1. Remote Sensing
Vivek.A
ECE, Methodist College of Engineering
Address
Vivek akkala@gmail.com
Abstract— Remote Sensing is the science and art of acquiring To georeference something means to define its existence in
information (spectral, spatial, and temporal) about material physical space. That is, establishing its location in terms of map
objects, area, or phenomenon, without coming into physical projections or coordinate systems.
contact with the objects, or area, or phenomenon under Another factor is that of the platen against which the film is
investigation. Without direct contact, some means of pressed can cause severe errors when photographs are used to
transferring information through space must be utilized. In measure ground distances.
remote sensing, information transfer is accomplished by use of
electromagnetic radiation (EMR). EMR is a form of energy that
reveals its presence by the observable effects it produces when it
strikes the matter. EMR is considered to span the spectrum of C.Classifications of RS
wavelengths from 10-10 mm to cosmic rays up to 1010 mm, the
broadcast wavelengths, which extend from 0.30-15 mm. There are two kinds of sensors in remote sensing: Passive and
Active
This paper emphasis on interpretation of the received data by the Passive sensors detect natural radiation that is emitted or
sensors which gives the details of the required object which reflected by the object or surrounding area being observed.
conserves our resources including time and it concentrates more Examples of passive remote sensors include film photography,
on types of sensors and the method of analysis done by them Infrared, charge-coupled devices, and radiometers.
Keywords— active and passive sources, EMR, Sea, Lake, and
Overland Surge from Hurricanes (SLOSH), resolution,
repitivity.
A. Introduction
In the broadest sense, remote sensing is the measurement of
information of some property of an object or phenomenon, using
a device that is not in physical or intimate contact with the
object or phenomenon under study (from aircraft, spacecraft, or Active collection emits energy in order to scan objects and areas
ship). The technique employs such devices as the camera, lasers, whereupon a sensor then detects and measures the radiation that
and radio frequency receivers, radar systems, etc. This is done is reflected or backscattered from the target. RADAR is an
by the analysis of electromagnetic radiation reflected absorbed example of active remote sensing
and scattered by the atmosphere, for the purpose of
understanding the Earth's resources and environment
B. Conventional Remote Sensing
In the early stages of remote sensing, photography was used.
This method suffers from one major drawback viz. distances are
accurate in the center of the image, with the distortion of
measurements increasing the farther you get from the center.
This problem is overcome by Georeferencing.
2. twenty-two perceptible shades of gray in the visible
Most remote sensing systems utilize the sun’s energy, which is a spectrum.
predominant source of energy. These radiations travel through
the atmosphere and are selectively scattered and/or absorbed II. Color Infrared Film (CIR): Detects longer wavelengths
depending upon the composition of the atmosphere and the somewhat beyond the red end of the light spectrum. Can be
wavelengths involved. These radiations upon reaching the used for temperature mapping.
earth’s surface interact with the target objects and are collected
by the sensors which gives the idea of the required
object. III. Thermal Infrared Multispectral Scanner (TIMS): Superior
to CIR and uses a six channel scanner that measures the
Generally speaking, remote sensing works on the principle of thermal radiation given off by the ground, with accuracy to
the inverse problem. While the object or phenomenon of interest 0.1 degree centigrade. The pixel (picture element) is the
(the state) may not be directly measured, there exists some other square area being sensed, and the size of the pixel is
variable that can be detected and measured (the observation), directly proportional to sensor height.
which may be related to the object of interest through the use of
a data-derived computer model. The common analogy given to
describe this is trying to determine the type of animal from its
footprints. For example, while it is impossible to directly IV.Airborne Oceanographic Lidar (ADI): The laser beam
measure temperatures in the upper atmosphere, it is possible to pulses to the ground 400 times per second, striking the
measure the spectral emissions from a known chemical species surface every three and a half inches, and bounces back to
(such as carbon dioxide) in that region. The frequency of the its source. In most cases, the beam bounces off the top of
emission may then be related to the temperature in that region the vegetation cover and off the ground surface; the
via various thermodynamic relations. difference between the two give information on forest
height, or even the height of grass in pastures
The quality of remote sensing data and the inference we draw
depends on spatial, spectral, radiometric and temporal
resolutions. Remote sensing not only gives the geographic locations of
stationary targets, but with the advancement in the
technology like Synthetic Aperture Radars and Sequential
Spatial resolution
Image Capturing it has been able to provide details of the
The size of a pixel that is recorded in a raster image -
targets in motion which enables the prediction of weather
typically pixels may correspond to square areas ranging
accurately- movement of Hurricanes were predicted very
in side length from 1 to 1,000 metres (3.3 to 3,280 ft).
accurately.
Spectral resolution
The number of different frequency bands recorded -
usually, this is equivalent to the number of sensors
carried by the platform(s).
Radiometric resolution
E. A typical example highlighting the benefits of Remote
Sensing.
The number of different intensities of radiation the
sensor is able to distinguish. Typically, this ranges
from 8 to 14 bits, corresponding to 256 levels of the The Sea, Lake, and Overland Surge from Hurricanes (SLOSH)
gray scale and up to 16,384 intensities or "shades" of model was developed by the National Oceanic and Atmospheric
colour, in each band. Administration (NOAA) National Weather Service (NWS). The
Temporal resolution model identifies the potential surge zones associated with the
The frequency of flyovers by the satellite or plane, and various storm categories on the Saffir-Simpson hurricane scale
is only relevant in time-series studies or those requiring through the Remote Sensing Data.
an averaged or mosaic image as in deforesting The hurricane's track, size, and intensity obtained from the
monitoring. remote Sensing data must be specified before the model is run.
When these parameters are put into the model, a model wind
field is produced, which in turn gives the surface stresses. The
stresses act as the driving forces to move the water. Friction, the
surface wind stress, and the pressure gradient cause the water to
D.Detection in Remote Sensing pile up along the coast. The model repeatedly sends the
I. Black and White photography: Black and white theoretical hurricanes into shore at various angles of approach.
The end result is a near accurate prediction of the oncoming
photography is commonly used but it only records about
hurricane in the geographic region under study. A maximum
3. depth of inundation is calculated for each and every location on
the map. The output from the model is used by emergency
preparedness professionals to decide who may be at risk from an
approaching hurricane. G. Industrial Usage and Other application:
• Coastal Applications
F. Graphical Analysis Remote sensing data can be used to monitor and
evaluate shoreline changes both pre- and post-
The field of view of the optics is 43 degrees providing a swath beach renourishment used to study shoreline and
of 1420 km from 720-km altitude. bluff erosion.
The super cyclone that hit Orissa on Oct, 27th, 1999, has
brought drastic changes widely through out the coastal districts • Oceanic Applications
and in order to monitor the changes that occurred before and Large scale events such as ocean circulation,
after the event. current systems, upwelling and eddy formation can
be better understood by using satellite imagery
• Hazard Assessment
A hazard event could include large storms,
earthquakes,
Remote sensing can be used both to aid in
identifying resources prior to an event and also to
asses the damage following an event.
H. Conclusions:
Remote sensing has been able to provide an all round
development in various fields like Synoptic View - facilitates
the study of various earths’ surface features in their spatial
relation to each other and helps to delineate the required features
and phenomena.
Repitivity – provide repetitive coverage of the earth and this
temporal information is very useful for studying landscape
dynamics.
Accessibility- it possible to gather information about the area
when it is not possible to do ground survey like in mountainous
areas and foreign areas.
Time Conservation - information about a large area can be
gathered quickly, the techniques save time and efforts of human.
Cost Effective.- It is a cost-effective technique as again and
again fieldwork is not required and also a large number of users
can share and use the same data.
1. References:
[1]http://www.ucalgary.ca/UofC/faculties/SS/GEOG/Virtual/re
moteintro.html
[2] www.geo.mtu.edu
[3] http://rst.gsfc.nasa.gov/Intro/Part2_1.html
[4] http://earthobservatory.nasa.gov/Features/RemoteSensing
