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Mars Global Surveyor: MOLA MEGDRs

April 19, 2007. New polar planetary radius maps now accompany the polar topography maps in this data set.

Mission Experiment Gridded Data Records

The MOLA Mission Experiment Gridded Data Records (MEGDRs) are global topographic maps of Mars created by binning altimetry values from the MOLA PEDR products acquired over the entire MGS mission. MEGDRs have been produced at resolutions of 4, 16, 32, 64, and 128 pixels per degree. (Polar maps are in resolutions of 128, 256, and 512 pixels per degree.)

The final version of the MEGDRs was released May 7, 2003. These products supersede all earlier releases of MEGDR and IEGDR  (Initial Experiment Gridded Data Record) products. A MEGDR file may be identified as a final version by these keywords in its PDS label:  PRODUCT_VERSION_ID = "2.0" and PRODUCT_CREATION_TIME = 2003-03-21 or later.

A MEGDR product consists of a set of three or four maps:

  1. The planetary radius as recorded by the MOLA instrument

  2. The areoid, a model for an equipotential surface of Mars, analogous to "sea level" on Earth (this map is omitted for the 32, 64 and 128 pixel/degree and polar MEGDRs)

  3. The topography computed as the difference between the planetary radius and the areoid

  4. Counts (number of observations) per cell in the map

MEGDR Data Online

Use the links below for direct access to any part of the MOLA MEGDR archive. Or follow this link for FTP access to this data set. (FTP users, read our FTP instructions first.)

AAREADME.TXT Introduction to the archive
ERRATA.TXT Notes and errata for the archive
INDEX directory An index to all MEGDR products
DOCUMENT directory The MEGDR Software Interface Specification document
CATALOG directory PDS catalog information, including descriptions of the data set and instrument, and references
MEG004 directory MEGDR data and labels, 4 pixels per degree
MEG016 directory MEGDR data and labels, 16 pixels per degree
MEG032 directory MEGDR data and labels, 32 pixels per degree
MEG064 directory MEGDR data and labels, 64 pixels per degree
MEG128 directory MEGDR data and labels, 128 pixels per degree
POLAR directory MEGDR data and labels, north and south poles, 128, 256, and 512 pixels per degree

Online Tools

Mars Orbital Data Explorer - Provides search, display, and download  tools for this data set.

MEGDR File Naming and Organization (for polar files, skip to here)

MEGDR data files are named according to the scheme MEGkxxdyyyrv.IMG, where:
k = A for areoid, C for counts, R for radius, T for topography
xx = latitude of pixel in upper left corner of the image
d = N for north latitude, S for south
yyy = longitude of the pixel in the upper left corner of the image (0-360 east)
r = map resolution in pixels per degree, e.g.
C = 4 pix/deg
E = 16 pix/deg
F = 32 pix/deg
G = 64 pix/deg
H = 128 pix/deg
v = version letter.

The 4, 16, and 32 pixel/degree MEGDR maps are stored as images in single files, one file for each of the planetary radius, areoid, topography, and counts maps. Each file is accompanied by a PDS label in a separate file with the same name, extension ".LBL". The label is a text file that describes the content and format of the map.

MEGDR Image Files and Labels at 4, 16, and 32 Pixels Per Degree

Directory File Name Map Type Area Covered Resolution
(pixels/degree)
meg004 mega90n000cb.img,
mega90n000cb.lbl
areoid 90N to 90S latitude

0E to 360E longitude

4
megc90n000cb.img,
megc90n000cb.lbl
counts
megr90n000cb.img,
megr90n000cb.lbl
radius
megt90n000cb.img,
megt90n000cb.lbl
topography
meg016 mega90n000eb.img,
mega90n000eb.lbl
areoid 90N to 90S latitude

0E to 360E longitude

16
megc90n000eb.img,
megc90n000eb.lbl
counts
megr90n000eb.img,
megr90n000eb.lbl
radius
megt90n000eb.img,
megt90n000eb.lbl
topography
meg032 megc90n000fb.img,
megc90n000fb.lbl
counts 90N to 90S latitude

0E to 360E longitude

32
megr90n000fb.img,
megr90n000fb.lbl
radius
megt90n000fb.img,
megt90n000fb.lbl
topography

 

The 64 and 128 pixel/degree MEGDR maps are so large that they are broken into smaller files called tiles for easier handling. Each file is accompanied by a PDS label.

MEGDR Tiling Schemes at 64 and 128 Pixels Per Degree

90                
                 
0                
-90                
  0     180     360
MEGDR tiles, 64 pixel/degree map
88                
44                
0                
-44                
-88 0 90 180 270 360
MEGDR tiles, 128 pixel/degree map

MEGDR Tiled Image Files and Labels at 64 Pixels Per Degree

 

MEGDR Tiled Image Files and Labels at 128 Pixels Per Degree

Area Covered 88N to 44N lat,
0E to 90E lon
88N to 44N lat,
90E to 180E lon
88N to 44N lat,
180E to 270E lon
88N to 44N lat,
270E to 360E lon
Counts megc88n000hb.img,
megc88n000hb.lbl
megc88n090hb.img,
megc88n090hb.lbl
megc88n180hb.img,
megc88n180hb.lbl
megc88n270hb.img,
megc88n270hb.lbl
Radius megr88n000hb.img,
megr88n000hb.lbl
megr88n090hb.img,
megr88n090hb.lbl
megr88n180hb.img,
megr88n180hb.lbl
megr88n270hb.img,
megr88n270hb.lbl
Topography megt88n000hb.img,
megt88n000hb.lbl
megt88n090hb.img,
megt88n090hb.lbl
megt88n180hb.img,
megt88n180hb.lbl
megt88n270hb.img,
megt88n270hb.lbl
Area Covered 44N to 0 lat,
0E to 90E lon
44N to 0 lat,
90E to 180E lon
44N to 0 lat,
180E to 270E lon
44N to 0 lat,
270E to 360E lon
Counts megc44n000hb.img,
megc44n000hb.lbl
megc44n090hb.img,
megc44n090hb.lbl
megc44n180hb.img,
megc44n180hb.lbl
megc44n270hb.img,
megc44n270hb.lbl
Radius megr44n000hb.img,
megr44n000hb.lbl
megr44n090hb.img,
megr44n090hb.lbl
megr44n180hb.img,
megr44n180hb.lbl
megr44n270hb.img,
megr44n270hb.lbl
Topography megt44n000hb.img,
megt44n000hb.lbl
megt44n090hb.img,
megt44n090hb.lbl
megt44n180hb.img,
megt44n180hb.lbl
megt44n270hb.img,
megt44n270hb.lbl
Area Covered 0 to 44S lat,
0E to 90E lon
0 to 44S lat,
90E to 180E lon
0 to 44S lat,
180E to 270E lon
0 to 44S lat,
270E to 360E lon
Counts megc00n000hb.img,
megc00n000hb.lbl
megc00n090hb.img,
megc00n090hb.lbl
megc00n180hb.img,
megc00n180hb.lbl
megc00n270hb.img,
megc00n270hb.lbl
Radius megr00n000hb.img,
megr00n000hb.lbl
megr00n090hb.img,
megr00n090hb.lbl
megr00n180hb.img,
megr00n180hb.lbl
megr00n270hb.img,
megr00n270hb.lbl
Topography megt00n000hb.img,
megt00n000hb.lbl
megt00n090hb.img,
megt00n090hb.lbl
megt00n180hb.img,
megt00n180hb.lbl
megt00n270hb.img,
megt00n270hb.lbl
Area Covered 44S to 88S lat,
0E to 90E lon
44S to 88S lat,
90E to 180E lon
44S to 88S lat,
180E to 270E lon
44S to 88S lat,
270E to 360E lon
Counts megc44s000hb.img,
megc44s000hb.lbl
megc44s090hb.img,
megc44s090hb.lbl
megc44s180hb.img,
megc44s180hb.lbl
megc44s270hb.img,
megc44s270hb.lbl
Radius megr44s000hb.img,
megr44s000hb.lbl
megr44s090hb.img,
megr44s090hb.lbl
megr44s180hb.img,
megr44s180hb.lbl
megr44s270hb.img,
megr44s270hb.lbl
Topography megt44s000hb.img,
megt44s000hb.lbl
megt44s090hb.img,
megt44s090hb.lbl
megt44s180hb.img,
megt44s180hb.lbl
megt44s270hb.img,
megt44s270hb.lbl

 

North and South Polar Map File Names

North and south polar maps have names in the form MEGk_p_rrr_v.IMG, where

k = "T" for topography, "R" for radius, or "C" for counts
p = "N" for north pole or "S" for south pole
rrr = resolution in pixels per degree (128, 256, or 512)
v = product version.

Polar images are square, with the pole at the center, lines of latitude in concentric circles around the pole, and lines of longitude radiating from the pole.  In the north pole image, Longitude 0 extends straight down from the center and Longitude 90 East extends to the right. In the south pole image, Longitude 0 extends straight up from the center, and Longitude 90 East extends to the right. For map projection details, see the map projection information in the image labels and the file DSMAP_POLAR.CAT.

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