Post Graduation Diploma in Remote Sensing Technology and Geographic Information Systems

Technical Components of Remote Sensing 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. 6 The 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.