Remote
Sensing
Is the
science of acquiring, processing and interpreting images that record the
interaction between Electromagnetic energy & matter or RS is the science of
acquiring information about the Earth's surface without actually being in
contact with it. Observed object size,
shape and character without direct contact with them.
Process
of Remote Sensing
Energy
Source or Illumination - Illuminates or provides
electromagnetic energy to the target of interest.
Radiation
and the Atmosphere – The energy travels to target and it
will come in contact with target to the sensor.
Interaction
with the Target – 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 - after the energy emitted from the target,
sensor to collect and record the EM radiation.
Transmission,
Reception, and Processing – The energy transmitted from electronic
form, to a receiving and processing station where the data are processed into
an image.
Interpretation
and Analysis – The processed image is interpreted, to
extract information about the target which was illuminated.
Application
– Apply the information we have been able to extract from the
imagery about the target in order to better understand it.
Fields
of Application
Meteorology - Weather forecast,Climate Studies,Global Change
Hydrology -Water
balance,Energy balance,Agrohydrology
Soil
Science - Land evaluation,Soil Mapping
Biology/Nature
Conservation-Vegetation mapping/monitoring,Vegetation condition assessment
Forestry -Forest
mapping,de-/re-forestation,forest fire detection
Environmental
studies -pollution,(Ground) water quality,Climate Change
Agriculture
Engineering -Landuse development,Erosion assessment,Water management
Physical
Planning -Physical Planning,Scenario studies
Land
Surveying -Topography (DTM),Spatial Data Models,GIS
Advantages
of remote sensing
• Enables
to observe a broad area at a time.
• Enables
to observe the area for a long period.
• Enables
us to know the condition without visiting the area.
• Enables
us to know invisible information.
Type
of RS: -
Visible and reflective IR RS- The sun reflectance:
Optical energy Visible Reflectance, Near Infrared Reflectance, Thermal Infrared
Thermal Radiation
(Drown the
diagram- source – sensor)
Thermal RS – Object thermal radiation
emissivity, temp: Optical energy Visible Reflectance, Near Infrared
Reflectance, Thermal Infrared Thermal Radiation
(Drown the
diagram – sensor)
Microwave RS – Microwave radiation/ radar
backscatter coefficient: Object Microwave - Microwave Radiation.
Spatial
Data Acquisition
Collection
Processing
Analysis
Need
for spatial data
Urban
planer
Engineer
Landuse planner
Data
acquisition
- Ground
based method (Surveying & mapping, Photogrammetric)
- Remote
sensing methods (Field observation by performing land surveying)
Classification
of Sensors
A sensor
that measures and records electromagnetic energy. Sensors can be divided into two
groups
– Passive Sensors: Depend on
an external source like Sun, For all reflected energy, this can only take place
during the time when the sun is illuminating the earth.
– Active Sensors: Active
sensors have their own source of energy. Active sensors include the laser
altimeter and radar.
Advantages
for active sensors:
– The
ability to obtain measurement anytime. Regardless of the time of the day,
season or weather.
– Examine
wavelengths that are not sufficiently provided by the Sun.
– To
better control the way that a target is illuminated.
Platforms:
There are
three types of flatforms in RS. These sensing is from 1m to 36,000km height.
- Ground based- Surveying & mapping,
Photogrammetry, ground observation
–
Airborne : Observations are carried out
using aircraft with special modification to carry sensors.
It is above 100m to 40 km height. This system can collect
information any time from the earth surface.
–
Spaceborne : This is base on satellites
system, Satellites are positioned in orbits between 150 – 36,000 km altitude.
Due to repetitive coverage of the Earth surface on a continuing basis.
Remote
Sensing Platforms
Platform
Altitude(km)
•
Geostationary Sat. 36,000
•
Earth Observation sat. 400 – 1000
•
Space shuttle 240 – 350
•
Airplane 0.3 – 7.5
Scanner
It
is a one line, or row, in a raster scanning pattern, such as a line of video on
a CRT display of a television. Raster data may need to be analyzed at the level
of scan lines in order to convert between formats. This radiation level called
digital numbers mulitispectral scanners(MSS), have range of 0.3 to 14um. Two
type of scanners, pushbroom scanners- Along track scanners, Wishbroom scanners
– Across track scanner.
pushbroom scanners- Linear
array CCD,Each pixel has its own detector, recording one entire line at the
time
Wishbroom scanners-
Combination of singal detectors and rotating mirror across track scanner
Benefits med resolution sat in urban area-
Scope
: Vass area maps can be prepared.
Specially vegetation, soil map land
use map, forestry maps etc.
Benefits:
As this is law resolution images, the primary cost will be less. As there
is not much data, we can reduce processing coast.
Swath-
When
the satallte move around the earth in obrbit, it sees the portion of earth
surface. This image referred as swath
Electromagnetic
Radiation
Electromgnetic
radiation consist with electrical field(E) and magnetic field(M). RS required
energy source to illuminate the target. The two characteristics of EM radiation
is wavelength and frequency. By
measuring the energy that is reflected by targets on earth’s surface in
different wavelengths. The pattern can be identify the pattern of different
fatures. It is 10-11 to 108 wavelength. Microwave
10-2 ,Infrared 10-5, Visible 0.5 – 10-6,Ultraviolet
10-8
The
visible spectrum
•
The light which our eyes our "remote sensors“can detect.
•
Note how small the visible portion is relative to the rest of the spectrum.
•
The visible wavelengths cover a range from approximately 0.4 to 0.7µm.
Violet:
0.400 - 0.446 µm
Blue:
0.446 - 0.500 µm
Green:
0.500 - 0.578 µm
Yellow:
0.578 - 0.592 µm
Orange:
0.592 - 0.620 µm
Red:
0.620 - 0.700 µm
Infra red and Thermal IR:
Infra
red portion; Covers the wavelength range from approximately 0.7 µm to 100
µm.Reflected IR region (0.7 µm to 3.0 µm) is used for remote sensing purposes
in ways
very similar to radiation in the visible portion.
Thermal
IR; region (3.0 µm to 100 µm) is quite different than the visible and reflected
IR portions, as this energy is essentially the radiation that is emitted from
the Earth„s surface in the form of heat. From
1µm - 6µm mid range. From 6µm - 100µm far range. The mid range is reflective
and the far range is emissive radiative thermal. From 1µm - 5µm covered
short wave.
Visible(reflected) IR range : It
is easy to separate vegetation and water boundaries
as vegetation are reflected energy and the water is absorbing the energy.
Not only vegetation and water but also dry soil, wet soil, clear water and turbid
water, etc.
Thermal IR range : It
is possible to take images (collect data or reflect energy) with
sun or without sun. We can take visible or invisible images. This process is time
irrespective.
