What is Remote Sensing Technology
Remote Sensing
Introduction
The term
"remote sensing," first used in the United States in the 1950s by Ms.
Evelyn Pruitt of the U.S. Office of Naval Research. ‘Remote’ means far away and
‘sensing’ means observing or acquiring some information.
Therefore, remote
sensing is the acquisition of information about an object or phenomenon without
making physical contact with the object.
In our everyday living, one employ remote sensing to view different objects. Our eyes can be considered as sensors that respond to the light reflected from various objects. The data acquired by our eyes are the impulses corresponding to the amount of light reflected from light and dark areas of the object.
This data is analyzed and interpreted by our brain
which works like computer, to enable us to recognize the object.
This process involves the detection and measurement of radiation of different wavelengths reflected or emitted from
distant objects or materials, by which they may be identified and categorized by class/type, substance, and spatial distribution.
Source:
Remarks: Brown color
indicates absorption areas
Green color indicates reflection
areas and useful for Remote Sensing
Paul R. Baumann
(2010). http://www.oneonta.edu/faculty/baumanpr/geosat2/RS-Introduction/RS-Introduction.html
Remote
Sensing is broadly classified into two categories based on sensors.
1. Passive Remote Sensing:
It uses sun as a source of electromagnetic energy. Passive
sensors detect energy that is naturally emitted or reflected by the object or
surrounding areas.
Examples:
Charge-coupled device (CCD) cameras, infrared sensors, imaging spectrometers.
2.Active Remote Sensing:
It uses its own source of electromagnetic energy. The
sensor emits radiation which is directed toward the target/object and return
energy is measured by the sensor.
Examples:
RADAR, LIDAR.
Remote Sensing Data Acquisition Process
It involves seven processes as illustrated in
figure shown below
(1) Energy
source- First requirement for remote sensing data acquisition is
the energy source that illuminates or radiates electromagnetic energy (EM) to
the earth’s surface features. Passive RS systems rely on Sun as the source of energy;
however active RS systems use its own source of energy.
(2) Energy propagation through earth’s atmosphere - The EM energy travels
from its source to the target through the atmosphere. Earth’s atmosphere modifies the strength and spectral distribution of energy and its effect varies with wavelength.
(3) Energy interaction with target – EM energy interaction with earth’s surface
features generates reflected/emitted signals (spectral response patterns or
signatures). These signatures are helpful in detection, identification and
analysis of earth’s surface features.
(4) Energy
received by the sensors – The EM energy reflected/emitted from the
target is recorded by the sensor. Sensors are electronic instruments which are
mounted on board satellites. These sensors are highly sensitive to wavelengths.
No single sensor is sensitive to all wavelengths and has fixed limits of
spectral and spatial sensitivity.
(5) Data
transmission, reception and processing – EM energy recorded by
the sensor is transmitted in electronic form to the ground based earth station.
After various levels of corrections, these data sets are processed into an
image.
(6) Data
interpretation and analysis – The processed image is interpreted visually/digitally
by the trained people to extract the information about the earth’s surface
features.
(7) Application
– The information extracted from imagery can be utilized for
several applications and mapping such as natural resource management, wildlife habitat protection,
land use/land cover change, crop monitoring and crop damage assessment, urban expansion/encroachment etc.
Fig. Remote Sensing System Process
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