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 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, analyzing
and applying that information
 In much of remote sensing, the process involves an
interaction between incident radiation and the target
of interest.
 The work of geologists would be much
easier if Earth were transparent and they
could simply look down into the ground as
they would into the sky.
 But the ground is not transparent and for
that matter, it is the sky, to which
meteorologists look for information
regarding atmospheric and weather
 Some places are hard to see, and many are
difficult or even impossible to visit
 Some places, such as the Sun or the Earth's
core, could not be approached physically
even by unmanned technology.
 Hence the need for remote sensing, or the
gathering of data without actual contact
with the materials or objects being studied.
 Some earth scientists define the term more
narrowly, restricting "remote sensing" to the
use of techniques involving radiation on the
electromagnetic spectrum.
 The latter category includes visible,
infrared, and ultraviolet light as well as
lower-frequency signals in the
microwave range of the spectrum.
 This definition excludes the study of
force fields involving gravitational or
electromagnetic force.
 Remote sensing is used for a variety of
measuring and mapping applications.
 Applications of remote sensing go far
beyond cartography (map making) and
 Remote sensing makes it possible for earth
scientists to collect data from places they
could not possibly go.
 In addition, it allows for data collection in
places where a human being would be
"unable to see the forest for the trees"—
which in places such as the Amazon valley is
quite literally the case.
a) Each eye sends a signal to a processor (your brain) which
records the data and interprets this into information.
b) Several of the human senses gather their awareness of
the external world almost entirely by perceiving a variety
of signals, either emitted or reflected, actively or
passively, from objects that transmit this information in
waves or pulses.
c) Thus, one hears disturbances in the atmosphere carried
as sound waves, experiences sensations such as heat
(either through direct contact or as radiant energy),
reacts to chemical signals from food through taste and
smell, is cognizant of certain material properties such as
roughness through touch, and recognizes shapes,
colours, and relative positions of exterior objects and
classes of materials by means of seeing visible light
issuing from them.
Remote Sensing
Without direct contact, some means of transferring
information through space must be utilised.
• What is it??
Electro-Magnetic Radiation
Electro-Magnetic Radiation
 EMR is a form of energy that reveals its presence by
the observable effects it produces when it strikes the
 EMR is considered to span the spectrum of
wavelengths from 10^(-10) mm to cosmic rays up to
10^(10) mm.
 Remote Sensing Technology makes use of the wide
range Electro-Magnetic Spectrum (EMS) from a very
short wave "Gamma Ray" to a very long 'Radio Wave'.
 The first requirement for remote sensing is to have an
energy source which illuminates or provides
electromagnetic energy to the target of interest
 The sun provides a very convenient source of energy
for remote sensing. The sun’s energy is either reflected,
as it is for visible wavelengths, or absorbed and then
re-emitted, as it is for thermal infrared wavelengths.
Types of Remote Sensing
 In respect to the type of Energy Resources:
 Passive Remote Sensing
 Active remote Sensing
 In respect to Wavelength Regions:
 Visible and Reflective Infrared Remote Sensing
 Thermal Infrared Remote Sensing
 Microwave Remote Sensing
 Band Use Remote Sensing
 Remote sensing system which measure energy that is
naturally available
 Can only be used to detect energy when the naturally
occurring energy is available
 For all reflected energy, this can only take place during
the time when the sun is illuminating the earth
 Provide their own energy source for illumination
 The sensors emits radiation which is directed toward
the target to be investigated
 The radiation reflected from that target is detected
and measured by sensor
 Example:
 Laser fluorosensor
 Synthetic Aperture Radar (SAR)
 Advantages
 Able to obtain measurement anytime, regardless of the
time of day or season
 Can be used for examining wavelengths that are not
sufficiently provided by the sun
 Disadvantages
 Require the generation of a fairly large amount of energy
to adequately illuminate targets
 Energy source : object itself
 Any object with normal temperature will emit
electromagnetic radiation with a peak about 10 μm
 The visible remote sensing devices operate in the
visible, near infrared, middle infrared and short wave
infrared portion of the electromagnetic spectrum.
 It makes use of visible, near infrared and short-wave
infrared sensors to form images of the earth's surface
by detecting the solar radiation reflected from targets
on the ground.
 Different materials reflect and absorb differently at
different wavelengths. Thus, the targets can be
differentiated by their spectral reflectance signatures
in the remotely sensed images
 These devices are sensitive to the wavelengths ranging
from 300 nm to 3000 nm.
 The longest visible wavelength is red and the shortest
is violet. Common wavelengths of what we perceive as
particular colors from the visible portion of the
 The visible and reflective remote sensing region is split into
a number of bands, each of which is useful in
distinguishing land cove features. The following is just a
guide based on LISS 3/4 and LANDSAT Bands 1-4.
 Band 1 (0.45-0.52 µm): coastal water mapping, soil/vegetation
discrimination, forest classification, man-made feature
 Band 2 (0.52-0.60 µm): vegetation discrimination and health
monitoring, man-made feature identification.
 Band 3 (0.63-0.69 µm): plant species identification, manmade feature identification.
 Band 4(0.76-0.90 µm): soil moisture monitoring, vegetation
monitoring, water body discrimination
The curve (a) and (b) are
intersect at about 3.0 μm, spectral
reflectance is mainly observed,
while in region more than 3.0 μm,
thermal radiation is measured.
The two curve (a) and (b) shows
the black body spectral radiances
of sun at temperature of 6000 ̊K
and an object with temperature of
300 ̊K without atmospheric
Example of visible and reflective IR
remote sensing
 Photographic.—
 Cameras and film are used. Photography provides the
best spatial resolution but less flexibility in spectral data
collection and image enhancement. Spatial resolution is
dependent on altitude, focal length of lenses, and the
types of film used.
 Spectral resolution is limited to visible and near infrared
 Electronic Spectral Sensors.—
 Detectors are used, usually scanners, that may have less
spatial resolution than photographs but can gather
spectral data over wide spectral ranges that enable a
wide variety of imaging processing, mineral, and
geologic identification. These remote sensing systems
include satellites, such as Landsat, airborne sensors
carried on aircraft, andspectrometers carried on the
ground. This type of remote sensing has several
categories, including multispectral, hyperspectral, and
imaging spectroscopy.
 Vidicon. –
 A television-type system. Vidicon systems generally are
inferior to other types both spatially and spectrally.
They are used mostly on space probes because of
operational constraints.
 Electromagnetic waves with a wavelength range
between 3.5 and 20 micrometers.
 Most remote sensing applications make use of the 8 to
13 micrometer range.
 The source of radiant energy used in thermal infrared
remote sensing is the object itself, because any object
with a normal temperature will emit electro-magnetic
radiation with a peak at about 10 m .
 Can provide important measurements of surface
energy fluxes and temperatures, which are integral to
understanding landscape processes and responses.
 One example of this is the successful application of
TIR remote sensing data to estimate
evapotranspiration and soil moisture, where results
from a number of studies suggest that satellite-based
measurements from TIR remote sensing data can lead
to more accurate regional-scale estimates of daily
Thermal infrared remote sensing focuses on far infrared
and mid infrared
 The main difference between thermal infrared and the
infrared (color infrared - CIR) is thermal infrared
emitted energy that is sensed digitally, whereas the
near infrared "photographic infrared" is reflected
energy that causes a chemical reaction in film
 Thermal remote sensing exploits the fact that
everything above absolute zero (0 K or -273.15 °C or –
459 °F) emits radiation in the infrared range of the
electromagnetic spectrum.
 How much energy is radiated, and at which
wavelengths, depends on the emissivity of the surface
and on its kinetic temperature
 Emissivity is the emitting ability of a real material
compared to that of a black body
Factors Affecting the Kinetic
Can be categorised in two groups
a)Heat energy budget
Heat energy budget includes factors such as solar
heating, longwave upwelling and downwelling
radiations, heat transfer at the earth-atmosphere
interface and active thermal sources such as fires,
volcanoes etc.
b) Thermal properties of the materials
Thermal properties of material include factors such as
thermal conductivity, specific heat, density, heat
capacity, thermal diffusivity and thermal inertia of the
• Thermal property of a material is representative of upper
several centimeters of the surface.
• It proves to be complementary to other remote sensing
data and even unique in helping to identify surface
materials and features such as rock types, soil moisture,
geothermal anomalies etc.
• The ability to record variations in infrared radiation has
advantage in extending our observation of many types of
phenomena in which minor temperature variations may be
significant in understanding our environment.
• Thermal infrared remote sensing reserves immense
potential for various applications.
Limitations of thermal infrared
remote sensing
 It can be very expensive to acquire and process
 Most thermal imaging systems have strict operational/technical
- detector materials must be kept extremely cold during use
 Thermal infrared imaging systems are notoriously difficult to calibrate
- because temp differences can be very subtle and interactions with
atmospheric moisture are unpredictable
 The data collected is computationally expensive due to the iterative
nature of filtering software
 Thermal images can be difficult to interpret compared with other types
of imagery, it takes some getting used too (false color helps)
 Thermal images of water measures only the very top layer of the water
- because those wavelengths are attenuated/absorbed very rapidly,
especially in water
Where Radar comes from….??
 Radar was originally developed in the 1950s,
 1st airborne system --> SLAR (Side-Looking Airborne
 Later, SAR (synthetic Aperture Radar) was developed
and widely used in many countries for civilian
What is the Radar (Microwave)
Remote Sensing
 RADAR stands for "RAdio Detection And Ranging“ ----
> sending out pulses of microwave electromagnetic
 Known as "active sensor“ will measures the time
between pulses and their reflected components to
determine distance.
 Wavelength of Radar in range between <1 mm to 1m
Advantages of Radar
 It have long wavelength, allows the systems to "see"
through clouds, smoke, and some vegetation.
 it can be operated day or night  an active systems
 Radar wave can penetrate clouds, haze, dust and so on
but the heaviest of reflected depends on channel used.
Effect using Radar in imaging
Color Aerial Photography
Processed Radar Imagery
Color Photography
Radar Derived DEM (Digital Elevation
Disadvantages of Radar
 Its the non-unique spectral properties of the returned
radar signal.
 Its only shows the difference in the surface roughness
and geometry and moisture content of the ground (the
complex dielectric constant).
Types of Imaging Radar
(Side-Looking Airborne Radar)
 develop by guess who in the
 airborne, fixed antenna
width, sends one pulse at a
time and measures what gets
scattered back
 resolution determined by
wavelength and antenna size
(narrow antenna width =
higher resolution)
(Synthetic Aperture Radar)
 developed by those responsible
for SLAR,
 this configuration not depend
on the physical antenna size
although to achieve higher
 the receiving antenna
components and transmitter
components need to be
 "synthesizes" a very broad
antenna by sending multiple
Imaging Radar
Side-looking Airborne
Radar (SLAR)
Synthetic Aperture Radar
Radar Resolution
Radar resolution has two components
"range" resolution
"azimuth" resolution
Radar Resolution
 As seen in this diagram, if the
distance between the two
houses labeled A and B were
greater than {Pulse Length ÷
2} then they would be
discerned as two separate
 Since, in this figure the slant
range distance is less than
{Pulse Length ÷ 2}, the
reflected signals are "blurred.”
Radar Resolution
Azimuth Resolution
 is the ground distance definition in the azimuth direction
(i.e. the direction of the aircraft).
 The azimuth resolution, Ra, is at a 90° angle to the ground
range, GR.
 Azimuth resolution may be expressed as:
 Ra = GR * Beta,
GR is the ground range, and
Beta is the beam width=Wavelength ÷ Antenna Length
Bands Used in Remote Sensing
 Emission of EMR from gases is due to atoms and
molecules in the gas.
 Atoms consist of a positively charged nucleus
surrounded by orbiting electrons, which have discrete
energy states.
 Transition of electrons from one energy state to the
other leads to emission of radiation at discrete
 The resulting spectrum is called line spectrum.
Bands Used in Remote Sensing
 Molecules possess rotational and vibrational energy
 Transition between which leads to emission of
radiation in a band spectrum.
 The
atoms/molecules, are also the ones, which are
absorbed by them.
 Emission from solids and liquids occurs when they are
heated and results in a continuous spectrum. This is
called thermal emission and it is an important source
of EMR from the viewpoint of remote sensing.
Bands Used in Remote Sensing
 The Electro-Magnetic Radiation (EMR), which is
reflected or emitted from an object, is the usual source
of Remote Sensing data.
 However, any medium, such as gravity or magnetic
fields, can be used in remote sensing.
Bands Used in Remote Sensing
 Wavelength regions of electro-magnetic radiation have
different names ranging from Gamma ray, X-ray,
Ultraviolet (UV), Visible light, Infrared (IR) to Radio
Wave, in order from shorter wavelength to longer one.
 The optical wavelength region, an important region for
remote sensing applications, is further subdivided as
Wavelength (mm)
Optical wavelength
1. Portion Visible
2. Near IR
3. Middle IR
Far IR (Thermal,
Bands Used in Remote Sensing
 Microwave region (1mm to 1m) is another portion of
EM spectrum that is frequently used to gather valuable
remote sensing information.