title: Invited Article: Deep Impact instrument calibration.
abstract: 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 [ approximately 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 approximately 9 pixels. The charge coupled device (CCD) read noise is approximately 1 DN. Electrical cross-talk between the CCD detector quadrants is correctable to <2 DN. The IR spectrometer response nonlinearity is correctable to approximately 1%. Spectrometer read noise is approximately 2 DN. The variation in zero-exposure signal level with time and spectrometer temperature is not fully characterized; currently corrections are good to approximately 10 DN at best. Wavelength mapping onto the detector is known within 1 pixel; spectral lines have a FWHM of approximately 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 approximately 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.
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 306-392, 4800 Oak Grove Dr., Pasadena, California 91109, USA. kenneth.p.klaasen@jpl.nasa.gov
authors.forename: Kenneth P
authors.initials: KP
authors.lastname: Klaasen
authors.forename: Michael F
authors.initials: MF
authors.lastname: A'Hearn
authors.forename: Michael
authors.initials: M
authors.lastname: Baca
authors.forename: Alan
authors.initials: A
authors.lastname: Delamere
authors.forename: Mark
authors.initials: M
authors.lastname: Desnoyer
authors.forename: Tony
authors.initials: T
authors.lastname: Farnham
authors.forename: Olivier
authors.initials: O
authors.lastname: Groussin
authors.forename: Donald
authors.initials: D
authors.lastname: Hampton
authors.forename: Sergei
authors.initials: S
authors.lastname: Ipatov
authors.forename: Jianyang
authors.initials: J
authors.lastname: Li
authors.forename: Carey
authors.initials: C
authors.lastname: Lisse
authors.forename: Nickolaos
authors.initials: N
authors.lastname: Mastrodemos
authors.forename: Stephanie
authors.initials: S
authors.lastname: McLaughlin
authors.forename: Jessica
authors.initials: J
authors.lastname: Sunshine
authors.forename: Peter
authors.initials: P
authors.lastname: Thomas
authors.forename: Dennis
authors.initials: D
authors.lastname: Wellnitz
mesh_terms: D016477:Artifacts; D002138:Calibration; D004867:Equipment Design / Q000295:instrumentation*; D013026:Space Flight; D018531:Spacecraft / Q000295:instrumentation*; D013055:Spectrophotometry, Infrared; D013686:Telemetry; D014481:United States; D018557:United States National Aeronautics and Space Administration