Date of Award
Master of Science in Applied Physics
Department of Engineering Physics
Anthony L. Franz, PhD
Snapshot multi-spectral sensors allow for object detection based on its spectrum for remote sensing applications in air or space. By making these types of sensors more compact and lightweight, it allows drones to dwell longer on targets or the reduction of transport costs for satellites. To address this need, I designed and built a diffractive plenoptic camera (DPC) which utilized a Fresnel zone plate and a light field camera in order to detect vegetation via a normalized difference vegetation index (NDVI). This thesis derives design equations by relating DPC system parameters to its expected performance and evaluates its multi-spectral performance. The experimental results yielded a good agreement for spectral range and FOV with the design equations but was worse than the expected spectral resolution of 6.06 nm. In testing the spectral resolution of the DPC, it was found that near the design wavelength, the DPC had a spectral resolution of 25 nm. As the algorithm refocused further from design the spectral resolution broadened to 30 nm. In order to test multi-spectral performance, three scenes containing leaves in various states of health were captured by the DPC and an NDVI was calculated for each one. The DPC was able to identify vegetation in all scenes but at reduced NDVI values in comparison to the data measured by a spectrometer. Additionally, background noise contributed by the zeroth-order of diffraction and multiple wavelengths coming from the same spatial location was found to reduce the signal of vegetation. Optical aberrations were also found to create artifacts near the edges of the final refocused image. The future of this work includes using a different diffractive optic design to get a higher efficiency on the first order, deriving an aberrated sampling pattern, and using an intermediate image diffractive plenoptic camera to reduce the zeroth-order effects of the FZP.
DTIC Accession Number
Naranjo, Tristan R., "Mult-Spectral Imaging of Vegetation with a Diffractive Plenoptic Camera" (2020). Theses and Dissertations. 4127.