Data Set Overview  :  This data set contains the spectral radiance (W/(m**2*sr*micron))  data from the Dawn VIR instrument infrared channel for all cruise  mission phases. The data cover the time period between  2007-10-17 and 2011-03-15.   Required Reading  :  The format of all VIR data are described in detail by the SIS document  located in the /DOCUMENT directory. VIR team strongly recommends  reading this documentation before using the data.   VIR Cruise Observations  :  The following table contains a listing of VIR cruise calibrations.   -------------------------------------------------------------------------  Dawn Cruise Calibration Observations  ------------------------------------------------------------------------  Start Mission Activity Activity  Date Phase Name Description  :  2017-09-28 ICO ICO Initial Checkout  -------------------------------------------------------------------------  2007-10-17 ICO FUNC VIR Functional Test  2007-12-11 ICO STAR_CAL 33 IR & VIS Qubes centered on Arcturus  -------------------------------------------------------------------------  2008-01-19 EMC EMC Earth-Mars Cruise  -------------------------------------------------------------------------  2008-04-07 EMC CAL Full scan/slew qubes of Canopus & Mars  -------------------------------------------------------------------------  2009-03-23 MVC MVC Mars-Vesta Cruise  -------------------------------------------------------------------------  2009-12-03 MVC GEOCAL Scan/slew qubes of Canopus (IR) to compute  mounting geometry - unsuccessful  2010-04-26 MVC GEOCAL Scan/slew qubes of Canopus (IR) to compute  mounting geometry - unsuccessful  2010-05-10 MVC MMConfig 6Gb memory configuration test  2010-07-21 MVC GEOCAL Full scan/slew qubes of Canopus (IR) to  compute mounting geometry - succeeded  2011-03-15 MVC FUNC Pre-Vesta VIR Functional Test  -------------------------------------------------------------------------- 2012-09-10 VCC VCC Vesta-Ceres Cruise  -------------------------------------------------------------------------- There are no calibrated data from the Vesta-Ceres cruise phase. Activities during this phase did  not open the cover. There are raw (EDR) versions of the check-out data. Functional checkouts were  performed on 2012-352, 2013-320, and 2014-174.  -------------------------------------------------------------------------- The first two geometric calibrations failed to observe Canopus which  was being used to determine the sensor alignments, because the cubes  acquired were not large enough. The combination of ephemeris and pointing  errors were larger than anticipated at the time when the observations  were designed. The cube size was increased for the final observation  which was successful.   Processing  :  The data in this data set are calibrated, CODMAC Level 3 data. The  data processing includes spectral, geometric, flat-field, and  radiometric calibration. The details of how these calibrations were  performed are described in the VIR_CALIBRATION document contained  the DOCUMENT/VIR_CALIBRATION directory of this archive. This document  describes how the calibration parameters were derived an gives a  procedure for generating the calibrated data set from the raw EDR  data set DAWN-X-VIR-2-EDR-IR-CRUISE-SPECTRA-V1.0.    Data  :  The data are in PDS format. A detailed description of the data format  is given in the VIR SIS document located in the DOCUMENT directory of  this data set.    Calibration  :  These data all use the same calibration files and procedures that were  used in the processing of the Vesta data set archived on the PDS volume  DWNVVIR_I1B. The calibration tables described in the calibration  procedure can be found on the Vesta volume in the /CALIB directory off  of the root. In particular, the labels for the data cubes on this volume  refer to the instrument responsivity file 'DAWN_VIR_IR_RESP_V1.DAT'.  This is one of the calibration tables provided on the Vesta data volume.    Housekeeping Data  :  Housekeeping data from the raw/EDR data set provided here are duplicated  for the user's convenience.    Ancillary Data  :  No ancillary data included in this data set.    Coordinate System  :  The geometry items SC_SUN_POSITION_VECTOR,  SC_TARGET_POSITION_VECTOR and SC_TARGET_VELOCITY_VECTOR  provided in the label of the data product are relative to the  Earth Mean Equator frame of J2000.

Confidence Level Overview  :  Data confidence is nominal, meaning that all data have been  validated by the VIR team and found as expected. Any exceptions  are noted by the DATA_QUALITY field in the label files.    Review  :  These are the same data files that were utilized by the Dawn Science  Team. Any errors or deficiencies reported by the Science Team were  corrected by the VIR team. Note, however, that the geometry information  provided in the PDS labels was updated to reflect the IAU (Claudia Double  Prime) coordinate system and peer review issues have been resolved.  A full PDS peer review was conducted of all products in this data set.   Unexplained variations in star spectra  :   At the PDS review of the VIR cruise data in July 2015, it was noted that  there are significant variations in the shape of the radiance spectra for  various observations of the star Canopus. Assuming the instrument is well characterized and a good calibration is in place, reviewers expected that  all observations of the same star would produce similar radiance curves.  Reviewers requested an explanation of source of the variation.   Inquiries to the VIR team produced this response: 'These kind of targets  have to be considered as sub-pixel targets, so they can't be calibrated  using the current responsivity file, suitable for full pixels only.  Indeed, our main purpose when observing these kind of target, is the  measurement of geometric alignment rather than radiance value.'   The reviewers then noted that whereas radiance values are meaningless for  sub-pixel sources and that they would need to be converted to flux to be  meaningful, this would not change the shape of the spectrum but would just scale it. They suggested that possible candidates for effects which could change the shape of the spectrum include   - the spectral dispersion may not be aligned with the detector pixels.  - the conversion to radiance may be nonlinear and not well understood.  - the ITF may not be fully characterized outside the conditions expected  for 'normal' operations, which is understandable but which should be  documented so it is understood where the calibration can be applied.   Reviewers requested a better explanation of the source of the variation,  and also requested that if there is a certain DN or radiance limit under  which the ITF is no longer appropriate, that this limit be documented so  users can understand under what circumstances the calibration can be used.  The VIR team responded to this follow-up inquiry with this information:  'The radiance values are meaningless for sub-pixel sources (stars), as the responsivity matrix is not applicable for such targets. The only purpose  when observing this kind of targets is the geometric calibration. So the  Level 1B data of these observations cannot be used to compare the spectra  with other observations performed in nominal conditions (a fully space  resolved target).'   An internal SBN reviewer noted that if images are undersampled in a way  that compromises the photometry, the astrometry is also compromised as  there is covariance between astrometry and photometry in undersampled  images.   These variations in the shape of the calibrated spectra of different  observations of the same star have not been satisfactorily explained, so  we provide this note to document the issue.    Data Coverage and Quality  :  Data quality is good unless otherwise noted by the DATA_QUALITY  keyword.   Calibrated values in the spectral range [2.534E-06 m to 3.272E-06 m] are  under verification, as a result these values have been set to null in  the ITF.   Limitations  :  These data were acquired to monitor instrument health and to  determine various geometrical and spectral calibrations. These  are not intended as science data.