Computer Science – Robotics
Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999nvm..conf....2a&link_type=abstract
Workshop on New Views of the Moon 2: Understanding the Moon Through the Integration of Diverse Datasets, p. 2
Computer Science
Robotics
Imaging Techniques, Lunar Observatories, Lunar Soil, Lunar Surface, Moon, Photometry, Free Electron Lasers, Spacecraft Instruments, Robotics, Astronomical Observatories
Scientific paper
As part of the calibration program for the NASA Earth Observing System (part of NASA's Earth Science Enterprise), the U.S. Geological Survey operates the Robotic Lunar Observatory (ROLO). The ROLO project is designed to produce a photometric model of the nearside lunar surface for all phase and libration angles visible from Flagstaff [2]. Goals for this photometric model are 2.5 % absolute and 1.0% relative uncertainty. Although the model is principally intended to produce radiance images of the Moon for use in calibration of Earth-orbiting spacecraft, the ROLO data and model will also provide important information for studies of the lunar soil. Instrumentation: An astronomical observatory dedicated to the radiometry of the Moon has been constructed on the campus of the U.S. Geological Survey Flagstaff Field Station in Arizona. Two separate camera systems are attached to a single telescope mount and boresighted to the same pointing direction. The visible/near infrared (VNIR) camera uses a 512 x 512 pixel CCD and 23 intermediate width interference filters for wavelength selection. The shortwave infrared (SWIR) camera uses a 256 x 256 pixel cooled-HgCdTe infrared array and nine intermediate-width interference filters. Table I and Fig. I provide information on the instrumental passbands. Separate 20-cm-diameter Ritchey-Cretien telescopes are provided for the two cameras. The optics are designed to image the entire Moon within each camera's field of view, resulting in instrument pixel scales of 4 and 8 arcsec /pixel (about 7.4 and 15 km/pixel for the sub-Earth point on the Moon) for VNIR and SWIR respectively. Detailed information on the instrumentation can be found in Anderson et al. Observations: Routine imaging has been in progress since late 1995 for VNIR and late 1997 for SWIR, and is expected to continue through at least 2002. ROLO observes the Moon every clear night between the first and last quarter phases of the moon. On such nights, the Moon is imaged through all 32 filters at half-hour intervals during the time that the Moon is above the 60 deg. zenith angle. Observations of standard stars to measure atmospheric extinction and detector responsivity drifts occupy the remainder of the nighttime. Measurements of the dark current and detector bias levels are made during the dusk and dawn periods for VNIR and throughout the night for SWIR. Flat field corrections and absolute radiance calibrations are provided through observations of a Spectralon plate illuminated by a NIST-traceable 1000 W FEL lamp. Raw data are converted to ISIS cubes and stored on CD-ROM. Detailed information on the observing procedure is also found. As the development of data-reduction software for the ROLO project progresses and additional data are accumulated, the raw data are repeatedly processed into a calibrated form. Corrections for instrument response characteristics, photon scattering processes, and atmospheric extinction are applied to the raw lunar images to produce exoatmospheric radiance images of the Moon. These images are then transformed to a fixed selenographic-grid projection designed to accommodate all of the possible viewing geometries of the ROLO telescope. A preliminary discussion of results for the total irradiance of the Moon derived from ROLO VNIR images acquired through April 1998 was published by Kieffer and Anderson. At that time, difficulties in adequately determining the atmospheric extinction limited the accuracy of the derived lunar irradiance values. Significant improvements in the reduction software have been developed since that time and measurement scatter is expected to be reduced to approximately = or <2% for the data-processing run planned for the summer of 1999. As of June 1999 , ROLO has acquired over 2200 cubes of raw Moon images with VNIR and over 1200 cubes with SWIR. By 2002, ROLO expects to have acquired roughly 3500 images of the Moon through each VNIR filter and nearly 3000 images through each SWIR filter, or more than 100,000 absolutely calibrated images of the Moon. These data are used to create photometric models of the lunar surface that are position, phase, and wavelength dependent. Kieffer and Anderson and Grant et al. provide examples of calibrating spacecraft instruments with existing ROLO data. The dataset will also provide a wealth of information about the geological properties of the lunar surface. The photometric function of many thousands of points on the Moon will be measured for phase angles between 2 and 90 deg for wavelengths within 0.35-2.4 micron. Absolute and normalized color ratios and their phase-angle dependence will enable detailed studies of the mineral abundances of the Lunar soil. Information on the photometric function dependence on phase and wavelength will aid investigations of the surface particulate structure of the soil. Additional information contained in original.
Anderson Jeffrey M.
Kieffer Hugh H.
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