This paper presents the techniques and results of Hyperion laboratory characterization. Hyperion is a hyperspectral imager scheduled to fly on the Earth-Orbiter 1 (EO-1) spacecraft for the New Millennium project. The other payloads on the spacecraft are ALI (Advanced Land Imager) and AC (atmospheric corrector). The payloads were integrated into the spacecraft at Goddard Space Flight Center (GSFC). An End-to-End imaging test was conducted at GSFC which demonstrated integrity of Hyperion performance after environmental tests. The performance characterization procedures described here include: crosstrack MTF, spectral and spatial co-alignment, spectral wavelength calibration, signal to noise, polarization, spectral response function and scene generation. The characterization was carried out with the TRW Imaging Spectrometer Characterization Facility which is based on a 250 watt QTH lamp, a monochromator, a collimator and a fine pointing mirror. A selection of narrow slits and a knife edge are illuminated at the exit slit of the monochromator for sub-pixel performance characterization parameters such as MTF. Special attention is devoted to the spectral calibration technique using rare earth doped Spectralon panels. This was the technique used at the End-to-End test to verify spectral performance of Hyperion after GSFC environmental tests. It is a particular useful technique when the optical test setup does not allow for the use of a monochromator.
The tremendous potential for hyperspectral imagery as a remote sensing tool has driven the development ofTRW's TRWIS ifi hyperspectral imager. This instrument provides 384 contiguous spectral channels at 5 nm to 6.25 nm spectral resolution covering the 400 rim to 2450 rim wavelength range. The spectra ofeach 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 1 1 m depending on the aircraft altitude and speed. Meeting critical performance requirements for image quality, coregistration of spectral samples, spectral calibration, noise, and radiometric accuracy are important to the success ofthe instrument. TRWIS ifi performance has been validated and the instrument has been radiometrically calibrated using TRW's Multispectral Test Bed (MSTB). This paper discusses the characterization and calibration process and results ofthe measurements. An example ofresults 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, the ground resolution can be varied from approximately 30 cm to 1 1 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 (MSTB). This paper discusses the characterization and calibration process, results of the measurements, and instrument artifacts of potential interest to data users.
Since 1989 Hughes has been investigating ion cleaning of contaminant films from spacecraft optics while on-orbit. Two of the most successful methods of ion cleaning without damage have been developed on the Advanced Removal Techniques by Ion Cleaning (ARTIC) Program. The first method utilizes energetic electron sputtering, and the second method utilizes low-energy oxygen ion (LEOI) reactive etching. We have successfully removed water, ammonia and carbon dioxide cryofilms with electron sputtering. The mirror materials being cleaned include bare beryffium and protected aluminum coated optics. No damage to these ultra-low-scatter mirror materials has been observed even when the mirrors are purposely over-cleaned with electrons by many orders of magnitude. Current electron cleaning rates are on the order of 200 Angstroms per minute over approximately a 50 cm diameter area. A broad-beam of electrons from a flight-qualified Penning discharge source is being used for the electron cleaning, so no rastering is necessary.Low-energy oxygen-ion cleaning is being used to reactively clean organic films. Since the energy of the ions is much lower than the sputter threshold of the mirror materials, the mirror materials cannot be damaged using this technique. The current cleaning rates are on the order of 20 Angstroms per minute over approximately a 10 cm diameter area. A broadbeam flight-prototype ion source is being used that has been developed by the Hughes Research Laboratories for extremely long life, low power applications.
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