This paper describes a design concept for a Landsat-class imaging spectrometer. The challenge is to match the
Landsat data parameters, including a 185 Km swath and a 30 meter ground sample distance (GSD) from a 705 Km
sun-synchronous orbit with a sensor that has contiguous spectral coverage of the solar reflected spectrum (400 to
2500 nm). The result is a remote sensing satellite that provides global access imaging spectrometer data at moderate
spatial resolution. Key design trades exist for the spectrometer, focal plane array, dispersive element, and calibrator.
Recent developments in large format imaging spectrometers at Raytheon are presented in support of a monolithic
spectrometer approach. Features of the design include (1) high signal-to-noise ratio, (2) well-corrected spectral
fidelity across a 6,000 pixel push-broom field-of-view, (3) straightforward calibration of the data to units of absolute
spectral radiance, and (4) real-time simulation of Thematic Mapper bands, vegetation indices, and water vapor maps
for direct continuous downlink.
We present results of studies of instrument concepts for a spaceborne imaging Fabry-Perot interferometer to measure tropospheric ozone. Ozone is recognized as one of the most important trace constituents of the troposphere. Tropospheric ozone is responsible for acute and chronic human health problems and contributes toward destruction of plant and animal populations. Furthermore, it is a greenhouse gas and contributes toward radiative forcing and climate change. Tropospheric ozone levels have been increasing and will continue to do so as concentrations of precursor gases (oxides of nitrogen, methane, and other hydrocarbons) necessary for the photochemical formation of tropospheric ozone continue to rise. Space-based detection and monitoring of tropospheric ozone is critical for enhancing scientific understanding of creation and transport of this important trace gas and for providing data needed to help develop strategies for mitigating impacts of exposure to elevated concentrations of tropospheric ozone. Measurement concept details are discussed in a companion paper by Larar et al. Development of an airborne prototype instrument for this application is discussed by Cook et al. in another companion paper.
This paper describes a design concept for a Landsat-class imaging spectrometer. The challenge is to match the Landsat data parameters, including a 185 kilometer swath and a 30 meter ground sample distance (GSD) from a 705 km sun-synchronous orbit with a sensor which has contiguous spectral coverage of the solar reflected spectrum (400 to 2500 nanometers). The result is a dual purpose remote sensing satellite that provides global access imaging spectrometer data sets as well as fulfilling the needs of the Landsat Data Continuity Mission. Key features of the design include (1) high signal-to-noise ratio, (2) well corrected spectral fidelity across a 6000 pixel pushbroom field-of-view, (3) real-time simulation of Thematic Mapper bands 1-5, and 7 for direct continuous downlink and (4) straightforward calibration of the data to units of absolute spectral radiance.
Imaging spectrometers have recently moved out of the spaceflight environment, in which they were developed, to a host of other applications. Some of these new uses include the graphics and printing industry, process control, bio-medicine, clinical diagnostics and agriculture. For any of these applications, new approaches are necessary to design compact, portable instruments that can be easily and reliably calibrated. This paper presents one such implementation of an imaging spectrometer suitable for field use.
A demonstration imaging spectrometer using a liquid crystal tunable filter (LCTF) was built and tested on a hot air balloon platform. The LCTF is a tunable polarization interference or Lyot filter. The LCTF enables a small, light weight, low power, band sequential imaging spectrometer design. An overview of the prototype system is given along with a description of balloon experiment results. System model performance predictions are given for a future LCTF based imaging spectrometer design. System design considerations of LCTF imaging spectrometers are discussed.
KEYWORDS: Calibration, Sensors, Spectroscopy, Data archive systems, Data acquisition, Spectral calibration, Signal to noise ratio, Optical filters, Camera shutters, Sensor calibration
AVIRIS operations at the Jet Propulsion Laboratory consist primarily of a sensor task and a data facility task. These two activities are supported by an experiment coordination, a calibration and a management effort. The sensor task is responsible for AVIRIS sensor maintenance, laboratory calibration, and field operations. The AVIRIS data facility is responsible for data archiving, data calibration, quality monitoring and distribution. In this paper we describe recent improvements in these two primary AVIRIS tasks. The inflight performance of AVIRIS in 1992 and 1993 that resulted from these improvements is also presented.
The concept of imaging spectrometry is finding broad application in scientific instrumentation for Earth-based, airborne, and space applications. An imaging spectrometer is characterized by the combination of imaging with complete sampling in the spectral domain. In so doing, material identification can be accomplished and displayed in conjunction with the conventional recognizable image. An imaging spectrometer incorporates a wide variety of technologies, including focal plane arrays, imaging and spectrometer optics, and spectral dispersing devices. The design of a successful system involves a complex set of trade-offs incorporating the properties and limitations of the various technologies. For applications in the infrared, additional technologies such as focal plane cooling are required, and the other technologies present more limitations and constraints. This paper describes the system design process for a typical application, and discusses the system performance parameters and trade-offs, including choice of system architecture, signal to noise ratio, system resolution, spectral performance, calibration, and the effect of artifacts such as detector non-uniformity.
An upgraded version of AVIRIS, an airborne imaging spectrometer based on a whiskbroom-type scanner coupled via optical fibers to four dispersive spectrometers, that has been in operation since 1987 is described. Emphasis is placed on specific AVIRIS subsystems including foreoptics, fiber optics, and an in-flight reference source; spectrometers and detector dewars; a scan drive mechanism; a signal chain; digital electronics; a tape recorder; calibration systems; and ground support requirements.
KEYWORDS: Data archive systems, Spectroscopy, Data processing, Data acquisition, Imaging systems, Interference (communication), Calibration, Sensors, Imaging spectroscopy, Signal to noise ratio
The modifications made to both the AVIRIS instrument and the data processing facility since the instrument made its initial flight in the summer of 1987 are described. Historical development of the data system is discussed and attention is given to enhancements to instrument stability and noise performance. AVIRIS data facility objectives include rapid and automated decommutation and archiving of data, the ability to assess the quality of the data and health of the instrument, and the provision of an automated procedure for applying radiometric corrections to the data and providing responsive processing of data requests from investigators. The modifications described have resulted in an overall radiometric stability of better than 10 percent, with stability of only a few percent during a single flight.
The laboratory procedures, algorithms, measurements, and uncertainties associated with generation of the spectral and radiometric calibration of data acquired by AVIRIS are described. AVIRIS is an airborne sensor that obtains high-spatial-resolution image data of the earth in 224 spectral channels in four spectrometers covering the range from 400 to 2450 nm. The spectral calibration of AVIRIS agrees with the in-flight data to within two nanometers, and the absolute radiometric calibration is consistent with the in-flight verification to 10 percent over the spectral range. In-flight radiometric stability as measured by five consecutive passes over the surface calibration site is reported to be between three and five percent.
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