INTRODUCTION AND SOME BASIC INFORMATION ABOUT THE REMOTE SENSING PROCESS.

2. Dhaval Jalalpara

4.  ‘REMOTE’ means far away and ‘SENSING’ means
believing or observing or acquiring some information.
 Remote sensing means acquiring information of
objects from a distance. Human eye is perhaps the most
familiar example of a remote sensing system.
 The advantage of remote sensing is the bird’s eye
view or synoptic view it provides, so that data covering a
large area of earth can be captured instantaneously and
then can be processed to generate map like products.
 Remote sensing occurs at a distance from the
object or area of interest. Interestingly , there is no clear
distinction about this distance. It could be
1m,100m,1000m or greater than 1 million meters from
the object or area of interest.
 In fact, virtually all astronomy is based on Remote

6.  Remote sensing is the science and art of
obtaining information about an object area or
phenomenon through and analysis of the data
acquired by a device which is not in contact with
the object, area or phenomenon under
investigation.
 Therefore, it consist of collecting and
interpreting information about an object , area or
phenomenon without being in physical contact
with them.
 Remote sensing is the methodology
employed to study from a distance the physical
and/or chemical characteristic of objects.

8.  Remote sensing is a tool or technique or
methodology similar to mathematics.
 However, the term remote sensing is restricted to
methods that employ electromagnetic energy(such as
light , heat , microwave) as means of detecting and
measuring target characteristics.
 Aircraft and satellites are the common platforms
used for remote sensing. Collection of data is usually
carried out by highly sophisticated sensors (i.e. camera,
multispectral scanner, radar, etc.).
 The information carrier or communication link is
the electromagnetic energy. Thus , remote sensing
includes all the methods of obtaining pictures or other
forms of electromagnetic records of the earth’s surface
from a distance, their processing and interpretation.

9.  Remote sensing data basically consists of wave
length intensity information by collecting the
electromagnetic radiation leaving the objects at specific
wavelength and measuring its intensity.
 Most of the remote sensing methods make use
of the reflected infrared bands, thermal infrared bands
and microwave portion of the electromagnetic spectrum.
 They are so high that they can make images of a
very large area. Nowadays, remote sensing is mainly
done from space using satellite.
 It functions in harmony with other spatial data
collection techniques or tools of the mapping sciences,
including cartography and geographic information
systems(GIS).

10.  REMOTE SENSING is broadly classified into
two categories.
(a) Passive remote sensing and
(b) Active remote sensing

11. (a) Passive Remote Sensing:
It uses sun as a source of EM
energy and records the energy that is naturally
radiated and/or reflected from the objects. In this
system photography are taken on clear bright day.
Without illumination from the sun no photographs
can be taken with camera.
(b) Active Remote Sensing:
It is used its own source of EM
energy, which is directed towards the object and
return energy is measured. A system which utilizes
man-made sources of energy for data collection is
called active system.

13.  Now consider, if the energy being remotely
sensed comes from the sun, the energy is radiated by
atomic particles at the sources(the sun), propagates
through the vacuum of the space at the speed of light,
interacts with the earth’s atmosphere, interacts with the
earth’s surface, some amount of energy reflects back,
interacts with the earth’s atmosphere once again and
finally reaches the remote sensors which are mounted on
satellite.
 The following seven elements ( A to G ) that
comprise the most common remote sensing process from
beginning to end is illustrated in under fig.

15.  The first requirement for remote sensing
is to have an energy source that illuminates or
radiates electromagnetic energy to the target of
interest.
 The passive RS system relies on the sun
as the strongest sources of EM energy and
measures energy that is either reflected and/or
emitted from the earth’s surface features.
 However, active RS systems use their own
source of EM energy.

16.  As the EM energy travels from its sources to the
target , it will come in contact with and interact with
the atmosphere on its way to earth’s surface.
 Also after reflection from the earth’s surface, it
again passes through the atmosphere on its way to
sensor.
 When the energy source is the sun, then first of
all the energy comes through vacuum where no
interaction happen before interacting with the earth’s
atmosphere
 The atmosphere modifies the wave length and
spectral distribution of energy to some extent and this
modification varies particularly with the wave length.

17.  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.
 The interaction of EM energy, with earth’s
surface features generates reflected and/or emitted
signals (spectral response pattern or signatures).
 The spectral response pattern play a central role
in detection , identification and analysis of earth’s
surface features.
 As the reflected (or emitted) energy travels
from its target to the sensing or imaging device, it
interacts with the atmosphere once again(B).

18.  After the energy has been reflected by or
emitted from the target , we require a sensor
(remote ,not in contact with the target)to collect
and record the EMR(Electro Magnetic Radiation)
 Sensors are mounted on satellite. They are
highly sensitive to wave lengths , yielding data on
the absolute brightness from the object as a
function of wavelength.

19.  The energy recorded by the sensor has to be
transmitted, often in electronic form, to a receiving and
processing station on the ground where the data are
processed into an image.
 The real time (instantaneous) data handling system
consist of high density data tapes for recording and
visual devices (such as television) for quick look displays.
 The data products are mainly classified into two
(1) Pictorial or photographic product(analogue) and
(2) Digital product

20.  The processed image is interpreted , visually
and/or digitally or electronically, to extract information
about the target of interest .
 The data analysis process involve examining the
data using various viewing instruments to analyse
pictorial data, which is called the visual image
interpretation techniques.
 Use of computers to analyse digital data
through a process is known as digital image processing
techniques.
 The analysis of a data utilizing visual image
interpretation involves use of the fundamental pictures
elements, namely tone, texture, pattern, size, and
shape in order to detect and identify various objects.

21.  Finally we apply the information about the
target of interest to better understand it.
 The set of data becomes various forms of
information for different users with the
understanding of their field and interpretation
skills.
 Hopefully, the people can information to
make improved management decisions.

22.  Remote sensing has application in a wide
spectrum of area.
 Remote sensing affords a practical means for
accurate and continuous monitoring of the earth’s
natural and other resources and of determining the
impact of man’s activities on air, water and land.
 Remote sensing data can be used for taking sound
decisions for planning many human developmental
activities.
 It is also possible to take preventive action as in
the case of forest fires and natural disasters.
 Weather forecasting is another important
application. Some of the application areas are given

23. 1) Agriculture : Crop statistic,
management system analysis and
horticulture.
2) Forestry : Forest area, types and
density, biomass, and grassland.
3) Environment : Impact analysis,
wetlands, pollution, and abatement.
4) Coastal mapping : Coastal Land use,
landforms, habitat processes.
5) Marine application : Potential fishing gene,
forecast modeling, primary productivity
6) Urban environment : Road development
planning, route analysis.

24. (7) Land and water : Land and water
conservation
Resources development and development,
groundwater targeting, snow melt, runoff recharge.
(8) Geology : Mineral targeting, oil
exploration mapping, groundwater studies
(9) Landuse/Land cover : Mapping development
and planning
(10) Information : Integrated spatial and
attribute data, query and modeling