Physics – Optics
Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999nvm..conf...21h&link_type=abstract
Workshop on New Views of the Moon 2: Understanding the Moon Through the Integration of Diverse Datasets, p. 21
Physics
Optics
Imaging Techniques, Moon, Spatial Resolution, Spectral Resolution, Spectrometers, Very Long Base Interferometry, Lunar Composition, Lunar Geology, Cameras, Differential Pulse Code Modulation, Signal To Noise Ratios, Lunar Photography
Scientific paper
The Moon is the nearest celestial body to the Earth. The investigation of the Moon gives clues as to the origin and evolution of not only the Moon itself, but also the Earth. ISAS (Institute of Space and Astronautical Science) and NASDA (National Space Development Agency of Japan) are cooperatively planning to launch a Moon explorer named SELENE (Selenological and Engineering Explorer) in 2003. Phase C study has been started since last April 1999. SELENE will load 14 mission instruments to obtain scientific data of the Moon. The scientific data will be also used for investigating the possibility of future utilization of the Moon. SELENE will carry out the orbiter mission for one year and subsequently separate the propulsion module that will be a lander and send the radio signal for the differential VLBI for two months. The orbiter will end its role when the propulsion module is separated. Imagery and spectral profiling are most useful techniques for understanding the structure and materials of a planetary surface. From the SELENE mission, we will obtain data with high spatial and spectral resolution by LISM (Lunar Imager/SpectroMeter). LISM consists of three sensors: a terrain camera (TC), a multiband imager (MI), and a spectral profiler (SP). We introduce LISM in this paper. LISM will obtain digitized global imaging and spectral profiling data of the Moon with high-quality spatial resolution, wavelength resolution, and signal-to-noise ratio. Data of LISM will be also combined and analyzed with the data of other mission instruments of SELENE. The LISM group consists of about 20 researchers, who have responsibility on LISM development including science requirement decision, instrumentation, software development, and operation. The current status of LISM development is in phase C, or PM (preflight model) designing and making phase. From the next year, we will start designing FM (flight model). The main purpose of TC is global stereo mapping with high spatial resolutions. To investigate subkilometer size morphology for all over the Moon in detail, we used images with spatial resolution of 10 m and height resolution of 20-30 m. TC consists of two slant telescopes, each of which has a linear CCD detector, and takes images by pushbroom scanning. The swath of TC is 35 km. when the altitude of SELENE orbiter is 100 km, so that images taken at serial paths are overlapped for across-track direction. DCT lossy compression method has been adopted to reduce the tremendous data. The data will be nominally compressed to 30% or less. The main purpose of MI is global multiband mapping of spatial resolution of 20 m for visible range, and 60m for near-infrared range. MI consists of two telescopes, each of which has a two-dimensional detector with band-path filters. Data of several lines of the detectors, each of which correspond to band assignments, are read out. MI takes images by pushbroom scanning. The swath of MI is 20 km when the altitude of SELENE orbiter is 100 km. We adopt a DPCM loss-less compression method to avoid irreparable loss of information about subtle difference of reflectance. The main purpose of SP is to obtain detailed continuous spectral data of the Moon in the 500-2600-nm range to understand distribution and chemical composition of minerals on the surface. SP has one set of optics with three detectors for three ranges (VIS: 500-1000 nm NIRI: 900-1700 nm, and NIR2: 1700-2600 nm. NIR2 is cooled to 220 K by a peltier cooler. The spatial resolution is 500 m for across-track and along track directions. Since we require high accuracy to analyze SAM data, we execute on-board calibration with using halogen lamps. The spectral profiler will be operated in all daytime. The total amount of data of TC and MI is so large that TC and MI are not operated at the same time. Still, operations of TC and Mi should be carried out in limited daytime. To identify where SP is observing, however, highly compressed TC images or one-band images of MI are planned to be taken simultaneously with SP data.
Haruyama Junji
Matsunaga Takahiro
Otake Hisashi
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