There are four possibilities of stereo
image processing for the DEM generation.
The combinations are Fore - Aft, Fore-
Nadir, Aft – Nadir and Fore-Aft-Nadir
images as a pair. Out of many cases, an
area in the south polar region acquired
on 15-11-2008 is given here as a sample
case for DEM generation. The region
is a part of the crater Moretus with
location -70.6 deg lat and -1.4 deg long.
The DEM generated for all the cases
are shown in figure-3. The three camera
triplet image (Fore-Aft-Nadir, figure-3e)
produced the best matching results with
100 % success in point matching while
nearly 87% success in pattern matching.
Due to the relatively large angles between
FORE and AFT the matching was poor,
which was shown as dark points in the
DEM (figure -3c). A colour coding of the
DEM is also shown in figure-3f, which
clearly show the height range of the crater
from -1500m to 4000 m with respect to
the mean radial surface of the moon.
A large strip of 1800 km (location:
Coulomb C crater) has been divided into
3 individual strips of 600 km and DEMs
have been derived for all three strips
separately. This break up is done to reduce
the processing time in DEM generation.
The DEMs and their visualisations
are shown in figures-5, 6 and 7.
Lunar Atlas [2, 3]
with TMC Data
The high level data products defined for
Chandrayaan-1 mission are the Lunar Atlas
and maps. The objective of Chnadrayaan-1
lunar atlas and map products are to prepare
maps for the entire surface (~37.8 Million
Sq. km) of moon and it’s visualisation.
Atlas will consist of Terrain Mapping
Camera (TMC) and Hyper Spectral (HySI)
orthoimage and Image mosaics, Digital
elevation model derived from TMC
triplets, Contributory themes from each
payloads and annotations. Lunar atlas will
be in softcopy while in the hardcopy form
it will be represented in map catalogue
form. Maps of earth’s surface have been
produced primarily by piecing together
large-scale sketches and diagrams since
centuries. Control networks were derived
through extensive and laborious ground
surveying. By the late nineteenth century,
regional maps were produced in this fashion
that was relatively accurate. With twentiethcentury
technology, the ability to obtain the
synoptic view has emerged. Photographs
taken from earth-orbiting satellites enabled
the rapid production of accurate maps.
When combined with well established
control networks, these maps have enabled
surface features on earth to be located
precisely. Planetary explorers, on the other
hand, have had the global perspective from
the beginning, and they have progressed
from global, through regional, to local
vantages. The naming of features is as
much a part of map making as is the
measuring and plotting of their locations.
Without names, communication of ideas is
impossible. The names applied by explorers
on earth often bear their provincial outlook.
Ambiguities abound; settles on different
parts of the same river often know the
river by different names. The tradition
that the privilege of naming belongs to the
discoverer resulted in hopeless ambiguities,
redundancies and inconsistencies. The
International Astronomical Union (IAU)
has therefore assumed control of the
naming process. It’s working groups are
composed of planetary scientists from
many nations. The main inputs for the
planned lunar atlas from Chandrayaan-
1 are the DEM and Orthoimages from
TMC and other associated layers from
the other payload data along with
annotations. The absolute accuracy of
the Lunar DEM in turn depends on the
basic control used in the modelling the
imaging geometry. As the initial results
show, it is possible to derive relatively
accurate DEMs from Chandrayaan-1
TMC imagery, which is the prime input
for DEM generation towards Lunar Atlas
preparation. Three CCD imagery in the
triplet form, when compared to stereo
pair leads to a good DEM in terms of
detail due to the better point and pattern
matching accuracies. The DEMs at
25 m grid interval depicts a very good
representation of the terrain, which can
be a prime input to the science analysis,
when used along with the other payload
data sets from Chandrayaan-1, in addition
to its usage in the 3D mapping of moon.
Figure-5: Orthoimage, DEM with
colour coding and Visualisation of Image
draped over DEM (Coulomb C Crater)
Figure-6: Part of Mare Orientale (a) Orthoimage (b) colour coded DEM (20 km x 65 km long) (c)
Contour Image
Reference:
1. A quest for moon, Narendra
Bhandari, Current Science, Vol.
83, No.4, 25 August 2002
2. Lunar Cartographic
Dossier Vol-1, Lawrence A.
Schimerman, NASA , 1973
3. Planetary Mapping, Ronald
Greeley and Raymond M. Batson;
Cambridge University Press 1991
4. Scientific Challenges of Chandrayaan-
1:The Indian Lunar polar orbiter
mission, Narendra Bhandari,
Vol. 86, No. 11, 10 June 2004
5. ISRO page: http://www.isro.gov.in
6. webgis.wr.usgs.gov/download/ClementineUVVIS/Mosaic
7. webgis.wr.usgs.gov/download/
ClementineUVVIS ULCN2005.warp
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