The Hyperion Imaging Spectrometer is one of three principal instruments aboard the EO-1 spacecraft. Its mission as a technology demonstrator is to evaluate on-orbit issues for imaging spectroscopy and to assess the capabilities of a space-based imaging spectrometer for earth science and earth observation missions. The instrument provides earth imagery at 30 meter spatial resolution. 7.5 km swath width in 220 contiguous spectral bands at 10 nm spectral resolution. Spectral range is from 0.4 micrometers to 2.5 micrometers . The instrument includes internal and solar calibration sub- systems. This paper will review the design, construction and calibration of the Hyperion instrument. The on-orbit plans and operations will be presented along with updated calibration and characterization measurements.
The Hyperion Imaging Spectrometer is one of three principal instruments aboard the EO-1 spacecraft. Its mission as a technology demonstrator is to evaluate on-orbit issues for imaging spectroscopy and to assess the capabilities of a space- based imaging spectrometer for earth science and earth observation missions. For the latter activity, a science team has been selected, which is complemented by commercial applications teams. This paper will review the design, construction and calibration of the Hyperion instrument. The on-orbit plans and operations will be presented along with updated calibration and characterization measurements.
The TRW Imaging Spectrometer III airborne hyperspectral imager was competed in 1996. The spectrometer is a pushbroom sensor that gathers information in 384 contiguous spectral channels covering the 400nm to 2450nm wavelength range. TRWIS III was designed to fly on many different aircraft platforms and to meet critical performance requirements for image quality, co-registration of spectral samples, spectral calibration, noise and radiometric accuracy. Along with its first several seasons of operational demonstrations, the instrument has undergone laboratory performance validation, radiometric calibration, and system upgrades. This paper will describe the current TRWIS III system, the data calibration and correction system, and the instrument's applications to remote sensing.
The tremendous potential for hyperspectral imagery as a remote sensing tool has driven the development of TRW's TRWIS III hyperspectral imager. This instrument provides 384 contiguous spectral channels at 5 nm to 6.25 nm spectral resolution covering the 400 nm to 2450 nm wavelength range. The spectra of each pixel in the scene are gathered simultaneously at signal to noise ratios of several hundred to one for typical Earth scenes. Designed to fly on a wide range of aircraft and with variable frame rate, the ground resolution can be varied from approximately 50 cm to 11 m depending on the aircraft altitude and speed. Meeting critical performance requirements for image quality, co- registration of spectral samples, spectral calibration, noise, and radiometric accuracy are important to the success of the instrument. TRWIS III performance has been validated and the instrument has been radiometrically calibrated using TRW's Multispectral Test Bed. This paper discusses the characterization and calibration process and results of the measurements. An example of results from a flight at the end of 1996 is included.
The tremendous potential for hyperspectral imagery as a remote sensing tool has driven the development of TRW's TRWIS III hyperspectral imager. This instrument provides 384 contiguous spectral channels at 5 nm to 6.25 nm spectral resolution covering the 400 nm to 2450 nm wavelength range. The spectra of each pixel in the scene are gathered simultaneously at signal to noise ratios of several hundred to one for typical Earth scenes. Designed to fly on a wide range of aircraft and with variable frame rate, eh ground resolution can be varied from approximately 30 cm to 11 m depending on the aircraft altitude. Meeting critical performance requirements for image quality, co-registration of spectral samples, spectral calibration, noise, and radiometric accuracy are important to the success of the instrument. TRWIS III performance has been validated and the instrument has been radiometrically calibrated using TRW's multispectral test bed. This paper discusses the characterization and calibration process, results of the measurements, and instrument artifacts of potential interest to data users.
An imaging spectrometer has been developed for the NASA small satellite technology initiative (SSTI) which provides 30 meter resolution earth images in 384 continuous spectral bands from 0.4 micrometers to 2.5 micrometers . The instrument includes a 5 meter resolution Panchromatic camera and a calibration subsystem. The hyperspectral imager (HSI) payload was developed for the Lewis satellite in 24 months and is scheduled to fly later this year. This paper describes the HSI design, development and performance.
The past decade has seen the development of multispectral and hyperspectral imaging spectrometers for use in remote sensing applications in the aerospace business. Correspondingly, advanced electronic imaging techniques have been exploited for use in industrial inspection and manufacturing process control. TRW has been involved in hyperspectral imaging since 1989 for use in remote sensing of earth resources and has developed many instruments and related technologies which can easily be re-applied to unique industrial inspection applications. These instruments operate in the visible, near-infrared and short-wave infrared wavebands covering the range from 0.4 microns to 2.5 microns depending on the application. The exploitation of hyperspectral imagers for remote sensing has shown the power of spectral imaging for typing and discrimination tasks, which can be readily applied to industrial applications. In this paper we explain the relevant fundamentals of hyperspectral imaging and how it can be exploited for industrial inspection and process control tasks, particularly those that require color or spectral typing and discrimination. The associated technologies used to perform measurements and reduce the data also are described.
TRW has been involved in hyperspectral imaging since late 1989. The first instruments were constructed from commercially available components and were restricted in wavelength response to the visible and near IR (i.e., about 0.48 micrometers to 0.88 micrometers). They were used to take data from airborne platforms to support phenomenology studies. An instrument was then constructed to make measurements in the SWIR (i.e., out to 2.5 micrometers). It used mostly commercial components and contained some custom developments such as the foreoptics. These early instruments all recorded data using videotape recorders. A real time processor has been constructed which performs real time spectral template matching on six spectral templates. This significantly reduces operator load for systems where spectrally known targets are being sought. We are currently developing three new systems using custom components. The first is a high performance, aircraft based instrument called TRWIS III; the second, called HSI, will be the first hyperspectral imager in space, and is being developed for the NASA Small Satellite Technology Initiative; and the third is an ocean color instrument, known as the Low Resolution Camera, using the hyperspectral approach. Each of these instruments will be briefly described.
The clouds and the Earth's radiant energy system (CERES) program continues the long term monitoring of the Earth's radiant energy budget begun by the Earth Radiation Budget Experiment (ERBE) scanning radiometer instruments. The CERES instrument contains three thermal detector based radiometers with broadband spectral responses. The relative spectral responses must be characterized at far infrared wavelengths out to 200 micrometers in support of absolute radiometric calibration. This will be accomplished with a Fourier transform spectrometer as a spectral source, relay optics and a vacuum chamber containing the sensors. This facility currently under development for the CERES program will measure end-to-end sensor spectral response relative to a spectrally flat well characterized reference detector also located in the vacuum chamber. Facility design and controls on the measurement process to assure spectral accuracy are discussed.
Stability of the solar constant makes the Sun an attractive on-orbit calibration source for radiometers operating at visible and near IR wavelengths. Direct viewing of the Sun provides a radiance or irradiance that is significantly above the dynamic range of most earth observing system (EOS) radiometers, thereby requiring attenuated viewing of the Sun. To provide radiometric repeatability, the attenuator used must be stable over time at all in-band wavelengths, uniformly flood the radiometer aperture and field of view, and be invariant over the range of solar viewing angles. The Earth Radiation Budget Experiment (ERBE) radiometers flown in the mid-1980s carried a mirror attenuator mosaic (MAM) to attenuate the solar energy. This device, consisting of specularly reflective, closely packed concave hemispheres with a black mask covering the area between the spheres, was successfully used to calibrate the ERBE shortwave (0.3 to 3.5 micrometers ) and total (0.3 to > 50 micrometers ) radiometer channels. For CERES, the calibration accuracy requirements have been tightened (+/- 1% shortwave, +/- 0.5% total channel, end-of-life, 1 (sigma) ). While the stability and uniformity demonstrated by the ERBE MAM are sufficient for CERES, the variation with solar incidence angle is not. Improvements to the ERBE design have been made for CERES and sample MAMs have been fabricated and tested. The results of this study as well as the features and details of the MAM design are addressed.
The clouds and the earth's radiant energy system (CERES) experiment will provide consistent data bases of radiation and cloud fields. The CERES instrument consists of a scanning thermistor bolometer package with built-in flight calibration systems. Two bolometer packages will be launched on the earth observing system (EOS) platforms to measure the Earth/atmosphere-reflected solar shortwave and Earth/atmosphere-emitted long wave radiances with measurement accuracy goals approaching 1.0% and 0.5%, respectively. In each package, there are three different bolometers. All bolometers will be calibrated in a unique TRW vacuum facility equipped with blackbodies, a cryogenically cooled active-cavity radiometer, shortwave sources, and other specialized calibration devices. The blackbodies are tied to the International Temperature Scale of 1990 (ITS'90). Using math models, the calibration measurements will define the instrument filtered gains and offsets. This paper outlines the CERES instrument design and radiometric calibrations.
Several molecular species (hydrocarbons) outgassed from spacecraft materials adhere and darken on satellite optical surfaces when exposed to solar ultraviolet (UV) radiation. This absorbing molecular film of photolyzed contamination can severely degrade spacecraft optical system performance. In the Optical Scatter and Contamination Effects Facility (OSCEF) at TRW outgassed molecular species can be photo-deposited onto witness optics and an adjacent quartz crystal microbalance with vacuum ultraviolet radiation, simulating a spacecraft UV illuminated environment. Measurement of outgassing rates and concomitant photodeposition efficiencies provides useful data required in the selection of present and new spacecraft materials and accurate predictions of platform operating lifetimes. This paper will describe the methods used to measure the molecular outgassing and photodeposition rates of species from several spacecraft materials in which the samples are used in their operational configurations (no heating or grinding of the sample as in the ASTM E595 test), thus providing data highly representative of on-orbit photodeposition conditions.
Molecular species outgassed from spacecraft materials adhere tenaciously to and darken spacecraft surfaces when exposed to solar ultraviolet (UV) radiation. Such deposits severely degrade the performance of optical systems operating at UV and visible wavelengths. Data is presented which demonstrates the feasibility of a UV/Ozone cleaning technique in removing such deposits in a space-compatible configuration without damage to the optical surface. The technique involves the UV irradiation of the optical surface in the presence of low pressure molecular oxygen, resulting in the photolytic formation of ozone (O3) and subsequent photochemical removal of the contamination.
Enhancements which have been made in the Radiometric Calibration Facility (RCF) of the CERES payload are described. These include narrow field blackbody and wide field of view blackbody sources, an active cavity radiometer, and a shortwave reference source. They permit the RCF to calibrate the CERES instruments to better than +/- 0.5 percent absolute radiometric accuracy in the 3.5 to above 50 micron wavelength region and to +/- 1.0 percent in the 0.3-3.5 micron region.
The Cloud and the Earth's Radiant Energy System (CERES) program continues the long term monitoring of the Earth's energy budget begun by the Earth Radiation Budget Experiment (ERBE) scanning radiometer instruments. The radiometic ground calibration sources employed for ERBE were designed to cover the very large (all Earth) field of view of the non-scanning radiometers. The ERBE radiometer ground and flight calibration proved to be more accurate than the requirement. The ground calibration sources to be used for CERES will be optimally designed to calibrate the much more narrow field of view of the scanning radiometer to improve on the absolute calibration performance. In addition, the shortwave calibration will be made in narrow bands to eliminate uncertainty in the spectral shape of the shortwave calibration source. Each shortwave band will be absolutely calibrated by transfer to a blackbody using a cryogenic active cavity radiometer fitted with the same telescope optics as the CERES radiometers.
Molecular and particulate contamination of spacecraft optical surfaces can be extremely detrimental to optical system performance degrading system throughput and increasing stray light background. Data that characterize the impact of various contaminants especially cryo- and photo-deposited molecular films on transmission reflection and scatter from optical surfaces are needed for allocation of spacecraft contamination budgets. A facility has been developed to measure the effects of molecular and particulate contaminants on optical component performance. The TRW Optical Scatter and Contamination Effects Facility (OSCEF) is capable of measuring the Bidirectional Reflectance/Transmittance Distribution Function (BRDF or BTDF) and specular reflectance/transmittance in ambient (ex-situ) as well as cryogenic vacuum (in-situ) environments. Light sources for scatter and reflectance/transmittance measurements include Argon ion HeNe Nd:YAG and CO2 lasers at wavelengths from 351 nm to 10. 6 um. Ex-situ scatter measurements can be performed on hardware to 30 cm diameter (1 meter with some reconfiguration) over nearly 4irsr1 of scatter angle space and to within 0. 3 degrees of the specularly reflected beam. In-situ measurements can be performed on 12. 5 mm diameter witness samples at temperatures from 20 K to 373 K while contaminants from representative spacecraft materials are cryo- and/or photo-deposited onto the sample surface. Contaminant layer thickness is monitored by a thermally controlled quartz crystal microbalance (TQCM) located adjacent to the witness sample. A xenon continuum lamp (1450 to 1 800 A) is available for photochemically
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