PDS_VERSION_ID = PDS3 RECORD_TYPE = "STREAM" LABEL_REVISION_NOTE = " 2015-09-01, S. Joy/E. Ammannito - initial version; 2016-01-26, J. Mafi - Corrected peer review liens; 2016-04-22, J. Mafi - HAMO Update;" OBJECT = DATA_SET DATA_SET_ID = "DAWN-A-VIR-3-RDR-IR-CERES-SPECTRA-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = " DAWN VIR CAL (RDR) CERES INFRARED SPECTRA V1.0" DATA_SET_TERSE_DESC = "Calibrated data from the VIR instrument infrared channel on the DAWN spacecraft during the Ceres Encounter mission phases." ABSTRACT_DESC = "This data set contains the spectral radiance (W/(m**2*sr*micron)) data from the Dawn VIR instrument infrared channel for all Ceres encounter mission phases. The data cover the time period between 2014-12-26 and 2016-06-01." CITATION_DESC = "De Sanctis, M.C., M.T. Capria, M. Giardino, E. Ammannito, S. Fonte, DAWN VIR CAL (RDR) CERES INFRARED SPECTRA V1.0, DAWN-A-VIR-3-RDR-IR-CERES-SPECTRA-V1.0, NASA Planetary Data System, 2015." DATA_OBJECT_TYPE = "QUBE" ARCHIVE_STATUS = "LOCALLY ARCHIVED" DATA_SET_COLLECTION_MEMBER_FLG = "N" DETAILED_CATALOG_FLAG = "N" DATA_SET_RELEASE_DATE = 2015-09-01 PRODUCER_FULL_NAME = "MARIA CRISTINA DE SANCTIS" START_TIME = 2015-01-13T19:36:00 STOP_TIME = 2015-10-21T04:26:48 DATA_SET_DESC = " 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 infrared channel for all Ceres encounter mission phases. The data cover the time period between 2014-12-26 and 2016-06-30. VIR Ceres Observations ====================== The following table contains a listing of VIR observations at Ceres. ------------------------------------------------------------------------ Dawn Science 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 15-01-25 CSA OPNAV_002 Ride-along cubes to FC OpNav images 15-02-04 CSA OPNAV_003 Ride-along cubes to FC OpNav images 15-02-12 CSA RC1 Ride-along cubes to FC rotational characterization movie #1 15-02-19 CSA RC2 Ride-along cubes to FC rotational characterization movie #2 15-02-25 CSA OPNAV_004 Ride-along cubes to FC OpNav images 15-03-01 CSA OPNAV_005 Ride-along cubes to FC OpNav images 15-04-10 CSA OPNAV_006 Ride-along cubes to FC OpNav images 15-04-15 CSA OPNAV_007 Ride-along cubes to FC OpNav images ======================================================================== 15-04-24 CSR RC3 Ceres Science Rotational Characterization 3 ------------------------------------------------------------------------ 15-04-25 CSR RC3 RC3 Equatorial Limb 001 (South) high phase 15-04-30 CSR RC3 RC3 Equatorial Limb 002 (North) high phase 15-05-04 CSR RC3n RC3 North lit side 15-05-05 CSR RC3e RC3 Equator lit side 15-05-07 CSR RC3s RC3 South lit side ------------------------------------------------------------------------ 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 15-05-22 CTS OPNAV_009 Ride-along cubes to FC OpNav images ------------------------------------------------------------------------ 15-06-05 CSS SURVEY Ceres Science Survey Phase (range ~4850 km) ------------------------------------------------------------------------ 15-06-05 CSS CYCLE1 Survey Cycle (orbit) 1 15-06-08 CSS CYCLE2 Survey Cycle (orbit) 2 15-06-11 CSS CYCLE3 Survey Cycle (orbit) 3 15-06-14 CSS CYCLE4 Data lost to instrument reset, all data lost 15-06-17 CSS CYCLE5 Survey Cycle (orbit) 5 VIS-Only 15-06-21 CSS CYCLE6 Survey Cycle (orbit) 6 15-06-24 CSS CYCLE7 Survey Cycle (orbit) 7 VIS-Only 15-06-27 CSS CYCLE8 Data lost to instrument reset, all data lost ------------------------------------------------------------------------ 15-07-01 CTH TRANSFER_ Ceres Transfer to HAMO Phase TO_HAMO ------------------------------------------------------------------------ No science observation in this phase ------------------------------------------------------------------------ 15-08-18 CSH HAMO Ceres Science HAMO Phase (avg rng ~1950 km) ------------------------------------------------------------------------ 15-08-18 CSH CYCLE1 12 orbits of pushbroom nadir imaging 15-08-29 CSH CYCLE2 12 orbits of pushbroom off-nadir imaging 15-09-09 CSH CYCLE3 12 orbits of pushbroom off-nadir IR-only 15-09-20 CSH CYCLE4 12 orbits of pushbroom off-nadir imaging 15-10-01 CSH CYCLE5 12 orbits of pushbroom near nadir IR-only 15-10-12 CSH CYCLE6 12 orbits of pushbroom off-nadir imaging ------------------------------------------------------------------------ 15-10-23 CTL TRANSFER_ Ceres Transfer to LAMO Phase TO_LAMO ------------------------------------------------------------------------ No science observation in this phase 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/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-A-VIR-2-EDR-IR-CERES-SPECTRA-V1.0. Files containing the calibration parameters and referenced in the calibration procedure are located in the CALIB directory of this archive. After operations at the asteroid Vesta, the VIR team identified some artifacts in the instrument responsivity in the 2.5-3.5 micron region, which is where several absorption bands of OH and H2O occur. Those artifacts were systematic, and therefore they did not prevent the detection of relative spectral variations associated with OH and H2O. Actually, the only paper published [DESANCTISETAL2012] in which are discussed spectra in this range used a different calibration method described in the paper itself. This method used a simple correction of the response function based on an empirical calibration correction that is appropriate to recover the signal in that specific range. However, the absolute absorption band depth of OH and H2O could not be calculated. To compute a new instrument responsivity the team used the internal lamp of the spectrometer. This lamp, made of a tungsten filament, is characterized by a black body-like emission at about 2400K ([MELCHIORRIETAL2003]). Since the spectrum of the infrared radiation emitted by the tungsten filaments is featureless, a polystyrene filter was inserted for a wavelength calibration of the IR channel. The idea was to use the black body radiation of this lamp to retrieve a relative Instrument Responsivity in the 2.5-3.5 micron region. First the signal from the internal calibration lamp was calibrated with the on-ground responsivity, and the equivalent temperature of the radiation fitting a Planck curve was determined. The next step was to compute the Planck function at the equivalent temperature. The new Instrument Responsivity is the result of the ratio between the raw signal of the lamp and the Planck function. This ratio must be multiplied by a factor to take into account the integration time used to acquire the signal, the transmittance of the polystyrene filter, and the viewing geometry. The new instrument responsivity function minimizes most calibration residuals that were showing as artifact peaks between 2.5 and 2.9 microns in the previous calibration. It now allows the use of VIR spectra to identify absorption bands of OH and H2O, without requiring additional empirical corrections. As calibration is always an ongoing process, the instrument team is looking forward to enable the interpretation of absolute absorption band depths, which is a required step for the calculation of surface material abundances. 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_NOTE = " 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 distored in the raw data cubes and care must taken to properly correct the geometry when calibrating and interpretting 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. 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 these data were completely lost. 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. 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. Limitations =========== No limitations on these data" END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_MISSION MISSION_NAME = "DAWN" END_OBJECT = DATA_SET_MISSION OBJECT = DATA_SET_TARGET TARGET_NAME = "1 CERES" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = "DAWN" INSTRUMENT_ID = "VIR" END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "AMMANNITOETAL2006" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "DESANCTISETAL2010" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "DESANCTISETAL2012" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "FILACCHIONEETAL2006" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "MELCHIORRIETAL2003" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END