01. Introduction to Remote Sensing

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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.

01. Introduction to Remote Sensing

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