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Articles 1 - 12 of 12
Full-Text Articles in Signal Processing
Temperature Determination And Scene Change Artifact Mitigation When Using Fourier-Transform Spectroscopy On Targets With Time-Varying Temperature, Kode A. Wilson, Michael L. Dexter, Benjamin F. Akers, Anthony L. Franz
Temperature Determination And Scene Change Artifact Mitigation When Using Fourier-Transform Spectroscopy On Targets With Time-Varying Temperature, Kode A. Wilson, Michael L. Dexter, Benjamin F. Akers, Anthony L. Franz
Faculty Publications
Fourier-transform spectroscopy is a widely used technique for determining the spectral and thermal properties of a target. However, target temperature variations during measurement can compromise the spectral accuracy. Temperature fluctuations induce oscillations superimposed on the target spectrum. These oscillations, referred to as scene-change artifacts, degrade the spectral accuracy. The literature is divided, with theoretical predictions suggesting negligible artifacts and growing experimental evidence reporting significant artifacts. This paper presents a theory and experimental validation of scene-change artifacts originating from target temperature variations. Traditionally, the interferogram offset is assumed to be constant, an invalid assumption for a changing scene. The error is …
Proposed Methodology For Correcting Fourier-Transform Infrared Spectroscopy Field-Of-View Scene-Change Artifacts, Kody A. Wilson, Michael L. Dexter, Benjamin F. Akers, Anthony L. Franz
Proposed Methodology For Correcting Fourier-Transform Infrared Spectroscopy Field-Of-View Scene-Change Artifacts, Kody A. Wilson, Michael L. Dexter, Benjamin F. Akers, Anthony L. Franz
Faculty Publications
Fourier-transform spectrometers are widely used for spectral measurements. Changes in the field of view during measurement introduce oscillations into the measured spectra known as scene-change artifacts. Field-of-view changes also introduce uncertainty about which target the measured spectrum represents. Though scene-change artifacts are often present in dynamic data, their significance is disputed in the current literature. This work presents a theoretical framework and experimental validation for scene-change artifacts. Field-of-view changes introduce variable interferogram offsets, which standard processing techniques assume are constant. The error between the interferogram offset and its estimate is Fourier-transformed, yielding scene-change artifacts, often confused with noise, in the …
Method For Target Detection In A High Noise Environment Through Frequency Analysis Using An Event-Based Vision Sensor, Will Johnston, Shannon Young, David Howe, Rachel Oliver, Zachary Theis, Brian Mcreynolds, Michael L. Dexter
Method For Target Detection In A High Noise Environment Through Frequency Analysis Using An Event-Based Vision Sensor, Will Johnston, Shannon Young, David Howe, Rachel Oliver, Zachary Theis, Brian Mcreynolds, Michael L. Dexter
Faculty Publications
Event-based vision sensors (EVSs), often referred to as neuromorphic cameras, operate by responding to changes in brightness on a pixel-by-pixel basis. In contrast, traditional framing cameras employ some fixed sampling interval where integrated intensity is read off the entire focal plane at once. Similar to traditional cameras, EVSs can suffer loss of sensitivity through scenes with high intensity and dynamic clutter, reducing the ability to see points of interest through traditional event processing means. This paper describes a method to reduce the negative impacts of these types of EVS clutter and enable more robust target detection through the use of …
Digital Holography Efficiency Experiments For Tactical Applications, Douglas E. Thornton
Digital Holography Efficiency Experiments For Tactical Applications, Douglas E. Thornton
Theses and Dissertations
Digital holography (DH) uses coherent detection and offers direct access to the complex-optical field to sense and correct image aberrations in low signal-to-noise environments, which is critical for tactical applications. The performance of DH is compared to a similar, well studied deep-turbulence wavefront sensor, the self-referencing interferometer (SRI), with known efficiency losses. Wave optics simulations with deep-turbulence conditions and noise were conducted and the results show that DH outperforms the SRI by 10's of dB due to DH's strong reference. Additionally, efficiency experiments were conducted to investigate DH system losses. The experimental results show that the mixing efficiency (37%) is …
A Focal Plane Array And Electronics Model For Cmos And Ccd Sensors In The Afit Sensor And Scene Emulation Tool (Asset), Fernando D. Fernandez
A Focal Plane Array And Electronics Model For Cmos And Ccd Sensors In The Afit Sensor And Scene Emulation Tool (Asset), Fernando D. Fernandez
Theses and Dissertations
Electro-optical and infrared (EO/IR) sensor models are useful tools that can facilitate understanding a system's behavior without expensive and time-consuming testing of an actual system. EO/IR models are especially important to the military industry where truth data is required but is sometimes impractical to obtain through experimentation due to expense or difficulties in procuring hardware. This work describes implementation of a focal plane array (FPA) model of charge-coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) photodetectors as a component in the Air Force Institute of Technology (AFIT) Sensor and Scene Emulation Tool (ASSET). The FPA model covers conversion of photo-generated …
The Fresnel Zone Light Field Spectral Imager, Francis D. Hallada
The Fresnel Zone Light Field Spectral Imager, Francis D. Hallada
Theses and Dissertations
This thesis provides a computational model and the first experimental demonstration of a Fresnel zone light field spectral imaging (FZLFSI) system. This type of system couples an axial dispersion binary diffractive optic with light field (plenoptic) camera designs providing a snapshot spectral imaging capability. A computational model of the system was developed based on wave optics methods using Fresnel propagation. It was validated experimentally and provides excellent demonstration of system capabilities. The experimentally demonstrated system was able to synthetically refocus monochromatic images across greater than a 100nm bandwidth. Furthermore, the demonstrated system was modeled to have a full range of …
Automated Synthetic Scene Generation, Ryan N. Givens
Automated Synthetic Scene Generation, Ryan N. Givens
Theses and Dissertations
First principles, physics-based models help organizations developing new remote sensing instruments anticipate sensor performance by enabling the ability to create synthetic imagery for proposed sensor before a sensor is built. One of the largest challenges in modeling realistic synthetic imagery, however, is generating the spectrally attributed, three-dimensional scenes on which the models are based in a timely and affordable fashion. Additionally, manual and semi-automated approaches to synthetic scene construction which rely on spectral libraries may not adequately capture the spectral variability of real-world sites especially when the libraries consist of measurements made in other locations or in a lab. This …
An Experimental Evaluation Of Image Quality For Various Scenarios In A Chromotomographic System With A Spinning Prism, Kyle J. Dufaud
An Experimental Evaluation Of Image Quality For Various Scenarios In A Chromotomographic System With A Spinning Prism, Kyle J. Dufaud
Theses and Dissertations
A lab and eld based hyperspectral chromotomographic imager has been developed at the Air Force Institute of Technology. It is a prototype used to study the requirements for a space-based system. The imager uses a high speed visible band camera behind a direct-vision prism to image both spatial dimensions and the spectral dimension at the same time. Capturing all 3 simultaneously allows for the hyperspectral imaging of transient events. The prism multiplexes the spectral and spatial information, so tomographic reconstruction algorithms must be used to separate hyperspectral channels. Experiments were conducted to compare reconstructed image quality as a function of …
Comparative Analysis Of Reconstructed Image Quality In A Simulated Chromotomographic Imager, Ryan L. Tervo
Comparative Analysis Of Reconstructed Image Quality In A Simulated Chromotomographic Imager, Ryan L. Tervo
Theses and Dissertations
A hyperspectral chromotomographic instrument has been developed to determine the spatial and spectral distribution of a target. It does this by recording the dispersed images produced by a rotating direct vision prism with a high speed camera. The recorded images are processed through a tomographic reconstruction algorithm to produce a reconstructed hypercube. A physics-based system model was developed to investigate three areas. The first was how the prism angle selection and range of angles used impacted the reconstructed image quality. The second was an assessment of a new iterative reconstruction algorithm developed to remove artifacts produced in the Back Projection …
Discrimination Between Child And Adult Forms Using Radar Frequency Signature Analysis, Stephanie R. Keith
Discrimination Between Child And Adult Forms Using Radar Frequency Signature Analysis, Stephanie R. Keith
Theses and Dissertations
In this thesis we develop a method to discriminate between adult and child radar signatures. In particular, we examine radar data measured from behind a wall, which introduces radar signal attenuation and multipath effects. To investigate the child/adult discrimination problem in a through-wall, multipath scenario, a previously developed free-space human scattering model was expanded to incorporate multiple paths, and the effects of transmission through, and reflections from, walls and ground. The ground was modeled as a perfectly reflecting surface, while the walls were modeled as homogeneous concrete slabs. Twenty-five reflection paths were identified, involving the direct paths, as well as …
Development And Characterization Of A Chromotomosynthetic Hyperspectral Imaging System, Randall L. Bostick
Development And Characterization Of A Chromotomosynthetic Hyperspectral Imaging System, Randall L. Bostick
Theses and Dissertations
A chromotomosynthetic imaging (CTI) methodology based upon mathematical reconstruction of a set of 2-D spectral projections to collect high-speed (100 Hz) 3-D hyperspectral data cube has been proposed. The CTI system can simultaneously provide usable 3-D spatial and spectral information, provide high-frame rate slitless 1-D spectra, and generate 2-D imagery equivalent to that collected with no prism in the optical system. The wavelength region where prism dispersion is highest (500 nm) is most sensitive to loss of spectral resolution in the presence of systematic error, while wavelengths 600 nm suffer mostly from a shift of the spectral peaks. The quality …
Passive Ranging Using A Dispersive Spectrometer And Optical Filters, Jacob A. Martin
Passive Ranging Using A Dispersive Spectrometer And Optical Filters, Jacob A. Martin
Theses and Dissertations
Monocular passive ranging using atmospheric oxygen absorption has been demonstrated in the past using an FTS. These instruments are very sensitive to vibration making them di cult to use on an airborne platform. This work focuses on whether passive ranging can be done with instruments that are easier to deploy. Two potential instruments are tested and compared: a diffraction grating spectrometer and optical filters. A grating spectrometer was able to estimate range to within 5% for a static solid rocket motor ring at a distance of 910 m using the NIR absorption band of oxygen. Testing at shorter ranges produced …