UVVCDR – Calibrated Data Record

Instrument: MESSENGER Mercury Atmospheric and Surface Composition Spectrometer


For more information about MASCS UVVCDR products, see the UVVS CDR/DDR Product SIS.

The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) Ultraviolet and Visible Spectrometer (UVVS) Calibrated Data Record (UVVCDR) data products contain UVVS uncalibrated observations. The UVVS experiment is a scanning grating monochromator equipped with three photomultiplier tubes. There are three UVVEDR data products, one for each detector, which cover the wavelength ranges of the far ultraviolet (FUV) (115-190 nm), middle ultraviolet (MUV) (160-320 nm), and visible (VIS) (250-600 nm), with a resolution of 0.5 nm for the FUV channel and 1.0 nm for the MUV and VIS channels.

The UVVCDR consists of two files. The Header file (HDR) contains values for the instrument command parameters set that apply for the entirety of the observation encapsulated by the product. The Science file (SCI) data are the counts accumulated by the photomultiplier tube at a given position of the grating, in the order that the counts were collected. By using the values of the specific observing parameters that are related to the grating start position, number of grating steps, pattern of grating steps, and number of scans, each grating position can be determined and mapped to a specific wavelength. All other per-step information on counts, calibrated data, spacecraft time and orientation, target location, and other pointing parameters, are kept in the Science file.

MASCS UVVS 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 UVVS are shown below.



Start Position

The start position where the grating drive begins a scan.

Step Size

The step size in units of grating step.  One grating step is equal to one arcmin.  The wavelength delta of a single UVVS grating step is detector dependent.  Wavelength and sensitivity tables are provided in the UVVS_EDR2CDR document, and the equations describing step wavelengths are provided in the MASCS_CAL_RPT document.

Step Count

The number of steps the grating drive will take in a scan.  The Step count multiplied by the Step Size relates to the range of wavelengths that will be observed in one UVVS observation.

Integration Time

Integration time in grating drive loop control interrupt periods (nominally 3000 Hz).

Step Time

The step time in the grating drive loop control interrupt periods (nominally 3000 Hz).

Phase Offset

The phase offset between the beginning of the grating drive step and the start of a PMT integration in units of 0.3 milliseconds.  Default value is 0 (no phase offset).  By setting the phase offset to a non-zero value (reserved for contingency operations), the user will tell the software to initiate a step before the end of an integration, accounting for latencies in the motor controller.

Number of Scan Cycles

The number of times to repeat a scan.

Zigzag Option

Indicates whether grating drive moves in a “triangle” (stepping up, then stepping down), or “sawtooth” (stepping up, then “flying” down) motion.  A “triangle” observation takes one grating scan stepping up into the grating, then reverse direction and takes the next grating scan stepping back down the grating.  A “sawtooth” observation takes one grating scan stepping up the grating, then “flies” the grating back to the Start Position to take the next observation.


Selects between 16-bit data (uncompressed) or 9-bit data (compressed).

Slit Mask Position

Indicates whether the slit mask is in the atmospheric (open) or surface (closed) position.  Atmospheric slit results in a 1 deg. by 0.04 deg. instantaneous field of view (iFOV).  Surface slit results in a 0.05 deg. by 0.04 deg. iFOV.


Select if the far ultraviolet photomultiplier tube is powered on or off.


Select if the middle ultraviolet photomultiplier tube is powered on or off.


Select if the visible photomultiplier tube is powered on or off.

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

UdC_mmm_xx_yyddd_hhmmss_zzz.DAT (with detached PDS label)


d = detector




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

xx = 2-digit macro id; 00 for data created prior to the existence of UVVS macros or when PIPE (software) cannot determine the macro id used; value 48 or 49 for surface observations

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

zzz = data type

HDR = per observation (science header) data

SCI = per step (science CDR) data

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