Remote Sensing - Fundamentals, Active and Passive Remote Sensing

1. REMOTE SENSING - FUNDAMENTALS
Dr. Ajay Singh Lodhi
Assistant Professor
College of Agriculture, Balaghat
Jawahar Lal Krishi Vishwa Vidyalaya, Jabalpur (M.P.)

2. REMOTE SENSING SENSORS
 Passive sensors: Passive
system record energy reflected or
emitted by a target illuminated by
sun.
 e.g. normal photography, most
optical satellite sensors.
 Active sensors: Active system
illuminates target with energy and
measure reflection.
 e.g. Radar sensors,

3. Passive Remote Sensing
 Doesn’t employ any external source of energy.
 Measures either reflected radiation from Sun (can be
operated only during daytime) or the emitted radiation from
the surface (day/night operation).
 Suffers from variable illumination conditions of Sun and
influence of atmospheric conditions
Active Remote sensing
 Has its own source of energy
 Active sensors emit a controlled beam of energy to the
surface and measure the amount of energy reflected back
to the sensor.
 Controlled illumination signal
 Day/night operation

4. Passive sensors : collect electromagnetic radiation in the
visible and infra-red part of the spectrum.
 Aerial Photographs
 Low resolution: Landsat,, SPOT, IRS
 High Resolution: Quickbird, IKONOS
Active sensors : generate their own radiation.
 Air-borne RADAR
 Space borne RADAR: ERS 1 / 2, Radarsat
 LiDAR (laser scanner)

5. FUNDAMENTAL PHYSICS OF REMOTE SENSING
 Remote Sensing relies on the measurement of Electro
Magnetic (EM) energy.
 The most important source of EM energy is the sun Some
sensors detect energy emitted by the Earth itself or provide
their own energy (Radar) .
 All matter reflects, penetrate, observes and emits of EMR
in unique way, which called spectral characteristics
 Two characteristic of electromagnetic radiation are
particularly important for understanding remote sensing.
These are the wavelength and frequency.

6.  The wave length is the length of one
wave cycle which can be measured
as the distance between successive
Wave crests.
 Wave length is usually represented
by the lambda wave length is
measured in meter (M) or some
factors of meters such as
nanometers (nm) micrometers(um) ,
centimeters (cm)
 Frequency refers to the number of
cycles of waves passing a fixed point
per unit of time. Frequency is
normally measured in hertz (Hz),
equivalent to one cycle per second
and various multiples of hertz.

7.  Relation between Wavelength and Frequency: Wavelength
and frequency are related by the following formula:
𝐶 = 𝜆𝑣
Where
𝜆 = Wavelength (m)
𝑣= frequency (cycles per second, Hz)
c = speed of light (3x108 m/s)
Therefore, the two are inversely related to each other. The
shorter the wave length, the higher the frequency. The longer
the wave length, the lower frequency

8.  Electro-magnetic spectrum (EMS) is an array of all EMR,
which moves velocity of light, characteristic of wavelength
and frequency of energy.
 The electromagnetic spectrum ranges from the shorter
wavelengths (including gamma and x-rays) to the longer
wavelengths (including microwaves and broadcast radio
waves)
 There are several regions of the electromagnetic spectrum
which are useful for remote sensing.
Electromagnetic Spectrum (EMS)

10. Ultraviolet Range
 This radiation is just beyond the violet portion of the visible
wavelengths
 Some Earth surface materials, primarily rocks and minerals,
emit visible light when illuminated by UV radiation.
Visible Range
 The light which our eyes - our "remote sensors" can detect
is part of the visible spectrum.
 The visible wavelengths cover a range from approximately
0.4 to 0.7 µm. The longest visible wavelength is red and the
shortest is violet .This is the only portion of the spectrum we
can associate with the concept of colours.

16. REMOTE SENSING OBSERVATION PLATFORM
 Sensor-the device that actually gathers the remotely
sensed data
 Platform-the device to which the sensor is attached
 The vehicles or carriers for remote sensing are called the
platform.
 Based on its altitude above earth surface typically platform
are satellite and aircraft but they can also, aero plane,
balloons, kites. platform may be classified as,
1) Ground borne
2) Air borne
3) Space borne

17.  Air born and space born
platform have been in use in
remote sensing of earth
resources.
 The ground based remote
sensing system for earth
resources studies are
mainly used for collecting
the ground truth or for
laboratory simulation
studies.

22. Thank You