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Adverse air quality impacts human health and climate and has implications for environmental equity. The Compact Hyperspectral Air Pollution Sensor (CHAPS) is a newly designed small imaging spectrometer for remote sensing of nitrogen dioxide (NO2) and other air pollutants from space. It incorporates two emerging technologies, to achieve the miniaturization necessary to fit within a 6U CubeSat. The first is freeform optics, which can be used to reduce the size of an imaging spectrometer without compromising optical performance. We report the science requirements; preliminary, fully freeform and fully reflective optical design of the CHAPS demonstrator, CHAPS-D; and model its performance. The second technology is additive manufacturing, coupled with topology optimization, which has a number of potential advantages over traditional subtractive manufacturing. The instrument mechanical structure, including optical mounts and integral light baffles, and two of the optical elements will be additively manufactured using a high-strength nextgeneration aluminum alloy. We show preliminary results of additive manufacturing tests. CHAPS-D is currently being developed for ground-based and airborne testing.

Compositions of the Amazonian-aged Tharsis and Elysium volcanic provinces of Mars have been largely obscured in Mars-orbital remote sensing data by windblown dust. Fresh impact craters formed within the last few years have disturbed surface dust, providing unique windows to explore these regions' relatively dust-free mineralogic compositions. Such fresh craters, plus other small exposures of less dusty materials, are resolved spatially in high-resolution targeted observations of visible/short-wave infrared spectral reflectance by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Analysis of CRISM observations of small, relatively dust-free locations in the Tharsis and Elysium regions shows that these provinces are dominated by high-Ca pyroxene and olivine, similar to volcanic materials of Hesperian age. Thus, the mafic mineral compositions of Hesperian and Amazonian volcanic materials appear similar to each other, but distinct from the olivine- and low-Ca pyroxene-rich compositions that dominate Noachian rocks. In the core regions of both provinces, where thermal infrared data indicate the thickest dust cover, the dust is sufficiently thick that few fresh craters penetrate to expose the underlying volcanics. These results may be consistent with low Si contents of surface materials in Elysium and western Tharsis measured by gamma-ray spectroscopy resulting from a thick cover of dust depleted in Si-rich phases, possibly due to eolian sorting.

The investigation of hyperspectral data from the Mars Reconnaissance Orbiter Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and the Observatoire pour la Minéralogie, L'Eau, les Glaces et l'Activitié (OMEGA) on Mars Express has revealed an increasingly diverse suite of minerals present on the Martian surface. A revised set of 60 spectral parameters derived from corrected spectral reflectance at key wavelengths in CRISM targeted observations and designed to capture the known diversity of surface mineralogy on Mars is presented here as “summary products.” Some of the summary products have strong heritage to OMEGA spectral parameter calculations; this paper also presents newly derived parameters that highlight locations with more recently discovered spectral signatures. Type locations for the diversity of currently identified mineral spectral signatures have been compiled into a library presented in this work. Our analysis indicates that the revised set of summary products captures the known spectral diversity of the surface, and successfully highlights and differentiates between locations with differing spectral signatures. The revised spectral parameter calculations and related products provide a useful tool for scientific interpretation and for future mission landing site selection and operations.

The observations of Mars by the CRISM and OMEGA hyperspectral imaging spectrometers require correction for photometric, atmospheric and thermal effects prior to the interpretation of possible mineralogical features in the spectra. Here, we report on a simple, yet non-trivial, adaptation to the commonly-used volcano-scan correction technique for atmospheric CO_2, which allows for the improved detection of minerals with intrinsic absorption bands at wavelengths between 1.9-2.1 $\mu$m. This volcano-scan technique removes the absorption bands of CO_2 by ensuring that the Lambert albedo is the same at two wavelengths: 1.890 $\mu$m and 2.011 $\mu$m, with the first wavelength outside the CO_2 gas bands and the second wavelength deep inside the CO_2 gas bands. Our adaptation to the volcano-scan technique moves the first wavelength from 1.890 $\mu$m to be instead within the gas bands at 1.980 $\mu$m, and for CRISM data, our adaptation shifts the second wavelength slightly, to 2.007 $\mu$m. We also report on our efforts to account for a slight ~0.001 $\mu$m shift in wavelengths due to thermal effects in the CRISM instrument., Comment: 17 pages, 6 figures, accepted for publication in 'Planetary and Space Science'

[1] The part of the Compact Reconnaissance Imaging Spectrometer (CRISM) for Mars investigation conducted during the Mars Reconnaissance Orbiter's (MRO's) primary science phase was a comprehensive investigation of past aqueous environments, structure of the planet's crust, past climate, and current meteorology. The measurements to implement this investigation include over 9500 targeted observations of surface features taken at spatial resolutions of better than 40 m/pixel, monitoring of seasonal variations in atmospheric aerosols and trace gases, and acquisition of a 200 m/pixel map covering over 55% of Mars in 72 selected wavelengths under conditions of relatively low atmospheric opacity. Key results from these data include recognition of a diversity of aqueous mineral-containing deposits, discovery of a widespread distribution of phyllosilicates in early to middle Noachian units, the first definitive detection of carbonates in bedrock, new constraints on the sequence of events that formed Hesperian-aged, sulfate-rich layered deposits, characterization of seasonal polar processes, and monitoring of the 2007 global dust event. Here we describe CRISM's science investigations during the Primary Science Phase, the data sets that were collected and their calibration and uncertainties, and how they have been processed and made available to the scientific community. We also describe the ongoing investigation during MRO's extended science phase.

Long-term measurements of the global distributions of clouds, trace gases, and surface re”ectance are needed forthe study and monitoring of global change and air quality. The Geostationary Imaging Fabry Perot Spectrom-eter (GIFS) instrument is an example of a next-generation satellite remote sensing concept. GIFS is designedto be deployed on a geostationary satellite, where it can make continuous hemispheric imaging observations ofcloud properties (including cloud top pressure, optical depth, and fraction), trace gas concentrations, such as tro-pospheric and boundary layer CO, and surface re”ectance and pressure. These measurements can be made withspatial resolution, accuracy, and revisit time suitable for monitoring applications. It uses an innovative tunableimaging triple-etalon Fabry Perot interferometer to obtain very high resolution line-resolved spectral images ofbackscattered solar radiation, which contains cloud and trace gas information. An airborne GIFS prototype andthe measurement technique have been successfully demonstrated in a recent “eld campaign onboard the NASAP3B based at Wallops Island, Virginia. In this paper, we present the preliminary GIFS instrument design anduse GIFS prototype measurements to demonstrate the instrument functionality and measurement capabilities.Keywords: Fabry Perot, high-resolution, spectroscopy, cloud properties, trace gases, geostationary

The Self-Calibrating H2O and O3 Nighttime Environmental Remote Sensor (SCHOONERS) is a compact, integrated UV-IR imaging spectrograph and imager. The instrument has a 25 cm diameter aperture and employs a two- axis gimbaled telescope to provide acquisition and tracking of the star. It also uses a two-axis high-precision vernier mirror to correct for spacecraft jitter and maintain the star within the field-of-view. The imaging spectrograph, covering a spectral range between 300 and 900 nm, measures the varying absorption of starlight as a star sets through the nighttime Earth's atmosphere to determine vertical profiles of atmospheric constituents. The relative star position measured by the co-aligned imager not only provides position feedback to the acting tracking loop of the vernier mirror, but also measures the star refraction angle for determining the atmospheric density and temperature profiles. The SCHOONERS scanning platform and its high- precision tracking mirrors provide 44 microradian azimuth pointing stability and 60 microrad altitude tracking accuracy (3(sigma) ). Its built-in image tracking and motion compensation mechanism, coupled with its small size and limited spacecraft resources required, makes it suitable for deployment on existing and future commercial spacecraft platforms as an instrument-of-opportunity after the year 2002. A laboratory facility has been developed to demonstrate the instrument performance, especially its capability to acquire and track a setting, refracting, and scintillating star, to compensate for various degrees of platform jitter, and to provide the pointing knowledge accuracy required for the determination of atmospheric density and temperature. Hardware includes an accurately moving variable intensity point source to simulate the star and motion stages to generate jitter at the instrument. Software simulates the stellar refraction, attenuation, and scintillation for a full end-to-end test of the instrument.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

M. Frank MorganRussell A. ChipmanDouglas G. TorrDepartment of PhysicsUniversity of Alabama in HuntsvilleHuntville, AL 35899ABSTRACTA polarilneter for characterization of the instrumental polarization of art imaging ultraviolet (UV) spectrorn-eter has been designed and calibrated. The spectrometer is a diffraction grating spectrograph and is thereforeexpected to show strong polarization effects. Since the spectrometer is used for observations of partially polarizedlight, we need to measure the sensitivity of the spectrometer to the polarization state of incident light. A dualrotating retarder polarimeter has been developed to address this need. The polarimeter includes a linear diatten-uator and a rotating retarder to control the polarization state of light entering the spectrometer, and a similarpair of elements to analyze the polarization state of light emerging from the instrument. With this polarimeterit is possible to measure the Mueller matrix of the spectrometer as a function of wavelength.In the course of calibrating the polarimeter, the quarter-wave retarders were observed to possess polariza-tion properties other than pure linear retardance. This forced the development of a complex procedure for thecalibration of the retarders and a new generalized approach to polarimetric analysis. These developments are themain subjects of this paper.1.

Diffraction grating spectrometers exhibit a complex dependance on the polarization state of incident light. We have characterized the polarization properties of a high resolution echelle grating spectrometer. Large variations of instrument response with incident polarization state at ultraviolet wavelengths were found. The Imaging Stratospheric Ultraviolet Spectrometer (ISUS) is a high resolution spectrometer for remote sensing of atmospheric trace constituents. Weak line emissions are observed against the bright, partially polarized Rayleigh scattered sky background. To determine the air density from the Rayleigh scattering intensity the effects of polarization on the spectrometer response must be known. It was anticipated that such polarization effects could be significant in the ISUS instrument, which includes a fold mirror, a cross dispersing plane diffraction grating and an echelle grating. Measurements of the sensitivity of ISUS to linearly polarized light at 312.6 nm showed a peak-to-peak variation of 72% as the plane of polarization is rotated. The results of these measurements are presented and nine elements of the sixteen element system Mueller matrix which describes the behavior of ISUS in partially linearly polarized light are measured. The implications of the observed instrumental polarization for remote sensing observations and its impact on a technique for discriminating against the polarized Rayleigh scattered background to improve the measurement sensitivity are discussed. Subject terms: polarization; spectrometers, polarimetry, polarization aberration; instrumental polarization, Mueller calculus.