Data Set Overview : This data set consists of the MESSENGER MASCS VIRS calibrated  data records (CDRs). 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 is a data overlap  with UVVS in the VIS wavelength range. There are three standard  VIRS EDR data products: VIS data, NIR data, and Housekeeping  data. The housekeeping EDR contains instrument parameters that  may be useful in analyzing the VIRS data. Housekeeping data are  incorporated into the two standard CDR data products (one each  for VIS and NIR). Instrument Overview : The MASCS instrument consists of a small Cassegrain telescope that simultaneously feeds the UVVS and VIRS experiments. The  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. 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 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. Calibration Overview : This data set consists of calibrated data derived from MASCS VIRS Experimental Data Records (EDR). The EDRs are the raw data  records used to derive surface reflectance data used for  scientific analysis. The science EDRs contain raw counts of the  VIRS detectors for the assigned integration times and pointing  orientations. The VIRS instrument shutter can be closed for  on-board dark observations, or the instrument can be pointed to  empty space for space-darks. Additionally there are two on-board  'grain-of-wheat' size lamps that are periodically used to  illuminate the detectors to acquire 'flat field' observations.  Wavelength range and sensitivity of each detector are documented  in the MASCS Calibration Report, MASCS_CAL_RPT.PDF, provided in  the DOCUMENT directory. Before the science data can be used for  scientific analysis, the count values in the EDRs 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 Calibrated Data Records  (CDRs). The processing steps from the EDR to the CDR level include: 1. Determine time (integration) for each spectrum of a given VIRS observation. 2. The first scan of the VIS detector is anomalous in magnitude- set the first scan to the average of the next few scans. 3. Determine dark curve and subtract darks from data. 4. Subtract scattered light, other corrections  (e.g. temperature).  5. Apply lab-measured sensitivity, wavelength correction, convert  to radiance at sensor. 6. Determine pointing parameters for every spectrum. 7. Assign data quality flags and indicators. The processing steps are detailed in the documents VIRS_CDR_DDR_SIS  and VIRS_EDR2CDR, located in the DOCUMENT directory. Coordinate Systems : 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. Data : There are two VIRS CDR data products, one for each detector  (VIS, NIR). Data from the MASCS housekeeping EDR product  generated by the MASCS instrument, which is the same for both the  UVVS and VIRS components of the MASCS experiment, are  incorporated into the CDRs. The CDR 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 resultant 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 CDR. A separate CDR is created for the VIS and NIR data. Normal MASCS  operations will acquire data for both VIS and NIR detectors  simultaneously.

Confidence Level Overview : The MASCS VIRS Calibrated Data Record (CDR) released for the VIRS  consists of the calibrated data converted to physical units and  represented in physical coordinate systems. Data presented here  are an accurate representation of the VIRS data as received from  the spacecraft, and reflect the processing steps from the MASCS  VIRS Experimental Data Records (EDRs) to CDR level detailed in  the document VIRS_EDR2CDR located in the DOCUMENT directory. The  UTC and MET time tags have been corrected for timing latencies in  the instrument so that the UTC and MET correspond to the physical  time of the observation. Review : The VIRS CDR was reviewed internally by the MASCS team prior to release to the PDS. PDS also performed an external review of the MASCS VIRS CDRs (both VIS and NIR detectors have separate CDR types). Data Coverage and Quality : Data reported are the calibrated data received from the  spacecraft during the 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, Mercury Orbit Year 4, and Mercury Orbit Year 5. 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) Mercury Orbit Year 5 18 Mar 2015 (077) 30 Apr 2015 (120)  To validate the initial CDR dataset, the MASCS team did the following: * Examined the Mercury 1 flyby dataset from Jan 14 2008 in detail. These were the most scientifically significant observations that had been made at the time of initial  validation. - Checked all data columns for format and sanity numbers - Compared calibration numbers for earlier independent analysis before CDR development - Compared pointing information (vectors, lats, lons, distances, angles) to previous independent solutions * Spot checked additional data sets preceding Mercury 1 flyby.   The orbital CDR dataset is evaluated on an ongoing basis,  checking for completeness and data integrity.  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 CDR validation. Lower level 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 (6-10), Starcals, Venus Mercury Orbit Year 2 18 Mar 2012 (078) 17 Mar 2013 (076) Mercury (11, 12), Starcals Mercury Orbit Year 3 18 Mar 2013 (077) 17 Mar 2014 (076) Mercury (13), Starcals  Mercury Orbit Year 4 18 Mar 2014 (077) 17 Mar 2015 (076) Mercury (13), Comet Encke, Comet ISON, Starcals Mercury Orbit Year 5 18 Mar 2015 (077) 30 Apr 2015 (120) Mercury (14) 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) Temperature Effects in Orbit: Current calibration for VIRS was established before orbital  insertion and includes a detector-temperature sensitivity  correction. Operational temperatures in Mercury orbit are on  average 10-15 degrees higher than originally predicted  during instrument design and testing, with detector  temperatures approaching 45-50 deg. C during the  'hot-seasons' of noon-midnight orbits. The IR detector  especially, as described in the calibration document,  experiences increasing background noise as temperature  increases. Thermal background noise adversely affects the  science quality of the IR detector starting above  approximately 25-30 deg. C, with significant thermal noise  and pixel saturation beginning around 35 deg. C. The VIRS  VIS detector experiences elevated noise at hot temperatures  as well, but not to the level of the NIR detector. Caution  should be exercised when using MASCS spectral data at  elevated temperatures, especially with the NIR detector. PDS  delivery 7 includes a set of temperature dependent  'filters,' mapping out saturation temperatures of different pixels across the NIR detector. Pixels that are saturated due to elevated temperatures are assigned a data value of  1E32 in the calibrated radiance and noise spectrum data  columns. (8) Dark Subtraction: Closed-shutter-dark spectra are observed every N spectra in  an observation (N : 5, 10, 20, or 40, depending on  observation type). Dark signals are interpolated between  observations using a 2nd order polynomial for the VIS  detector and a 3rd order polynomial for the NIR detector.  Observations with too few darks reduce the polynomial order or pick a single dark value. Dark subtraction in VIRS  calibrated data has two weaknesses. The current calibration  pipeline considers each observation in stand-alone fashion.  The first N-1 spectra in an observation have poor polynomial  fitting. In addition, observations taken with fewer than 3  or 4 interleaved darks have bad fits and consequently bad  calibrated data. The next iteration of the calibration  software, for an upcoming PDS delivery will seek to improve  dark subtraction by utilizing darks from preceding and  following observations. (9) Solar particle effects on VIRS NIR background levels:  NIR background DN has been slowly increasing over the  orbital mission, but took two spikes that coincided with  solar events denoted by high 73keV cout rates by the  MESSENGER EPS instrument. NIR dark signal went from an  average of 32500 to 34700 to 36300 following events early  and late June. Elevated background continues to increase at  previous orbital rates. The primary effect of elevated  background is that NIR pixels will saturate sooner due to  elevated temperature.  (10) Additional solar events, and Single Event Upsets: 11250 X-Class solar flare, SEU 12064 EEPROM hit lost a few days of data (11) Occasional Solar events, SEUs. Current list of particle/ radiation events is appended below. These events have  affected (raised) background levels of some or all of the pixels of the NIR detector, sometimes on a permanent basis. (12) When VIRS is very hot (>44C) the shutter begins to behave erratically, failing to close (or open) entirely at hotter  instrument temperatures. This results in bad dark solutions  or all-dark observations (if the shutter is stuck shut) for  hot VIRS observations beginning in the second mission year,  primarily in the hot seasons. A list of CDRs excluded from  delivery show which observations have been identified as  having shutter-dark issues (EXTRAS/VIRS_CDR_EXCLUDED.TXT).  This file will be amended as new observations are affected  during hot seasons, and as new dark subtraction and  synthesis methods are developed to mitigate at least some of  the observations. (13) Single event upsets and 'VIRS stuck in scanning mode'  incidents continue, but more rarely during this period after VIRS reset is commanded every orbit. Shutter exclusions due to temperature continue.  (14) Final orbit operations are mostly ride-along. Otherwise as  note #13.  MASCS particle/radiation events: 04-10-2011 06-05-2011 (large) 06-06-2011 06-07-2011 06-08-2011 08-10-2011 08-15-2011 09-10-2011 09-20-2011 10-04-2011 11-01-2011 11-15-2011 12-01-2011 12-05-2011 12-22-2011 01-01-2012 01-20-2012 03-05-2012 (large) 06-01-2012 06-20-2012 06-25-2012 07-10-2012 08-10-2012 09-20-2012 09-21-2012 10-10-2012 04-24-2013 04-25-2013 08-20-2013 08-21-2013 09-01-2014 09-02-2014 09-03-2014 09-04-2014 12-04-2014 12-13-2014 12-14-2014 12-15-2014 12-16-2014 03-24-2015  Cruise operations/observations have additional details in the  Master Cruise Table (a Microsoft Excel file) in the Extras  directory.  Limitations : This data set is calibrated data. The data are received from the  spacecraft telemetry and ingested into the MESSENGER Science  Operations Center (SOC), then run through the MASCS calibration  pipeline. No data uncharacterized gaps have been identified for  any of the MASCS operational periods.