MESSENGER MDIS Digital Elevation Model

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 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 = source product list file

TAB = point cloud 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_EQ_H06_DM_222_c_Vnn.xxx (with detached PDS labels for each product)

where:

MSGR = mission = MESSENGER

DEM = product type = Digital Elevation Model

DLR = producer institution = German Aerospace Center

EQ = equirectangular

H06 = Kuiper quadrangle

DM = product type = primary 16-bit DEM product

222 = map scale in m/pixel truncated to the nearest integer

c = product code

I = image format file

J = JPEG 2000 file

P = PNG file

nn = 2-digit version number

xxx = file extension

IMG = image file

JP2 = JPEG2000

In ODE, DLR DEM products have the following product IDs:

MSGR_DEM_DLR_EQ_H06_DM_222_C_VNN