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Note for Remote Sensing and GIS - RSG By JNTU Heroes

  • Remote Sensing and GIS - RSG
  • Note
  • Jawaharlal Nehru Technological University Anantapur (JNTU) College of Engineering (CEP), Pulivendula, Pulivendula, Andhra Pradesh, India - JNTUACEP
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processing of the picture data… Remote Sensing then in the widest sense is concerned with detecting and recording electromagnetic radiation from the target areas in the field of view of the sensor instrument. This radiation may have originated directly from separate components of the target area, it may be solar energy reflected from them; or it may be reflections of energy transmitted to the target area from the sensor itself. According to American Society of Photogrammetry, Remote Sensing imagery is acquired with a sensor other than (or in addition to) a conventional camera through which a scene is recorded, such as electronic scanning, using radiations outside the normal visual range of the film and camera- microwave, radar, thermal, infra-red, ultraviolet, as well as multispectral, special techniques are applied to process and interpret remote sensing imagery for the purpose of producing conventional maps, thematic maps, resource surveys, etc. in the fields of agriculture, archaeology, forestry, geography, geology and others. According to the United Nations (95th Plenary meeting, 3rd December, 1986), Remote Sensing means sensing of earth’s surface from space by making use of the properties of electromagnetic wave emitted, reflected or diffracted by the sensed objects, for the purpose of improving natural resource management, land use and the protection of the environment. According to James B.Campell (1996), Remote Sensing is the practice of deriving information about the earth’s land and water surfaces using images acquired from an overhead perspective, using electromagnetic radiation in one or more regions of the electromagnetic spectrum, reflected or emitted from the earth’s surface. So the stages of Remote Sensing include (Fig.1): - A source of electromagnetic radiation or EMR (Sun) - Transmission of energy from the source to the surface of the earth, through atmosphere - Interaction of EMR with earth’s surface. - Transmission of energy from surface to Remote Sensor mounted on a platform, through atmosphere - Detection of energy by the sensor. - Transmission pf sensor data to ground station - Processing and analysis of the sensor data - Final data output for various types of application

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Detection of energy by sensors Source of EMR Sensor data output Transmission through atmosphere Transmission of sensor data to ground station Data processing and analysis Interaction of EMR with earth surface Fig.1: Stages of Remote Sensing History of Remote Sensing The knowledge about the history of Remote Sensing is necessary for better understanding of the subject and its scope, and also for future development, particularly for the welfare of human society. The development of remote sensing over time can be broadly divided into following six phases. Phase I (Up till 1920): Initial Phase Man always inquisitive about the things across a forest or a mountain, which he can not see directly. So, since time immemorial man has always tried to reach greater heights, such as tree tops, mountains etc. to observe phenomena of his interest on the earth surface, viz. to decide habitat places, farming and other day-to-day activities. This inquisitiveness to get a bird’s eye view prompted man to take photographs of earth from elevated platforms. So, the initial photographs of earth were captured from elevated platforms on the surface of the earth. However, the actual beginning of Remote Sensing can be traced back in 1958, when free balloons were used for photography by the French Gaspard Felix Tournachon (known as Nadar) to photograph the village of Petil Becetre near Paris. In 1860, a part of Boston and Massachusetts were photographed from a captive balloon at 1200 feet height in USA. In 1909,

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the first aerial photograph was taken from an aero plane, piloted by Wilbur Write over Centocelli, Italy. World War I provided a boost in the use of aerial photography. During that time, aerial photographs were used for two purposes – spying and mapping. Phase II (1920-1945): Development of Platforms and Sensors Improvement in aero planes, cameras, films etc. resulted in the development of aerial photography during this period. The proper planning of flight for photographic purpose was also started. Topographical mapping was the main thrust of the aerial photography. However, a number of scientists like geologists, botanists, soil scientists, geographers began interpreting the photographs to get information of their interest, especially for development of natural resources. During this period photographic coverage were increased both on the large and medium scale. World War II gave a real boost to photo interpretation technique, which was widely used for military intelligence purposes. The mapping of strategic location, military targets and assessments of damages could be done accurately. Phase III (1945-50): Development of Teaching and Training After World War II, much emphasis on teaching and training of this technique was given due to previous experience of its wide use in different spheres. Many courses on Remote Sensing were started in reputed universities of United States and Western European countries. A commission on the utilization of aerial photographs was set up by International Geographical Union (IGU) in 1949. The members of the commission emphasized the need of knowledge of those parts of world which were not earlier photographed and also attention was given to cover more area by aerial photographs and techniques essential for interpretation. Phase IV (1950-60): Development of Instruments for Interpretation In this phase, the techniques of photo interpretation became much more an applied technique. A number of instruments was developed and introduced for interpretation during this period, which may be termed as a landmark in the progress of these techniques. It opened a new horizon for accurate and fast analysis and also for monitoring the changes. Hence a considerable advanced

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interpretation was made in many disciplines such as Geography, Geology, Geophysics, Agriculture and Archaeology. Phase V (1960-1985): Significant Phase This phase is very significant in the history of Remote Sensing as artificial satellites were launched in the space for acquiring information of earth surface. Though two American satellites, i.e. Explorer I and II were launched in 1958 and 1959 respectively under Explorer and Discover Programme, they were not important from Remote Sensing point of view. On 1st April, 1960, one satellite of eight members of TIROS (Television and Infrared Observation Satellites) family was launched as a research and development project. As TIROS’s name suggested, the satellite carried two types of sensing devices – firstly, television, camera etc. which took picture of the visible spectrum; and secondly, infrared detectors which measured the non visible part of spectrum and provided information of local and regional temperature of earth’s surface. The supply of remotely sensed data of earth surface was greatly increased with the launching of ERTS-I (Earth Resources Technology Satellite) on 23rd July, 1972. It was placed in a sunsynchronous polar orbit about 600 miles above the earth surface. It makes 14 revolutions in a day around the earth and its sensors were covering a series 160 kms. wide strip. Then it was followed by ERTS-2 in 1975. With the launch of this satellite, the name of these satellites has been changed from ERTS-1, 2 to LANDSAT-1, 2 respectively. Four other satellites in these series were launched one after another in this phase, with improved cameras and sensors. Beside this, many other satellites were launched in the space by European and Asian Countries during this period. Phase VI (1985 onwards): Recent Development Phase In this period, Remote Sensing technique has been improved in two ways. Firstly, there have been developments of sensors which can use infrared and microwave spectrum other than visible spectrum to get information about earth’s surface. Secondly, there have been very important advances with respect to the platforms in which sensors are mounted. Besides, satellites have been launched for specific purposes and with specific capability. The ground resolution is continuously increasing till today. Hence, interpretation and mapping is becoming very easy, accurate and purposive. The European Radar satellite (ERS-I) launched in 1991 opened the

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