This document provides an overview of remote sensing and describes its key principles and applications. It defines remote sensing as acquiring information about planetary surfaces from a distance without direct contact. The main components of a remote sensing system are described as the energy source, atmosphere, target interaction, sensor recording, transmission and processing, interpretation and analysis, and applications. Common data types like raster and vector data are also explained. Remote sensing techniques like digital image processing, classification, and analysis are outlined. Examples of satellite imagery and classifications are provided.

1. Dr. Rishitosh K. Sinha
Scientist/Engineer SE
Planetary Remote Sensing Section
Physical Research Laboratory, Ahmedabad
Email: rishitosh@prl.res.in
Mobile: +91 8128785486
PRINCIPLES AND
APPLICATIONS

3. What is Remote Sensing?
Remote sensing is the science (and to some extent, art) of acquiring
information about any planet’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.
Remote sensing is the process of detecting and monitoring the physical
characteristics of an area by measuring its reflected and emitted radiation at a
distance (typically from satellite or aircraft).

4. 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 of
interest.
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.
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.
Recording of Energy by the Sensor (D) -
after the energy has been scattered by, or
emitted from the target, we require a sensor
(remote - not in contact with the target) to
collect and record the electromagnetic
radiation.
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 digital).
Interpretation and Analysis (F) - the processed
image is interpreted, visually and/or digitally or
electronically, to extract information about the target
which was illuminated.
Application (G)

5. What is Electromagnetic Radiation?
The first requirement for remote sensing
is to have an energy source to illuminate
the target. This energy is in the form of
Electromagnetic radiation.
The above diagram shows an electromagnetic wave
propogating in the x direction, if the electric field is in
the y direction and the magnetic in the z direction.
Electromagnetic radiation consists of
an electrical field (E) which varies in
magnitude in a direction perpendicular
to the direction in which the radiation is
traveling, and a magnetic field (M)
oriented at right angles to the electrical
field. Both these fields travel at the
speed of light (c).

6. What is Electromagnetic Radiation?
Low frequency
Medium frequency
High frequency
Inversely proportional
Wavelength is the length of one wave cycle.
It is measured in nanometers, micrometers
etc.
Frequency refers to the number of cycles of
a wave passing a fixed point per unit of
time. It is normally measured in hertz (Hz),
equivalent to one cycle per second.

7. What is Electromagnetic Spectrum?
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.
Use in remote sensing:

8. Interactions with the Atmosphere
Before radiation used for remote sensing reaches the planet's surface it has to
travel through some distance of the planet's atmosphere. Particles and gases in the
atmosphere can affect the incoming light and radiation. These effects are caused
by the mechanisms of scattering and absorption.
Scattering refers to a change in the direction of motion of a particle because of a collision with
another particle. How much scattering takes place depends on several factors including the
wavelength of the radiation, the abundance of particles or gases, and the distance the radiation
travels through the atmosphere. There are three (3) types of scattering which take place.
Rayleigh scattering occurs when particles are very small compared to the wavelength of the
radiation (small specks of dust or nitrogen and oxygen molecules).
Mie scattering occurs when the particles are just about the same size as the wavelength of the
radiation (Dust, pollen, smoke and water vapour).
The final scattering mechanism of importance is called nonselective scattering. This occurs
when the particles are much larger than the wavelength of the radiation (water droplets and
dust).

9. The blue colour of the sky results from
Rayleigh scattering, as the size of the gas
particles in the atmosphere is much smaller
than the wavelength of visible light.
Rayleigh scattering is much greater for blue
light than for other colours due to its shorter
wavelength. As sunlight passes through the
atmosphere, its blue component is Rayleigh
scattered strongly by atmospheric gases but
the longer wavelength (e.g. red/yellow)
components are not.
The sunlight arriving directly from the Sun
therefore appears to be slightly yellow, while
the light scattered through rest of the sky
appears blue.
In contrast, the water droplets that make up clouds are of a comparable size to the
wavelengths in visible light, and the scattering is described by Mie's model rather than that
of Rayleigh. Here, all wavelengths of visible light are scattered approximately identically, and
the clouds therefore appear to be white or grey.

10. The Atmospheric Window

11. Target Interactions
We refer to two types of reflection, which represent the two extreme ends of
the way in which energy is reflected from a target: specular reflection and
diffuse reflection.

13. Passive vs. Active Sensing

15. Satellite Characteristics: Orbits and Swaths
The path followed by a satellite is referred to as its orbit.

17. Spatial Resolution, Pixel Size, and Scale
The detail discernible in an image is dependent on the spatial resolution of
the sensor and refers to the size of the smallest possible feature that can be
detected. Spatial resolution of passive sensors depends primarily on their
Instantaneous Field of View (IFOV).
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.

19. Spectral Resolution
The higher the number of bands of a remote sensing sensor, the
higher the spectral resolution of a satellite.
Using several bands for earth observation, these techniques are called multispectral
remote sensing. But there are sensors with 200 or more bands as well; those systems
are not called multispectral but hyperspectral.
Two fundamental conditions have to be considered in order to determine which
spectral bands are appropriate for a sensor: On the one hand, the atmospheric window
and, on the other hand, the spectral signature of the object in question.

22. Radiometric Resolution
Every time an image is acquired on film or by a sensor, its sensitivity to the
magnitude of the electromagnetic energy determines the radiometric resolution.
The radiometric resolution of an imaging system describes its ability to discriminate
very slight differences in energy The finer the radiometric resolution of a sensor, the
more sensitive it is to detecting small differences in reflected or emitted energy.

23. Temporal Resolution
The revisit period of a satellite sensor is usually several days. Therefore the
absolute temporal resolution of a remote sensing system to image the exact
same area at the same viewing angle a second time is equal to this period.

24. True and false colour composites

25. Image Analysis – Visual interpretation

27. Ghunghutta Reservoir
Shape

28. Gandhi Stadium
Shape and size

29. Pattern
Collectorate office
Kala Kendra

30. Bus Stand
Association

31. Raipur Airport
Pattern

32. Shadow/Pattern

33. Shape/Pattern/Association
Railway station

36. Credit: USGS

37. Digital Image Processing
All image interpretation and analysis involves some element of digital processing.
In order to process remote sensing imagery digitally, the data must be recorded and
available in a digital form suitable for storage on a computer tape or disk.
Image processing functions available in image analysis systems can be categorized into
the following four categories:
• Preprocessing: required prior to analysis/interpretation of the image
• Image Enhancement: mainly done to improve the appearance of the image to
enhance interpretation from the image (applied to increase differences between
features within an image)
• Image Transformation: similar to image enhancement; however, the transformation
involve combined processing of images from multiple bands
• Image Classification and Analysis: used to digitally identify and classify pixels in the
data.

38. Preprocessing
Landsat – 7 Image Destriping

39. Image Enhancement
Contrast enhancement

40. Pan Sharpening
Image Transformation

43. Image Classification
There are two broad subdivisions based on the methods used:
1. supervised classification,
2. and unsupervised classification.
In a supervised classification, the analyst identifies in the imagery homogeneous
representative samples of the different surface cover types (information classes) of
interest. These samples are referred to as training areas.
The computer uses a special program or algorithm (of which there are several
variations), to determine the numerical "signatures" for each training class.
Once the computer has determined the signatures for each class, each pixel in the
image is compared to these signatures and labeled as the class it most closely
"resembles" digitally.
Thus, in a supervised classification we are first identifying the information classes
which are then used to determine the spectral classes which represent them.

44. Supervised Classification

45. In unsupervised classification, spectral classes are grouped first, based solely on the
numerical information in the data, and are then matched by the analyst to information
classes (if possible).
Programs, called clustering algorithms, are used to determine the natural (statistical)
groupings or structures in the data.
Usually, the analyst specifies how many groups or clusters are to be looked for in the
data.
The final result of this iterative clustering process may result in some clusters that the
analyst will want to subsequently combine, or clusters that should be broken down
further - each of these requiring a further application of the clustering algorithm.
Thus, unsupervised classification is not completely without human intervention.
However, it does not start with a pre-determined set of classes as in a supervised
classification.

46. Unsupervised Classification

47. Supervised and Unsupervised Classification

48. Information Technology and
Geography
1. What is Information?
2. What is Geographic Information?
3. What are Geographic Information System?

49. What is Information?
• Information is data that have been organized (processed) and
communicated in a meaningful manner.
• Data is converted into information and information is
converted into knowledge.

50. What is Information?
Quantity Bucket number Item name Quantity of items
25 2 Fruits and vegetables 12 apples+13 potatoes
30 1 Vegetables 12 onions+15 potatoes+3 brinjal
21 5 Fruits 12 mangoes+5 apples+4 oranges
19 7 Eggs 19 eggs
24 3 Fruits, vegetables, and eggs 8 apples+12 potatoes+4 eggs
06 6 Vegetables 6 potatoes
21 4 Fruits and vegetables 15 oranges+6 onions
Data

51. Quantity Bucket number Item name Quantity of items
25 2 Fruits and vegetables 12 apples+13 potatoes
30 1 Vegetables 12 onions+15 potatoes+3 brinjal
21 5 Fruits 12 mangoes+5 apples+4 oranges
19 7 Eggs 19 eggs
24 3 Fruits, vegetables, and eggs 8 apples+12 potatoes+4 eggs
06 6 Vegetables 6 potatoes
21 4 Fruits and vegetables 15 oranges+6 onions
What is Information?
Information
Data

52. What is Geographic Information?
Geographic information describes:
• Physical location from where the information is coming
• Relationship between associated objects included in the information
Name and location of
cities
• Population
• Temperature
• Distance
• Density
• Land use

53. • Spatially related
• Can be assigned coordinates
or any spatial reference.
• On the surface of the earth.
• Involves location and
organization.
• Scale
• Can be from general to
specific.
• Simple to complex.
• Dynamics
• Spatial dynamics (variations
in space).
• Temporal dynamics
(variations in time).
Coordinate system
Scale
Time 1 Time 2
What is Geographic Information?

54. What is Geographic Information System?
• A geographic information system (GIS) integrates hardware, software, and
data for capturing, managing, analyzing, and displaying all forms of
geographic information.
• GIS allows us to view, understand, question, interpret, and visualize data in
many ways that reveal relationships, patterns, and trends in the form of
maps, globes, reports, and charts.
• A GIS helps you answer questions and solve problems by looking at your
data in a way that is quickly understood and easily shared.
• GIS technology can be integrated into any enterprise information system
framework.

56. What is Geographic Information System?
Geographic Information System
Encoding
• Information Systems
• Information system
specializing in the input,
storage, manipulation,
analysis and reporting of
geographical (spatially
related) information.
Management
Reporting
Analysis
Digitizing maps
Encoding spatial data
(census, vegetation,
topography, etc…)
Geographic
database in a
spatial data format
Spatial analysis
Thematic maps

57. Key features of GIS
• Information from different
sources
 Computer databases
 Digital maps
 GPS receiver
 Satellite image
• Data integration
• Projection
• Information retrieval
• Data output
• Overlay

58. Key components of GIS
Methods
People
Informa-
tion
Software
Hardware
GIS
• Hardware
Hardware is the computer on which a GIS operates.
• Software
GIS software provides the functions and tools needed
to store, analyze and display the geographic
information.
• People
GIS users range from technical specialists who design
and maintain the system, to those who use it to help
them do their everyday work.
• Methods
A successful GIS operates according to a well-
designed plan and business rules, which are the
models and operating practices unique to each
organization.
• Information
Geographic information and related tabular data can
be collected in-house or bought from a commercial
data provider. Most GIS employ a DBMS to create
and maintain a database to help organize and manage
data and information.

59. Data representation in GIS
• Raster Data
 Represent images as a
collection of pixels
 A grid of cells covering an
image / area
 Higher data volume
 Example of raster formats
 GeoTiff
 ARC/INFO ASCII Grid
 ARC/INFO GRID
 ECW
 IMG
• Vector Data
 Use geometrical shapes
(Lines, Points, Polygons)
 Low data volume
 Example of vector formats
 Shape files
 MapInfo TAB

60. Data representation in GIS
• RASTER
• VECTOR
• Real World

61. Entity representation in GIS
Points - simplest element, no
length or Width.
Lines (arcs) - set of connected
points, must have a beginning
and an ending point.
Polygons - set of connected
lines, can be used to describe a
feature as having an area.
We typically represent objects in space as three distinct
spatial elements:
We use these three spatial elements to represent real world features and
attach locational information to them.

62. Data types in GIS
Spatial/Geospatial/Geographic Data
• Latitude and longitude
• Street address
• x and y coordinates
• Range and township
• Location shown on a map
Non Spatial Data
• Name
• Gender
• Income
• ID number

63. Attributes in GIS

64. Data Assembly
Maps RSI
Intel Database Direct Entry
Keyboard
GPS
Functions in GIS

65. GIS
Desktop GIS Web GIS Mobile GIS
Types of GIS
The two primary desktop
applications for GIS
professionals are ArcMap
and ArcGIS Pro, and both
are part of ArcGIS
Desktop.
Web GIS is a type of
distributed information
system, comprising at
least a server and a client,
where the server is a GIS
server and the client is a
web browser, desktop
application, or mobile
application.
A mobile GIS allows
users out in the field to
capture, store, update,
manipulate, analyze,
and display geospatial
data and information.

66. Why to use GIS?
If you have a question, a map, tabular data, a computer, and
a GIS software application, you can utilize GIS to answer
your question.
Who uses GIS?
GIS are rapidly becoming the essential tools of analysis at all
levels of public- and private-sector management,
administration and planning.
People with the skill to use GIS are in demand across a broad
range of professions, in government, business and nonprofit
organizations.
How to use GIS?
GIS provides a set of tools for planning, decision-making,
operations management and inventory. GIS has a wide range
of applications.

67. What we can do with GIS

68. https://www.qgis.org/en/site/

69. https://earthexplorer.usgs.gov