Airborne multiband imaging spectrometer
First Claim
1. A geological, geophysical, and environmental survey instrument adapted for use in a moving vehicle, comprising:
- optical imaging means, comprising;
wide-angle rotating mirror means having a plurality of reflective surfaces for providing a substantially continuous image with respect to time of radiant spectral emissions at a predetermined angular field of view, and first fixed mirror means for redirecting said image of spectral emissions from said rotating mirror means through an aperture to collimating means for providing a collimated output thereof;
spectrometer means, comprising second fixed mirror means angularly disposed for directing said collimated output to first beam splitter means, said first beam splitter means integrally located in the optical path of said collimating means for receiving said output and for providing at least first and second bands of spectral emissions having different predetermined wavelengths to frequency selective optical means, said frequency selective optical means selectively responsive to one of said first and second bands of spectral emissions for providing a predetermined angular dispersion of said one band of spectral emissions, the number and bandwidth of said dispersed spectral emissions selected for maximizing a temperature difference, and for transmitting at a second angular dispersion one other than said one band of spectral emissions;
detector means, comprised of a plurality of photoresponsive sensing elements configured in a line array, each of said sensing elements so constructed and adapted for responding to a given bandwidth of spectral emissions and spatially disposed for alignment with one of said angularly dispersed spectral emissions, said sensing elements being incrementally spaced in proportion to a given wavelength to which each of said elements are responsive, for providing a signal representative of a given spectral emission amplitude as a function of wavelength, said frequency selective optical means and said detector means cooperating in alignment to maintain registration of said angularly disposed spectral emissions with predetermined ones of said plurality of sensing elements; and
signal processing means simultaneously operative for each of said sensing elements, comprising means for averaging and holding a detected signal at a substantially constant value to provide a continuous signal output for a predetermined period of time, means for periodically sampling said continuous signal output in synchronism with rotation of said rotating mirror means and for producing an updated sample corresponding to the interval between successive pixels as said mirror means traverses said angular field of view, and an analog-to-digital converter, thereby to provide a continuous signal output in digital form at each of said sensed spectral wavelengths.
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Abstract
A multichannel imaging spectrometer for airborne geological, geophysical and environmental surveys in a moving vehicle. An optical scanner employs a rotating polygon allowing reduced scan optics with increased data acquisition efficiency. Multiple spectrometers integrally registered allow channelization of the received signal to optimize noise performance in the range from ultraviolet through infrared. Output data is in a form for recording and real time display. A staring mode configuration provides enhanced sensitivity by using a two-dimensional detector array and adjustable mirror orientation. A scanning mode embodiment employs a two-dimensional detector array with time delay integration and three-dimensional storage of temporal spatial data and spectral wavelength and intensity. Thus, all channels are acquired simultaneously, resulting in perfect band-to-band registration with continuous spectral curves over the field of view.
80 Citations
17 Claims
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1. A geological, geophysical, and environmental survey instrument adapted for use in a moving vehicle, comprising:
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optical imaging means, comprising;
wide-angle rotating mirror means having a plurality of reflective surfaces for providing a substantially continuous image with respect to time of radiant spectral emissions at a predetermined angular field of view, and first fixed mirror means for redirecting said image of spectral emissions from said rotating mirror means through an aperture to collimating means for providing a collimated output thereof;spectrometer means, comprising second fixed mirror means angularly disposed for directing said collimated output to first beam splitter means, said first beam splitter means integrally located in the optical path of said collimating means for receiving said output and for providing at least first and second bands of spectral emissions having different predetermined wavelengths to frequency selective optical means, said frequency selective optical means selectively responsive to one of said first and second bands of spectral emissions for providing a predetermined angular dispersion of said one band of spectral emissions, the number and bandwidth of said dispersed spectral emissions selected for maximizing a temperature difference, and for transmitting at a second angular dispersion one other than said one band of spectral emissions; detector means, comprised of a plurality of photoresponsive sensing elements configured in a line array, each of said sensing elements so constructed and adapted for responding to a given bandwidth of spectral emissions and spatially disposed for alignment with one of said angularly dispersed spectral emissions, said sensing elements being incrementally spaced in proportion to a given wavelength to which each of said elements are responsive, for providing a signal representative of a given spectral emission amplitude as a function of wavelength, said frequency selective optical means and said detector means cooperating in alignment to maintain registration of said angularly disposed spectral emissions with predetermined ones of said plurality of sensing elements; and signal processing means simultaneously operative for each of said sensing elements, comprising means for averaging and holding a detected signal at a substantially constant value to provide a continuous signal output for a predetermined period of time, means for periodically sampling said continuous signal output in synchronism with rotation of said rotating mirror means and for producing an updated sample corresponding to the interval between successive pixels as said mirror means traverses said angular field of view, and an analog-to-digital converter, thereby to provide a continuous signal output in digital form at each of said sensed spectral wavelengths. - View Dependent Claims (2)
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3. Imaging apparatus for an airborne vehicle, said apparatus comprising:
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mirror means having a plurality of reflective surfaces for providing an image of a field of view, said image being acquired transverse to the flight path of said airborne vehicle, said mirror means being adapted for disposal at a predetermined angle of reflection, said angle being variable with respect to the nadir, spectrometer means, comprising optical collection means for receiving a reflected image of said field of view and for focusing said image upon a slit aperture oriented with its length in the cross-track direction of flight, collimating means for applying said focused image to beam splitter means for reflecting a first predetermined spectral portion of said image and for transmitting a second predetermined spectral portion of said image, grating means for directing said first and second spectral portions to lens means, said lens means for focusing and applying said first and second portions of said image to respective first and second two dimensional detector arrays, said detector arrays comprised of a matrix of sensor elements, said sensor elements being arranged in rows and columns, the number of rows in said arrays corresponding to a predetermined number of in-track picture elements, the number of columns corresponding to the number of spectral channels of a given average bandwidth, wherein said image is resolved by said spectrometer means into a matrix of spectral channels as a function of the spatial image, each predetermined spatial increment along the cross-track direction corresponding to a continuous spectral distribution in the in-track direction, each spectral channel corresponding to a given plurality of sensor elements, each sensor element storing an electrical signal representative of said average band of wavelengths and an intensity corresponding to the temporal image incident thereupon, means for reading all said electrical signals in parallel and digitally transferring said signals to storage means, and means synchronized to the in-track motion of the airborne vehicle for clearing said electrical signals and energizing said sensor elements with a new image corresponding to the in-track displacement of the vehicle, whereat said storage means is operative to provide a continuous spectral distribution temporally synchronized with a continuous spatial field traversed by said aircraft. - View Dependent Claims (4, 5, 16, 17)
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6. Imaging apparatus for an airborne vehicle, said apparatus comprising:
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scanning mirror means having a plurality of reflective surfaces for providing an image of a field of view, said image being acquired as said mirror is rotated transverse to the flight path of said vehicle over a predetermined lateral swath, spectrometer means, comprising optical collection means for receiving a reflected image of said field of view and for focusing said image upon a slit aperture oriented with its length in the in-track direction of flight, collimating means for applying said focused image to beam splitter means for reflecting a first predetermined spectral portion of said image and for transmitting a second predetermined spectral portion of said image, grating means for directing said first and second spectral portions to lens means, said lens means for focusing and applying said first and second portions of said image to respective first and second two dimensional detector arrays, said detector arrays comprised of a matrix of sensor elements, said sensor elements being arranged in rows and columns, the number of rows in said arrays corresponding to a predetermined number of picture elements in the flight direction, the number of columns corresponding to the number of spectral channels of a given average bandwidth, wherein said image is resolved by said spectrometer means into a matrix of spectral channels as a function of the spatial image, each predetermined spatial increment along the cross-track direction corresponding to a continuous spectral distribution in the in-track direction, each spectral channel corresponding to a given plurality of sensor elements, each sensor element storing an electrical signal representative of said average band of wavelengths and an intensity corresponding to the temporal image incident thereupon, means for reading all said electrical signals in a given column in parallel as said mirror rotates and digitally transferring said signals to storage means, and means synchronized to the in-track motion of the airborne vehicle for clearing said electrical signals and energizing said sensor elements with a new image corresponding to the in-track displacement of the aircraft, whereat said storage means is operative to provide a continuous spectral distribution temporally synchronized with a continuous spatial field traversed by said aircraft. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15)
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Specification