Instrument Information |
|
IDENTIFIER | urn:nasa:pds:context:instrument:its.dii::1.0 |
NAME |
DEEP IMPACT IMPACTOR TARGETING SENSOR - VISIBLE CCD |
TYPE |
IMAGER |
DESCRIPTION |
Instrument Overview =================== The Impactor Targeting Sensor (ITS) consisted of an f/17.5 Cassegrain telescope feeding directly onto a CCD for direct, optical imaging. It was an exact clone of the Medium Resolution Instrument (MRI) and its visual CCD camera except that the filter wheel had been deleted. In all other respects it was identical. The ITS telescope was a classical Cassegrain design with the following parameters: Primary aperture : 12.0 cm diameter, round Primary focal ratio : 3.75 Secondary Obscuration : 6.6 cm diameter, round Secondary magnification : 4.75x (net Cassegrain focal length 210 cm) Back focal distance : 30.0 cm The detector was a 1024 x 1024 split-frame, frame-transfer CCD with 21-micron-square pixels. The electronics allowed readout of centered sub-frames in multiples of 2: 64x64, 128x128, and so on, with or without rows of overscan. Transfer time, to move the two halves of the image from the exposing area to the two shielded areas was about 5.2 milliseconds. There were readout amplifiers in each of the four quadrants. Readout time for a full frame was 1.8 seconds. Net pixel scale was 10 microradians/pixel (2 arcseconds/pixel). The surface scale was 0.2 meters/pixel at 20 kilometers. Images were transmitted to the flyby spacecraft for re-transmission to Earth. The ITS instrument was mounted behind the main deck of the impactor spacecraft and looked through a rectangular cutout on one edge of the copper cratering mass at the front of the impactor. For a detailed discussion of the instrument, see Hampton, et al. (2005) [HAMPTONETAL2005]. This instrument overview was provided by Dr. Michael A'Hearn, the principal investigator for the Deep Impact mission. Instrument Calibration ====================== The ITS instrument was calibrated by using in-flight data as well as pre-launch data taken during a thermal-vacuum test (TV3) performed in January and February 2003. The calibration of the ITS instrument was discussed in the 'Deep Impact Instrument Calibration' paper by Klaasen, et al. (2006) [KLAASENETAL2006]. The two central rows of the CCD are physically 1/6-pixel narrower and collect only 5/6 of the charge of a normal row (Klaasen, et al., 2008 [KLAASENETAL2006]; Klaasen, et al., 2012 [KLAASENETAL2011]). However, the data pipeline reconstructs images with uniform row spacing, which introduces a 1/3-pixel extension at the center of the raw and calibrated image arrays. Thus for two features on either side of the midpoint line outside of the two central rows, the vertical component of the true angular separation between those features is one-third of a pixel less than their measured separation in the reconstructed image. As for all geometric distortions, correction of this 1/3-pixel extension will require resampling of the image and an attendant loss in spatial resolution. The data pipeline process does not perform this correction in order to preserve the best spatial resolution. However, it does correct for the 1/6 decrease of signal in the two central rows by the flat-field division so that the pixels in those two rows have the correct scene radiance in the calibrated images. Thus, the surface brightness measurement is preserved anywhere in the geometrically distorted but calibrated images. Point source or disk-integrated photometric measurements using aperture photometry that includes these central rows will be slightly distorted unless special adjustments are made, such as subtracting 1/6-pixel worth of signal to the two central rows and adjusting for the geometric distortion in the calibrated images, as described in Appendix A of Belton, et al. (2011) [BELTONETAL2011]. Flight Performance ================== The ITS instrument generally performed as expected during flight. This instrument description was originally provided by Dr. Michael A'Hearn for the Deep Impact mission, then updated during the EPOXI mission. |
MODEL IDENTIFIER | |
NAIF INSTRUMENT IDENTIFIER |
not applicable |
SERIAL NUMBER |
not applicable |
REFERENCES |
Belton, M.J.S., K.J, Meech, S. Chesley, Y. Pittichova, B. Carcich, M. Drahus,
A. Harris, S. Gillam, J. Veverka, N. Mastrodemos, W. Owen, M.F. A'Hearn, S.
Bagnulo, J. Bai, L. Barrera, F. Bastien, J.M. Bauer, J. Bedient, B.C. Bhatt, H.
Boehnhardt, N. Brosch, M. Buie, P. Candia, W.-P. Chen, P. Chiang, Y.-J. Choi,
A. Cochran, C.J. Crockett, S. Duddy, T. Farnham, Y.R. Fernandez, P. Gutierrez,
O.R. Hainaut, D. Hampton, K.A. Herrmann, H. Hsieh, M.A. Kadooka, H. Kaluna, J.
Keane, M.-J.Kim, K. Klaasen, J. Kleyna, K. Krisciunas, L.M. Lara, T.R. Lauer,
J.-Y. Li, J. Licandro, C.M. Lisse, S.C. Lowry, L. McFadden, N. Moskovitz, B.
Mueller, D. Polishook, N.S. Raja, T. Riesen, D.K. Sahu, N. Samarasinha, G.
Sarid, T. Sekiguchi, S. Sonnett, N.B. Suntzeff, B.W. Taylor, P. Thomas, G.P.
Tozzi, R. Vasundhara, J.-B. Vincent, L.H. Wasserman, B. Webster-Schultz, B.
Yang, T. Zenn, and H. Zhao, Stardust-NExT, Deep Impact, and the accelerating
spin of 9P/Tempel 1, Icarus, Volume 213, Issue 1, p. 345-368, 2011,
doi:10.1016/j.icarus.2011.01.006. Hampton, D.L., J.W. Baer, M.A. Huisjen, C.C. Varner, A. Delamere, D.D. Wellnitz, M.F. A'Hearn, and K.P. Klaasen, An Overview of the Instrument Suite for the Deep Impact Mission, Space Science Reviews, 117, 43-93, 2005, doi:10.1007/s11214-005-3390-8. Klaasen, K.P., B. Carcich, G. Carcich, E.J. Grayzeck, and S. McLaughlin, Deep Impact: The Anticipated Flight Data, Space Science Reviews, 117, 335-372, 2005, doi:10.1007/s11214-005-3385-5. Klaasen, K.P., M.F. A'Hearn, M. Baca, A. Delamere, M. Desnoyer, T. Farnham, O. Groussin, D. Hampton, S. Ipatov, J. Li, C. Lisse, N. Mastrodemos, S. McLaughlin, J. Sunshine, P. Thomas, and D. Wellnitz, Deep Impact Instrument Calibration, Rev. Sci. Instrum., 79, 091301, 2008, doi:10.1063/1.2972112. Klaasen, K.P., M. A'Hearn, S. Besse, D. Bodewits, B. Carcich, T. Farnham, L. Feaga, O. Groussin, D. Hampton, M. Huisjen, M.S. Kelley, S. McLaughlin, F. Merlin, S. Protopapa, J. Sunshine, P. Thomas, and D. Wellnitz, EPOXI Instrument Calibration, Icarus, 225(1), 643-680, 2013, doi:10.1016/j.icarus.2013.03.024. |