Mark A. Folkman

EO-1/Hyperion Hyperspectral Imager Design, Development, Characterization, and Calibration

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.

Application of hyperspectral-imaging spectrometer systems to industrial inspection

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.

EO-1 Hyperion hyperspectral aggregation and comparison with EO-1 Advanced Land Imager and Landsat 7 ETM+

The EO-1 spacecraft, launched November 21, 2000 into a Sun-synchronous orbit behind Landsat 7, hosts advanced technology demonstration instruments, whose capabilities are currently being assessed by the user community for future missions. A significant part of the program is to perform data comparisons between the Hyperion Imaging Spectrometer and Advanced Land Imager (ALI) payloads on the EO-1 spacecraft with the Landsat 7 ETM+ sensor. To perform the absolute radiometric comparison, an aggregation method was developed and used to combine the proper portions of the Hyperion 10 nm bands to emulate the broader multispectral response of the ALI and ETM+. The aggregation capability allows radiometric comparisons between different instruments with different spectral response functions. This paper reviews the aggregation methodology, and presents absolute comparison results. A demonstration of the replication of portions of ALI and ETM+ scenes through a synthesis of Hyperion hyperspectral data is also provided. The capability of synthesizing broad band data from a hyperspectral sensor will enable users to test the selection of broad bands for future missions by using various combinations of Hyperion bands.

Development and operations of the EO-1 Hyperion Imaging Spectrometer

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.

Updated results from performance characterization and calibration of the TRWIS III hyperspectral imager

The tremendous potential for hyperspectral imagery as a remote sensing tool has driven the development of TRWs 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 TRWs 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.

Airborne and satellite imaging spectrometer development at TRW

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.

TRWIS III hyperspectral imager: instrument performance and remote sensing applications

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 instruments applications to remote sensing.

Lewis hyperspectral imager payload development

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.

Far-IR spectral response measurements of the Clouds and the Earth's Radiant Energy System (CERES) sensors using a Fourier transform spectrometer and pyroelectric reference detector

The clouds and the Earths radiant energy system (CERES) program continues the long term monitoring of the Earths 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.

Radiometric calibration plan for the Clouds and the Earth's Radiant Energy System scanning instruments

The Cloud and the Earths Radiant Energy System (CERES) program continues the long term monitoring of the Earths 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.