MESSENGER MDIS Digital Elevation Model
DEM – MDIS Digital Elevation Model
Instrument: MESSENGER Mercury Dual Imaging System
PDS4 Bundle: urn:nasa:pds:messenger_mdis_dem_1001DOI: 10.17189/sj95-jj49
For more information about MDIS DEM products, see the DEM Product SIS.
The Mercury Dual Imaging System (MDIS) Digital Elevation Model (DEM) data products are gridded (raster) products that record elevation values of a given terrain in each pixel. Corresponding metadata include map projection information so pixels can be associated with latitude and longitude. Values are measured relative to the planetary geoid reference radius of 2,439.4 km (i.e. elevation).
The primary PDS product is a DEM provided in both PDS image (.IMG) and JPEG 2000 (.JP2) format files. Associated with some of the DEM products is a list of lower-level MDIS products provided either as an accompanying table (.TAB) file or as text (.TXT) files.
Generally, the DEM products are derived from MESSENGER MDIS image data. The DEMs are typically derived using stereo photogrammetry (i.e. stereo pairs or sets) techniques. There are several institutions participating in the MESSENGER mission that each apply different techniques to derive their products. The U.S. Geological Survey (USGS) produces global Mercury DEM products and the German Aerospace Center (DLR) produces regional DEM products.
USGS Global (including Polar) DEM Products
The USGS global products are created using Narrow-angle camera (NAC) and Wide-angle camera (WAC) 750 nm filter G images, which constitute a subset of all the images acquired from March 18, 2001 (Mercury orbit insertion) to November 1, 2014. WAC images were typically used in the northern hemisphere and higher-resolution NAC images were selected in the southern hemisphere. In the equatorial region, both WAC and NAC observations were used. This strategy results in the collection of a more uniform set of images with comparable resolution.
Ultimately 100,432 (63,536 NAC and 36,896 WAC-G) images were utilized in the creation of the control network. The resulting point cloud from the control network was used to generate the USGS DEM through interpolation. USGS selected NAC and WAC-G images with a pixel resolution between 75 and 800 meters/pixel. Additional image selection considerations included images with incidence angles < 86° and emission angles < 65°. However, exceptions had to be made in some areas where these criteria created data gaps (e.g., poles). Images with high incidence angles, the angle between the Sun and the surface normal, produce shadows that make image registration difficult. Elevations in any shadowed areas, including the poles, are determined by interpolation.
MDIS USGS DEM products have the following file names:
MSGR_DEM_USG_pp_c_Vnn.xxx (with detached PDS labels for each product)
where:
MSGR = mission = MESSENGER
DEM = product type = Digital Elevation Model
USG = producer institution = U.S. Geological Survey
pp = projection
SC = Simply Cylindrical
NP = North Polar Stereographic
SP = South Polar Stereographic
00 = not applicable
c = product code
I = image format file
J = JPEG 2000 file
S = source product list file
C = point cloud file
nn = 2-digit version number
xxx = file extension
IMG = image format file
JP2 = JPEG 2000 file
TXT = free format text file
TAB = text table file
XML = USGS auxiliary (AUX) file with XML metadata useful for displaying JPEG2000 images with GDAL tools
NOTE: It may be necessary to rename these files to *.aux.xml when used with Geospacial Data Abstraction Library (GDAL)-based tools.
LBL = PDS label file
In ODE, USGS DEM products have the following product IDs:
MSGR_DEM_USG_PP_C_VNN
DLR Regional DEM Products
The DLR regional DEM product delivered to PDS covers the H06 Kuiper quadrangle (lat. -22.5 to 22.5 degrees, long. 288 to 360 degrees east). DLR selected ~9,850 images in total that have resolutions between 50 and 350 m/pixel and the “optimal” stereo conditions (see the table below). In total, about 7,300 images were used in creation of the DEM. This quadrangle is chosen because it contains the Hun Kal crater that is used as the cartographic reference point of longitude for Mercury’s coordinate system. The final product has a lateral spacing of 222 m/pixel (~192 pixels/degree) and a vertical accuracy of about 30 m. The DEM covers 5.87 million square kilometers of Mercury’s surface (about 7.8 percent of the surface). The topographic range of that area is about 9 km.
Characteristics of images used in DLR stereo coverage map:
|
Parameter |
Angles |
|
Differences in illumination |
0-10° |
|
Stereo angle |
15-45° |
|
Emission angle |
0-55° |
|
Incidence angle |
5-55° |
|
Phase angle |
5-180° |
MDIS DLR DEM products have the following file names:
MSGR_DEM_DLR_pp_Haa_mm_sss_c_Vnn.ext (with detached PDS labels for each product)
where:
MSGR = mission = MESSENGER
DEM = product type = Digital Elevation Model
DLR = producer institution = German Aerospace Center
pp = projection
EQ = equirectangular
LC = lambert conformal
SC = simple cylindrical
00 = not applicable
aa = the IAU-defined quadrangle number on planet Mercury 00-11
(See Greely, R. and R.M. Batson, Planetary Mapping, Cambridge University Press, 1990)
mm = product type
DM = primary 16-bit DEM product
sss = map scale in m/pixel truncated to the nearest integer, “000” if not applicable
c = product code
I = image format file
J = JPEG 2000 file
T = GeoTIFF format
P = PNG file (if available for EXTRAS directory)
nn = 2-digit version number
ext = file extension indicating file type
IMG = image file
JP2 = JPEG2000
TIF = TIFF files
PNG = PNG file
LBL = PDS label file
In ODE, DLR DEM products have the following product IDs:
MSGR_DEM_DLR_PP_HAA_DM_SSS_C_VNN