A new approach for the design and fabrication of a miniaturized hyperspectral imager is described. A unique and compact instrument has been developed by taking advantage of light propagation within bonded solid blocks of optically transmitting glass. The resulting series of micro-hyperspectral imaging (microHSI™) spectrometer has been developed, patented, and built as a visible near-infrared (VNIR) hyperspectral sensor capable of operating in the 400- to 1000-nm wavelength range. The spectrometer employs a blazed, convex diffraction grating in Offner configuration embedded within the optical blocks for ruggedized operation. This, in combination with fast spectrometer operation at f/2.0 , results in high optical throughput. The resulting microHSI™VNIR spectrometer weighs 0.54 kg, including foreoptics and camera, which results in a 2× decrease in spectrometer volume compared with current air-spaced Offner spectrometers. These instruments can accommodate custom, ruggedized foreoptics to adapt to a wide range of field-of-view requirements. These fast, telecentric foreoptics are chromatically corrected for wideband spectral applications. Results of field and laboratory testing of the microHSI™ spectrometers are presented and show that the sensor consistently meets technical performance predictions.
A new approach for the design and fabrication of a miniaturized SWIR Hyperspectral imager is described.
Previously, good results were obtained with a VNIR Hyperspectral imager, by use of light propagation
within bonded solid blocks of fused silica. These designs use the Offner design form, providing excellent,
low distortion imaging. The same idea is applied to the SWIR Hyperspectral imager here, resulting in a
microHSI<sup>TM</sup> SWIR Hyperspectral sensor, capable of operating in the 850-1700 nm wavelength range. The
microHSI spectrometer weighs 910 g from slit input to camera output. This spectrometer can
accommodate custom foreoptics to adapt to a wide range of fields-of-view (FOV). The current application
calls for a 15 degree FOV, and utilizes an InGaAs image sensor with a spatial format of 640 x 25 micron
pixels. This results in a slit length of 16 mm, and a foreoptics focal length of 61 mm, operating at F# = 2.8.
The resulting IFOV is 417 μrad for this application, and a spectral dispersion of 4.17 nm/pixel. A
prototype SWIR microHSI was fabricated, and the blazed diffraction grating was embedded within the
optical blocks, resulting in a 72% diffraction efficiency at the wavelength of 1020 nm. This spectrometer
design is capable of accommodating slit lengths of up to 25.6 mm, which opens up a wide variety of
applications. The microHSI concepts can be extended to other wavelength regions, and a miniaturized
LWIR microHSI sensor is in the conceptual design stage.
This paper presents the development status of a 50-million pixel, large-format, electro-optical framing charge-coupled device (CCD) with on-chip graded forward motion compensation. The development addresses the requirements set forth by the US Naval Research Lab for Ultra-high Resolution reconnaissance. A 5,040 by 10,080 element CCD has been developed and demonstrated to meet the 100-Mpixel/s UHR requirement.
The Minimum Resolvable Temperature Difference (MRTD) is the standard for measuring the performance of infrared imaging systems. Refined and validated modeling programs can accurately predict MRTD for scanning and staring Forward Looking Infrared (FLIR) imaging systems operating at video frame rates. However, there is a need to predict the MRTD performance of infrared systems that display imagery as static frames. Infrared imaging systems used for reconnaissance operate at low frame rates of about 1 to 5 Hz (framing cameras), or continuously gather imagery line by line (line scanners). Typically, each image is of a different scene and is displayed as a static image or in a waterfall display. Under normal lighting conditions, the human eye has a temporal bandwidth of approximately 10 Hz. Therefore, the perceived sensitivity, measured at MRTD, of these low frame rate systems is lower than a comparable video frame rate imaging system. The low frame rate systems do not benefit from the temporal filtering effect of the human eye as video frame rate systems do, and should exhibit a higher MRTD. This paper presents data comparing predicted MRTD performance calculated by the FLIR92 program with measured performance.
Time-Delay and Integration (TDI) CCD sensors have been proven to increase the effective sensitivity in imaging applications where the image is scanned across the focal plane. This paper describes the development of a 6032 element, 32-stage TDI imager for airborne reconnaissance applications. The device is fabricated using a 3-poly 3-phase NMOS process, incorporating buried channel CCDs throughout. It is one-side buttable to produce an array of over 12,000 contiguous elements and is capable of read rates of over 4000 lines per second. For fast readout, the design incorporates dual horizontal CCDs for a total of four outputs in the abutted configuration. The architecture also allows dynamic selection in the number of TDI stages.
Time-delay and integration (TDI) CCD sensors have been proven to increase the effective sensitivity in linescan imaging applications. This paper describes the design and initial test results of a 6032 element, 32-stage TDI imager for airborne reconnaissance applications. The device is fabricated using a 3-poly 3-phase NMOS process, incorporating buried channel CCDs throughout. It is one-side buttable to produce an array of over 12,000 contiguous elements and is capable of read rates of over 4000 lines per second. For fast readout, the design incorporates dual horizontal CCDs for a total of four outputs in the abutted configuration. The architecture also allows dynamic selection in the number of TDI stages.