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. In addition, there is a calibration procedure document that defines the data processing steps and the proper usage of the calibration files that are part of this data set.   Data Set Overview : This data set contains the spectral radiance (W/(m**2*sr*micron)) data from the Dawn VIR instrument visible channel for all Ceres encounter mission phases. The data cover the time period between 2014-12-26 and 2018-08-05.   VIR Ceres Observations : The following table contains a listing of VIR observations at Ceres.  ------------------------------------------------------------------------ Dawn Science Prime Mission Observations : Start Mission Activity Activity Date Phase Name Description : 14-12-26 CSA APPROACH Ceres Science Approach Phase ------------------------------------------------------------------------ 15-01-13 CSA OPNAV_001 Ride-along cubes to FC OpNav images - 4 obs 15-01-25 CSA OPNAV_002 Ride-along cubes to FC OpNav images - 4 obs 15-02-04 CSA OPNAV_003 Ride-along cubes to FC OpNav images - 5 obs 15-02-12 CSA RC1 Ride-along cubes to FC rotational - 10 obs characterization movie #1 - 8 obs 15-02-19 CSA RC2 Ride-along cubes to FC rotational - 3 obs characterization movie #2 - 3 obs 15-02-25 CSA OPNAV_004 Ride-along cubes to FC OpNav images - 3 obs 15-03-01 CSA OPNAV_005 Ride-along cubes to FC OpNav images - 3 obs 15-04-10 CSA OPNAV_006 Ride-along cubes to FC OpNav images - 3 obs 15-04-15 CSA OPNAV_007 Ride-along cubes to FC OpNav images - 3 obs ------------------------------------------------------------------------ 15-04-24 CSR RC3 Ceres Science Rotational Characterization 3 ------------------------------------------------------------------------ 15-04-25 CSR RC3 RC3 Equator Limb 1 (S) high phase - 10 obs 15-04-30 CSR RC3 RC3 Equator Limb 2 (N) high phase - 16 obs 15-05-04 CSR RC3n RC3 North lit side - 16 obs 15-05-05 CSR RC3e RC3 Equator lit side - 16 obs 15-05-07 CSR RC3s RC3 South lit side - 16 obs ------------------------------------------------------------------------ 15-05-09 CTS TRANSFER_ Ceres Transfer to Survey Phase TO_Survey ------------------------------------------------------------------------ 15-05-16 CTS OPNAV_008 Ride-along cubes to FC OpNav images - 7 obs 15-05-22 CTS OPNAV_009 Ride-along cubes to FC OpNav images - 7 obs ------------------------------------------------------------------------ 15-06-04 CSS SURVEY Ceres Science Survey Phase (range ~4850 km) ------------------------------------------------------------------------ 15-06-04 CSS CYCLE1 Survey Cycle (orbit) 1 - 44 obs 15-06-08 CSS CYCLE2 Survey Cycle (orbit) 2 - 49 obs 15-06-11 CSS CYCLE3 Survey Cycle (orbit) 3 - 44 obs 15-06-14 CSS CYCLE4 Data lost to instrument reset, sci data lost 15-06-17 CSS CYCLE5 Survey Cycle (orbit) 5 VIS-only - 51 obs 15-06-21 CSS CYCLE6 Survey Cycle (orbit) 6 VIS bad - 50 obs 15-06-24 CSS CYCLE7 Survey Cycle (orbit) 7 VIS-only - 49 obs 15-06-27 CSS CYCLE8 Data lost to instrument reset, sci data lost ------------------------------------------------------------------------ 15-07-01 CTH TRANSFER_ Ceres Transfer to HAMO Phase TO_HAMO ------------------------------------------------------------------------ No science observations in this phase ------------------------------------------------------------------------ 15-08-17 CSH HAMO Ceres Science HAMO Phase (avg rng ~1950 km) ------------------------------------------------------------------------ 15-08-17 CSH CYCLE1 12 orb pushbroom nadir imaging - 62 obs 15-08-29 CSH CYCLE2 12 orb pushbroom off-nadir imaging - 71 obs 15-09-09 CSH CYCLE3 12 orb pushbroom off-nadir IR-only - 108 obs 15-09-20 CSH CYCLE4 12 orb pushbroom off-nadir imaging - 85 obs 15-10-01 CSH CYCLE5 12 orb pushbroom near nadir IR-only - 84 obs 15-10-12 CSH CYCLE6 12 orb pushbroom off-nadir IR-only - 73 obs ------------------------------------------------------------------------ 15-10-23 CTL TRANSFER_ Ceres Transfer to LAMO Phase TO_LAMO ------------------------------------------------------------------------ No science observations in this phase ------------------------------------------------------------------------ 15-12-16 CSL LAMO Ceres Science LAMO Phase (range ~850 km) ------------------------------------------------------------------------ 15-12-16 CSL CYCLE0 nadir pushbroom imaging IR-only - 2 obs 15-12-18 CSL CYCLE1 nadir pushbroom imaging IR-only - 9 obs 16-01-10 CSL CYCLE2 nadir scan mirror imaging IR-only - 11 obs 16-02-02 CSL CYCLE3 nadir scan mirror imaging IR-only - 15 obs 16-02-25 CSL CYCLE4 nadir scan mirror imaging IR-only - 18 obs 16-03-19 CSL CYCLE5 off-nadir scan mirror IR-only - 34 obs 16-04-11 CSL CYCLE6 off-nadir scan mirror IR-only - 30 obs 16-05-04 CSL CYCLE7 off-nadir scan mirror imaging - 24 obs 16-05-27 CSL CYCLE8 off-nadir scan mirror imaging - 33 obs ------------------------------------------------------------------------ Dawn Science Extended Mission 1 Observations : 16-06-19 CXL XMO1 Ceres Extended LAMO Phase (range ~850 km) ------------------------------------------------------------------------ 16-06-19 CXL CYCLE9 off-nadir scan mirror imaging - 40 obs 16-07-13 CXL CYCLE10 off-nadir scan mirror VIS-only - 38 obs 16-08-10 CXL CYCLE11 off-nadir scan mirror imaging - 29 obs ------------------------------------------------------------------------ 16-09-02 CTJ TRANSFER_ Ceres Transfer to Juling Phase TO_JULING ------------------------------------------------------------------------ No VIR science observations in this phase ------------------------------------------------------------------------ 16-10-10 CXJ XMO2 Ceres Extended Juling Phase (range ~1950 km) ------------------------------------------------------------------------ 16-10-10 CXJ CYCLE1 off-nadir imaging IR-only - 12 obs 16-10-24 CXJ CYCLE2 off-nadir imaging IR-only - 6 obs ------------------------------------------------------------------------ 16-11-03 CTG TRANSFER_ Ceres Transfer to GRaND Phase TO_GRAND ------------------------------------------------------------------------ No VIR science observations in this phase ------------------------------------------------------------------------ 16-12-14 CXG XMO3 Ceres Extended GRaND Phase (range ~8000- 9500 km) ------------------------------------------------------------------------ 16-12-14 CXG CYCLE1 No science observations 17-01-21 CXG CYCLE2 off-nadir pushbroom imaging VIS-only - 5 obs 17-02-17 CXG CYCLE3 No science observations ------------------------------------------------------------------------ 17-02-23 CTO TRANSFER_ Ceres Transfer to Opposition Phase TO_OPPOSITION ------------------------------------------------------------------------ No VIR science observations in this phase ------------------------------------------------------------------------ 17-04-28 CXO XMO4 Ceres Extended Opposition Phase (range 14-55E3 km) ------------------------------------------------------------------------ 17-04-29 CXO Opposition off-nadir scann mirror imaging - 7 obs ------------------------------------------------------------------------ Dawn Science Extended Mission 2 Observations : 16-07-01 CX2 XMO5 Ceres Extended Mission 2 (CX2) Holding orbit ------------------------------------------------------------------------ 18-01-18 CX2 Checkout Annual instrument checkout - 1 obs ------------------------------------------------------------------------ 18-04-15 CTI TRANSFER_ Ceres Transfer to Intermediate Phase TO_INTERMEDIATE ------------------------------------------------------------------------ No VIR science observations in this phase ------------------------------------------------------------------------ 18-05-15 C2I XMO6* Ceres Extended 2 Intermediate (C2I) ------------------------------------------------------------------------ 18-05-16 C2I SEG1 nadir scan mirror imaging IR-only - 11 obs 18-05-17 C2I SEG2 nadir scan mirror imaging IR-only - 22 obs 18-05-20 C2I SEG3 nadir scan mirror imaging IR-only - 20 obs 18-05-23 C2I SEG4 nadir/off-nadir scan mirror IR-only - 19 obs 18-05-26 C2I SEG5 nadir/off-nadir scan mirror IR-only - 20 obs 18-05-30 C2I SEG6 nadir/off-nadir scan mirror IR-only - 8 obs ------------------------------------------------------------------------ 18-05-31 CTE TRANSFER_ Ceres Transfer to Elliptical Phase TO_ELLIPTICAL ------------------------------------------------------------------------ No VIR science observations in this phase ------------------------------------------------------------------------ 18-06-09 C2E XMO7** Ceres Extended 2 Elliptical (C2E) ------------------------------------------------------------------------ 18-06-09 C2E C1-SEG1 nadir scan mirror imaging IR-only - 6 obs 18-06-11 C2E C1-SEG2 nadir scan mirror imaging IR-only - 6 obs 18-06-14 C2E C1-SEG3 nadir scan mirror imaging IR-only - 9 obs 18-06-17 C2E C1-SEG4 nadir scan mirror imaging IR-only - 6 obs 18-06-19 C2E C1-SEG5 nadir scan mirror imaging IR-only - 3 obs 18-06-23 C2E C2-SEG1-2 nadir scan mirror imaging IR-only - 8 obs 18-06-25 C2E C3-SEG1 nadir scan mirror imaging IR-only - 3 obs 18-07-04 C2E C3-SEG2 nadir scan mirror imaging IR-only - 3 obs 18-07-11 C2E C3-SEG3 nadir scan mirror imaging IR-only - 3 obs 18-07-15 C2E C3-SEG4 nadir scan mirror imaging IR-only - 4 obs 18-07-23 C2E C3-SEG5 nadir scan mirror imaging IR-only - 4 obs 18-07-30 C2E C3-SEG6 nadir scan mirror imaging IR-only - 4 obs 18-08-05 C2E C3-SEG7 nadir scan mirror imaging VIS-only - 1 obs nadir scan mirror imaging IR-only - 3 obs 18-08-12 C2E C3-SEG8 nadir scan mirror imaging IR-only - 5 obs 18-08-18 C2E C3-SEG9 nadir scan mirror imaging IR-only - 4 obs 18-08-25 C2E C3-SEG10 nadir scan mirror imaging IR-only - 5 obs 18-06-09 C2E C4-SEG1 nadir scan mirror imaging IR-only - 10 obs 18-06-09 C2E C5-SEG1 nadir scan mirror imaging IR-only - 3 obs ------------------------------------------------------------------------ * XMO6 observations typically consisted of 6 deep southern nadir cubes and 4 or 5 observations of selected targets further to the north. The first 5 orbits were all acquired at nadir. The XMO6 orbit was designed to target Juling crater in orbit 6 with a backup observing opportunity in orbit 7 (segment 4). Beginning in orbit 6, off-nadir imaging was used to try and observe targets of interest. There were no VIS cubes acquired in XMO6. Segments were defined as the intervals between downlinks. ** XMO7 observations consist typically of one push-broom cube per orbit targeting either Occator or Urvara crater, depending on the predicted geometry. XMO7 cycle1 was the phasing for Cerealia cycle, cycle 2 were the Cerealia targeted orbits, cycle 3 consisted of hydrazine savings orbits, and cycles 4 and 5 (star calibration) were special activities after periapsis had crossed to the dark side of Ceres. Segments were intervals between playbacks. During the phasing orbits, these occurred between periapsis passes every 2-3 orbits, in cycle 2 they occurred every orbit, and for the remainder of the mission they occurred once every 6 orbits and last for roughly 40 hours.  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 and describes a procedure for generating the calibrated data set from the raw EDR data set DAWN-A-VIR-2-EDR-VIS-CERES-SPECTRA-V1.0. Files containing the calibration parameters and referenced in the calibration procedure are located in the CALIB directory of this archive.  It is VIR team practice to consider the entire collection of calibration files as a single unit so the version number of every file was incremented to V2 even though only the IR responsivity file was updated.  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.   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.  SUB_SPACECRAFT_LATITUDE, SUB_SPACECRAFT_LONGITUDE are given in the PLANETOCENTRIC coordinate system. These parameters are corrected for planetary and stellar aberrations. Distances are given in km, angles in degrees.

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.  Following the loss of the 2nd reaction wheel during Vesta departure, Dawn had to rely on the RCS thrusters, rather than reaction wheels, to maintain pointing. While the Dawn system does not employ true dead-banding, the net result of the thruster firings is to introduce pointing offsets of up to +/- 0.64 degrees in +X and +Y, and rates of up to 0.01 degrees/second (or ~ 0.7 VIR pixels/second). The combination of long VIR integration times with large pointing and pointing rate errors complicates interpreting the data acquired as normal spectral cubes. When Dawn is near to Ceres, the timing of the thruster firings is moderately predicable with the most common attitude near one of the deadband limits. When Dawn is far from its selected target the thruster firing is more random and the impact of not being pointed at Ceres nadir is amplified. This is especially apparent in the VIR cubes since each frame of the cube effectively has its own pointing. During Approach and RC3, Ceres is highly distorted in the raw data cubes and care must taken to properly correct the geometry when calibrating and interpreting these data.  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 coordinate system updated to Dawn derived pole right ascension and declination values. A full PDS peer review was conducted of all products in this data set.  Data Coverage and Quality : Data coverage is good unless otherwise noted by the DATA_QUALITY keyword.  VIR spectra are affected by residual systematic errors due to imperfect radiometric and spectral calibration that influence the quality of imaging spectrometer data.  The data are affected by systematic deviations from spectrum of the target due to imperfect radiometric standards, by spectral miscalibration, and by systematic errors resulting from uncertainties in the solar reference spectrum. The spectral images can show 'stripes' due to the slight deviation that exists between the input/output transfer function of each sample of the detector. These stripes are particularly evident when the signal is very low. Visible channels with a wavelength > 0.95 microns cannot be used for scientific analysis, because of the straylight effect which currently has no correction. By excluding these wavelengths from the spectrum, the offset between the visible and the infrared channels in the range where they meet disappear. In some sporadic cases where this offset can still be observed, the instrument team recommends scaling the IR channel to the VIS channel, having the latter a good agreement with the Framing Camera dataset.  The instrument team is working to resolve some of the issues described here. The team plans to release, in the near future, a new level of derived data products that will partially solve the problems above reported. Regarding the misalignment of the VIR spectra with respect of the ground based spectra, the instrument team has released a correction factor that is designed to be applied to the VIR 'denoise' (L-1C) dataset to obtain the agreement with the ground based spectra. The 'denoise' data set is planned for future release.  Dropouts that may be observed in some images are due to instrument saturation. The spectral range in which these dropouts occur varies depending upon exposure duration, target topography, and incidence angle.  A feature of the spectra near 0.8 microns is under investigation at the time of delivery to determine whether it is real or an artifact.  The spacecraft safed as it entered the RC3 mission phase. As a result, the cubes in the first rotation of the RC3 Equatorial Limb 001 (South) high phase observations were lost.  The VIR instrument reset in Survey Cycles 4 and 8 before any science data were discharged to spacecraft memory so only the cal lamp cubes were preserved. Prior to and during the first few orbits of the Survey mission phase, the VIR cryocooler began showing signs of aging. As a result, Survey Cycles 5 and 7 were acquired in VIS-only mode with the cryocooler turned off to preserve it for use during the HAMO mission phase. In Cycle 6 both IR and VIS data were collected, however, the VIS spectra had integration times near zero. As a result the VIS data for Survey Cycle 6 are not useful for science and have been omitted from the L-1B (RDR) data volume.  During the HAMO mission phase, the cryocooler set point was raised from 75 deg Kelvin to 80 deg Kelvin to reduce the strain on the cooler. There is a slight decrease in the signal to noise ratio as a result of running the cooler at a warmer temperature. Cycles 3 and 5 of HAMO were acquired in IR-only mode in order to increase the number of IR frames that could be acquired. Orbit 6 of HAMO cycle 1 was also an IR-only orbit. After HAMO sequences were initially built and delivered to the Dawn project, the team decided to reduce the repetition time between frames in each cube. This reduced the size of the gaps between frames within cubes but increased the gaps between cubes. In LAMO Cycle 5, the cryocooler began to exhibit signs of further deterioration. In Cycle 6, IR cubes were acquired with set points of 80, 83, and 87 deg K. After examination of the signal to noise ratio, the instrument team determined that the set point could be raised to 85 deg K with minimal impact.  During Ceres extended mission 2, there was a long time period where no science data were acquired while the low altitude mission was designed and planned. In order to ensure that all of the mechanical systems would work when needed, a cruise-style semi-annual checkout was performed during the X2 holding phase. This activity included a calibration cube and a full-range scan mirror cube (VIS-only) with the cover closed. Only the raw data (L1a) are archived from any calibration or checkout activity.  In addition, during Ceres extended mission 2 science observations, the relative ground speed of the spacecraft was so fast that making VIR VIS observations was not a good use of the limited downlink bandwidth. The long integration times required by the VIS channel results in extreme smearing. Only a single VIS science cube was acquired during orbit 25 of C2E (cycle 3, segment 7) mission phase.  Summary of Data Acquisition[1] Plan and Losses : Mission IR IR IR VIS VIS VIS Phase Cubes Cubes Frames Cubes Cubes Frames Activity Plan Lost Lost Plan Lost Lost Comment : CSA OpNav1 3 0 0 3 0 0 CSA OpNav2 3 0 0 3 0 0 CSA OpNav3 4 0 0 4 0 0 CSA RC1 9 0 0 9 0 0 CSA RC2 7 0 0 7 0 0 CSA OpNav4 2 0 0 2 0 0 CSA OpNav5 3 0 0 3 0 0 Lost cal-lamp cubes CSA OpNav6 2 0 0 2 0 0 Lost to DSN outage CSA OpNav7 2 0 0 2 0 0 ------------------------------------------------------------------------ RC3 HPSouth 20 10 1400 20 10 1400 S/C safing RC3 HPNorth 20 0 0 20 0 0 RC3 North 15 0 0 15 0 0 RC3 Equator 15 0 0 15 0 0 RC3 South 15 0 0 15 0 0 ------------------------------------------------------------------------ CTS OpNav8 6 0 0 7 0 0 CTS OpNav9 6 0 0 7 0 0 ------------------------------------------------------------------------ Survey C1 43 0 0 43 0 0 Survey C2 48 0 0 48 0 0 Survey C3 43 0 0 43 0 0 Survey C4 48 48 2880 48 48 2880 VIR reset, sci data lost Survey C5 0 0 0 50 0 0 VIS-only Survey C6 49 0 0 49 0 0 IR-only Survey C7 0 0 0 48 0 0 VIS-only Survey C8 0 0 0 48 48 2915 VIR reset, sci data lost ------------------------------------------------------------------------ HAMO C1 61 0 0 55 0 0 HAMO C2 72 1 78 72 1 78 HAMO C3 108 1 68 0 0 0 IR-only HAMO C4 84 0 0 70 0 0 HAMO C5 84 1 68 0 0 0 IR-only HAMO C6 72 0 0 0 0 0 IR-only ------------------------------------------------------------------------ LAMO C0 16 0 0 0 0 0 IR only LAMO C1 160 88 4400 0 0 0 IR only, DSN? LAMO C2 88 0 0 0 0 0 IR only, DSN? LAMO C3 120 0 0 0 0 0 IR only LAMO C4 147 2 185 0 0 0 IR only, DSN? LAMO C5 275 0 0 0 0 0 IR only LAMO C6 120 30 1560 0 0 0 IR only, segs. aborted [2] LAMO C7 53 0 0 146 0 0 Minor data loss, DSN? LAMO C8 54 40 2282 254 218 11337 Segments aborted [2] ------------------------------------------------------------------------ CXL C9 51 21 1300 192 12 624 CXL C10 0 0 0 454 0 0 CXL C11 15 0 0 140 0 0 multiple plans [3] ------------------------------------------------------------------------ CXJ C1 36 18 900 0 0 0 CXJ C2 24 6 400 0 0 0 ------------------------------------------------------------------------ CXG C1 0 0 0 0 0 0 CXG C2 0 0 0 58 0 0 VIS only CXG C3 0 0 0 0 0 0 ------------------------------------------------------------------------ CXO Opp 1 0 0 19 0 0 ------------------------------------------------------------------------ CX2 checkout 1 0 0 1 0 0 ------------------------------------------------------------------------ C2I SEG1 11 0 0 0 0 0 C2I SEG2 22 0 0 0 0 0 C2I SEG3 20 0 0 0 0 0 C2I SEG4 19 0 0 0 0 0 C2I SEG5 20 0 0 0 0 0 C2I SEG6 8 0 0 0 0 0 ------------------------------------------------------------------------ C2E C1S1 6 0 0 0 0 0 C2E C1S2 6 0 0 0 0 0 C2E C1S3 9 0 0 0 0 0 C2E C1S4 6 0 0 0 0 0 C2E C1S5 3 0 0 0 0 0 C2E C2S1-2 8 0 0 0 0 0 C2E C3S1 3 0 0 1 1 30 C2E C3S2 3 0 0 0 0 0 C2E C3S3 3 0 0 0 0 0 C2E C3S4 4 0 0 0 0 0 C2E C3S5 4 0 0 0 0 0 C2E C3S6 4 0 0 0 0 0 C2E C3S7 3 0 0 1 0 0 C2E C3S8 5 0 0 0 0 0 C2E C3S9 4 0 0 0 0 0 C2E C3S10 5 0 0 0 0 0 C2E C4S1 10 0 0 0 0 0 C2E C5S1 3 0 0 0 0 0 ------------------------------------------------------------------------ [1] Cube and frame counts are for science data only and do not include calibration cubes. [2] Segments which were not expect to acquire the planned targets were aborted. [3] CXL C11: Multiple plans were developed for this phase. Ultimately individual segments were selected and run such that the actual data acquisition did not match any of the plans.  Limitations : No limitations on these data