Theses and Dissertations at Montana State University (MSU)
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Item Calibration and characterization of a VNIR hyperspectral imager for produce monitoring(Montana State University - Bozeman, College of Engineering, 2020) Logan, Riley Donovan; Chairperson, Graduate Committee: Joseph A. Shaw; Joseph A. Shaw was a co-author of the article, 'Measuring the polarization response of a VNIR hyperspectral imager' in the journal 'SPIE proceedings' which is contained within this thesis.; Bryan Scherrer, Jacob Senecal, Neil S. Walton, Amy Peerlinck, John W. Sheppard, and Joseph A. Shaw were co-authors of the article, 'Hyperspectral imaging and machine learning for monitoring produce ripeness' in the journal 'SPIE proceedings' which is contained within this thesis.Hyperspectral imaging is a powerful remote sensing tool capable of capturing rich spectral and spatial information. Although the origins of hyperspectral imaging are in terrestrial remote sensing, new applications are emerging rapidly. Owing to its non-destructive nature, hyperspectral imaging has become a useful tool for monitoring produce ripeness. This paper describes the process of characterizing and calibrating a visible near-infrared (VNIR) hyperspectral imager for obtaining accurate images of produce to be used in machine learning algorithms for analysis. In this work, many calibrations and characterization are outlined, including: a radiance calibration, the process of calculating reflectance, pixel uniformity and image stability testing, spectral characterization, illumination source analysis, and measurement of the polarization response. The images obtained by the calibrated hyperspectral imager were converted to reflectance across a spectral range of 387.12 nm to 1023.5 nm, with a spectral resolution of 2.12 nm. A convolutional neural network was used to perform age classification for Yukon Gold potatoes, bananas, and green peppers. Additionally, a genetic algorithm was used to determine the wavelengths carrying the most useful information for age classification. Experiments were run using red green blue (RGB) images, full-spectrum hyperspectral images, and the wavelengths selected by the genetic algorithm feature selection method. Preliminary data from these analyses show promising results at accurately classifying produce age. The genetic algorithm feature selection method is being used to develop a low-cost multispectral imager for use in monitoring produce in grocery stores.Item Characterization of a division-of-focal-plane polarization imager(Montana State University - Bozeman, College of Engineering, 2020) Syed, Musaddeque Anwar Al Abedin; Chairperson, Graduate Committee: Joseph A. ShawPolarization is a fundamental property of light that can be detected with polarization-sensitive instruments. Imaging polarimetry has an immensely wide range of applications, and while much has been accomplished in recent years, there is still a need for sensor systems with improved accuracy, precision, and stability. This paper presents the optical characterization of a commercial division-of-focal plane (DoFP) polarization imager, in an effort to evaluate its performance as a promising instrument in the application of ground-based cloud thermodynamic phase detection. Radiometric characterization values were well within the acceptable region, but the polarimetric contrast was in the range of 20-30, much lower than expected, which may be a result of the broadband measurements being impaired by poor polarizer performance at the blue end of the spectrum. Later, a narrowband polarimetric measurement at 532 + or - 5 nm produced a much enhanced result, with polarimetric contrast in the higher 300s, making the imager a viable option for many remote sensing applications. Also, all-sky imaging of clear daytime sky and its analysis of degree of linear polarization (DoLP) showed encouraging result.Item A study of atmospheric polarization in unique scattering conditions at twilight, during a solar eclipse, and for cloud phase retrievals using all-sky polarization imaging(Montana State University - Bozeman, College of Engineering, 2018) Eschelman, Laura Marie; Chairperson, Graduate Committee: Joseph A. ShawPolarization is a fundamental property of light that can be detected with polarization-sensitive instruments for many remote sensing applications. To quantitatively interpret the remote sensing data, an understanding how naturally occurring polarization depends on wavelength and environmental parameters is needed. The most obvious source of naturally occurring polarization is atmospheric scattering. For a clear-sky environment, Rayleigh scattering dominates, resulting from scattering by atmospheric gas molecules that are much smaller than the optical wavelength, and a distinct all-sky polarization pattern exists. A band of maximum degree of linear polarization can be observed 90? from the sun with polarization vectors orientated perpendicular to the scattering plane (i.e. the plane containing the incident and scattered light). However, aerosols, clouds, and underlying surface reflectance can alter the observed sky polarization. Military, environmental, and navigational applications exploit the sky polarization pattern to detect objects, retrieve aerosol and cloud properties, and to find compass headings based on the sky polarization pattern. Sky polarization is also being used to calibrate the polarization response of large telescopes. It is important to understand how partially polarized skylight can vary with environmental factors, as well as with wavelength and solar position, so that polarization measurements can be interpreted correctly. The direction of polarization when aligned to a specific reference frame can provide additional information beyond the basic polarization pattern. This dissertation expands the current knowledge of skylight polarization by validating radiative transfer simulations in the shortwave infrared, by reporting the first-ever retrievals of cloud thermodynamic phase from all-sky polarization images using the Stokes S1 parameter referenced in the scattering plane, and by quantifying how partially polarized skylight varied under unique scattering conditions during the 2017 solar eclipse. In order to accurately predict cloud thermodynamic phase and to analyze the temporal distribution of skylight during a total solar eclipse, a physics-based understanding of the Stokes parameters and angle of polarization (AoP) with respect to the instrument, scattering, and solar principal planes was also developed. Through each experiment, two underlying threads were observed. First, in order to accurately interpret results, environmental parameters needed to be characterized. Second, when rotated into a specific reference frame, the Stokes parameters and AoP can be utilized differently and provide unique insights when analyzing all-sky polarization data.Item Development of polarizing spectral bandpass filter using dual subwavelength metallic gratings(Montana State University - Bozeman, College of Engineering, 2017) Hohne, Andrew Joseph; Chairperson, Graduate Committee: Wataru NakagawaRecent work in climate science has shown the need for a polarizing spectral bandpass filter in order to passively and remotely determine cloud water phase. Presented here is a novel design of such a filter based on two subwavelength gold gratings separated by a dielectric surface relief grating. It is shown that a Fabry-Perot resonance occurs in the cavity between the gold gratings while surface plasmon polariton resonances occur at the two metal/dielectric interfaces. It is further shown that these two resonance effects couple together to create a spectral bandpass that is high and narrow enough for the remote sensing application. These resonance effects can be changed in shape and position by adjusting the width, height, period, and separation between the gold gratings. It is further observed that the surface plasmon polariton resonances also have the effect of suppressing light transmission at certain wavelengths, allowing the spectral bandpass shape to be tuned, reducing out-of-band transmission. The polarizing effect of these gratings results from the rejection of light polarized along the grating rulings, a phenomenon that is well documented to occur in subwavelength wire grids. Experimental data on prototype gratings show good agreement with predicted performance calculated using numerical rigorous-coupled wave analysis once we account for uncertainties in the material properties and device geometry due to fabrication and processing variabilities. This numerical method is used in conjunction with analytical approximations like zero-order effective medium theory to develop a design process that can be extended to any wavelength in the shortwave infrared region. All devices undergo a final global parameter optimization procedure to account for any subtle near-field effects. Finally, I present designs of three devices optimized for operation at wavelengths of 1550 nm, 1640 nm, and 1700 nm. These devices share characteristics that make them able to be simultaneously fabricated on the same substrate, a crucial step if they are to be built into an array. The final devices all have a peak transmission of greater than 80%, and spectral widths of less than 40 nm.Item The visible-to-short-wave-infrafred spectrum of skylight polarization(Montana State University - Bozeman, College of Engineering, 2015) Dahl, Laura Marie; Chairperson, Graduate Committee: Joseph A. ShawSkylight becomes partially polarized when sunlight is scattered in the atmosphere. The resulting degree of linear polarization (DoLP) depends on the optical wavelength, atmospheric properties (especially aerosol content), and surface reflectance. The degree of linear polarization for a clear sky was calculated previously for the visible-to-near-infrared (VNIR) spectral range using a successive-orders-of-scattering radiative transfer model and the calculations were validated through comparison with measurements from an all-sky polarization imager. Results from that study showed that VNIR skylight polarization in the visible to the near-infrared spectrum could trend upward, downward, or even have unusual spectral discontinuities that arose because of sharp features in the optical properties of underlying surface and atmospheric aerosols. However, the results were limited to wavelengths below 1 microns from a lack of data at longer wavelengths. This report describes skylight polarization calculations from 0.35 microns to 2.5 microns (visible to SWIR). Inputs to the model included spectral extrapolations of aerosol properties retrieved from a ground-based solar radiometer and measurements of spectral surface reflectance from a hand-held spectrometer. The simulations were run for different environments: a Rayleigh-scattering environment (no aerosol optical depth and no surface reflectance), varied aerosols over a constant-reflectance surface, spectrally constant aerosols over varied surfaces, and a set of more realistic environments that coupled different measured surface reflectance spectra with actual aerosol conditions. Results showed skylight polarization dependence on aerosols and surface reflectance when one element was added, changed, or taken out of an environment. The results were also compared against skylight polarization measurements taken with a SWIR-MWIR polarimeter. Polarization results in the SWIR were highly dependent on the aerosol size distribution and the resulting relationship between the aerosol and Rayleigh optical depths. Once the aerosol optical depth became greater than the Rayleigh optical depth, the predicted polarization deviated significantly from Rayleigh scattering theory. As aerosol optical depths increased, the degree of linear polarization spectrum generally decreased with wavelength at a rate dependent on the aerosol size distribution. Unique polarization features in the modeled results were attributed to the surface reflectance and the skylight DoLP generally decreased as surface reflectance increased.