Unit-I

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Unit – I REMOTE SENSING
Basic principles of Remote Sensing: Remote Sensing usually refers to the gathering and processing of information about the earth’s environment. It is natural and cultural resources with photos and related data acquired from aircraft or satellite. 1) Aircraft remote sensing (platform is aircraft): This type of science is known as photogrammetry.
2) Satellite remote sensing (platform is satellite):

Satellite remote sensing refers to the science of taking pictures or the reflectance data of the objects on the earth’s surface and its interpretation to identify the objects.


Satellite is a celestial object moving around the earth. First satellite launched into the space by USA in the year 1972 (ERTS – I). This is used for natural resources mapping. It is also known as Landsat – I.


Satellites lunched are basically two types:
1. Geostationary satellites:

The geostationary satellites revolve around their orbit in a period equal to the period of earth and hence stay on a place static with respective earth. Indian geostationary satellites are: INSAT – 1A INSAT - 1B These satellites at a distance of 35,000 kilometers from the earth’s surface, used for telecommunications, metrological studies.
2. Polar satellites or sun synchronous satellites:

These satellites moves around the earth in a time of hundred minutes, they move in an orbit inclined from east to west such that the time gap between two places is spent in traversing the distance between the places.

• •

900 kilometers from the earth’s surface Used for disaster management, resource assessments and thematic mapping.

Eg. Indian polar satellites are: IRS – 1A, IRS – 1B, IRS – 1C, IRS – P2, IRS – P3 etc., History of remote sensing in India: The Indian space research was organized by Indira Gandhi in 1972 by Department of Space (DOS). It has following centers: 1. ISRO (Indian Space Research Organization), 2. NRSC (National Remote Sensing Centre) 3. IIRS (Indian Institute of Remote Sensing) Some of satellites: Aryabatta 1 in 975 with USSR, Bhaskara – 1 in 1979, Bhaskara – 2 in 1981, Apple (Ariane Passenger Pay Load Experiment) in 1981, SLV – 3 (Rohini series). INSAT is the first operational space system for telecommunications, radio and T.V. broadcast. INSAT – 1D in the year 1990 - still in operation. INSAT – 2E, which is under fabrication. Electro Magnetic Radiation (EMR): The objectives of remote sensing are accomplished by measuring EMR emitted or reflected by the surface of the earth. The complete process of remote sensing data acquisition are by transfer of energy as follows: 1. A source of EMR is either Sun or active emission source like Radar. 2. Transmission of the energy from source to the surface of the earth, which are to be detected by the sensors. 3. Interaction of EMR with the earth surface through reflection and reemission. 4. Transmission of energy from surface to the remote sensor, which is the device that records the reflected energy. 5. Sensor data output 6. Transmission of data to earth for processing and analysis 7. The EMR received by the sensor symbolizes the object from which it is reflected and this is the basic principle of object identification and mapping through remote sensing. Fig.:

Physics of remote sensing: The sun is the main source of the energy for the solar system. Energy from Sun propagates in the form of electromagnetic waves. The various types of waves are grouped in to following bands of energy: Rays Cosmic rays Gama rays ‘X’ rays Ultra violet rays Visible rays Infra red rays Micro waves Radio waves λ (Wave length) <10-13mts 10-13 - 10-10 mts 10-10 - 10-8 mts 0.01 - 0.4 micro mts. 0.40 - 0.76 micro mts. 0.8 mm - 1 mm. 1 mm - 1 mt. > 1 mt.

It is only the optical wavelength region consisting of visible, near the infrared and middle infrared bands ranging from 0.3 micro mts. to 16 micro mts. In wavelength, that are used by various remote sensing sensors. When radiation from sun is instant, the greater part is reflected by the surface, a part is absorbed by the surface, and the balance is transmitted, when the EMR pass from sun or other sources to the objects a number of changes take place in magnitude, direction, wavelength and polarization etc. These changes are detected by the remote sensors and enable the analyst to obtain useful information about the object and intercept the remote sensing data contains both special information i.e. signs, shape, orientation, spectral information, tone, color and spectral signatures. Radiant Energy (Q): It is the energy carried by electromagnetic radiation. Radiant energy causes detector element of the sensor to respond to EMR appropriate time. Radiant flux (Ф): It is rate of flow of radiant energy. (Ф) = ∆Q/∆t joules/sec. Irradiance (E): It is the radiant flux intercepted by a plane surface per unit area of the surface. E = Ф/A w/m2

Fig.:

Emitance (M): It is the radiant flux leading a surface per unit area of the surface. M = E = Ф/A w/m2 Fig.:

Solid Angle (W): It is the cone angle subtended by the portion of a spherical surface at the center of the sphere. Fig.:

Spectral signature: Spectral signature of the objects refers to the reflections of the various bands of the wavelengths from the objects, which is received by the sensors from the identification of the objects. As the thumb impressions of two persons do not tallies, similarly the spectrum signature of two objects do not talley and this is the basic principle of remote sensing based object identification. Fig.:

Spectrum signatures are basically the criteria for object identification. Interaction of EMR with Earth surface: The most crucial part electromagnetic spectrum is the optical wavelength between 0.3 µm to 16 µm, which is subdivided in to three layers: 1. Reflective median 0.3 µm to 3 µm – radiation received by the sensor in this band is due to the solar energy reflected by the Earth surface. 2. Thermal infrared (8 µm to 14 µm) the energy available in this band for remote sensing is due to the thermal remittance from the Earth surface. 3. Micro wave (3 µm to 5.5 µm) It is important for both reflection and self-emission, the microwave remote sensing system depends on active data (or) passive data.

The active radar sensor provides its own source of EMR. The passive radar system uses the radiation emitted by the terrain in the microwave terrain, which is recorded by the microwave radiometer. The intensity of electromagnetic wave reflected from the substance depends on many features such as: a) Reflecting properties of the media b) Surface roughness of objects c) Wave length of EMR under consideration d) Angle of incidence e) Polarization of EMR caused in the interaction Reflection from an ideal specular object: The smoothness or roughness objects on Earth’s surface decide the reflections whether it shall be specular or defuse. Types of remote sensing: Remote sensing can be divided in to following two major groups: 1. Arial photo graphy 2. Satellite remote sensing Arial photography Satellite remote sensing 1 It gives photos of Earth features The satellite used data from the from a few kilometers and gives longer distance, so does not contain more details. The platform is clear information as Arial Aeroplane. photography particularly in respect of the height of the terrain. The platform is space borne. 2 Not repetitive unless the aircraft is The major advantage of satellite flow again. data is the capability of getting the information once in a few days or few weeks. 3 More costly and time taking. Satellite products are cheap and easily available. 4 Used for large scale maps Used for small scale maps 1 in 2,500; 1 in 5,000 1:25,000; 1:50,000 5 Acquisition of aerial photos Defense clearance not required. required defense clearance. 6 It is extensively used for Not used to that extent. preparation and update of topographic maps of Survey of India by use of digital stereo plotters. Platforms and sensors: Platform: Platform is referred to a stage which mountains the camera or sensor.

There are three types of platforms: 1. Ground based platform 2. Air borne platform (used for aerial photography) 3. Space borne platform (satellites) existing geo stationary or sun synchronous satellites. Sensors: sensors are the devices, which gather energy and convert it to a signal and present it in a form suitable for obtained information about the target under investigation. There are two types of sensors: 1. Passive sensor: source of energy is emitted by sun. 2. Active sensor: source of energy is emitted by sensor itself. Eg. Radar. Sensor consists of either photo film or scanners. There are two types of scanners: 1. Whiskbroom scanner: scanning across the track of satellite. Eg. MSS and TM scanners of LandSat-5. 2. Pusli broom type of scanner: scanning along the track of satellite. Eg.LISS-1, LISS-2 scanners of SPOT and IRS 1A, IRS 1B. The satellite basically records the fraction of EM energy reflected by the object of the earth surface in various bands. The size of the smallest area on the earth of which satellite records the reflectance is known as ‘Pixel’. A satellite digital image is the reflectance the use of a larger number of pixels covering in India in one or many bands. Satellite imagery is the conversion of these reflectance values, are usally called ‘DN’ numbers in to primary colors, which are red, green and blue, which are R.G.B Characteristics of remote sensing instruments:
Sl. No 1 Satellit e IRS 1C Sensor PAN Liss III Liss III MIR WIFS WIFS (visible) WIFS (MIR) MOS – A MOS – B MOS – C LISS-A Resolution in Area in mts. k.m. 5.8 70 x 70 23.50 141 x 141 7.20 14.8 x 14.8 188 810 x 810 188 810 x 810 188 X 246 2500 X 2500 727 X 580 1000 X 727 72.5 810 X 810 148 X 174 Max scale 1:12500 1:50000 1.2 mts 1.2 mts 1:2,50,00 Date availability Jan’1996 Jan’1996 Jan’1996 1/1/96 March’1996 April’88 TO

2

IRS P3

3

IRS

1A,1B LISS-2 4 5 6 7 LANDS AT SPOT ERS-1 NOAA MSS TM PLA MLA SAR AVHRR 36.25 80 30 10 20 30 1100 74 X 87 185 X 185

0 1:50,000

1:2,50,00 0 170 X 185 1:50,000 60 X 60 1:25,000 60 X 60 1:25,000 100 X 100 1:1,25,00 0 2700 X 2200

1992 1991 onwards 1979-92 1984 1987-90 1987-90 1991 onwards 1985 onwards

Data Interpretation: These data interpretations are two types:
1) Visual Interpretation: Visual interpretation of satellite data is the

most widely used method of satellite data interpretation. Visual interpretation is more widely used than the digital classification. The visual interpretation is easier to learn and practice. It does not require costly equipment like a computer or image processing softwares. It has advantages in the sense that the human control exists in the identification of features on the photo elements.
2) Digital Interpretation: The interpretation of satellite data by using

digital image software. The nine elements of photography image interpretation is deciding the identification of the object are as follows:
1) Shape

2) Size 3) Tone spatial describe 4) Shadow 5) Pattern cultural
6) Texture

: helps greatly in identifying the object. : length, width, height, areas and volumes of image. : picture tone, color or density for discrimination of many Variables. The terms light, medium and dark are used to variations in tone. : useful in geomorphologic studies. : refers to the repetitive arrangements of both natural & features. : smooth, lineated, irregular and rippled. Eg. Two vegetation types may have same tone, but different textures.

7) Site : location of the object. 8) Resolution : resolution should be such as to resolve to nearly located objects of interest. 9) Stereo data : aerial photos having overlap give a stereo viewing facility such as 3D view of the object. Data products The different kinds of products that can be supplied by NDC (NRSC Data Centre) are as follows:
1. Raw product: this data is raw in the sense that neither any correction

nor resampling is done in this product.
2. Browse product: little correction or resampling is usually done on the

raw data.
3. Partially

corrected data: radiometrically corrected and partially corrected for geometric corrections. 4. Standard products: data is corrected for geometric and radiometric distortions; this is the most widely used product by the user community. This is available for a full scene with stereo pairs. 5. Geo – coded product: it is a standard product made to match with survey of India topo sheets in terms of area, scale and alignment. It is available on 1:50,000 scale. 6. Special product: products are generated after further processing of standard products by extracting, enhancing, mosaicking and merging. All the above satellite datas are supplied as photographic and digital products.

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