Description of the Nathair Facula Topography and Photometric Cube Data bundle V1.0
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Bundle Generation Date: 2023-12-20


Content description for the Nathair Facula Topography and Photometric Cube Data
bundle
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This bundle contains topography and photometric data for two regions within
Nathair Facula. For each Mercury Dual Imaging System (MDIS) image, four cubes
were generated; I/F (reflectance), Local Phase Angle, Local Emission Angle,
and Local Incidence Angle. Each photometric cube pixel represents the value at
each vertex of the DTM, thus each pixel location in each cube represents the
same location on the surface.

MDIS images are used irrespective of the filter. About 40% of the WAC images
used filter G, which has a similar center wavelength to the NAC instrument that
has no filter. No filter B (i.e. broadband or clear) images were used to
generate the products in this bundle. Non-calibrated images are used, but a
correction for geometric distortion and a frame transfer smear are applied by
SPC. 8 bit images are converted to 16 bit images using a Look Up Table provided
by the MESSENGER team. The image list for each DTM, as well as the kernel list,
are included as text documents.
 
The topography data is provided both in cubes readable by the USGS ISIS program,
and as a geoTiff which can be read by programs such as ArcGIS. We generated
photometric data (in cube format) that is aligned to, and has the same
horizontal spacing as, the topographic cube data. To aid the data user,
filenames end with a "c" to designate ISIS cubes or a "g" to designate geoTiffs.

DTM nafn35066 has a Ground Sample Distance (GSD) of 120 m and a size of 130 by
130 km. DTM nafn36064 has a GSD of 60 m and a size of 80 by 80 km. The two DTMs
only partially overlap. Both DTMs contain, but are not centered on, a volcanic
vent at 35.86 Lat 63.93 E Lon. The uncertainty of SPC DTMs with sufficient
imagery, such as the products in this bundle, are typically one or two times
the GSD of the model. The 60 m DTM has an estimated uncertainty of 60-120 m and
a FormU (see the Product Description document) of 73.4 m, while the 120m DTM
has an estimated uncertainty of 120-240 m and a FormU of 97.2 m.


Caveats to the data user
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For the photometric data, while some cubes have values for all pixels, only
pixels that correspond to non-zero values in the reflectance cube (i.e. I/F or
"ioverf") are valid.

The geoTiff files are resampled and projected topography, and as such the
accuracy of the heights may be affected.