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optimization of the tomographic scanning imager
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Optimization of the tomographic scanning (TOSCA) imager
Harald Hovland
Norwegian Defence Research Institute (FFI), Postboks 25, N-2027 Kjeller, NORWAY.
harald.hovland@ffi.no
ABSTRACT
The tomographic scanning (TOSCA) imager was invented by the author in 2003. Initially, the system was based on
reconstructing an image from the signal of a simple single pixel, conical scan FM-reticle sensor using tomographic
techniques. Although the system has been used for several decades for real-time tracking purposes, the imaging
properties of the single pixel conical scan reticle system was left undiscovered until recently, although multi-target
discrimination was demonstrated with multi-spectral versions of the system. The initial system presented by the author
demonstrated the ability to discriminate between multiple spots in the field of view in a fairly simple scenario.
Advances have been made in both theory and technology, mainly with the introduction of the nutating circular aperture
in the scanning optics, and the use of Fourier transform ramp filters during reconstruction, and TOSCA is in principle
found to be a perfect imaging system, only limited by practical aspects such as the number of angular scans, the spatial
sampling, noise and vibration. The simplicity of the hardware, together with the rapid advances in high performance,
low cost computing means the system has a potential for low-cost applications such as in expendable multi-spectral
thermal imagers.
This paper will present the current state of the technology, including improvements in algorithms and reticle shapes, and
look at artefacts found in various images due to different geometries, as well as ways to handle these artefacts. Several
noise generating processes and their effects will be presented and illustrated with results from digital simulations.
Requirements for image processing in terms of computing power are investigated, together with the potential for
parallelization.
Keywords: Tomography, imaging system, conical scan, reticle, tracking.
1. INTRODUCTION
Infrared (IR) radiation has been known to man for more than two centuries, due to the discoveries of Herschel
[1]
. The
first known suggestion for the use of this radiation in military applications is almost a century old with the proposals by
Lindemann during World War I
[2]
. The actual application was not put in place for several decades, mainly because
materials with sufficient sensitivity or speed were not available, and were not in place until well after World War II
despite both Allied and German efforts
[2,3]
. In 1953, the first successful test of an IR seeker was made with the AIM-9
“Sidewinder” missile
[4]
. Simplicity was a success factor in missile design for several decades, but more complex and
hostile scenarios as well as efficiency requirements have pushed the requirements for seeker performance to a point
where imaging of the scene has been found advantageous, and several missile systems are now being fielded with
imaging sensors, notably the new AIM-9X Sidewinder, IRIS-T, ASRAAM and Python-5. The highly sophisticated
seekers in these missiles contribute to a significant portion of the total system cost, and the Tomographic Scan
(TOSCA) concept is looked upon as a low-cost alternative to traditional imaging sensors. Although the TOSCA
principle is an imaging concept based on a (non-imaging) seeker design, it is not limited to missile seeker applications.
As an example, expendable UAVs may be an interesting platform for hosting low cost imaging IR sensors for search
and rescue, or for research purposes in various fields, such as geosciences.
Reticles in use for tracking and guidance was conceived by the Germans during World War II and almost made ready
for production
[5]
. The first open literature description of the use of reticles for tracking was made by Clark
[6]
, and a lot
of activity in this area followed in the two following decades
[5]
. The use of reticle trackers enabled tracking with
Acquisition, Tracking, Pointing, and Laser Systems Technologies XXI, edited by Steven L. Chodos, William E. Thompson,
Proc. of SPIE Vol. 6569, 65690I, (2007) · 0277-786X/07/$18 · doi: 10.1117/12.719501
Proc. of SPIE Vol. 6569 65690I-1
Downloaded from SPIE Digital Library on 10 Oct 2010 to 210.45.114.20. Terms of Use: http://spiedl.org/terms
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