MESSENGER MDIS Narrow-angle Digital Elevation Model (DEMNAC)

DEM – MDIS Digital Elevation Model

Instrument: MESSENGER Mercury Dual Imaging System

PDS Data Set ID: MESS-H-MDIS-5-DEM-ELEVATION-V1.0DOI: 10.17189/1520282

For direct access to the IMG files, go here.

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).

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. Currently, DEMs generated only using Narrow-angle camera (NAC) images are only produced by Arizona State University.

These products are regional DEMs that highlight certain features on Mercury’s surface. These products are provided in equirectangular projection with positive east longitudes. Longitude and resolution ranges vary by product. Regional DEM products are created by aggregating individual DEM pairs into a single DEM product. Image selection is described below.

Images for DEMs are selected using a two-step process. First, images with acceptable illumination conditions, such as incidence, emission, and phase angles as well as image resolution are identified according to criteria defined in Becker et al, 2015. Next, acceptable stereo overlap is determined by considering resolution ratios, strength of stereo (parallax/height ratio), illumination compatibility, and percentage of stereo overlap.

The figure below indicates the stereo image criteria used for ASU regional DEMs. Red indicates values that are unacceptable, yellow indicates values that are marginally acceptable and may be used, and green indicates acceptable values that produce good stereo pairs.

The primary PDS product is a DEM provided in both PDS image (.IMG) and JPEG 200 (.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.

MDIS DEM NAC-only products have the following file names:

MSGR_DEM_ASU_EQ_aaaaabb_mm_ss_c_Vnn.xxx (with one detached PDS label for each set of files)

where:

MSGR = spacecraft = MESSENGER

DEM = product type = Digital Elevation Model

ASU = producer institution = Arizona State University

EQ = projection = equirectangular

aaaaa = designation of the site name that the DEM covers

bb = designation of the stereo pair

<nn> = a uniquely number integer stereo pair for the site

MS = mosaic of the site containing all the stereo pairs

mm = product type

DM = primary 16-bit DEM product

CF = confidence map

OR = 16-bit orthorectified image

ss = map scale in m/pixel truncated to the nearest integer, 00 if not applicable

c = product code

I = image format file

T = GEOTIFF file

S = source product list file

nn = 2-digit version number

ext = file type

IMG = PDS image format

TXT = ancillary free format text file

TIF = TIFF files

In ODE, DEMNAC products have the following product IDs:

MSGR_DEM_ASU_EQ_AAAAABB_MM_SS_I_VNN