High-speed infrared video system for detection of thermal aliasing.

Persistent Link:
http://hdl.handle.net/10150/186604
Title:
High-speed infrared video system for detection of thermal aliasing.
Author:
Flath, Laurence Martin.
Issue Date:
1994
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The acquisition of images in video recording is inherently a sampling process. In most current systems, a frame is recorded once every 1/30 second (30 frames per second). Scene events that occur faster than the Nyquist rate (one-half the sampling frequency, or 15 Hz, in this case) result in an effect called aliasing, which gives misleading information about the scene's true temporal content. Decreasing the camera's integration time (analogous to shutter speed) reduces blurring in the image, but the presence of aliasing is solely determined by the camera's frame rate. In visible systems, video aliasing is often accompanied by visual (spatial) cues in the resulting imagery; e.g. wagon wheel rotating slowly and/or backward. But in the infrared, where the scene is a temperature/emissivity map, drawing conclusions about what is really happening is much more difficult. The term thermal aliasing is used to describe the effect of temporal subsampling in infrared video. Fluctuations in an object's temperature occurring at greater than the Nyquist rate give no visual cues, so there is no way to tell by just looking at the scene whether its frequency distribution is real or aliased. For this reason, some method of determining whether the IR camera's frame rate is sufficiently high to prevent thermal aliasing is essential to provide valid scene information. Using a triggerable infrared video camera with variable integration time, like the one described in this thesis, allows the aliasing-status of an infrared image sequence to be ascertained. Changing the integration time has the effect of shaping the recorded scene's frequency spectrum; how these spectra relate to each other is different depending on whether aliasing is occurring or not. This thesis describes the theory of video sampling with its application to infrared video systems, including thermal aliasing. Also, the design and use of a triggerable, short integration time platinum silicide infrared video camera system is described.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Dissertations, Academic.; Mathematics.; Electrical engineering.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Optical Sciences; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Dereniak, Eustace

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleHigh-speed infrared video system for detection of thermal aliasing.en_US
dc.creatorFlath, Laurence Martin.en_US
dc.contributor.authorFlath, Laurence Martin.en_US
dc.date.issued1994en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe acquisition of images in video recording is inherently a sampling process. In most current systems, a frame is recorded once every 1/30 second (30 frames per second). Scene events that occur faster than the Nyquist rate (one-half the sampling frequency, or 15 Hz, in this case) result in an effect called aliasing, which gives misleading information about the scene's true temporal content. Decreasing the camera's integration time (analogous to shutter speed) reduces blurring in the image, but the presence of aliasing is solely determined by the camera's frame rate. In visible systems, video aliasing is often accompanied by visual (spatial) cues in the resulting imagery; e.g. wagon wheel rotating slowly and/or backward. But in the infrared, where the scene is a temperature/emissivity map, drawing conclusions about what is really happening is much more difficult. The term thermal aliasing is used to describe the effect of temporal subsampling in infrared video. Fluctuations in an object's temperature occurring at greater than the Nyquist rate give no visual cues, so there is no way to tell by just looking at the scene whether its frequency distribution is real or aliased. For this reason, some method of determining whether the IR camera's frame rate is sufficiently high to prevent thermal aliasing is essential to provide valid scene information. Using a triggerable infrared video camera with variable integration time, like the one described in this thesis, allows the aliasing-status of an infrared image sequence to be ascertained. Changing the integration time has the effect of shaping the recorded scene's frequency spectrum; how these spectra relate to each other is different depending on whether aliasing is occurring or not. This thesis describes the theory of video sampling with its application to infrared video systems, including thermal aliasing. Also, the design and use of a triggerable, short integration time platinum silicide infrared video camera system is described.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectDissertations, Academic.en_US
dc.subjectMathematics.en_US
dc.subjectElectrical engineering.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineOptical Sciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairDereniak, Eustaceen_US
dc.contributor.committeememberWolfe, William L.en_US
dc.contributor.committeememberShepard, Stevenen_US
dc.identifier.proquest9424937en_US
dc.identifier.oclc722392827en_US
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