GCE Kannur

1. REMOTE SENSING

2. Introduction
Remote sensing is a general term which describes the
action of obtaining information about an object with a
sensor which is physically separated from the object.
Such sensors rely upon the detection of energy
emitted from or reflected by the object.
Two common examples of remote sensing are human
vision, which relies on the detection of reflected light,
and sonar, which detects sound waves.

3. A formal and comprehensive definition of applied remote sensing
Remote Sensing in the most generally accepted meaning refers
to instrument-based techniques employed in the acquisition and
measurement of spatially organized (most commonly,
geographically distributed) data/information on some
property(ies) (spectral; spatial; physical) of an array of target
points (pixels) within the sensed scene that correspond to
features, objects, and materials, doing this by applying one or
more recording devices not in physical, intimate contact with
the item(s) under surveillance (thus at a finite distance from the
observed target, in which the spatial arrangement is
preserved); techniques involve amassing knowledge pertinent
to the sensed scene (target) by utilizing electromagnetic
radiation, force fields, or acoustic energy sensed by recording
cameras, radiometers and scanners, lasers, radio frequency
receivers, radar systems, sonar, thermal devices, sound
detectors, seismographs, magnetometers, gravimeters,

4. Basic Components
All remote sensing technologies are based on
certain common concepts, and all remote
sensing systems consist of the same basic
components. These four basic components of a
remote sensing system include a target, an
energy source, a transmission path, and a
sensor.

5. Basic Components
The target is the object or material that is being studied. The
components in the system work together to measure and record
information about the target without actually coming into physical
contact with it. There must also be an energy source which
illuminates or provides electromagnetic energy to the target.

6. Target Interactions
The energy interacts with the target, depending on the
properties of the target and the radiation, and will act as a
medium for transmitting information from the target to the
sensor. The sensor is a a remote device that will collect and
record the electromagnetic radiation. Sensors can be used
to measure energy that is given off (or emitted) by the target,
reflected off of the target, or transmitted through the target.

7. Target Interactions
Once the energy has been recorded, the resulting set
of data must be transmitted to a receiving station
where the data are processed into a usable format,
which is most often as an image. The image is then
interpreted in order to extract information about the
target. This interpretation can be done visually or
electronically with the aid of computers and image
processing software.

8. Classification
1. In respect to the type of Energy Resources
Active remote sensing
Passive remote sensing
2.In respect to Wavelength Regions:
Remote Sensing is classified into three types in respect to the
wavelength regions
Visible and Reflective Infrared Remote Sensing.
Thermal Infrared Remote Sensing.
Microwave Remote Sensing.

9. Active remote sensing
Direct radiation of a particular form towards an
object and then detect the amount of that energy
which is radiated by the object. These active
remote sensing systems operate in the
microwave and radio wave regions of the EM
spectrum.
Lidar (laser imaging radar) systems are active
remote sensors which operate in the ultraviolet,
visible and near infrared wavelengths.

10. Passive remote sensing
Relies on the radiation originating from some other
source, principally the sun. Reflected solar energy is
detected by passive remote sensing devices in the
visible, near infrared and middle infrared regions while
the Earth's emitted energy may be detected in the
middle infrared and thermal infrared wavelengths.
Certain microwave sensors are also in the passive
detector category. Aerial photography and Landsat
satellite imagery are examples of data collected by
passive remote sensing systems.

11. Electromagnetic Energy
The underlying basis for most remote sensing
methods and systems is simply that of
measuring the varying energy levels of a single
entity, the fundamental unit in the
electromagnetic (which may be abbreviated
"EM") force field known as the photon

12. Electromagnetic Spectrum
Variations in photon energies (expressed in
joules or ergs) are tied to the parameter
wavelength or its inverse, frequency. EM
radiation that varies from high to low energy
levels comprises the electromagnetic spectrum
(EMS). Radiation from specific parts of the EM
spectrum contain photons of different
wavelengths whose energy levels fall within a
discrete range of values.

13. Electromagnetic energy and
interactions
Radiation from specific parts of the EM spectrum
contain photons of different wavelengths whose
energy levels fall within a discrete range of
values. When any target material is excited by
internal processes or by interaction with
incoming EM radiation, it will emit or reflect
photons of varying wavelengths whose
radiometric quantities differ at different
wavelengths in a way diagnostic of the material.

14. Energy Interactions, Spectral Reflectance and Colour
Readability in Satellite Imagery
All matter is composed of atoms and molecules with particular
compositions. Therefore, matter will emit or absorb electro-
magnetic radiation on a particular wavelength with respect to
the inner state. All matter reflects, absorbs, penetrates and
emits Electro-magnetic radiation in a unique way. Electro-
magnetic radiation through the atmosphere to and from matters
on the earth's surface are reflected, scattered, diffracted,
refracted, absorbed, transmitted and dispersed. For example,
the reason why a leaf looks green is that the chlorophyll
absorbs blue and red spectra and reflects the green. The
unique characteristics of matter are called spectral
characteristics.

15. Any beam of photons from some source passing through
medium 1 (usually air) that impinges upon an object or
target (medium 2) will experience one or more reactions

16. Electromagnetic Energy
The sun provides most of the energy which we sense as
light. This energy consists of electromagnetic (EM)
waves which travel in harmonic, sinusoidal motion as
shown.

18. Electromagnetic Spectrum
"Electromagnetic radiation is energy propagated through space
between electric and magnetic fields. The electromagnetic
spectrum is the extent of that energy ranging from cosmic rays,
gamma rays, X-rays to ultraviolet, visible, and infrared radiation
including microwave energy."
Electromagnetic Waves
Electromagnetic waves may be classified by frequency or
wavelength, and the velocity of ALL electromagnetic waves is
equal to the speed of light, which we (along with Einstein) will refer
to as c.

19. • Electromagnetic energy is continuously emitted
at all wavelengths by every material with a
temperature above absolute zero (-273.15°C or
0 K).
• With no other objects in the universe, a material
would gradually cool to 0 K by radiating all of its
energy.
• Absorption of energy increases both the
temperature and rate of emission of a material.
• If the material is 'black' in that it absorbs all
radiation that reaches it (a perfect absorber is
referred to as a 'blackbody'), then the spectral
composition and intensity of emission are well
defined and follow Planck's laws

20. Because the Earth, and its surface materials, are
not black, they do not absorb all the sun's
radiation but reflect and scatter radiation as well.
The spectral composition of radiation from the
Earth therefore consists of both reflected and
emitted components. The intensity of radiation
emitted from Earth, when viewed from space, is
greatest where the sun's radiation is greatest
(that is, in the visible region) due to the
reflectance of solar energy.

21. Much of the longer wavelength energy cannot be seen
or photographed but can be sensed with radiometers
and scanners. The range of wavelengths in which
various sensors can operate is shown in Figure

22. The interaction of incoming radiation with surface
features depends on both the spectral reflectance
properties of the surface materials and the surface
smoothness relative to the radiation wavelength. A
relatively 'smooth' surface which reflects energy
without any scattering (that is, the angle of incidence
equals the angle of reflection) is called a 'specular' or
'mirror' reflector. 'Diffuse' or 'Lambertian' reflectance
occurs when the surface is rough relative to the
wavelength(s) of the incoming radiation and causes
the energy to be reflected equally in all directions.