MESSENGER MASCS VIRS Derived Analysis Product (VIRDAP)

VIRDAP – Derived Analysis Product

Instrument: MESSENGER Mercury Atmospheric and Surface Composition Spectrometer

PDS Data Set ID: MESS-E/V/H-MASCS-5-VIRS-DAP-V1.0

For more information about MASCS VIRDAP products, see the VIRS DAP Product SIS.

The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) Visible and Infrared Spectrograph (VIRS) Derived Analysis Product (VIRDAP) consists of a mosaic map of VIRS spectral data for footprints covering the planet Mercury. Data products are derived from science data collected by the VIRs detector during orbital operations of Mercury.

One VIRDAP contains 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 Calibrated Data Records (VIRCDRs) converted to photometrically corrected reflectance. 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.

There is one VIRDAP 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 VIRCDR and the spectrum of the topmost spectrum at a given map location.

  1. Reflectance @ 750 nm, taken from Derived Data Product (VIRDDR) for spectrum with maximum M value

  2. Interpolated reflectance @ 750 nm derived from layer 1 using a spatial interpolation algorithm

  3. Incidence angle (of maximum M value spectrum), taken from VIRCDR

  4. Emission angle (of maximum M value spectrum), taken from VIRCDR

  5. Phase angle (of maximum M value spectrum), taken from VIRCDR

  6. Observation area (of maximum M value spectrum), derived from footprint dimension of VIRCDR

  7. Observations, VIRCDR date (of maximum M value spectrum)

  8. Observations, VIRCDR time (of maximum M value spectrum)

  9. Observations spectrum number, taken from VIRCDR (of maximum M value spectrum)

MASCS VIRDAP layers are named according to the following file naming convention:

VIRS_DAP_500MPP_Vxx_aaaaaaa.IMG (with one detached PDS label for all 9 layers)

where:

500MPP = map scale, 500 meters per pixel

xx = version number

aaaaaaa = map layer type

RFL = reflectance at 750 nm at given coordinate

INTRFL = interpolated reflectance at given coordinate

INC = incidence angle at given coordinate

EMI = emission angle at given coordinate

PHA = phase angle at given coordinate

AREA = footprint area at given coordinate

CDRDATE = date of acquisition of the footprint at given coordinate

CDRTIME = time of acquisition of the footprint at given coordinate

SPENUM = spectrum number within the VIRCDR of the footprint at given coordinate

In ODE, the VIRDAP products appear under the following product ID:

VIRS_DAP_500MPP_VXX