Remote Sensing: Definition, components and Types

1. Remote Sensing: Definition, components and Types Prince Mohan Assistant Professor, Dept. of Geography, GDC Theog-171201 e-mail. prince88hpu@gmail.com

2. Nomenclature The term “Remote Sensing," was firstly used by Ms. Evelyn Lord Pruitt of the U.S. Office of Naval Research, United States in the 1950s. The term ‘Remote Sensing’ is composed of two words which implies: • Remote – away from or at a distance • Sensing – detecting a property or characteristic Ms. Evelyn Lord Pruitt (1918-2000) Source: Downloaded from Google

3. Remote Sensing: Everyone do remote sensing in day to day life • Our Natural Remote Sensors: • Human beings have a multitude (5) of natural sensors. Of our five sensors, we use three as remote sensors when we • Watch a cricket match from the stadium (Eyes: utilizes light waves). • Hear a telephone ring (Ears: utilizes sound waves). • Smell freshly cooked curry in the oven (Nose: utilizeswind energy). • By virtue of these three remote sensors, we can acquire information about an object from a distance, without touching it. • Remaining two sensors i.e. Tongue and Skin are not used as remote sensors? • Try to feel the smoothness of a desktop (Skin: Sense of touch) • Eat a mango to check the sweetness (Tongue: Sense of taste) • In the last two cases, we are actually touching the object by our organs to collect the information about the object. Source: Downloaded from Google (Adapted from B. Bhatta, 2008)

4. Definition What is Remote Sensing? • If you are watching this Power Point Presentation, you are doing Remote Sensing. Infact, any information acquired from the object without touching is Remote Sensing. Following is a scientific definition of Remote Sensing. • Science and art of obtaining information about an object, area or phenomenon through an analysis of data acquired by a device that is not in direct contact with the area, object or phenomenon under investigation. Device may use reflected or emitted energy to obtain data. Lillesand, Thomas M. and Ralph W. Kiefer, “Remote Sensing and Image Interpretation” John Wiley and Sons, Inc, 1979, p. 1 Source: 2008 KoKoLwin

5. Contd… Components of Ideal RSS • A uniform energy source • This energy source provides energy: • Over all wavelengths (i.e. over the whole EMS). • At a constant, known, high level of output. • Irrespective of time and place. Source: Downloaded from Google

6. Contd… Components of Ideal RSS 2. A noninterfering atmosphere This would be an atmosphere that: • Does not modify energy in any manner. • Is transparent to all different forms (wavelengths) of energy. 3.Unique energy-matter interactions • Energy interacts with each feature of interest in a known, invariant, and unique manner. • Each feature can, thus, be identified / recognized from its unique energy-matter interaction. 4. A Supersensor This is a sensor that: • is highly sensitive to all wavelengths of EMS. • Yields spatially detailed data on the absolute brightness (or radiance) from the scene as a function of wavelength throughout the EMS. • Is simple and reliable. • Requires virtually no power or space. • Is accurate • Is easy to operate.

7. Components of Ideal RSS 5. Real-time data processing and supply system. • The radiance-versus-wavelength response would be transmitted to the ground receiving facility instantaneously. • The transmitted response would be instantaneously corrected geometrically and radiometrically as required. • Response is processed into a readily interpretable format. • Each element of the earth’s surface will be identified and this information will be provided to the users immediately (in a timely manner). 6. Multiple Data Users Data user community will be: • Having knowledge of great depth both of their respective disciplines and the RS data acquisition and analysis techniques. • Using the same RS data for different purposes. Various forms of information will be generated from the RS data. • Getting information faster, at less expense, and over larger areas of interest than any other source of information. • Making profound, wise decisions about how best to manage the earth’s resources under scrutiny. • These management decisions will be implemented with all the sincerity.

8. Contd… Types of Remote Sensing System RS systems can be classified on different bases which include: • Technology used. • Nature of source of energy. • Part or parts of EMS recorded. • Method of recording spectral response. • Spatial resolution (size of the smallest object decipherable). • Spectral resolution (smallest part of the EMS measured). • Temporal resolution (smallest part of time for which data are collected).

9. Contd… a. On the basis of Source of Energy Passive Remote Sensing Naturally available EME based Passive RS system (usually sun’s energy) reflected from the target is recorded by any technology). Ordinary camera photography done in sunlight is an example. Emitted energy-based Passive RS system (energy emitted by the target by virtue of its temperature is measured by any technology). IR photography (done on CD (camouflage detection) film or digitally) is an example Active Remote Sensing The RS device generates its own energy, throws it on the target, and measures the strength and other characteristics of reflected energy. Camera photography with flash is one example. RADAR that generates microwave energy and records reflected energy is another example. Source: Downloaded from Google

10. Contd… b. On the basis of the location of RS platform • Terrestrial or earth-bound RS Platform: a camera or a digital scanning device that is earth-bound. Images are similar to the views we are normally used to. • Aerial or air-borne RS platform: the RS device is off-ground or air-borne but is within the earth’s atmosphere. Views are ‘vertical’, ‘oblique’, or ‘horizontal’ (or ‘panoramic’) depending on the orientation of the optical axis of the instrument in relation to the horizontal earth’s surface. Source: Downloaded from Google • Space-based RS platform: the RS device is out of the earth’s atmosphere and in the outer space. Could be onboard a spacecraft (like Space Shuttle) or an earth-orbiting satellite (like IRS, INSAT etc.).

11. Contd… C. On the basis of part of EMS used • Panchromatic system (measures spectral response in the whole visible part of the EMS as a single band. Produces monochromatic / B&W / gray tone image. • Single band system (measures spectral response in any one well-defined band of EMS and produces monochromatic / B&W / gray tone image. • Multispectral RS system (measures spectral response in more than one (usually not more than 10) well-defined bands of EMS simultaneously. Single band images are monochromatic / B&W / gray tone images but can produce false colour composites (FCCs) using any three of the bands. • Hyperspectral RS system (measures spectral response in very large number (several hundreds) of well-defined narrow bands of the EMS. Single band images are monochromatic / B&W / gray tone images but can produce false colour composites (FCCs) using any three of the bands.

12. Contd… d. On the basis of method used (Technology) Primarily, distinction should be made between: • Photographic (analogue) system (uses chemical recording of spectral response), and • Digital system (uses electronic recording of spectral response). Clear distinction should also be made between: • Framing system (imaging the whole scene instantaneously) and • Scanning system (dividing the whole scene into pixels and measuring spectral response from each pixel). This can be done in many ways: - Pixel-by-pixel scanning system - Linear array scanningsystem - Area array scanning system - Cross-Track scanning system - Along-track scanning system - Circular scanning system - Side scanning system.

13. Contd… Framing System A framing system instantaneously acquires image of an area (or frame) on the terrain. Still camera photograph (whether film-based or digital CCD-based) is the most common example. Camera uses a lens to form an image of the scene at the focal plane, the plane at which the image is sharpest defined (this is the plane where either the photographic film or the area array of CCDs is located). The image might be analog or digital depending on the device. Vidiconis a special example of a framing system. Vidiconis a type of a television camera that records the image on a photosensitive electronically charged surface. An electron beam then sweeps the surface to detect the pattern of charge differences that constituted the image. This electron beam produces a signal that may be transmitted and recorded on magnetic tape (or other computer-compatible media) for eventual display on film / CRT.

14. Contd… Framing System Source: Downloaded from Google

15. Contd… Scanning Systems • A scanning system employs a single detector with a narrow ‘field of view’ which sweeps across the terrain to produce an image. When photons of EME radiated or reflected from the terrain encounter the detector, an electrical signal is produced that varies in proportion to the number of photons. The electrical signal is amplified, recorded on magnetic tape, and played back later to display an image. All scanning systems ‘sweep’ the ‘detector’s field of view’ across the terrain in a series of parallel scanlines.

16. Scanning Systems Analog Representation Digital Representation Source: Downloaded from Google