MESSENGER MASCS UVVS Experiment Data Record (UVVEDR)

UVVEDR – Experiment Data Record

Instrument: MESSENGER Mercury Atmospheric and Surface Composition Spectrometer

PDS Data Set ID: MESS-E/V/H-MASCS-2-UVVS-EDR-V1.0

For more information about MASCS UVVEDR products, see the UVVS EDR Product SIS.

The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) Ultraviolet and Visible Spectrometer (UVVS) Experiment Data Record (UVVEDR) 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 UVVEDR 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 scan data. The science scan 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.

The principal parameters when observing with the MASCS UVVS are shown below.

Parameter	Description
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.
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.
Compression	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.
FUV On	Select if the far ultraviolet photomultiplier tube is powered on or off.
MUV On	Select if the middle ultraviolet photomultiplier tube is powered on or off.
VIS On	Select if the visible photomultiplier tube is powered on or off.

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

UdE_mmm_xx_yyddd_hhmmss.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

VF1 = 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

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, UVVEDR products appear under the following product IDs:

UDE_MMM_XX_YYDDD_HHMMSS_DAT