Application Of Remote sensing, Remote Sensing Part 2, type of Remote Sensing platforms

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 a tripod (for field observation) and stationary
balloons or mobile like aircrafts and spacecrafts. 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. Cherry arm
configuration of Remote Sensing van and tripod are the two commonly used ground borne
platforms. They have the capability of viewing the object from different angles and are
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 of shapes, 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 these make extremely
difficult to predict whether the balloons will fly over the specific area of interest or not.
6The Association for Geographical Studies
In India, at present, Tata Institute of Fundamental Research, Mumbai, has set up a
National balloon facility at Hyderabad. Teethered balloons are connected to the earth
station by means of wires having high tensional strength and high flexibility. The
teethered line can carry the antenna, power lines and gas tubes etc. when wind velocity
is less than 35 km. per hour at 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
programmes. Powered balloons require some means of propulsion to maintain or
achieve station over a designated geographic location. These can be remotely
controlled and guided along with a path 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 as follows:
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: Ceiling height is 21 km. (for strategic photographic). Minimum speed is 798
km./hr.
ROCKELL X-15 (Research Craft): Ceiling height is 108 km. and speed is 6620 km./hr.
The advantages of using aircrafts as remote sensing platform are : high resolution
of data recorded, possibility of carrying large pay loads, capability of imaging large
area economically, accessibility of remote areas, convenience of selecting different
scales, adequate control at all time etc. However, due to limitations of operating
altitudes and range, the aircraft finds its greatest applications in local or regional
programme rather than measurements on global scale. Besides all these, aircrafts have
been playing an important role in the development of space borne remote sensing
7The Association for Geographical Studies
techniques. Testing of sensors and various systems and sub systems 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. These platforms 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 these space borne platforms, we get enormous amount
of remote sensing data and as a result Remote Sensing has gained international popularity.

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