Fundamentals of remote sensing

Fundamentals of remote

sensingBy

Ashok Peddi

Satellite image

Remote sensing is the science of acquiring information about the

Earth's surface without actually being in contact with it. This is done

by sensing and recording reflected or emitted energy and processing,

analysing, and applying that information.

Remote Sensing can be done by two different ways

1)Satellites –satellite Images 2)Aircrafts-Arial Photographs

Aerial photography

Aerial photography Satellite image

Examples

To analyze(Visual Interpretation) the satellite imagery we use different combination of bands where it will produce two variety of(composite) images1)True Color Composite(RGB)2)False Color Composite other( than RGB)

False Color True color

QuickbirdPAN – 61 cm

IKONOSMSS/XS – 4 mBagdad, Iraque

What is a satellite image?Satellite imagery consists of photographs of Earth or other planets made by means of artificial satellites which also gives an opportunity to process the image and conclude with analysis depending on your requirement.

Blue Green Red

Urban area

Urban area

River

3500 m

The different Bands

Vegetation

Description of a Satellite Image

Landsat TM 30 mSPOT XS 10 mNOAA/AVHRR 1100 mIKONOS 4 m

70

23

10

120

40

The value retained in each pixel is designated by digital number and it translates the solar energy reflected by the earth surface (covered by the pixel).

Spatial resolution

Radiometric Resolution

Blue Green Red

Urban area

Urban area

River

3500 m

Green

RedBlue

Near Infrared Middle Infrared Middle Infrared

TM 1 TM 2 TM 3

TM 4 TM 5 TM 7

7 4 3

4 3 2

Spectral Resolution

Components of a remote sensing system

A – Energy source of illumination

B – Interaction with the atmosphere

C – Interaction with the target

F – Transmissions, reception and processing

E – Recording of energy by the sensor

G – Interpretation and analysis

v = frequency(number of cycles per secondpassing 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, and various 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 = l u

c - velocity of light (3x108m/s)

Wavelength and frequency are inversely related to each other:

• the shorter the wavelength, the higher the frequency;• the longer the wavelength, the lower the frequency.

Electromagnetic spectrum

*The energy in remote sensing is in the form of

electromagnetic radiation.Electro magnetic

Radiation is a particular form of energy emitted

and absorbed by charged particles

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation.* The "electromagnetic spectrum" of an object has a different meaning, and is instead the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object.

The visible portion of the spectrum is a very 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 m The wavelengths smaller than 0.4 mm entails:• gamma rays• x rays• ultraviolet radiation

The part of the electromagnetic spectrum with wavelengths 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 can be 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 radiation with atmosphere

The atmosphere has a strong effect on the quantity and quality of the electromagnetic radiation captured by the satellite.

The atmosphere effect varies with:• radiation path (airplane, satellite)• wavelength• atmospheric conditions (particles, gases, …)• ...

Before radiation used for remote sensing reaches the Earth's surface it has to travel through some distance of the Earth's atmosphere.

Particles and gases in the atmosphere can affect the incoming light and radiation. These effects are caused by the mechanisms of:

• scattering• absorption.

What is the effect of atmosphere in the satellite images?

• Atmosphere reduces contrast• Atmosphere may blur the images• Atmospheres may reduce the quantity of radiation

I hope that was useful @ashokped

Thank you!