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Remote sensing for resources development and environmental management
Damen, M. C. J.

Figure 2. Terrestrial stereo-pair of left abutment of Supa Dam, a - excavated weathered basic dyke, x-x'
fold axis, b - shear zone.
200m deep gorge section of Kali river at Supa,
Karnataka. The left abutment of the Dam formed
an escarpment in the upper portion (Fig.2). Being
inaccessible it could not be mapped by conventional
methods. Utilizing terrestrial photogrammetric
technique maps of the area could easily be prepared
on 1:500 scale with a contour interval of 5 m.
Various significant geological details that could
be mapped out included weathered basic dykes, promi
nent shear zones and joint planes, traces of bedd
ing, faults and joints, and attitude of planar
surfaces. Folding pattern of the rocks was well
deciphered by correlating precise levels of the
fold axes on the left and the right abutment areas
(Agarwal 1985). Thus terrestrial photogrammetry
not only made it possible to accurately map an
inaccessible zone but also helped in the expeditious
completion of the geological exploration.
3.2 Geo-environmental study of Coconut island
Coconut Island off the west coast of India in the
Arabian sea, has been declared as a 'National Geolo
gical Monument' for preservation of its natural
exposures of columnar lava. The Island exhibits
highly irregular topographic features marked by
conspicuous scarps. This coupled with the remoteness
and accessibility constraints rendered accurate
mapping of the island through conventional methods
a tedious preposition. In this case also, terres
trial photogrammetric technique was applied to
map an important portion of the island on 1:500
scale with a contour interval of one metre. The
area was mapped with the help of three stereo-pairs
taken from three sides of the island. Apart from
topographic map, a geo-environmental map of the
area was also prepares simultaneously. Various
geo-environmental features recognised include wave
cut platform, dissected marine terraces, scarps,
sea side cliffs, gently sloping surface, stacks,
master joints, sandy and shingle beaches, bushes
and tree covered areas (Agarwal & Srivastava 1982)
The island exhibits a conspicuous erosional regi
me. A comprehensive geo-environmental evaluation
of the area could easily be brought out with the
help of the stereo-pairs.
3.3 Glacier mapping
Under International Hydrological Programme, a long
term ยป detailed glaciological study was initiated
on a glacier in NW Himalayas. The existing large
scale map of the glacier was on 1:50,000 scale
An accurate, large scale topographic base map
of the glacier was required for the project. It
was rather impossible to prepare the same through
the conventional plane table or theodolite survey,
mainly on account of following :
i) inaccessibility of many portions of the glacier,
especially the upper reaches,
ii) large survey time required, during which period
the glacier surface would have modified due to
ablation and glacier movements, and
iii) rugged and dissected nature of lower portion
of the glacier requiring considerable interpolation
and consequent generalisation.
Taking recourse to terrestrial photogrammetric
technique an accurate large scale topograpnic map
of the glacier could easily be prepared on 1:5000
scale with a contour interval of 10m. Five stereo-
-pairs taken from vantage points selected around
the lower portion of the glacier were used for
the purpose. A photo-interpreted glaciological
map was also prepared simultaneously showing mora
ine ridges, bergschrund, transient snowline, supra-
glacial channels, ice faces, crerasses and ice falls.
Results have clearly brought out that terrestrial
photogrammetry is the most appropriate technique
for glacier mapping.
3.4 Nilgiris landslide investigation
Nilgiris district of Tamil Nadu was ravaged by
numerous landslides on an unprecedented scale,
causing considerable damage to life and property,
following heavy rains during the winter monsoon
of 1978-79. This necessitated a quick appraisal
of the affected areas. As the conventional survey
technique is a time consuming process, terrestrial
photogrammetry was resorted, initially to map four
important landslides in the area. The maps were
prepared on 1:500 or 1:2000 scale with contour