The temporal variability, or phenology, of animals and plants in coastal zone and marine habitats is a function of geography and climatic conditions, of the chemical and physical characteristics of each particular habitat, and of interactions between these organisms. These conditions play an important role in defining the diversity of life. The quantitative study of phenology is required to protect and make wise use of wetland and other coastal resources. We describe a low cost space-borne sensor and mission concept that will enable such studies using high quality, broad band hyperspectral observations of a wide range of habitats at Landsat-class spatial resolution and with a 3 day or better revisit rate, providing high signal to noise observations for aquatic scenes and consistent view geometry for wetland and terrestrial vegetation scenes.
The Compact Reconnaissance Imaging Spectrometer for Mars, (CRISM) is a visible-infrared imaging spectrometer that
has been operating aboard the Mars Reconnaissance Orbiter (MRO) since November 2006. To achieve high spatial and
spectral resolution CRISM's optical sensor unit (OSU) is gimbaled so that apparent along track motion can be removed
by the scan system. Our paper describes the data processing flow, the physical scan control system and the performance
achieved so far in orbit around Mars.
This Paper will discuss the design of a triple redundant cryogenically cooled and isolated Focal Plane Assembly (FPA) for the Compact Remote Imaging Spectrometer for Mars (CRISM) instrument. The FPA is required to operate in the temperature range of 90 - 100K. The CRISM FPA isolation system was constructed from a ceramic fiber composite. The FPA was cooled by one of three cryocoolers individually connected to one of three diode heat pipes that were all connected to the FPA. The total heat load imposed by the isolation system was about 250 milliwatts at operating temperature. CRISM is expected to launch in August of 2005.
This paper describes the design of a two sided aluminum tracking mirror and mechanism for the CONTOUR Remote Imager and Spectrometer (CRISP) instrument flown on NASA's COmet Nucleus TOUR (CONTOUR) spacecraft launched in July 2002. The tracking mirror mechanism was designed to operate in a -60°C high vacuum space environment. The primary structure of the instrument and the tracking mirror assembly were all fabricated from solid billets of magnesium ZK60A-T5 alloy. Interfacing materials with drastically different coefficients of thermal expansion required significant analysis and close attention to details. By maintaining close symmetry, tight but not unrealistic tolerances, and simultaneous machining of interfaces, we were able to keep thermal distortions virtually identical on both ends of the mirror axis and thus maintain mirror flatness to mission requirements.
CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) is a hyperspectral imager that will be launched on the MRO (Mars Reconnaissance Orbiter) spacecraft in August 2005. MRO’s objectives are to recover climate science originally to have been conducted on the Mars Climate Orbiter (MCO), to identify and characterize sites of possible aqueous activity to which future landed missions may be sent, and to characterize the composition, geology, and stratigraphy of Martian surface deposits. MRO will operate from a sun-synchronous, near-circular (255x320 km altitude), near-polar orbit with a mean local solar time of 3 PM. CRISM’s spectral range spans the ultraviolet (UV) to the mid-wave infrared (MWIR), 383 nm to 3960 nm. The instrument utilizes a Ritchey-Chretien telescope with a 2.12° field-of-view (FOV) to focus light on the entrance slit of a dual spectrometer. Within the spectrometer, light is split by a dichroic into VNIR (visible-near-infrared, 383-1071 nm) and IR (infrared, 988-3960 nm) beams. Each beam is directed into a separate modified Offner spectrometer that focuses a spectrally dispersed image of the slit onto a two dimensional focal plane (FP). The IR FP is a 640 x 480 HgCdTe area array; the VNIR FP is a 640 x 480 silicon photodiode area array. The spectral image is contiguously sampled with a 6.6 nm spectral spacing and an instantaneous field of view of 61.5 μradians. The Optical Sensor Unit (OSU) can be gimbaled to take out along-track smear, allowing long integration times that afford high signal-to-noise ratio (SNR) at high spectral and spatial resolution. The scan motor and encoder are controlled by a separately housed Gimbal Motor Electronics (GME) unit. A Data Processing Unit (DPU) provides power, command and control, and data editing and compression. CRISM acquires three major types of observations of the Martian surface and atmosphere. In Multispectral Mapping Mode, with the gimbal pointed at planet nadir, data are collected at frame rates of 15 or 30 Hz. A commandable subset of wavelengths is saved by the DPU and binned 5:1 or 10:1 cross-track. The combination of frame rates and binning yields pixel footprints of 100 or 200 m. In this mode, nearly the entire planet can be mapped at wavelengths of key mineralogic absorption bands to select regions of interest. In Targeted Mode, the gimbal is scanned over ±60° from nadir to remove most along-track motion, and a region of interest is mapped at full spatial and spectral resolution. Ten additional abbreviated, pixel-binned observations are taken before and after the main hyperspectral image at longer atmospheric path lengths, providing an emission phase function (EPF) of the site for atmospheric study and correction of surface spectra for atmospheric effects. In Atmospheric Mode, the central observation is eliminated and only the EPF is acquired. Global grids of the resulting lower data volume observation are taken repeatedly throughout the Martian year to measure seasonal variations in atmospheric properties.
The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) will launch in 2005 on the Mars Reconnaissance Orbiter (MRO) mission, with its primary science objective to characterize sites with aqueous mineral deposits hyperspectrally at high spatial resolution. CRISM’s two Offner relay spectrometers share a single entrance slit with a dichroic beamsplitter. The IR focal plane contains a 640 (spatial) x 480 (spectral) HgCdTe FPA with a 980 nm to 3960 nm spectral bandpass. It is cooled to 110 K to minimize dark current, and coupled to a 28 mm long cold shield to minimize thermal background. The spectrometer housing is cooled to -90 C for the same reason. A three-zone IR filter consisting of two broadband filters and a linear variable filter overlays the IR focal plane, eliminating multiple grating orders and providing additional attenuation of the thermal background. The visible focal plane contains a 640 (spatial) x 480 (spectral) silicon photodiode array, with a 380-1050 nm spectral bandpass occupying approximately 106 rows of the detector. A two-zone filter comprised of two different Schott glasses eliminates multiple grating orders. The two focal planes together cover 544 spectral channels with a dispersion of 6.55 nm/channel in the VNIR and 6.63 nm/channel in the IR. The optics and focal planes are gimbaled, and a pre-programmed slew can be used to remove groundtrack motion while superimposing a scan across a target. CRISM will operate in two basic modes: a scanning, high resolution mode to hyperspectrally map small, targeted areas of high scientific interest, and a fixed, nadir-pointed, lower resolution pixel-binned mode using selected wavelength channels to obtain near-global coverage to find targets. Preliminary performance of the CRISM instrument is presented, and is compared with prior system design predictions.
The CONTOUR Remote Imager and Spectrometer (CRISP) was a multi-function optical instrument developed for the Comet Nucleus Tour Spacecraft (CONTOUR). CONTOUR was a NASA Discovery class mission launched on July 3, 2002. This paper describes the design, fabrication, and testing of CRISP. Unfortunately, the CONTOUR spacecraft was destroyed on August 15, 2002 during the firing of the solid rocket motor that injected it into heliocentric orbit. CRISP was designed to return high quality science data from the solid nucleus at the heart of a comet. To do this during close range (order 100 km) and high speed (order 30 km/sec) flybys, it had an autonomous nucleus acquisition and tracking system which included a one axis tracking mirror mechanism and the ability to control the rotation of the spacecraft through a closed loop interface to the guidance and control system. The track loop was closed using the same images obtained for scientific investigations. A filter imaging system was designed to obtain multispectral and broadband images at resolutions as good as 4 meters per pixel. A near IR imaging
spectrometer (or hyperspectral imager) was designed to obtain spectral signatures out to 2.5 micrometers with resolution of better than 100 meters spatially. Because of the high flyby speeds, CRISP was designed as a highly automated instrument with close coupling to the spacecraft, and was intended to obtain its best data in a very short period around closest approach. CRISP was accompanied in the CONTOUR science payload by CFI, the CONTOUR Forward Imager. CFI was optimized for highly sensitive observations at greater ranges. The two instruments provided highly complementary optical capabilities, while providing some degree of functional redundancy.
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.