MESSENGER MASCS VIRS Calibrated Data Record (VIRCDR)

VIRCDR – Calibrated Data Record

Instrument: MESSENGER Mercury Atmospheric and Surface Composition Spectrometer

PDS Data Set ID: MESS-E/V/H-MASCS-3-VIRS-CDR-CALDATA-V1.0

For more information about MASCS VIRCDR products, see the VIRS CDR/DDR/DAP Product SIS.

The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) Visible and Infrared Spectrograph (VIRS) Calibrated Data Record (VIRCDR) data products contain VIRS calibrated data derived from MASCS VIRS Experiment Data Records (VIREDRs). The VIRS experiment is a fixed concave grating spectrograph with a beam splitter that simultaneously disperses the spectrum onto two photodiode arrays.

The VIRCDR consists of entries for the spacecraft time and orientation, target location, values for the observing parameters set for the given observation, information about the observation, and is followed by the science spectral data. On each detector, the pixel number can be mapped to a specific wavelength, allowing a variable number of spectra. All of the data from one commanded observation are contained in one VIRCDR. Before science data from the VIRS system can be used for scientific analysis, the count values in the Experiment Data Record (VIREDR) must be converted to physical units and the data must be transformed into meaningful physical reference systems. This conversion yields calibrated data which are stored in VIRCDRs.

MASCS VIRS data are represented in the following coordinate systems:

• Planetocentric body fixed: The MBF coordinate system is defined by the planetocentric position; Cartesian X, Y, Z coordinates related to the planetocentric distance; latitude measured positive northward from the equator; and longitude measured positive eastward from the prime meridian.

• Cartographic: Surface observations use IAU planetocentric system with East longitudes being positive for planetary surfaces. The IAU2000 reference system for cartographic coordinates and rotational elements was used for computing latitude and longitude coordinates of planets.

The principal parameters when observing with the MASCS VIRS are shown below:

Parameter	Description
Integration Time	The amount of time that the array detectors will integrate photon counts.  Unit is 50 milliseconds.
Integration Count	The amount of integrations that will be taken.
Period	The interval time after which another integration will be started.  Integrations are started at the top of every period.  Time between integrations is the period time minus the integration time.  Unit is 0.05 seconds.
Dark Frequency	The frequency at which dark counts will be collected during a VIRS observation.  For an entered number n, dark counts will be collected every nth integration.
NIR Gain	Sets of the gain of the NIR array detector, to either low, high, or N/A when the VIS detector is enabled.
NIR Lamp On	The NIR flat field lamp is powered on or off.
VIS Lamp On	The VIS flat field lamp is powered on or off.
Binning	The number of pixels that were binned together in the data.
Start Pixel	Start pixel of data captured by the detector array.  For VIS, the value can be from 0-511.  For NIR, the value can be from 0-255.
End Pixel	End pixel captured by the detector array.  The end pixel value must be greater than the start pixel value.

MASCS VIRCDR products are named according to the following file naming convention:

VIRSdC_mmm_yyddd_hhmmss_zzz.DAT (with detached PDS label)

where:

d = detector

F = FUV

M = MUV

V = VIS

mmm = mission phase

LAU = launch

EAC = Earth cruise to Earth flyby

EAF = Earth flyby

VC1 = cruise, post-Earth flyby to pre-Venus 1 flyby

VC2 = cruise, post-Venus 1 flyby to pre-Venus 2 flyby

VF2 = Venus 2 flyby

MC1 = cruise, post-Venus 2 flyby to pre-Mercury 1 flyby

MF1 = Mercury 1 flyby

MC2 = cruise, post-Mercury 1 flyby to pre-Mercury 2 flyby

MF2 = Mercury 2 flyby

MC3 = cruise, post-Mercury 2 flyby to pre-Mercury 3 flyby

MF3 = Mercury 3 flyby

MC4 = cruise, post-Mercury 3 flyby to pre-orbit insertion

ORB = orbit insertion until end of nominal orbit mission

OB2 = second year of orbital operations

OB3 = third year of orbital operations

OB4 = fourth year of orbital operations

OB5 = fifth year of orbital operations

yy = 2-digit year in UTC converted from the first Mission Elapsed Time (MET) in the EDR

ddd = 3-digit day of year in UTC converted from the first MET in the EDR

hhmmss = 6-digit hour, minute, second in UTC converted from the first MET in the EDR

In ODE, VIRCDR products appear under the following product IDs:

VIRSDC_MMM_YYDDD_HHMMSS_DAT