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Introduction to Remote Sensing
Dr. Rohit Goyal
Professor, Civil EngineeringMalaviya National Institute of Technology
Jaipur
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Topics Covered
Definition of Remote Sensing
Is it an Science or Art?Schematic Diagram of RS Process
Major Milestones
Advantages & Limitations of RSDifferent Resolutions of RS
Status of Remote Sensing in India
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Definition of Remote Sensing
Oxford defines RS as the use of SATELLITES tosearch for and collect information about the earth.
Encarta defines RS as Process of obtaininginformation about land, water, or an object,without any physical contact between the sensorand the subject of analysis. Further according to Encarta, The term RS refers to
collection of data by instruments carried aboard aircraft orsatellites.
Remote sensing systems are used to survey, map, andmonitor the resources and environment of Earth.
They also have been used to explore other planets
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Definition of RS
Lillisand & Kiefer defines RS as
Science & Art of obtaininginformation about an object, areaor phenomenon through theanalysis of data acquired by adevice that is not in contact withthe object, area or phenomenonunder investigation.
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ASPRSDefinition
American Society for Photogrammetry &RS defines
The measurement or acquisition ofinformation of some property of anobject or phenomenon, by a recording
device that is not in physical or intimatecontact with the object or phenomenonunder study.
There are many other definitions
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Is it an Science orArt or both?
Science is defined as knowledge aboutthe structure and behavior of thenatural and physical world, based onfacts that can be proved throughexperiments or logic
Art is defined as the use of theimagination to express ideas orfeelings. The same thing could meandifferent things to different persons.
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RS is Science
RS is use of sophisticated sensors tomeasure the amount of reflected
electromagnetic radiation from adistance.
This information is then analyzed usingmathematical & statistical algorithms to
extract valuable informationAs more & more research is being
undertaken the RS scientific discipline isdeveloping in to higher & higher stage
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RS is art as well
The process of visual photo or imageinterpretation requires not only
scientific knowledge but also dependsupon the background of the personobtained through the lifetime.
An analyst who understand the
scientific principals better, is widelytraveled and have seen more landscape& objects first hand & can syntheses theknowledge to reach logical and correct
conclusion is better than others
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How Does it Works?
Remote Sensing uses PASSIVE and ACTIVE
sensors to MEASURE ENERGY released orreflected from objects on the earth (or other
planets)...
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Schematic Diagram of RS
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MajorMilestones 1858: First aerial photograph from a balloon
1873: Development for near infrared photography
1914-1918 World War I: Photo reconnaissance
1939-1945 WW II: Advanced Photo reconnaissance
1940: Radar invented
1942: False color composite by Kodak
1950: Thermal infrared remote sensing
1957: First satellite, Sputnik by Russia
1958: First USA satellite Explorer 1
Till 1960: Mostly Visual Interpretation, start of digitalprocessing
1961: Yuri Gagarin in Space
1970: Digital Image Processing comes of age
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Milestones 1972: ERTS-1 (LANDSAT-1) Launched
70s & 80s: Many RS Satellites, Weather Forecasting
1981: NASA SIR-A launched
1986: SPOT Launched
1988: IRS-1A Launched
1990s: Hyperspectral and LIDAR Sensors
1991: ERS-1 Launched
1995: RADARSAT Launched
1999: IKONOS Launched
2000: Quickbird & Orb View 3, 4 Launched
2001: Envisat
2002: IRS P-6
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Advantages Unobtrusive (Specially for passive RS). Does not disturb
object.
Systematic data collection with known spatial, spectraland temporal resolutions. Repetitive coverage
Near real time data collection
Coverage of large area, synoptic view (Some features suchas faults are better viewed)
Could provide fundamental scientific information such as
temperature, spatial location, elevation or depth, biomass,moisture content etc.
Cost effective for large area
Digital processing, less human induced errors
Applicable for inaccessible areas
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Limitations Could not provide all information needed for physical,
biological and social sciences
Since indirect observation, so must be calibrated, which may
introduce errors Very high initial cost
Powerful active RS systems such as Laser or Radar could beintrusive
Requirement of higher expertise for image analysis
Handling of large amount of data could be a problem
Phenomena which were not meant to be measured (for theapplication at hand) can interfere with the image and must beaccounted for. Examples for land cover classification:atmospheric water vapor, sun vs. shadow (these may bedesirable in other applications).
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Resolutions of RS
In order to understand utility of RS datait is essential to understand different
resolutions of RS SystemsResolution is defined as a measure of
the ability of an optical system todistinguish between signals that are
spatial near or spectrally similarFour different resolutions for an RSS are
Spectral, Spatial, Temporal &Radiometric
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Spectral Resolution
Number and dimensions of specificwavelength intervals in EMR to which a
remote sensing instrument is sensitive.Ex. LANDSAT MSS has four bends in
visible & infrared region
A Hyperspectral RS instrument acquires
data in hundreds of spectral bends.Usually Sensitivity of instrument follows
Gaussian distribution
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Spatial Resolution
Spatial resolution is a measure of the smallestangular or linear separation between two
objects that can be resolved by the sensor. Remote Sensing Systems which operate in
fixed orbits with fixed optical systems have aconstant instantaneous field of view known asIFOV. In such case Spatial Resolution is
defined as dimensions in meter of groundprojected IFOV
Ex. Resolution of IRS-1C, LISS III is 23.5meters
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Temporal Resolution Temporal resolution refers to how often a RS
system records imagery of a particular area
Usually RS satellites are placed in such a orbitaround earth so that they cover the entireearth in fixed number of days such as 16 or 22days and repeat the coverage of the same areaafter that man days.
Some systems have capabilities to view off
nadir & so can have repetitive coverage afteronly 6-7 days
Aqua and Terra Satellites have some sensors(MODIS), which could view the entire earthevery 1-2 days.
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Radiometeric Resolution Radiometeric resolution (also known as
quantization or dynamic range) is defined asthe sensitivity of the remote sensing detectorto differentiate in signal strength as it recordsthe radiant flux reflected or emitted from theterrain.
In other words it is defined as number ofdiscriminable signal levels and is usuallymeasured as number of bits
Example LANDSAT MSS records data in 6 bits(maximum 64 values in each band)
Usually the data products are converted to 8 bitsradiometric resolution, meaning 256 different values.
Some recent satellites have 10 bit radiometricresolution.
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Status of RS in India India started developing RS satellites quite early as
compared to many other developed countries Now we have fully functional RS system in place
comprising of many RS satellite and plans for manyother satellites We are also in process of development of Satellite
launch vehicles to become less dependent on othercountries for our space programme
NRSA, SAC, IIRS, ISRO are some of the pioneer centers
for development of space technologies in India Visit web sites of these agencies to know more aboutstatus of RS in India
Visit http://www.csre.iitb.ac.in/isro/ website forinformation on many past and present Indian satellites.
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