Rivix.com: MOLA DEMs

MOLA (Mars Orbiter Laser Altimeter)

Description

The Mars Orbiter Laser Altimeter (MOLA) is an instrument that orbitted around Mars on the Mars Global Surveyor (MGS) spacecraft between 1999 and 2001. MOLA collected high-resolution topographic data for Mars by transmitting infrared laser pulses toward the red planet at a rate of 10 Hz and accurately measuring the return time. MOLA was designed and built by the Laser Remote Sensing Branch of the Laboratory for Terrestrial Physics at Goddard Space Flight Center (GSFC/NASA).

As the MGS spacecraft circled Mars, it created DEMs of increasingly higher resolution. DEMs for the entire planet with grid spacings of 1/4, 1/8, 1/16, 1/32, 1/64, and 1/128 degree were produced and are available. NASA released a set of gridded elevation products with these grid spacings called MEGDRs (Mission Experiment Gridded Data Records). The final and highest-resolution MEGDR was released in 2003, but new DEM products based on the same raw data are still being developed (e.g. see the HiRISE project).

Mars has many dramatic topographic features, including (1) huge impact craters in the southern hemisphere, such as Hellas (9 km deep, 2100 km across), deep enough to hold Mount Everest, (2) a "super canyon" system, Valles Marineris (10 km deep, 5000 km long), that would span the US, (3) many large volcanoes, including Olympus Mons (26 km), three times taller than Mount Everest (8.8 km) and (4) erosional features that appear to be due to massive surface water fluxes.

Grid Information

Coord. System:	Geographic/Areographic decimal degrees, fixed-angle
Cell Size:	900 arcseconds (1/4 degree) 450 arcseconds (1/8 degree) 225 arcseconds (1/16 degree, 3.7 km at equator) 112.5 arcseconds (1/32 degree) 56.25 arcseconds (1/64 degree) 28.125 arcseconds (1/128 degree, < 0.5 km at equator)
Data Set Dimensions:	1440 columns x 720 rows 2880 columns x 1440 rows 5760 columns x 2880 rows 11520 columns x 5760 rows 23040 columns x 11520 rows 46080 columns x 23040 rows
Data Set Span:	360 degrees (-180 to 180) x 174 degrees (-87 to 87)
Data Type:	2-byte integer, signed (MSB)
Horizontal Datum:	Spherical planet model, radius = 3396.0 km, "areocentric"
Vertical Datum:	Spherical planet model, radius = 3396.0 km, "areocentric"
Vertical Units:	meters
Nodata Value:	Unknown
Formats:	MEGDR = Flat binary file (row major, no header), MSB with extension ".IMG". Georef. info. in separate ASCII file with extension ".LBL". (PDS3)

How to Import

Choose Import DEM → MOLA DEM for Mars from the File menu and then select the file, which should have the filename extension "*.img". Go to the File → Set Preferences, Planet Info panel and set the planet to Mars. Otherwise calculations of lengths, areas, slopes, etc. will be incorrect.

Data Source

Goddard Space Flight Center (GSFC) of NASA.

Data Availability

MEGDR gridded elevation data with many different grid spacings can be downloaded from the MGS MOLA web site listed below. Other DEMs derived from the same raw data are also available, such as those from the UW MOLA link below and HiRISE project. For more information, see:

Som S., Greenberg H. and Montgomery D. (2007) Limitations of the Mars Orbiter Laser Altimeter Dataset: Implications and Improvements, Intl. J. of Mars Science and Exploration.

Web Sites

MGS Home: http://pds-geosciences.wustl.edu/missions/mgs/

MGS MOLA Home: http://pds-geosciences.wustl.edu/missions/mgs/megdr.html

UW MOLA DEM Downloads: http://gis.ess.washington.edu/uwmola/index.html