Full text: Remote sensing for resources development and environmental management (Vol. 2)

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 » 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

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