Spectral imaging of moving objects with a stare down camera
View Patent ↗A spectral imaging system for collecting spectral information of a two dimensional heterogeneous objects while in motion relative to the imaging system without the use of a spectrograph, filters or any dispersive optics. The system includes a pulsed light source tunable in wavelength for producing short pulses of wavelength tuned light at a plurality of selected narrow band wavelengths within a spectral range and one or more optical components for conveying or directing the short pulses of light to a two dimensional region that is substantially stationary with respect to the imaging system and through which the two dimensional target is moving. The system also includes a many pixel camera synchronized with the tunable pulsed light source. The camera is adapted to detect light in the selected narrow band wavelengths produced by the tunable pulsed light source and reflected from or transmitted through the two dimensional target in motion relative to the imaging system and to provide image frame information with each frame at a defined wavelength band. A processor processes information from said tunable light source and said camera and to produce multi-spectral images of the target.
1. A spectral imaging system for collecting multi-spectral information of a two dimensional target in motion relative to the imaging system, said system comprising:
A) a pulsed light source tunable in wavelength for producing short pulses of wavelength tuned light at a plurality of selected narrow band wavelengths within a spectral range,
B) one or more optical components for conveying or directing said short pulses of light to a two dimensional region that is substantially stationary with respect to the imaging system and through which the two dimensional objects are moving relative to the imaging system, and
C) a camera synchronized with said tunable pulsed light source and comprising a many pixel array detector, said camera being adapted to:
i) detect light in the selected narrow band wavelengths produced by said tunable pulsed light source and reflected from or transmitted through said two dimensional target in motion relative to the imaging system and passing through a region imaged by the camera, said region or a portion of said region defining a two-dimensional target region and
ii) provide a plurality of two-dimensional image frames, each frame defining a plurality of two-dimensional pixels within each image frame of said plurality of image frames with each frame at a defined wavelength band,
D) a processor adapted to process information from said tunable light source and said camera and to produce multi-spectral image cubes of said target from said information, said image cubes identifying a plurality of optical values for each of said two-dimensional pixels of said target passing through the target region;
wherein system parameters are defined as follows:
Np=a number of pixels in a the motion direction
Nps=a number of pixels in a the strip's width
Ns=a number of strips in a the field of view
PIX=virtual pixel dimensions
PRR=pulse repletion rate of the laser
V=target speed (conveyor belt speed)
Δλ=a wavelength range
#F=number of frames (spectral bands in the spectral data)
SR=spectral resolution
Ws=strip width,
and the system parameters are adjusted such that each strip is exposed only once to each wavelength as it travels across the a target area so the a number of pulses that a strip is exposed to is equal to the number strips in the target area, which is also equal to the number of data points (#F) in the collected spectral data, so:
#
F
=
Ns
=
N
p
Nps
and the spectral resolution is equal to a total wavelength range scanned by the tunable laser divided by the number of the collected data points, i.e.
SR
=
Δ
λ
#
F
and for a desired number of frames #F the required speed V is the product of the pulse repetition rate and the width of the strip, so:
V=Ws*PRR=Nps*PIX*PRR.
2. The spectral imaging system as in claim 1 wherein the strip width is as narrow as a single pixel.
3. The spectral imaging system as in claim 1 wherein the strip width is wider than a single pixel.
4. The spectral imaging system as in claim 1 wherein the system is adapted such that a wavelength tuning scans over an entire wavelength range in the same time that it takes for an object to travel across a target area so that the time to complete the scan is provided by the following equation:
T
=
N
p
*
PIX
V
.