Data Set Overview : This data set consists of the MESSENGER MASCS VIRS derived anaylsis product (DAP). One DAP will contain a 500 meter per pixel mosaic map of 1 wavelength (750 nm) of VIRS spectral data for footprints covering the whole planet. MASCS/VIRS mosaics include MASCS/VIRS footprints collected after orbit insertion. A metric defined as M : footprint_area / (cos(e)*cos(i)) is computed for each footprint of each observation. In the case of individual spectra that cover the same location, spectra with the lowest metric value are stacked on top, and are the only ones to be captured in the final map layer. The spectra examined for inclusion in the mosaic come from CDRs converted to photometrically normalized reflectance using the same method as the VIRS Version 2 DDRs. Mosaicked spectra must have M > 0, emission angle < 80 degrees and incidence angle < 70 degrees for footprints with latitude in [-65,65] or incidence angle < footprint's latitude + 5 degrees for other footprints. This is version 2 of this data set. 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. Derived Product Overview : This data set consists of the MASCS VIRS Derived Analysis Product (DAP, calculated from the DDRs as described in the SIS). The DAP is a 500 meter per pixel mosaic map of 1 wavelength (750 nm) of VIRS spectral data for footprints covering the planet Mercury. The processing steps from the DDR to the DAP level include: 1. Ingest DDR dataset and select footprints. 2. Create map layers. More information on the DAP can be found in the document VIRS_CDR_DDR_DAP_SIS, 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 MESSENGER-derived reference system (pck00010_msgr_v21.tpc) for cartographic coordinates and rotational elements was used for computing latitude and longitude coordinates of planets. Data : There is one VIRS DAP data product, consisting of 9 layers. Each layer is provided as a separate image file (.IMG); the 9 layers are described by 1 detached PDS label (.LBL). Each layer information is derived from the CDR and the spectrum of the topmost spectrum at a given map location. 1) Reflectance @750 nm, taken from DDR for spectrum with maximum M value. 2) Interpolated reflectance @750nm derived from layer 1 using a spatial interpolation algorithm. 3) Incidence angle (of maximum M value spectrum), taken from DDR 4) Emission angle(of maximum M value spectrum), taken from DDR 5) Phase angle (of maximum M value spectrum), taken from DDR 6) Observation area, derived from footprint dimension from DDR 7) Observation DDR date (of maximum M value spectrum) 8) Observation DDR time (of maximum M value spectrum) 9) Observation spectrum number (of maximum M value spectrum)

Confidence Level Overview : The MASCS VIRS Derived Analysis Product (DAP) consists of the derived data converted to units of reflectance 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 Derived Data Records (DDRs) to DAP level. 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 DAP was reviewed internally by the MASCS team prior to release to the PDS. PDS also performed an external review of the MASCS VIRS DAP. Data Coverage and Quality : Data reported are the derived data received from the spacecraft during the orbital mission phases: 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) ------------------------- ----------------- ---------------- ORB: Mercury Orbit 04 Mar 2011 (063) 17 Mar 2012 (077) OB2: Mercury Orbit Year 2 18 Mar 2012 (078) 17 Mar 2013 (076) OB3: Mercury Orbit Year 3 18 Mar 2013 (077) 17 Mar 2014 (076) OB4: Mercury Orbit Year 4 18 Mar 2014 (077) 17 Mar 2015 (076) OB5: Mercury Orbit Year 5 18 Mar 2015 (077) 30 Apr 2015 (120) To validate the initial DAP dataset, the MASCS team did the following: * Examined several locales of Mercury map data in detail. - Checked all backplanes for format and sanity numbers. - Compared calibration numbers for earlier independent analysis before DAP development. * Spot checked additional data sets from orbit. The orbital DAP 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, but only resolved Mercury surface data from orbit are converted to DAP. Limitations : This data set is derived data. The data are received from the spacecraft telemetry and ingested into the MESSENGER Science Operations Center (SOC), then run through the MASCS pipeline. No data uncharacterized gaps have been identified for any of the MASCS operational periods.