Invited Article: Deep Impact instrument calibration
- Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 306-392, 4800 Oak Grove Dr., Pasadena, California 91109 (United States)
- Department of Astronomy, University of Maryland, College Park, Maryland 20742-2421 (United States)
- Science Applications International Corporation, 5180 Parkstone Drive, Suite 100, Chantilly, Virginia 20151 (United States)
- Delamere Support Services, 525 Mapleton Ave., Boulder, Colorado 80304 (United States)
- Cornell University, Space Science Building, Ithaca, New York 14853 (United States)
- Ball Aerospace and Technologies, 1600 Commerce St., Boulder, Colorado 80301 (United States)
- Johns Hopkins University Applied Physics Laboratory, SD/SRE, MP3/W-155, 7707 Montpelier Road, Laurel, Maryland 20723 (United States)
Calibration of NASA's Deep Impact spacecraft instruments allows reliable scientific interpretation of the images and spectra returned from comet Tempel 1. Calibrations of the four onboard remote sensing imaging instruments have been performed in the areas of geometric calibration, spatial resolution, spectral resolution, and radiometric response. Error sources such as noise (random, coherent, encoding, data compression), detector readout artifacts, scattered light, and radiation interactions have been quantified. The point spread functions (PSFs) of the medium resolution instrument and its twin impactor targeting sensor are near the theoretical minimum [{approx}1.7 pixels full width at half maximum (FWHM)]. However, the high resolution instrument camera was found to be out of focus with a PSF FWHM of {approx}9 pixels. The charge coupled device (CCD) read noise is {approx}1 DN. Electrical cross-talk between the CCD detector quadrants is correctable to <2 DN. The IR spectrometer response nonlinearity is correctable to {approx}1%. Spectrometer read noise is {approx}2 DN. The variation in zero-exposure signal level with time and spectrometer temperature is not fully characterized; currently corrections are good to {approx}10 DN at best. Wavelength mapping onto the detector is known within 1 pixel; spectral lines have a FWHM of {approx}2 pixels. About 1% of the IR detector pixels behave badly and remain uncalibrated. The spectrometer exhibits a faint ghost image from reflection off a beamsplitter. Instrument absolute radiometric calibration accuracies were determined generally to <10% using star imaging. Flat-field calibration reduces pixel-to-pixel response differences to {approx}0.5% for the cameras and <2% for the spectrometer. A standard calibration image processing pipeline is used to produce archival image files for analysis by researchers.
- OSTI ID:
- 21266413
- Journal Information:
- Review of Scientific Instruments, Vol. 79, Issue 9; Other Information: DOI: 10.1063/1.2972112; (c) 2008 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
- Country of Publication:
- United States
- Language:
- English
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