Classification of imaging spectrometers for remote sensing applications

The continuing development of new and fundamentally different classes of imaging spectrometers has increased the complexity of the field of imaging spectrometry. The rapid pace at which new terminology is introduced to describe the new types of imaging spectrometers sometimes leads to confusion, particularly in discussions of the relative merits of the different types. In some cases, multiple different terms are commonly used to describe the same fundamental approach, and it is not always clear when these terms are synonymous. Other terminology in common use is overly broad. When a single term may encompass instruments that operate in fundamentally different ways, important distinctions may be obscured. In the interest of clarifying the terminology used in imaging spectrometry, we present a comprehensive system for classification of imaging spectrometers based on two fundamental properties: the method by which they scan the object spatially, and the method by which they obtain spectral information

Limiting aspect ratios of Sagnac interferometers

Any two-beam interferometer may be employed as a Fourier transform spectrometer. The two most commonly used for Fourier transform spectrometry are the Michelson interferometer and the Sagnac interferometer, the relative merits of which have been discussed in the literature. Typically, it is the interferometer that limits the acceptable range of angles for the input beam, and this maximum acceptance angle in turn limits the etendue, and hence limits the responsivity of the instrument when viewing an extended source. In designs where the interferometer is in a diverging or converging beam, the allowable range of input angles limits the focal ratio of the instrument, while in designs where the beam is collimated through the interferometer, this effect limits the field-of-view of the instrument. In a Michelson, it is a loss of fringe contrast that limits the range of acceptance angles; a limitation that is discussed in many general texts on optics. A Sagnac, however, suffers no such loss of contrast as the range of acceptance angles is increased. The maximum acceptance angle for a Sagnac is instead limited by vignetting, caused by the geometry of the interferometer. The limitation for a Sagnac has an origin and behavior entirely different from that found for a Michelson, and has not been previously discussed in the literature. It is therefore important to understand this limitation when designing a Sagnac interferometer for Fourier transform spectrometry. This vignetting limitation may be quantified by an aspect ratio, which we define as the ratio of the separation of the entrance and exit apertures to the width of these apertures in the plane of the interferometer. To facilitate the design of Sagnac interferometers for Fourier transform spectrometry, we discuss the limitations on the aspect ratio and derive equations for the limiting aspect ratios for nine variations of the Sagnac interferometer

High-Grading Lunar Samples for Return to Earth

Astronauts on long-duration lunar missions will need the capability to "high-grade" their samples to select the highest value samples for transport to Earth and to leave others on the Moon. We are supporting studies to defile the "necessary and sufficient" measurements and techniques for highgrading samples at a lunar outpost. A glovebox, dedicated to testing instruments and techniques for high-grading samples, is in operation at the JSC Lunar Experiment Laboratory

Lunar Reference Suite to Support Instrument Development and Testing

Astronauts on long-duration lunar missions will need the capability to "high-grade" their samples - to select the highest value samples for transport to Earth - and to leave others on the Moon. Instruments that may be useful for such high-grading are under development. Instruments are also being developed for possible use on future lunar robotic landers, for lunar field work, and for more sophisticated analyses at a lunar outpost. The Johnson Space Center Astromaterials acquisition and Curation Office (JSC Curation) wll support such instrument testing by providing lunar sample "ground truth"

Imaging Fourier transform spectrometers for environmental sensing

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77073/1/AIAA-1998-291-523.pd

Paper Session II-B - High Efficiency Hyperspectral Imager for the Terrestrial and Atmospheric Multispectral Explorer

The Terrestrial and Atmospheric MultiSpectral Explorer1 (TAMSE) is a Space Shuttle Small Self- Contained Payload “Get-Away Special” (GAS) project, led by Principal Investigator Rolando Branly, and including remote sensing and microgravity experiments from Florida Space Institute member schools. One of these experiments is the High-Efficiency HyperSpectral Imager (HEHSI). The HEHSI project will provide a low-cost spaceflight demonstration of a novel type of imaging spectrometer with exceptional light gathering ability. HEHSI is also a demonstration of what can be achieved in space with a modest budget: $15K from the Florida Space Grant Consortium (FSGC) and$ 10K from the Florida Space Institute (FSI). Education and workforce development are important goals of the project, with all of the mechanical, electronics, and software design and testing being carried out by an interdisciplinary team of FSI students. These six students, who are about to graduate with bachelor’s degrees in engineering (three computer, one electrical, and two aerospace), have worked on the project and received course credit for two semesters. The matching funds from FSI support the involvement of the mentor for the HEHSI experiment, Glenn Sellar, who is also responsible for the optical design. Environmental testing (thermal and vibration) will be carried out by the students at KSC’s Physical Testing Laboratory, under a cooperative Space Act Agreement. As this instrument is the first remote sensing payload constructed in Florida (to the authors knowledge), it also serves as a seed for diversification of the space industry in Florida. An overview of the project is presented in this paper, including the science objectives, and the optical, mechanical, electrical, and software designs

Payload Design for the Lunar Flashlight Mission: Illuminating the Moon's South Pole

No abstract availabl

Comparison Of Relative Signal-To-Noise Ratios Of Different Classes Of Imaging Spectrometer

The continued development of new and fiindamentally different classes of imaging spectrometer has increased both the scope and the complexity of comparisons of their relative signal-to-noise ratios. Although the throughput and multiplex advantages of Fourier-transform spectrometers were established in the early 1950s, the application of this terminology to imaging spectrometers is often ambiguous and has led to some confusion and debate. For comparisons of signal-collection abilities to be useful to a system designer, they must be based on identical requirements and constraints. We present unambiguous definitions of terminology for application to imaging spectrometers and comparisons of signal-collection abilities and signal-to-noise-ratios on a basis that is useful to a systems designer and inclusive of six fundamentally different classes (both traditional and novel) of imaging spectrometers. © 2005 Optical Society of America

Comparison Of Signal Collection Abilities Of Different Classes Of Imaging Spectrometers

Although the throughput and multiplex advantages of Fourier transform spectrometry were established in the early 1950\u27s (by Jacquinot11,2,3 and Fellgettz4,5 respectively) confusion and debate6 arise when these advantages are cited in reference to imaging spectrometry. In non-imaging spectrometry the terms throughput and spectra! bandwidth clearly refer to the throughput of the entire field-of-view (FOV), and the spectral bandwidth of the entire FOV, but in imaging spectrometry these terms may refer to either the entire FOV or to a single element in the FOV. The continued development of new and fundamentally different types of imaging spectrometers also adds to the complexity of predictions of signal and comparisons of signal collection abilities. Imaging spectrometers used for remote sensing may be divided into classes according to how they relate the object space coordinates of cross-track position, along-track position, and wavelength (or wavenumber) to the image space coordinates of column number, row number, and exposure number for the detector array. This transformation must be taken into account when predicting the signal or comparing the signal collection abilities of different classes of imaging spectrometer. The invariance of radiance in an imaging system allows the calculation of signal to be performed at any space in the system, from the object space to the final image space. Our calculations of signal - performed at several different spaces in several different classes of imaging spectrometer - show an interesting result; regardless of the plane in which the calculation is performed, interferometric (Fourier transform) spectrometers have a dramatic advantage in signal, but the term in the signal equation from which the advantage results depends upon the space in which the calculation is performed. In image space, the advantage results from the spectral term in the signal equation, suggesting that this could be referred to as the multiplex (Fellgett) advantage. In an intermediate image plane the advantage results from a difference in a spatial term, while for the exit pupil plane it results from the angular term, both of which suggest the throughput (Jacquinot) advantage. When the calculation is performed in object coordinates the advantage results from differences in the temporal term