Data Set Information
DATA_SET_NAME MESSENGER E/V/H MASCS 4 VIRS DERIVED DATA V1.0
DATA_SET_ID MESS-E/V/H-MASCS-4-VIRS-DDR-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : This data set consists of the MESSENGER MASCS VIRS derived data records (DDRs). 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). DDR products (one each for VIS and NIR) are generated from on-planet (flyby and orbit) CDRs. 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. Derived Product Overview : This data set consists of MASCS VIRS Derived Data Records (DDRs) (calculated from the EDRs and CDRs as described in the SIS). The DDRs are the processed data records of derived surface reflectance used for scientific analysis. The science DDRs contain Mercury surface reflectance measured by the VIRS detectors. DDRs also contain photometrically normalized versions of the reflectance data. The VIRS instrument shutter can be closed for on-board dark observations, or the instrument can be pointed to empty space for space-darks. The processing steps from the CDR to the DDR level include: 1. Eliminate all CDR data not pointed at Mercury from consideration. 2. Eliminate dark and lamp calibrations. 3. Eliminate CDR data with stuck shutter due to elevated temperatures. 4. Divide VIRS radiance at sensor by solar irradiance spectrum convolved to VIRS wavelengths and scaled for solar distance. 5. Keep CDR saturated values as NaN or invalid number. 6. Propagate errors the same way. 7. Apply photometric normalization. Version 1 uses Lommel- Seeliger plus phase term, and for PDS16 has a factor of 2 correction applied to fix error in previous deliveries. The processing steps are detailed in the documents VIRS_CDR_DDR_DAP_SIS.PDF and VIRS_CDR2DDR.TXT, 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 are two VIRS DDR data products, one for each detector (VIS, NIR). Housekeeping and pointing data from the MASCS EDR and CDR are passed through to the DDR product. The DDR 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, and 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 DDR is created for the VIS and NIR data. Normal MASCS operations will acquire data for both VIS and NIR detectors simultaneously. Some CDR data are excluded from conversion to DDR. CDRs of shutter-closed observations (dark and lamp calibrations) and where the VIRS footprint is always in shadow (on Mercury nightside) and/or off the planet, are excluded. When VIRS is very hot (>44C) the shutter begins to behave erratically, failing to close entirely at hotter instrument temperatures. This results in bad dark solutions for hot VIRS observations beginning in the second mission year, primarily in the hot seasons. Observations identified as having shutter-dark issues are not released to PDS. A list of DDRs excluded from delivery (VIRS_DDR_EXCLUDED.TXT) is included in the EXTRAS directory. 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.
DATA_SET_RELEASE_DATE 2017-05-12T00:00:00.000Z
START_TIME 2008-01-14T07:12:55.000Z
STOP_TIME 2015-04-30T09:47:27.000Z
MISSION_NAME MESSENGER
MISSION_START_DATE 2004-08-03T12:00:00.000Z
MISSION_STOP_DATE 2015-04-30T12:00:00.000Z
TARGET_NAME MERCURY
TARGET_TYPE PLANET
INSTRUMENT_HOST_ID MESS
INSTRUMENT_NAME MERCURY ATMOSPHERIC AND SURFACE COMPOSITION SPECTROMETER
INSTRUMENT_ID MASCS
INSTRUMENT_TYPE VISIBLE/INFRARED SPECTROGRAPH
UV/VISIBLE SPECTROMETER
NODE_NAME Geosciences
ARCHIVE_STATUS ARCHIVED - ACCUMULATING
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : The MASCS VIRS Derived Data Record (DDR) 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 Calibrated Data Records (CDRs) to DDR level detailed in the document VIRS_CDR2DDR.TXT and 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 DDR was reviewed internally by the MASCS team prior to release to the PDS. PDS also performed an external review of the MASCS VIRS DDRs (both VIS and NIR detectors have separate DDR types). Data Coverage and Quality : Data reported are the derived data received from the spacecraft during the flyby and orbital mission phases: Mercury 1 Flyby, Mercury 2 Flyby, 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) ------------------------- ----------------- ---------------- MF1: Mercury 1 Flyby 31 Dec 2007 (365) 28 Jan 2008 (028) MF2: Mercury 2 Flyby 22 Sep 2008 (266) 20 Oct 2008 (294) 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 DDR dataset, the MASCS team did the following: * Examined several days of Mercury orbit data in detail. - Checked all data columns for format and sanity numbers. - Compared calibration numbers for earlier independent analysis before DDR development. - Compared reflectance and photometric conversions to previous independent solutions. Newer VIS photometric normalization available in V2.0 VIRS DDR data, available on PDS volume MESSMAS_2101. * Spot checked additional data sets from orbit. The orbital DDR dataset was 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 flybys and orbit are converted to DDR. Data quality information for DDR observations is the same as the DQI of matching CDRs. Cruise operations/observations have additional details in the Master Cruise Table (a Microsoft Excel file) in the Extras directory. 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.
CITATION_DESCRIPTION Izenberg, N., MESSENGER E/V/H MASCS 4 VIRS DERIVED DATA V1.0, MESS-E/V/H-MASCS-4-VIRS-DDR-V1.0, NASA Planetary Data System, 2013.
ABSTRACT_TEXT Abstract : This data set consists of the MESSENGER MASCS VIRS derived observations, also known as DDRs. The MASCS VIRS experiment is a fixed concave grating spectrograph with a beam splitter that simultaneously disperses the spectrum onto two photodiode arrays. There are two VIRS DDR data products, one for each array, which result in coverage of the wavelength ranges of the visible (VIS) and near infrared (NIR).
PRODUCER_FULL_NAME NOAM IZENBERG
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