Concept of Remole Sensing 29

Shadnagar

receiving station
Fig. 1.16 Approximate vicinity of Shadnagar ground
be
The data are received at the GRS in a digital format. They may then, if required,
raw

and atmospheric distortions to the imagery

processed to correct systematic, geometric, format. The data are written
Chapter 10), and be translated into a standardized image
(refer data are typically
such as tape, magnetic disk, or CD. The
to some form ofstorage medium
libraries of data are managed
archived at most receiving and processing stations, and full
well as commercial companies responsible for each satellite/
by government agencies as
sensor.
when
to provide customers
with quick-turnaround imagery
Note For many sensors, it is possible
data as quickly as possible
after it is collected. Near real-time processing systems
they need
low-resolution imagery in hard copy (paper
printout) or soft copy
are used to produce transfered
Such imagery can then be faxed or
format within hours of data acquisition.
(digital) is also used to preview
archived
end-users. Low-resolution quick-look imagery
digitally to of these types of data products
purchase. The spatial and radiometric quality
imagery prior to
overall quality, coverage, and cloud
cover

is degraded, but they are

useful for ensuring that the
of the data are appropriate.

I.13 INTERPRETATION AND ANALYSIS

before
It must be interpreted or analysed
Data alone cannot be used for decision making.
sensed data is performed using
a
extract information. The analysis of remotely
one can
techniques which fall into two broad
interpretation and processing
variety of image
categories (Fig. 1.17):
.visual imageinterpretation and
digital image processing (DIP)
30 Remote Sensing and GIS

(a) (b)
Fig. 1.17 Image processing: (a) visual and (b) digital
I.13.1 Visual Image Interpretation
Both analog and digital image data allow the analyst to perform scientific visualization,
defined as
'visually exploring data and information in such a way as to gain understanding
and insight into
the data'.
Most of the fundamental
elements of image interpretation are used in visual
analysis, including size, shape, shadow, colour (tone), image
association. The human mind is
parallax, pattern, texture, site, and
in an image or
amazingly adept at recognizing these complex elements
photograph because we constantly process the profile view of the earth
features every day and continually
process images in books and magazines and on
How to interpret a
remotely sensed image by means of visual interpretation television.
will be
discussed in Chapter9.

I.13.2 Digital Image Processing

Scientists have made significant advances in the digital image processing (computer
processing) of remotely sensed data for scientific visualization and hypothesis testing. It
iscommonly known that the human eye can discriminate only about 40-50 shades of
grey when interpreting a grey-scale image. If the data were
shades of grey, there may be more subtle information
originally recorded with 256
present in the image than the
interpreter can extract visually. A computer can
analyse each of the data in an image
using various digital image processing techniques. Further, several mathematical
operations on or among the images can be applied that can aid in information extraction
and analysis. The
major types of digital image processing include statistical and syntactical
pattern recognition.
Techniques involved in digital image processing and its
in detail in elements/types are explained
Chapter 10.
Information derived from remote sensor data usually summarized as an ennanceu
are
image, image map, orthophoto map, thematic map,
Thus the final output spatial database file, statistic, or grap.
products often require knowledge of remote sensing, geograpny»
cartography, geology, physics, mathematics, statistics,
science, informati0
technology, GIS, and obviously social science as well ascomputer
the systematic science
beng
 Concept of Remole Sensing 31

investigated (i.e., soils, agriculture, forestry, wetland, urban, etc.). The analyst who
understands the rules and synergistic rclationship between the technologies can produce
output products that communicate effectively.

I.14 APPLICATIONS OF REMOTE SENSING

Remotely-scnsed data analysed in a vacuum without the benefit of other collateral
information (such as soils, hydrology, agriculture, urban, etc.) is meaningless. Remote

sensing may be used for numerous applications including weapon guidance system (e.g..
the cruise missile), medical image analysis (e.g., X-raying a broken arm), non-destructive
evaluation of machincry and products (e.g., on the assembly line), analysis of the earth's
resources, etc. Earth resource information is defined as any information concerning
well as certain
vegetation, soils, minerals, water, and urban infrastructure as
terrestrial
of remote
atmospheric characteristics. This book focuses on the art and science applying
the application
sensing for the extraction of useful earth resource information. Though
broad categories are
ofremote sensing is not limited to 10 or 15, or even 100 cases, some
described in Chapter 12.

ADVANTAGES OF REMOTE SENSING

well as some limitations also. It is
Remote sensing has several unique advantages as

limitations of remote sensing, to use it

essential to understand both the advantages and
more effectively.
the electromagnetic
Remote sensing is unobtrusive if the sensor is passively recording
emitted by the phenomenon of interest. This is very important
a
energy reflected from
or
natural source of energy, e.g., the sun)
consideration, as passive remote sensing (using
of interest.
does not disturb the object or area
collect data systematically! This
sensing devices are often programmed to
CRemote bias introduced in some in situ
data collection can remove the sampling
systematic
investigations. the ability to
synoptic
has view. Synoptic view of a sensor is
Remote sensing sensor

of the sensor can reduce the data acquisition

see large areas at the same time. This ability
area in comparison
to the
over a large geographic
time (and thereby cost) dramatically
traditional surveying methods.
at a regular time interval.
can be performed repeatedly
Remote sensing from satellites
several earth-surface features continuously.
This can help in monitoring
data about areas that are physically and or
Remote can be used for collecting
sensing
politically inaccessible. fundamental
controlled conditions, sensing can provide
remote
Under carefully biomass, temperature,
locations, z elevation or depth,
biophysical data, including: x, y fundamental data
etc. In this sense, it is
much like surveying, providing
moisture content, unlike
investigations. However,
can use when conducting scientific
that other sciences
 32 Remote eIsing and G1S

much of surveying. the remotely senscd data may be obtained systematically over very
large geographie areas rather than just single point observations.
Remote sensing is also different from the other
mapping scicnces such as cartography
or GIS because they rely on data produced clsewhere. Remote
sensing science yields
fiundamental scientific information. For example, a properly calibrated thermal
infrared
remote sensing system can provide a gcometrically correct map of land or sea-surface
temperature without any other intervening scicnce. A good example is the digital elevation
modcls that are so important in nmany spatially
distributed GIS models. Digital elevation
modcls are now produccd almost exclusively through the analysis of remotely sensed
data' (Jenscn 2004).

I.16 LIMITATIONS OF REMOTE SENSING

Remote sensing science has various limitations. 'Perhaps the
greatest limitation is that its
utility is often oversold' (Jensen 2004). It is not a panacea that will provide all the
information needed for conducting physical, biological, social science. It
or
simply
provides some spatial, spectral, and temporal information.
Human beings select the most appropriate sensor to collect the data, specify the
resolution of the data, calibrate the sensor, select the platform that will carry the
sensor,
determine when the data will be collected, and specify how the data are
processed. Thus,
human method-produced error may be introduced, as the various remote
sensing
instrument and mission parameters are specified (Jensen 2004).
Powerful active remote sensor system, such as lasers or radars that emit their own
EMR, can be intrusive and affect the phenomenon being investigated.
Remote sensing instruments often become uncalibrated, resulting in uncalibrated remote
sensing data. Finally, remote sensor data may be expensive to collect, interpret, or analyse.
But, the information derived from the remote sensor data is so valuable that the
expense
is warranted.

17 IDEAL REMOTE SENSING SYSTEM

Having introduced some basic concepts, we now have the necessary elements to
conceptualize an ideal remote sensing system. In doing so, we can then appreciate some
of the problems encountered in the design and application of the various real remote
sensing systems examined in subsequent chapters.
The basic components of an ideal remote
sensing system include the following
components (Lillesand and Kiefer 1994):
A uniform energy source This source will provide energy all over wavelengths, at a
constant, known, high level of output, irrespective of time and place.
A non-interfering atmosphere This will be an atmosphere that will not
modify the energy
from the source in any manner, whether that energy is on its way to the earth's surface or
 Concept f Remote Senstng 33

coming from it. Again, ideally this will hold irrespective of wavelength, timne. place, and
sensing altitude involved.
matter interction at the earth 's surface These interactions
A series of unique energy
Will generate reflected and/or emitted signals that are not only selective in respect to

also known, invariant, and unique to cach and every earth surface
wavelengths, but are

feature type and subtype of interest.

A super sensor This will be a sensor, highly sensitive to all wavelengths. yielding
scene (a function

spatially detailed data on the absohute brightness (or radiance) from a

This super sensor simple and reliable.
will be
of wavclength). throughout the spectnunm.
and economical to operate
or space. and be accurate
require Virtually no power the radiance versus
system In this system, the instant
A real-time data handling transmitted to the
response over a terrain element is gencrated, it will be
wavelength as being unique
to the
interpretable format and recognized
ground and procesed into
an
will be performed nearly
from which it comes. This processing
particular terrain element Because of the consistent
nature
information.
instantancously (real time), providing timely data in the analytical
interactions, there will be no need for reference
of the energy-matter data will provide insight into the physical-chemical-biological
procedure. The derived
state of each feature of interest. of both, their
will have comprehensive knowledge
These people
Multiple data u s e r s data acquisition and analysis
techniques.
and of remote sensing users, because
respective disciplines forms of information for different
will become various
The s a m e set of data earth's r e s o u r c e s being
used.
about the particular does not exist.
of their vast knowledge as described herein,
remote sensing system,
an ideal real remote sensing
Unfortunately, us to evaluate the
understanding
can help
However, the preceding
limitations.
and/or
systems-their
capabilities

EXERCISES

Descriptive Questions
understand by r e m o t e sensing?
I. What do you process.
r e m o t e sensing spectrum?
2. Briefly explain EMR.What is
electromagnetic content of a photon.
of the energy
3. Explain wave
model frequency, and
the wavelength,
relation amongst with the atmosphere.
4. Derive the incident EM energy
i n t e r a c t i o n s of
various
5. Explain with the target.
interaction of EM enerEY transmittance,
and
reflectance.

6. Explain absorptance, remote

sensing'
utilities in
7. Explain
hemispherical
what are its
c u r v e and data.
reflectance
is spectral reception
of recorded
8. What t r a n s m i s s i o n and

the process
of interpretation?
9. Explain understand
analysis and
by sensing?
10. What
do you
and
limitations of remote
advantages
a r e the
I1. What