TYPES
OF PLATFORMS
The base, on which remote sensors are placed to acquire
information about the Earth's surface, is called platform. Platforms can be
stationary like atripod (for field observation) and stationary balloons or mobile
like aircrafts and spacecraft's. The types of platforms depend upon the needs
as well as constraints of the observation mission.
There are three main types of platforms, namely 1)
Ground borne, 2) Air borne and 3) Space borne.
1.GROUND BORNE PLATFORMS:
These platforms are used on the surface of the Earth.
Cherryarm configuration of Remote Sensing van and tripod are the two commonly
used ground borne platforms.
Theyhavethecapabilityofviewingtheobjectfromdifferentanglesandare
mainly used for collecting the ground truth or for laboratory simulation
studies.
2.AIR BORNE PLATFORMS:
These platforms are placed within the atmosphere of the
Earth and can be further classified into balloons and aircrafts.
a.
Balloons:
Balloons as platforms are not very expensive like aircrafts. They have a great variety o f s h a p
e s , sizes and performance capabilities. The balloons have low acceleration, require
no power and exhibit low vibrations. There are three main types of balloon systems,
viz. free balloons, Tethered balloons and Powered Balloons. Free balloons
can reach almost the top of the atmosphere; hence they can provide a platform
at intermediate altitude between those of aircraft and space craft.
Thousands
of kilograms of scientific payloads can be lifted by free balloons. Unless a
mobile launching system is developed, the flights can be carried out only from a fixed launching station. The free balloons are dependent on meteorological conditions, particularly winds. The
flight trajectory cannot be
controlled. All the semake
extremely difficult to predict whether
the balloon swill fly over the specific area of interest or not.
In
India, at present, Tata Institute of
Fundamental Research, Mumbai,
hassetupa National balloon facility at Hyderabad. Teethered balloon sare
connected to the earth station by means
of wire shaving hight ensional strength and high flexibility.
The
teethered line can carry the antenna, power lines and gas tubes etc.
when wind velocity is less than 35km.
perhourat the altitude of 3000m., sphere type balloon is used. When the
wind velocity is less than 30 km
per hour, natural shape balloons are restricted to be placed. Tethered balloons
have the capability of keeping the equipment at a fixed position for a long
time and thus, useful for many remote sensing programmers.Powered balloons
require some means of propulsion to maintain or achieve station over
adesignated geographic location. These can be remotely controlled and guided along with apath or fly
above a given area within certain limitations.
b.
Aircrafts: Aircrafts are commonly used as remote-sensing for obtaining Aerial
Photographs. In India, four types of aircrafts are being used for remote
sensing operations.These are asfollows:
DAKOTA:
The ceiling height is 5.6 to 6.2 km and minimum speed is 240 km./hr.
AVRO: Ceiling height is 7.5 km and minimum speed is
600 km./hr. CESSNA: Ceiling height is 9 km. and minimum speed is 350 km./hr.
CANBERRA: Ceiling height is 40 km. and minimum speed is 560 km./hr.
The following special aircrafts are being used in
abroad for remote sensing operations in high altitude photography.
U-2:Ceilingheightis21km.(for strategic photographic).Minimum
speedis798 km./hr.
ROCKELL X-15 (Research Craft): Ceiling height is 108
km. and speed is 6620 km./hr.
The advantages of using aircraft sasremotesensing platform
are : high resolution of data recorded, possibility of carrying large payloads,
capability of imaging large area economically, accessibility of remote areas, convenience
of selecting different scales, adequate controlatalltime etc. However, due to limitations
of operating altitudes and range, the aircraft find s its great est application
sinlocalor regional programmeratherthan measurements on global scale. Beside sallthese,
aircrafts have been playing an important role in the development of space borne
remote sensing Techniques. Testing of sensors and various systems and subsystems
involved in space borne remote sensing programme is always undertaken in a
well-equipped aircraft.
3.SPACE BORNE PLATFORMS:
Platforms in space, i.e.satellites are not affected by
the earth's atmosphere. The seplatforms move freely in their orbits around the earth.
The entire earth or any part of the earth can be covered at specified
intervals. The coverage mainly depends on the orbit of the satellite. It is through
the sespaceborne platforms, wegetenormous amount of remote sensing data and asaresult
Remote Sensing has gained international popularity. According to the orbital mode,
there are two types of satellites- Geostationary or Earth synchronous and
sun-synchronous.
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