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The presentation is about the basics of Remote Sensing. The presentation talks about its need and who uses Remote sensing. The process of remote sensing, its principles, platforms and sensors are discussed. The four types of resolutions- Spatial, Spectral, temporal and radiometric are also discussed.
Bhaikaka Centre for Human Settlements
APIED, V.V. Nagar
What is Remote Sensing?
Need for Remote Sensing
Who uses Remote Sensing and why?
Remote Sensing Process
Principle behind Remote Sensing
Sensors and Platforms
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.
What is Remote Sensing?
Systematic data collection
Inaccessible area- sometimes only solution
Need for Remote Sensing
the geographer, who looks for changes on the Earth's
surface that need to be mapped;
the forester, who needs information about what type of
trees are growing and if they have been affected by
disease or fire;
the environmentalist, who wants to detect, identify and
follow the movement of pollutants such as oil slicks on
the geologist, who is interested in finding valuable
Who uses Remote Sensing and
the farmer, who wants to keep an eye on how his crops
are growing and if they've been affected by drought,
floods, disease or pests;
the ship captain, who needs to find the best route through
the northern ice packs;
the firefighter, who sends out his crews based on
information about the size and movement of a forest fire.
the Urban Planner, who wants to map and monitor land
cover, land use, morphology ( the study of the form of
human settlements and the process of their formation and
Remote Sensing (RS) Process
satellite not in site
1. Energy Source or Illumination (A) – the first requirement
for remote sensing is to have an energy source which
illuminates or provides electromagnetic energy to the target
2. Radiation and the Atmosphere (B) – as the energy travels
from its source to the target, it will come in contact with and
interact with the atmosphere it passes through. This
interaction may take place a second time as the energy
travels from the target to the sensor.
3. Interaction with the Target (C) - once the energy makes
its way to the target through the atmosphere, it interacts
with the target depending on the properties of both the
target and the radiation.
4. Recording of Energy by the Sensor (D) - after the energy
has been scattered by, or emitted from the target, we require a
sensor to collect and record the electromagnetic radiation.
5. Transmission, Reception, and Processing (E) - the energy
recorded by the sensor has to be transmitted, often in
electronic form, to a receiving and processing station where
the data are processed into an image (hardcopy and/or
6. Interpretation and Analysis (F) - the processed image is
interpreted, visually and/or digitally or electronically, to
extract information about the target which was illuminated.
7. Application (G) - the final element of the remote sensing
process is achieved when we apply the information we have
been able to extract from the imagery about the target in order
to better understand it, reveal some new information, or assist
in solving a particular problem.
Electromagnetic energy reaching
the earth's surface from the Sun is
reflected, transmitted or absorbed.
Specific targets have an individual
and characteristic manner of
interacting with incident radiation
that is described by the spectral
response of that target.
Egs-soils of differed types, water
with varying degrees of impurities,
or vegetation of various species
Principle behind RS
Electromagnetic Radiation (EMR) like radio waves,
infrared (heat) waves make characteristic patterns as they
travel through space. Each wave has a certain shape and
length. The distance between peaks (high points) is called
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 (micrometre; 1 μm= 1×10−6 of a metre).
spectrum ranges from the
(including gamma and x-
rays) to the longer
broadcast radio waves).
There are several regions
of the electromagnetic
spectrum which are
useful for remote sensing.
An image is a two-dimensional representation of objects in
a real scene. Remote sensing images are representations of
parts of the earth surface as seen from space.
A digital image comprises of a two dimensional array of
individual picture elements called pixels arranged in
columns and rows.
Each pixel represents an area on the Earth's surface. A
pixel has an intensity value and a location address in the
two dimensional image.
A device that records Electromagnetic Energy
Carrier bed used to carry a sensor
Platforms and Sensors
Platforms are used to house the
sensors which obtain data for
remote sensing purposes.
The distance between the target
being imaged and the platform,
plays a large role in determining the
detail of information obtained and
the total area imaged by the sensor.
Airborne eg. Aircraft, Drone
Space borne eg. Satellite
Passive system record energy reflected or emitted by a target illuminated
e.g. normal photography, most optical satellite sensors
Active system illuminates target with energy and measure reflection.
e.g. Radar sensors, Laser altimeters
RADAR(Radio Detection and Ranging), LIDAR(Light Detection and Ranging)
Types of Sensors
The path followed by the satellite is called its orbit.
Types of Satellite Orbits
Satellite orbits are designed according to the capacity
and objective of the sensors they carry. Depending on
their altitude, orientation and rotation relative to the
earth, satellites can be categorized as-
Polar orbiting and Sun-synchronous
Satellites at very high altitudes (approximately 36,000
kilometres), view the same portion of the Earth's surface
at all times have geostationary orbits.
Geostationary satellites are always located directly
above the equator with a zero angle of inclination.
These satellites, revolve at speeds which match the
rotation of the Earth so they seem stationary, relative to
the Earth's surface.
This allows the satellites to observe and collect
information continuously over specific areas. Weather
and communications satellites commonly have these
types of orbits.
The remote sensing platforms are designed to follow
an orbit (basically north-south) which, in conjunction
with the Earth's rotation (west-east), allows them to
cover most of the Earth's surface over a certain period
These satellites cover each area of the world at a
constant local time of day. At any given latitude, the
position of the sun in the sky as the satellite passes
overhead will be the same within the same season.
This ensures consistent illumination conditions when
acquiring images in a specific season over successive
years, or over a particular area over a series of days.
This is an important factor for monitoring changes
between images or for mosaicking adjacent images
As a satellite revolves around the
Earth, the sensor "sees" a certain
portion of the Earth's surface. The
area imaged on the surface, is
referred to as the swath.
Ability of the system to render the information at the
smallest discretely separable quantity
in terms of distance (Spatial),
wavelength band of EMR(Spectral),
Time (Temporal) and
Spatial resolution refers to the amount of detail that can
be detected by a sensor/ Smallest unit-area measured.
Images where only large features are visible are said to
have coarse or low resolution. In fine or high resolution
images, small objects can be detected.
Detailed mapping of land use practices requires a much
greater spatial resolution
Spatial resolution of passive
sensors depends primarily on
their Instantaneous Field of View
The IFOV is the angular cone of
visibility of the sensor (A) and
determines the area on the Earth's
surface which is "seen" from a
given altitude at one particular
moment in time (B). The size of
the area viewed is determined by
multiplying the IFOV by the
distance from the ground to the
sensor (C). This area on the
ground is called the resolution cell
and determines a sensor's
maximum spatial resolution.
Fine/ high resolution
Coarse/ low resolution
Spectral Resolution describes the
ability of a sensor to define fine
This refers to the number of bands in
the spectrum in which the instrument
can take measurements
Higher Spectral resolution = better
ability to exploit differences in
Panchromatic- A single band image
generally displayed as shades of gray.
Multispectral- A multispectral image
consists of a few image layers, each layer
represents an image acquired at a
particular wavelength band.
Hyperspectral- A hyperspectral image
consists of about a hundred or more
contiguous spectral bands. The precise
spectral information contained in a
hyperspectral image enables better
characterisation and identification of
targets. Hyperspectral images have
potential applications in such fields as
precision agriculture (e.g. monitoring the
types, health, moisture status and
maturity of crops), coastal management.
Spectral resolution describes the ability of a sensor to
define fine wavelength intervals. The finer the spectral
resolution, the narrower the wavelength range for a
particular channel or band.
Revisit time (temporal resolution) = time between
two successive image acquisitions over the same area
Represents the frequency with which a satellite can
re-visit an area of interest and acquire a new image.
Depends on the instrument’s field of vision, and the
The time factor in imaging is important when:
Short-lived phenomena (floods, oil slicks, etc.) need
to be imaged
Multi-temporal comparisons are required (e.g. the
spread of a forest disease from one year to the next,
Sprawl of the city over the years)
The changing appearance of a feature over time can
be used to distinguish it from near similar features
(wheat / maize)
The radiometric characteristics of an image describe
the actual information content in an image. Its ability
to discriminate very slight differences in energy.
Sensitivity to the magnitude of the electromagnetic
energy determines the radiometric resolution.
The maximum number of brightness levels available
depends on the number of bits used in representing
the energy recorded. Thus, if a sensor used 8 bits to
record the data, there would be 2^8= 256 digital
values available, ranging from 0 to 255.
Image data are generally displayed in a range of grey
tones, with black representing a digital number of 0
and white representing the maximum value (for
example, 255 in 8-bit data).
By comparing a 2-bit image with an 8-bit image, we can see that there is a large
difference in the level of detail discernible depending on their radiometric
resolutions. Source: IIRS, ISRO Presentation
Source: IIRS, ISRO
Digital number in remote sensing systems, a variable assigned to a
pixel, usually in the form of a binary integer in the range of 0–255 (i.e.
a byte). The range of energies examined in a remote sensing system is
broken into 256 bins.
Collect information (Spatial, Spectral, Temporal & Radiometric
resolution, Swath, which country launched it) about the following
satellites in groups of five-
Code no. 1 to 5- IKONOS
Code no. 6 to 10- LANDSAT (1 to 8)
Code no. 11 to 15- SPOT (1 to 7)
Code no. 16 to 20- QuickBird
Code no. 21 to 25- NOAA (National Oceanic and Atmospheric Administration)
Code no. 26 to 30- Cartosat (1, 2, 2A, 2B)