Chennai: ISRO used its latest remote sensing
satellite Resourcesat-2 along with other satellites in the
search mission to locate the crashed helicopter that carried
late Arunachal Pradesh Chief Minister Dorjee Khandu.
Resourcesat-2 was launched into space from Sathish Dhawan
Space Centre, Sriharikota, on April 20.
ISRO referred to the "rough mountainous Himalayan terrain
covered with thick forested area, simultaneous persistent
cloudy conditions and incessant bad weather" for its limited
use of optical remote sensing data in locating the ill-fated
chopper.
Though the space agency used microwave remote sensing
data, "which can penetrate clouds and quickly image large
areas in all weather conditions" to locate the missing
helicopter, the target size in this case was expected to be of
2-3 metres only, thus requiring data of 1m spatial resolution,
an ISRO release said.
"Since microwave sensors are side looking, the grazing
angle and slope produce layovers, foreshortening and shadow
effects causing distortions in hilly terrain hampering the
interpretation and microwave data of short wavelength (X, C
bands) do not penetrate dense vegetation," the release said.
Despite the complexities associated with microwave data
especially in the mountainous regions, efforts were made to
identify objects with "bright signatures", it said.
Based on decision criteria, probable locations for search
operations were identified and communicated to Arunachal
Pradesh government.
Detailed base information like roads and drainage
network, spot heights and settlement areas along with a
virtual media clip showing the terrain conditions were also
provided to the ground team.
National Remote Sensing Centre (NRSC) of ISRO provided
the Arunachal Pradesh government with high resolution
satellite images acquired from its satellites -- Resouresat-1
and 2, RISAT-2, Cartosat and foreign satellite (Radarsat-2)
missions prior to and after the incident, it added.
The B3 single-engine four-seater helicopter with Khandu
and four others went missing after taking off from the Tawang
helipad on Saturday last and crashed in the mountains.
The bodies and the wreckage of the chopper were located
after a five-day search at Kyela, situated at an altitude of
4,500 metres, on May 4 in Tawang district.
PTI
First Published: Saturday, May 07, 2011, 18:37