Remote sensing is the science of acquiring information about the Earthssurface without actually being in contact with it. This is done by sensing andrecording reflected or emitted energy and processing, analysing, and applyingthat information.Remote Sensing can be done by two different ways1)Satellites –satellite Images 2)Aircrafts-Arial Photographs Satellite image Aerial photography
To analyze(Visual Interpretation) the satellite imagery we usedifferent combination of bands where it will produce twovariety of(composite) images1)True Color Composite(RGB)2)False Color Composite other( than RGB) True color False Color
What is a satelliteimage?Satellite imagery consists of photographsof Earth or other planets made by meansof artificial satellites which also gives anopportunity to process the image andconclude with analysis depending on yourrequirement.
Description of a Satellite Image Urban area River Urban area Vegetation 3500 m The different Bands Blue Green Red
Spatial resolution 23 40 Landsat TM 30 m 10 SPOT XS 10 m 70 NOAA/AVHRR 1100 m 120 IKONOS 4mThe value retained in each pixel is designated by digital number and ittranslates the solar energy reflected by the earth surface (covered by thepixel).
Components of a remote sensing systemA – Energy source of illumination F – Transmissions, reception and processingB – Interaction with the atmosphere G – Interpretation and analysisC – Interaction with the targetE – Recording of energy by the sensor
v = frequency (number of cycles per second passing a fixed point)Wavelength is measured in meters (m) or some factor of meters such as nanometres(nm, 10-9 m), micrometers (μm, 10-6 m) or centimeters (cm, 10-2 m).Frequency is normally measured in hertz (Hz), equivalent to one cycle per second, andvarious multiples of hertz.
Quantity of radiant energy is expressed in energy units.Quality of radiant energy is characterised by frequency(u) or wavelength (l). c=luc - velocity of light (3x108m/s)Wavelength and frequency are inversely related to eachother: • the shorter the wavelength, the higher the frequency; • the longer the wavelength, the lower the frequency.
Electromagnetic spectrumThe electromagnetic spectrum is the range of allpossible frequencies of electromagneticradiation.* The "electromagnetic spectrum" of anobject has a different meaning, and is instead thecharacteristic distribution of electromagneticradiation emitted or absorbed by that particularobject.*The energy in remote sensing is in the form ofelectromagnetic radiation.Electro magnetic Radiation isa particular form of energy emitted and absorbed bycharged particles
The visible portion of the spectrum is avery small part of the whole spectrum:•blue - 0.4 a 0.5 mm•green - 0.5 a 0.6 mm•red - 0.6 a 0.7 mm.1 mm = 10-6 mThe wavelengths smaller than 0.4mm entails:• gamma rays• x rays• ultraviolet radiation
The part of the electromagnetic spectrum withwavelengths larger than 0.7 mm entails:• infrared (0.7-10 mm),• microwaves (1mm-1m)• radio waves.Infrared goes from 0.7 mm to 10 mm and canbe divided in three areas:• Near infrared (0.7-1.0 mm),• medium infrared (1.3-3.0 mm)• thermal infrared (> 3 mm).
Interaction of electromagnetic radiationwith atmosphereThe atmosphere has a strong effect on the quantityand quality of the electromagnetic radiation capturedby the satellite.The atmosphere effect varies with:• radiation path (airplane, satellite)• wavelength• atmospheric conditions (particles, gases, …)• ...
Before radiation used for remote sensing reaches theEarths surface it has to travel through some distance ofthe Earths atmosphere.Particles and gases in the atmosphere can affect theincoming light and radiation. These effects are causedby the mechanisms of: • scattering • absorption.What is the effect of atmosphere in the satelliteimages? • Atmosphere reduces contrast • Atmosphere may blur the images • Atmospheres may reduce the quantity of radiation