764 research outputs found
An Engineering Trade Space Analysis for a Space-Based Hyperspectral Chromotomographic Scanner
Hyperspectroscopy for fast transient events such as battlefield explosions is an undeveloped area of spectral imaging. This thesis is a discussion of issues involved with taking a laboratory design for a rotating prism hyperspectral chromotomographic (CT) instrument and producing a first approximation satellite payload design, operating scheme and trade space analysis to support demonstration of this technology in low-earth orbit. This instrument promises the capability of adding a time dimension to the normal spatial and spectral data produced by most hyperspectral imagers. The ultimate goal is to conduct experiments demonstrating the ultimate viability of spectral definition of transient combustion events on the ground from space. The experiment will be designed to use the CT scanner to collect, store and transmit data from any suitable target on the earth surface in the orbit footprint
Seeing the Big Picture: System Architecture Trends in Endoscopy and LED-Based hyperspectral Subsystem Intergration
Early-stage colorectal lesions remain difficult to detect. Early development of neoplasia tends to be small (less than 10 mm) and flat and difficult to distinguish from surrounding mucosa. Additionally, optical diagnosis of neoplasia as benign or malignant is problematic. Low rates of detection of these lesions allow for continued growth in the colorectum and increased risk of cancer formation. Therefore, it is crucial to detect neoplasia and other non-neoplastic lesions to determine risk and guide future treatment. Technology for detection needs to enhance contrast of subtle tissue differences in the colorectum and track multiple biomarkers simultaneously. This work implements one such technology with the potential to achieve the desired multi-contrast outcome for endoscopic screenings: hyperspectral imaging. Traditional endoscopic imaging uses a white light source and a RGB detector to visualize the colorectum using reflected light. Hyperspectral imaging (HSI) acquires an image over a range of individual wavelength bands to create an image hypercube with a wavelength dimension much deeper and more sensitive than that of an RGB image. A hypercube can consist of reflectance or fluorescence (or both) spectra depending on the filtering optics involved. Prior studies using HSI in endoscopy have normally involved ex vivo tissues or xiv optics that created a trade-off between spatial resolution, spectral discrimination and temporal sampling. This dissertation describes the systems design of an alternative HSI endoscopic imaging technology that can provide high spatial resolution, high spectral distinction and video-rate acquisition in vivo. The hyperspectral endoscopic system consists of a novel spectral illumination source for image acquisition dependent on the fluorescence excitation (instead of emission). Therefore, this work represents a novel contribution to the field of endoscopy in combining excitation-scanning hyperspectral imaging and endoscopy. This dissertation describes: 1) systems architecture of the endoscopic system in review of previous iterations and theoretical next-generation options, 2) feasibility testing of a LED-based hyperspectral endoscope system and 3) another LED-based spectral illuminator on a microscope platform to test multi-spectral contrast imaging. The results of the architecture point towards an endoscopic system with more complex imaging and increased computational capabilities. The hyperspectral endoscope platform proved feasibility of a LED-based spectral light source with a multi-furcated solid light guide. Another LED-based design was tested successfully on a microscope platform with a dual mirror array similar to telescope designs. Both feasibility tests emphasized optimization of coupling optics and combining multiple diffuse light sources to a common output. These results should lead to enhanced imagery for endoscopic tissue discrimination and future optical diagnosis for routine colonoscopy
A Compact, High Resolution Hyperspectral Imager for Remote Sensing of Soil Moisture
Measurement of soil moisture content is a key challenge across a variety of fields, ranging from civil engineering through to defence and agriculture. While dedicated satellite platforms like SMAP and SMOS provide high spatial coverage, their low spatial resolution limits their application to larger regional studies. The advent of compact, high lift capacity UAVs has enabled small scale surveys of specific farmland cites.
This thesis presents work on the development of a compact, high spatial and spectral resolution hyperspectral imager, designed for remote measurement of soil moisture content. The optical design of the system incorporates a bespoke freeform blazed diffraction grating, providing higher optical performance at a similar aperture to conventional Offner-Chrisp designs.
The key challenges of UAV-borne hyperspectral imaging relate to using only solar illumination, with both intermittent cloud cover and atmospheric water absorption creating challenges in obtaining accurate reflectance measurements. A hardware based calibration channel for mitigating cloud cover effects is introduced, along with a comparison of methods for recovering soil moisture content from reflectance data under varying illumination conditions. The data processing pipeline required to process the raw pushbroom data into georectified images is also discussed.
Finally, preliminary work on applying soil moisture techniques to leaf imaging are presented
Optical Design and Wavelength Calibration of a DMD-based Multi-Object Spectrograph
The multi-object spectrograph (MOS) has been the benchmark for the current
generation of astronomical spectrographs, valued for its ability to acquire the
spectra of hundreds of objects simultaneously. In the last two decades, the
digital micromirror device (DMD) has shown potential in becoming the central
component of the MOS, being used as a programmable slit array. We have designed
a seeing-limited DMD-based MOS covering a spectral range of 0.4 to 0.7 m,
with a field of view (FOV) of and a spectral
resolution of . This DMD-MOS employs all-spherical refractive
optics, and a volume phase holographic (VPH) grism as the dispersive element
for high throughput. In this paper, we present the optical design and
optimization process of this DMD-MOS, as well as a preliminary wavelength
calibration procedure for hyperspectral data reduction. Using simulated data of
the DMD-MOS, a procedure was developed to measure hyperspectral imaging
distortion and to construct pixel-to-wavelength mappings on the detector. An
investigation into the relationships between DMD micromirrors and detector
pixels was conducted. This DMD-MOS will be placed on a 0.5 m diameter telescope
as an exploratory study for future DMD-based MOS systems.Comment: 15 pages, 32 figures, 1 table, SPIE Astronomical Telescopes +
Instrumentation 202
Image-Based Bidirectional Reflectance Distribution Function of Human Skin in the Visible and Near Infrared
Human detection is an important first step in locating and tracking people in many missions including SAR and ISR operations. Recent detection systems utilize hyperspectral and multispectral technology to increase the acquired spectral content in imagery and subsequently better identify targets. This research demonstrates human detection through a multispectral skin detection system to exploit the unique optical properties of human skin. At wavelengths in the VIS and NIR regions of the electromagnetic spectrum, an individual can be identified by their unique skin parameters. Current detection methods base the skin pixel selection criteria on a diffuse skin reflectance model; however, it can be observed that human skin exhibits a combination of specular and diffuse reflectance. The objective of this effort is to better characterize human skin reflectance by collecting image-based BRDF skin measurements for future model incorporation in the existing multispectral skin detection system. Integrating multispectral BRDF data should reduce misdetections and better describe skin reflectance as a function of illumination source, target, and detector orientation
Design of freeform diffraction gratings: performance, limitations and potential applications
Spectroscopy is a key technique in astronomy and nowadays most major telescopes include at least one spectrograph in their instrument suite. The dispersive element is one of the most important components and it defines the pupil size, spectral resolution and efficiency. Different types of dispersive elements have been developed including prisms, grisms, VPH and echelle gratings. In this paper, we investigate the design and optimization possibilities offered by metallic freeform gratings using diamond machining techniques. The incorporation of power in a diffraction grating enables several functionalities within the same optical component, such as the combination of dispersion, focusing and field reformat. The resulting benefit is a reduction in the number of surfaces and therefore, an improvement in the throughput. Freeform surfaces are also interesting for their enhanced optical performance by allowing extra degree of freedom in the optimization. These degrees of freedom include the shape of the substrate but also additional parameters such as the pitch or the number of blaze angle. Freeform gratings used as single optical component systems also present some limitations such as the trade-off between optical quality versus field of view or the spectral range versus spectral resolution. This paper discusses the possibility offered by the design of freeform gratings for low to medium spectral resolution, in the visible and near-infrared, for potential applications in ultra-compact integral field spectrographs
Scanning, non-contact, hybrid broadband diffuse optical spectroscopy and diffuse correlation spectroscopy system
A scanning system for small animal imaging using non-contact, hybrid broadband diffuse optical spectroscopy (ncDOS) and diffuse correlation spectroscopy (ncDCS) is presented. The ncDOS uses a two-dimensional spectrophotometer retrieving broadband (610-900 nm) spectral information from up to fifty-seven source-detector distances between 2 and 5 mm. The ncDCS data is simultaneously acquired from four source-detector pairs. The sample is scanned in two dimensions while tracking variations in height. The system has been validated with liquid phantoms, demonstrated in vivo on a human fingertip during an arm cuff occlusion and on a group of mice with xenoimplanted renal cell carcinoma. (C) 2016 Optical Society of Americ
Hyperspectral interferometry for single-shot profilometry and depth-resolved displacement field measurement
A new approach to the absolute measurement of two-dimensional optical path differences
is presented in this thesis. The method, which incorporates a white light interferometer and
a hyperspectral imaging system, is referred to as Hyperspectral Interferometry. A prototype
of the Hyperspectral Interferometry (HSI) system has been designed, constructed and
tested for two types of measurement: for surface profilometry and for depth-resolved
displacement measurement, both of which have been implemented so as to achieve single
shot data acquisition.
The prototype has been shown to be capable of performing a single-shot 3-D shape
measurement of an optically-flat step-height sample, with less than 5% difference from the
result obtained by a standard optical (microscope) based method. The HSI prototype has
been demonstrated to be able to perform single-shot measurement with an unambiguous
352 (m depth range and a rms measurement error of around 80 nm. The prototype has also
been tested to perform measurements on optically rough surfaces. The rms error of these
measurements was found to increase to around 4× that of the smooth surface.
For the depth-resolved displacement field measurements, an experimental setup was
designed and constructed in which a weakly-scattering sample underwent simple
compression with a PZT actuator. Depth-resolved displacement fields were reconstructed
from pairs of hyperspectral interferograms. However, the experimental results did not
show the expected result of linear phase variation with depth. Analysis of several possible
causes has been carried out with the most plausible reasons being excessive scattering
particle density inside the sample and the possibility of insignificant deformation of the
sample due to insufficient physical contact between the transducer and the sample
- …