NASA Logo, National Aeronautics and Space Administration
NASA Space Science Data Coordinated Archive Header

DAWN VIR CAL (RDR) CERES INFRARED SPECTRA V1.0 (PDS)

NSSDCA ID: PSSB-00627

Availability: Archived at NSSDC, accessible from elsewhere

Description

This description was generated automatically using input from the Planetary Data System.

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 docum

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.

These data are available on-line from the Planetary Data System (PDS) at:

http://sbn.psi.edu/archive/dawn/vir/DWNCAVIR_I1B/

Alternate Names

  • DAWN-A-VIR-3-RDR-IR-CERES-SPECTRA-V1.0

Discipline

  • Planetary Science: Small Bodies

Additional Information

Spacecraft

Experiments

Questions and comments about this data collection can be directed to: Dr. David R. Williams

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Maria Christina de SanctisData ProviderIstituto Nazionale di Astrofisicamariacristina.desanctis@iaps.inaf.it
[USA.gov] NASA Logo - nasa.gov