Northrop Grumman Aerospace Systems (NGAS) has a long
legacy developing and fielding hyperspectral sensors,
including airborne and space based systems covering the
visible through Long Wave Infrared (LWIR) wavelength
ranges. Most recently NGAS has developed the
Hyperspectral Airborne Terrestrial Instrument (HATI) family
of hyperspectral sensors, which are compact airborne
hyperspectral imagers designed to fly on a variety of
platforms and be integrated with other sensors in NGAS's
instrument suite. The current sensor under development is
the HATI-2500, a full range Visible Near Infrared (VNIR)
through Short Wave Infrared (SWIR) instrument covering the
0.4 - 2.5 micron wavelength range with high spectral
resolution (3nm). The system includes a framing camera
integrated with a GPS/INS to provide high-resolution
multispectral imagery and precision geolocation. Its compact
size and flexible acquisition parameters allow HATI-2500 to
be integrated on a large variety of aerial platforms. This
paper describes the HATI-2500 sensor and subsystems and its
expected performance specifications.
Northrop Grumman Aerospace Systems (NGAS) has developed the Hyperspectral Airborne Tactical Instrument (HATI), a compact
airborne hyperspectral imager designed to fly on a variety of platforms and to be integrated with other sensors in the NGAS
instrument suite. HATI has taken part in a variety of missions and flown in conjunction with other NGAS airborne sensors including
the recently-developed NGAS 3-D flash ladar system to demonstrate a multi-sensor data fusion approach. HATI is a push-broom
sensor which gathers information in the 400 nm to 1700 nm wavelength range. Its compact size allows HATI to be mounted on
commercial-of-the-shelf (COTS) aerial photography stabilization platforms and on a large variety of aerial platforms. In its most
recent flight season, the HATI sensor was used to gather data for applications including remote classification of vegetation, forests,
and man-made materials. The HATI instrument has undergone laboratory and in-situ performance validation and radiometric
calibration. This paper describes the HATI sensor and recent data collection campaigns.
Northrop Grumman Space Technology (NGST), using internal funding, has designed, built and is testing a Long Wave Hyperspectral Imaging Spectrometer (LWHIS) that operates in the 8 to 12.5 micron band. This instrument was designed to be compatible with aircraft platforms so that flight data in this wavelength band can be used for phenomenological analysis. The instrument provides up to 256 contiguous spectral channels with 17 nm of dispersion per pixel (pixels are binned in normal operation to provide 128 spectral channels). The entrance aperture is 3.5 cm and feeds a F2/5 reflective triplet front end. The focal plane is a 256 x 256 array of 40 micron pixels which can be binned to form an 80 micron superpixel. With a fixed frame rate of 60 Hz, the instrument provides a ground sample distance of 1m at 1.1km altitude. This paper describes the physical characteristics of the design and presents the predicted performance based on NGST internal models. Design trades and test data will be presented. A more detailed look at the characterization and calibration of this instrument will be presented in a companion paper "Long Wave Hyperspectral Imaging Spectrometer -- System Characterization and Calibration."
Northrop Grumman Space Technology (NGST) has developed and tested a Long-wave Hyperspectral Imaging Spectrometer (LWHIS) that operates in the 8 to 12.5 micron band. An overview of the system design has been described elsewhere. This paper describes the system characterization and radiometric calibration of this instrument using NGST’s Long-wave Hyperspectral Test Facility which uses a 1375K globar source assembly, a monochromator, a collimator and a fine pointing mirror to provide image quality and FPA alignment data. Image quality characterization results presented here include measurement of the instrument’s Modulation Transfer Function (MTF), spatial co-registration of spectral channels (spectral smile), cross-track spectral error (spatial smile), and spectral calibration. Radiometric calibration results for laboratory targets are also presented.
Ann add/drop multiplexer/demultiplexer using volumetric holographic crystal Bragg gratings and without use of circulators has been demonstrated. Multiplexed gratings with angle multiplexed reflection filters provide wavelength- selective reflection of one or more channels into or out of the fiber without disturbing the through channels. Overall channel add/drop losses of less than 3 dB and through channel losses of less than 0.5 dB have been demonstrated. Fabrication of holographic filters with the desired passband characteristics has also been demonstrated.
We present experimental results of holographic grating recording in the near ultra-violet (UV) in photorefractive LiNbO3 crystals. The UV wavelength limits of Fe-doped LiNbO3 crystals for UV grating filters have been established by characterizing the grating diffraction efficiency versus recording wavelength ranging from 300 to 400 nm. Methods for improving the UV performance of LiNbO3 have also been investigated. It has been shown that the material absorption loss of Fe:LiNbO3 crystals can be reduced and the grating efficiency can be a significantly improved by using proper post-grown oxidization treatment. Using the improved UV LiNbO3 crystal, a sub-Angstrom bandwidth holographic grating imaging filter for solar observation at the Ca K-line (393.3 nm) has also been fabricated. Narrow bandwidth (22 pm, FWHM), large numerical aperture (f/15), large field-of-view (35 mrad), large aperture (15 mm in diameter) and high in-band diffraction efficiency (25%) have been successfully demonstrated. These results indicate an improved performance at a reduced cost as compared with currently available Lyot filters for solar magnetic field sensing at Ca K-line. Applications of the UV photorefractive holographic grating devices include solar and planetary observing, lidar receiving sub-systems for Earth remote sensing and atmospheric monitoring, and high density UV optical data storage.
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