAdiation measurement System (CORAS) and airborne observations with the Spectral Modular Airborne Radiation measurement sysTem (SMART). The snow grain size and pollution amount (SGSP) algorithm, originally developed to analyze spaceborne reflectance measurements by the MODerate Resolution Imaging Spectroradiometer (MODIS), was modified in order to reduce the impact of the solar zenith angle on the retrieval results and to cover measurements in overcast conditions. Spectral ratios of surface albedo at 1280 and 1100 nm wavelength were used to reduce the retrieval uncertainty. The retrieval was applied to the ground-based and airborne observations and validated against optical in situ observations of SSA utilizing an IceCube device. The SSA retrieved from CORAS observations varied between 29 and 96 m2 kg-1. Snowfall events caused distinct relative maxima of the SSA which were followed by a gradual decrease in SSA due to snow metamorphism and wind-induced transport of freshly fallen ice crystals. The ability of the modified algorithm to include measurements in overcast conditions improved the data coverage, in particular at times when precipitation events occurred and the SSA changed quickly. SSA retrieved from measurements with CORAS and MODIS agree with the in situ observations within the ranges given by the measurement uncertainties. However, SSA retrieved from the airborne SMART data underestimated the ground-based results. The spatial variability of SSA in Dronning Maud Land ranged in the same order of magnitude as the temporal variability revealing differences between coastal areas and regions in interior Antarctica. The validation presented in this study provided an unique test bed for retrievals of SSA under Antarctic conditions where in situ data are scarce and can be used for testing prognostic snowpack models in Antarctic conditions. The HDRF of snow was derived from airborne measurements of a digital 180° fish-eye camera for a variety of conditions with different surface roughness, snow grain size, and solar zenith angle. The camera provides radiance measurements with high angular resolution utilizing detailed radiometric and geometric calibrations. The comparison between smooth and rough surfaces (sastrugi) showed significant differences in the HDRF of snow, which are superimposed on the diurnal cycle. By inverting a semi-empirical kernel-driven model for the bidirectional reflectance distribution function (BRDF), the snow HDRF was parameterized with respect to surface roughness, snow grain size, and solar zenith angle. This allows a direct comparison of the HDRF measurements with BRDF products from satellite remote sensing

A Comparative Study of the Bidirectional Reflectance Distribution Function of Several Surfaces as a Mid-wave Infrared Diffuse Reflectance Standard

The Bi-Directional Reflectance Distribution Function (BRDF) has a well defined diffuse measurement standard in the ultraviolet, visible, and near infrared (NIR), Spectralon(trade name). It is predictable, stable, repeatable, and has low surface variation because it is a bulk scatterer. In the mid-wave IR (MWIR) and long-wave IR (LWIR), there is not such a well-defined standard. There are well-defined directional hemispherical reflectance (DHR) standards, but the process of integrating BRDF measurements into DHR for the purpose of calibration is problematic, at best. Direct BRDF measurement standards are needed. This study use current calibration techniques to ensure valid measurements and then systematically investigates the BRDF and its variation for eight potential MWIR diffuse BRDF standards. Diffuseness, repeatability, and reflectance are all considered as required parameters necessary for a di use MWIR BRDF standard. This document shows comparatively that Spectralon is an excellent candidate for a diffuse MWIR BRDF standard