Scholarship & Research
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Item Radiometry and the Friis transmission equation(American Association of Physics Teachers, 2013) Shaw, JosephTo more effectively tailor courses involving antennas, wireless communications, optics, and applied electromagnetics to a mixed audience of engineering and physics students, the Friis transmission equation—which quantifies the power received in a free-space communication link—is developed from principles of optical radiometry and scalar diffraction. This approach places more emphasis on the physics and conceptual understanding of the Friis equation than is provided by the traditional derivation based on antenna impedance. Specifically, it shows that the wavelength-squared dependence can be attributed to diffraction at the antenna aperture and illustrates the important difference between the throughput (product of area and solid angle) of a single antenna or telescope and the throughput of a transmitter-receiver pair.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 Combining spectral and polarimetric methods to classify cloud thermodynamic phase(Montana State University - Bozeman, College of Engineering, 2019) Tauc, Martin Jan; Chairperson, Graduate Committee: Joseph A. Shaw; David W. Riesland, Laura M. Eshelman, Wataru Nakagawa and Joseph A. Shaw were co-authors of the article, 'Radiance ratios for CTP discrimination' submitted to the journal 'Journal of applied remote sensing' which is contained within this thesis.; Wataru Nakagawa and Joseph A. Shaw were co-authors of the article, 'The SWIR three-channel polarimeter for cloud thermodynamic phase detection' in the journal 'Optical engineering' which is contained within this thesis.Cloud thermodynamic phase--whether a cloud is composed of spherical water droplets or polyhedral ice crystals--is an important parameter for optical communication with space-based instruments, remote sensing of the atmosphere, and, perhaps most importantly, understanding weather and climate. Although some methods exist to detect the phase of clouds, there is still a need for passive remote sensing of cloud thermodynamic phase due to its low-cost, scalability, and ease of use. Two methods for cloud thermodynamic phase classification employ spectral radiance ratios in the short-wave infrared, and the S 1 Stokes parameter, a polarimetric quantity. In this dissertation, the combination of the two methods is realized in an instrument called the short-wave infrared three-channel polarimeter. The coalescence of radiance ratios in the short-wave infrared and polarization channels oriented parallel and perpendicular to the scattering plane provides better classification of cloud phase than either method independently. Despite the improvement, the low-cost system suffered from hardware and software limitations, which caused an increase in noise and polarimetric artifacts. These errors are analyzed and a subset of low-noise data shows even better classification ability. All together, the results attained from the deployment of the polarimeter in early 2019 showed promise that the combination of the two methods is an improvement over past techniques.Item Weed and crop discrimination with hyperspectral imaging and machine learning(Montana State University - Bozeman, College of Engineering, 2019) Scherrer, Bryan Joseph; Chairperson, Graduate Committee: Joseph A. ShawHerbicide-resistant weed biotypes are spreading across crop fields nationally and internationally and mapping them with traditional crop science methods - cloning plants and testing their resistance levels in a lab - are costly and time consuming. A segment of the field of precision agriculture is being developed to accurately and quickly map the location of herbicide-resistant and herbicide-susceptible weeds using advanced optics and computer algorithms. In our study, we collected hundreds of thousands of spectra of herbicide-resistant and herbicide-susceptible biotypes of the weeds kochia, mare's tail and lamb's quarter and of crops including barley, corn, dry pea, garbanzo, lentils, pinto bean, safflower, sugar beet at the Southern Agricultural Research Center in Huntley, Montana using a hyperspectral imager. Plants were imaged in a controlled greenhouse setting as well as in crop fields using ground-based and drone-based imaging platforms. The spectra were differentiated from one another using a feedforward neural network machine learning algorithm. Classification accuracies depended on what plants were imaged, the age of the plants and lighting conditions of the experiment. They ranged from 77% to 99% for spectra acquired on our ground-based imaging platform and from 25% to 79% on our drone- based platform.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 Ultra high-throughput fluorescence detection for single cell applications in drop microfluidics(Montana State University - Bozeman, College of Engineering, 2016) Schaefer, Robert Willman; Chairperson, Graduate Committee: Connie ChangConventional methods in microbiology can be limited by assay execution and analysis times, phenotypic dominance within bulk communities, reagent volumes, and single-use supply costs. These limitations can be overcome using drop-based microfluidics. In this discipline, pico-liter sized, water-in-oil emulsions serve as independent 'test tubes,' allowing for the compartmentalization of community constituents and interrogation at the single cell level. Furthermore, two-phase, continuous flow microfluidic devices enable drop populations to be manipulated and analyzed at kilohertz rates according to experimental needs. In this research, a fluorescence-based method for drop analysis and sorting was developed and applied, in conjunction with other microfluidic techniques, to perform assays in microbiology. The applications explored include cell dormancy within P. aeruginosa subpopulations, microalgae lipid accumulation for the production of biofuels, optimization of microbially-induced calcite precipitation (MICP), and human norovirus infectivity. Results from each application include: 1. The hibernation promoting factor (Hpf) was found to play a key role in the maintenance of P. aeruginosa viability during planktonic starvation. 2. Progress was made on a Nile Red based, ultra high-throughput, single cell algal lipid detection platform. 3. MICP was demonstrated at the single cell level. 4. A drop based human norovirus infection platform was attempted using human B cells as the viral host.Item Infrared cloud imaging systems characterization(Montana State University - Bozeman, College of Engineering, 2016) Riesland, David Walter; Chairperson, Graduate Committee: Joseph A. ShawInfrared cloud imaging (ICI) is a useful tool for characterizing cloud cover for a variety of fields. Clouds play an important role in free-space high frequency (optical and mm-wave) terrestrial communications. Ground-based infrared imagers are used to provide long-term, high resolution (spatial and temporal) cloud data without the need for sunlight. This thesis describes the development and characterization of two ICI systems for deployment at remote field sites in support of Earth-to-space mm-wave and optical communication experiments. The hardware upgrades, calibration process, sensitivity analysis, system validation, and algorithm developments are all discussed for these systems. Relative spectral response sensitivity analysis is discussed in detail, showing as much as 35% calibrated scene radiance uncertainties when using generic manufacturer data in comparison with measured spectral responses. Cloud discrimination algorithms, as well as cloud phase (ice or water discrimination) algorithms are also discussed.Item A practical method for determining pit depths using X-ray attenuation in EDX spectra(2015-04) Avci, Recep; Davis, Bret H.; Wolfenden, Mark L.; Kellerman, Laura R.; Lucas, Kilean; Martin, Joshua; Deliorman, MuhammedinA practical method has been developed for rapidly determining the depth of a corrosion micro-pit from the path lengths of X rays passing through the walls of the pit on their way to an X-ray detector. The method takes advantage of the attenuation of the Bremsstrahlung and characteristic X-ray radiation accompanying each X-ray spectrum, and the results are verified independently using AFM and the special pit geometry surrounding MnS inclusions in 1018 carbon steel. The method has general validity and is especially valuable in those cases where the pit depth-to-width ratio is too steep to measure using the conventional methods.Item Silicon nitride deformable mirrors for focus and spherical aberration correction in micro-optical systems(Montana State University - Bozeman, College of Engineering, 2002) Himmer, Phillip Alexander; Chairperson, Graduate Committee: David Dickensheets.Laser beam scanning systems benefit from dynamic focus control and aberration correction using a deformable mirror, enabling 3D real-time scanning. Designed for focus and spherical aberration control in optical beam scanning systems, these mirrors are capable of video rate bandwidths allowing real-time 3D imaging in micro-optical scanning systems. Field curvature aberration can also be corrected with the same mirror. Previous work with polysilicon deformable mirrors validated the concept of using specialized deformable optics in beam scanning systems. Fabrication of micro-optics in this dissertation was achieved using a modified surface micromachining technique with silicon nitride replacing polysilicon as the structural material. A bulk anisotropic silicon etch following a PSG release etch allows the creation of a variable cavity depth, overcoming the typical deformation limitations of standard surface micromachining. To perform as desired, parabolic curvature of the mirror surface is required with the ability to introduce positive and negative quartic curvature. Analytical theory showed that deformed simply supported plates have curvature closer to parabolic than deformed clamped plates. Segmentation and thinning of the perimeter was done to in order to emulate this simply supported boundary. Two annular actuation zones were implemented to give independent control over the second and fourth order curvatures. It was found that residual stress present in the silicon nitride structural plate improved the surface curvature and mechanical resonance at the expense of a larger actuation pressure. Mirrors with diameters of 1500, 1000, 750, and 300 microns were built and tested. Zonal actuation with annular electrodes proved successful in providing sufficient correction of the mirror surface curvature, allowing spherical aberration free focus control. Perimeter segmentation greatly reduced required actuation loads allowing improved focal ranges. It was found that the sacrificial layer thickness has a significant impact on the initial curvature of the mirror. Sacrificial layers 0.2 microns thick proved sufficient for release, improved device yield, and resulted in an initially flat mirror.Item Teaching and learning geometric optics in middle school through the Turning Eyes to the Big Sky project(2013-06) Leonard, M. J.; Hannahoe, R. M.; Nollmeyer, Gustave E.; Shaw, Joseph A.The Turning Eyes to the Big Sky project offered schools in southwestern Montana a unique opportunity to strengthen science instruction. The project implemented, in a formal setting, a nationally established informal science curriculum on light and optics, the Hands-on Optics Terrific Telescopes curriculum. Terrific Telescopes was implemented in eight middle-school classrooms and reached 166 students during the 2010 to 2011 school year. As part of the project, we conducted a teacher workshop and assessed student learning outcomes and teachers’ experiences with the curriculum. The goals of our assessments were to improve our understanding of how students learn key optics-related principles, provide evidence of the learning outcomes of Terrific Telescopes, and find out how teachers adapt the curriculum for use in formal settings. Our research established that students in every classroom learned optics concepts, uncovered student ideas about telescope optics, and identified ways to support and supplement the curriculum for use in classrooms.