Data Set Overview : This data set consists of the MESSENGER MASCS VIRS uncalibrated observations, also known as EDRs. Each VIRS observation results in data from two spectral regions. The spectra cover the wavelength ranges of the visible (VIS)(300-1050 nm) and near infrared (NIR) (850-1450 nm), with a resolution of 5 nm. There are three standard data products: VIS data, NIR data, and Housekeeping data. The housekeeping EDR contains instrument parameters that may be useful in analyzing the VIRS data.  Instrument Overview : The MASCS instrument consists of a small Cassegrain telescope that simultaneously feeds the UVVS and VIRS experiments. MASCS VIRS experiment is a fixed concave grating spectrograph with a beam splitter that simultaneously disperses the spectrum onto two solid-state array detectors: a 512-element silicon photodiode array, with a sensitivity to visible wavelengths (300-1050 nm), and a 256-element indium-gallium-arsenide photodiode array, to measure near infrared wavelengths (850-1450 nm). The VIRS detector will help to measure the surface reflectance and search for ferrous bearing minerals, Fe-Ti bearing phases, and ferrous iron on the surface of Mercury.  See the INST.CAT file for more information and [MCCLINTOCK&LANK2007] for full details.  Calibration Overview : This data set is NOT calibrated; it only provides the uncalibrated detector measurements.  Parameters : The principal parameters when observing with the MASCS VIRS are as follows:  * 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 second.  * 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.  Data : There are two VIRS EDR data products, one for each detector (VIS, NIR). There is also a MASCS housekeeping EDR data product generated by the MASCS instrument, which is the same for both the UVVS and VIRS components of the MASCS experiment.  The EDR for either the VIS or NIR detector 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 resulting spectra to be created. One observation can generate a variable number of spectra. All of the data from one commanded observation are contained in one EDR.  A separate EDR is created for the VIS and NIR data. Normal MASCS operations will acquire data for both VIS and NIR detectors simultaneously.  The MASCS Housekeeping EDR provides data about the voltage, current, and temperature readings, as well as record and software status, hardware settings, instrument status, and integration and reporting times. The MASCS Housekeeping EDR will contain all housekeeping packets generated in a given day.

Confidence Level Overview : The MASCS VIRS EDR data are the least processed data set released for the VIRS. Data presented here are an accurate representation of the VIRS data as received from the spacecraft, with minimal timing and spatial processing.  Review : The VIRS EDR was reviewed internally by the MASCS team prior to release to the PDS. PDS also performed an external review of the MASCS VIRS EDRs (both VIS and NIR detectors have seperate EDR types).  Data Coverage and Quality : Data reported are the minimally processed data received from the spacecraft during the eighteen mission phases: Launch, Earth Cruise, Earth Flyby, Venus 1 Cruise, Venus 1 Flyby, Venus 2 Cruise, Venus 2 Flyby, Mercury 1 Cruise, Mercury 1 Flyby, Mercury 2 Cruise, Mercury 2 Flyby, Mercury 3 Cruise, Mercury 3 Flyby, Mercury 4 Cruise, Mercury Orbit, Mercury Orbit Year 2, Mercury Orbit Year 3, and Mercury Orbit Year 4. These mission phases are defined as:  Start time End time Phase Name Date (DOY) Date (DOY) ----------------- ----------------- ----------------- Launch 03 Aug 2004 (216) 12 Sep 2004 (256) Earth Cruise 13 Sep 2004 (257) 18 Jul 2005 (199) Earth Flyby 19 Jul 2005 (200) 16 Aug 2005 (228) Venus 1 Cruise 17 Aug 2005 (229) 09 Oct 2006 (282) Venus 1 Flyby 10 Oct 2006 (283) 07 Nov 2006 (311) Venus 2 Cruise 08 Nov 2006 (312) 22 May 2007 (142) Venus 2 Flyby 23 May 2007 (143) 20 Jun 2007 (171) Mercury 1 Cruise 21 Jun 2007 (172) 30 Dec 2007 (364) Mercury 1 Flyby 31 Dec 2007 (365) 28 Jan 2008 (028) Mercury 2 Cruise 29 Jan 2008 (029) 21 Sep 2008 (265) Mercury 2 Flyby 22 Sep 2008 (266) 20 Oct 2008 (294) Mercury 3 Cruise 21 Oct 2008 (295) 15 Sep 2009 (258) Mercury 3 Flyby 16 Sep 2009 (259) 14 Oct 2009 (287) Mercury 4 Cruise 15 Oct 2009 (288) 03 Mar 2011 (062) Mercury Orbit 04 Mar 2011 (063) 17 Mar 2012 (077) Mercury Orbit Year 2 18 Mar 2012 (078) 17 Mar 2013 (076) Mercury Orbit Year 3 18 Mar 2013 (077) 17 Mar 2014 (076) Mercury Orbit Year 4 18 Mar 2014 (077) 17 Mar 2015 (076)  MASCS VIRS data were collected during all phases except Venus 1 Flyby. During these planned operational periods, the VIRS functioned nominally and the data quality was good. Additional numbered notes added as necessary. This is a high-level presentation of EDR validation. Lower level EDR (and CDR) details, including, e.g. dark observations, temperature alarms, and footprints on/off planet are best obtained through the Data Quality Index (DQI) of the VIRS CDR. Specific MASCS operational periods were:  Start time End time Phase Name Date (DOY) Date (DOY) Operations -------------------- ----------------- ----------------- -------------  Launch 03 Aug 2004 (216) 12 Sep 2004 (256) Checkout Earth Cruise 13 Sep 2004 (257) 18 Jul 2005 (199) Starcals (1) Cover Open Earth Flyby 19 Jul 2005 (200) 16 Aug 2005 (228) Earth/Moon Venus 1 Cruise 17 Aug 2005 (229) 09 Oct 2006 (282) Starcals Venus 1 Flyby 10 Oct 2006 (283) 07 Nov 2006 (311) n/a Venus 2 Cruise 08 Nov 2006 (312) 22 May 2007 (142) Starcals (2), Venus, Operation Tests Venus 2 Flyby 23 May 2007 (143) 20 Jun 2007 (171) Venus Mercury 1 Cruise 21 Jun 2007 (172) 30 Dec 2007 (364) Starcals (3), Operation Tests Mercury 1 Flyby 31 Dec 2007 (365) 28 Jan 2008 (28) Mercury, Lyman Alpha Mercury 2 Cruise 29 Jan 2008 (029) 21 Sep 2008 (265) Starcals, Operation Tests Mercury 2 Flyby 22 Sep 2008 (266) 20 Oct 2008 (294) Mercury, Lyman Alpha Mercury 3 Cruise 21 Oct 2008 (295) 15 Sep 2009 (258) Starcals (4), Venus Mercury 3 Flyby 16 Sep 2009 (259) 14 Oct 2009 (287) Mercury (5), Lyman Alpha Mercury 4 Cruise 15 Oct 2009 (288) 03 Mar 2011 (062) Starcals, Venus, Operation Tests Mercury Orbit 04 Mar 2011 (063) 17 Mar 2012 (077) Mercury (6), Starcals (7), Venus Mercury Orbit Year 2 18 Mar 2012 (078) 17 Mar 2013 (076) Mercury (8), Starcals (9) Mercury Orbit Year 3 18 Mar 2013 (077) 17 Mar 2014 (076) Mercury (10), Starcals Mercury Orbit Year 4 18 Mar 2014 (077) 17 Mar 2015 (076) Mercury (10), Comet Encke, Comet ISON, Starcals  Notes: (1) Starcals before June '05 viewed through cover window. (2) One Starcal missed target due to star tracker error. (3) S/C event during starcal, Instrument turned off during Starcal. (4) Pointing error during May '09 Starcal. Star not observed. (5) Flyby anomaly - no Data after Mercury Closest Approach until post-flyby Mercury-as-star observations. Safing event cut off one Mercury-as-star observation in the middle. (6) Elevated operational temperatures in orbit. Packet-packing error caused lost packets approximately 0.03% of the time. Known single lost packets are described in Extras directory. Flight software patch on 11208 solved issue. 58 total observations affected. Data is good, but VIS and NIR files don't match due to missing spectra in VIS. (7) Lost data Events during Orbit. 11123: FPP 'High Temperature' warning, Instrument off for 2 days, setting set too low. FPP temps reset to higher value. 11216-11215: Single event upset garbled VIRS data from MET 220978448 to MET 221033678. CDRs exist for this time, but with no valid science data. Data all shutter closed. 11249-11250: Single event upset garbled VIRS data from MET 223767753 to MET 223882987. CDRs exist for this time, but with no valid science data. Occurrence at the same time as X class solar flare. Dark currents in VIRS elevated after this event. (8) Occasional single event upsets, usually related to solar activity, usually resulted in either instrument shutdown, or accumulation of corrupted/useless data that is not delivered. Slowly increasing IR dark current as a function of age, with additional step functions coinciding with large solar particle events. (9) During hot seasons, when detector temps exceed ~44 deg. C, the VIRS shutter begins to fail to close in some observations, resulting in commanded dark observations that are not dark in a subset of observations. These data are excluded from CDR and DDR delivery until a compensatory calibration is derived. A table of excluded observations has been created. (10) Single event upsets and 'VIRS stuck in scanning mode' incidents continue, but more rarely during this period after VIRS reset is commanded every orbit.  Cruise operations/observations have additional details in the Master Cruise Operations Table (a Microsoft Excel file) in the Extras directory.  Limitations : This data set is minimally processed data. The data are received from the spacecraft telemetry and ingested into the MESSENGER Science Operations Center (SOC). No data gaps have been identified for any of the MASCS operational periods.