UNIT-3.pptx GIS INFORMATION SYSTEMFOR COMPUTING

UNIT-3
REMOTE SENSING PLATFORMS AND SENSORS

ORBITS OF REMOTE SENSING
SATELLITE:
Satellite is any object man made or natural
that revolves around the earth
TYPES OF ORBITS:
• Low Earth Orbit (LEO) < 2000 km
• Medium Earth Orbit (MEO) 2000-35786 km
• High Earth Orbit (HEO) > 35786 km

Low Earth Orbit:
Polar orbiting satellites:
• Satellite is pass above the
earth poles
• High resolution of images
is possible
• Crosses the equator at 90⁰

Low Earth Orbit:
Polar orbiting satellites:
• The advantage is every time the satellite view the
newer segment on the earth surface because of
earth’s rotation

Sun Synchronous Orbit
• Angle of inclination of
the orbit with respect
to the sun through out
the year is same
• Always crosses the
equator precisely the
same local sun time
• Mostly used for remote
sensing

Sun Synchronous Orbit

Near polar orbit
• Orbital plane inclined
at small angle with
respect to the earth
rotational axis

High Earth Orbit
Geo stationary orbit
• The satellite placed in
this orbit is stationary
with respect to the earth
• View the same area of
the earth at all times
• View 50% of global
surface (60⁰N to 60⁰S)
• Orbital period is 24 hours

High Earth Orbit
Advantages :
• Useful for meteorological
observation
• And also for commercial
broadcast and
communication purpose

High Earth Orbit
Dis-Advantages:
• Low resolution
• Approximately a pixel size
of 2.5 km on the ground
• Less information is
obtained

Choice of orbit:
• It is dependent on the its mission
• Remote sensing satellites placed in LEO
because it needs high resolution
• Commercial broadcast or Communication
satellites are provided in HEO because it
should receive and send signals from large
geographical are

Shapes of orbits:

Types of platforms :
Ground based platforms
Short range systems(50-100 m)
Medium Range Systems ( 150-250 m)
Long range Systems (up to 1 km)
Airborne platforms
Space-borne platforms
REMOTE SENSING PLATFORMS

Ground Based Platforms:
Mobile hydraulic platforms (up to 15 m height)

Portable Masts
• Unstable in wind conditions

Towers:
• Greater rigidity than masts

Weather Surveillance Radar
• Detects and tracks
typhoons and cloud masses

Airborne Platforms:
Balloons based :
• Altitude range is 22-40
km
• Tool to probing the
atmosphere
• Useful to test the
instruments under
development

Airborne Platforms:
Radiosonde:
Measure pressure,
Temperature and
Relative humidity in the
atmosphere
Rawinsonde:
Measure wind velocity,
temperature, pressure
and relative humidity

Aircraft:
Advantages:
• High spatial resolution (20
cm or less)
• Analog photography is
possible (analog photo gives
high resolution)
• Easily change their schedule
to avoid weather problems
• Sensor maintenance and
repair is easy

Aircraft:
Dis Advantages:
• Permission to intrude into foreign airspace is
required
• Many passes to cover larger area
• Swath is much less compare to satellite
• High cost per unit area

Space borne platforms:
• Sensors are mounted on-
board a spacecraft
• Rockets , satellites and
space shuttles
Advantages :
• Cover large area
• Repetitive coverage of an
area of interest

REMOTE SENSING SENSORS
Sensor :
Common Definition :
• Sensors are Sophisticated devices that are
frequently used to detect and respond to
electrical or optical signals
• A Sensor converts the Physical parameter
into a signal which can be measured
electrically

Sensor :
Definition in Remote Sensing :
• Sensor is a device that gathers energy (EMR)
converts into signal and present it into a signal and
present it in a form (image) suitable for obtaining
information about the objet under investigation

Types of sensors :

Types of sensors :
Active sensors:
These sensors detect reflected responses from
objects which are irradiated from artificially
generated energy sources
Ex : Radar, camera with flash light
Passive sensors:
These sensors detect reflected EMR from
natural source
Ex : camera without flash light (depends on
solar energy), and all RS sensors

Types of sensors :
Non Scanning or Framing sensors:
Measure the radiation coming from entire scene at
once
Ex: Our eyes, Photo cameras

Types of sensors :
Imaging sensors:
Form image by collected
radiation
1. Scanning sensors:
The scene is sensed by point
by point or measure the
radiation coming from point
by point (equivalent to small
areas with in the scene)
Along track Scanners:
Image is acquired by line by
line

Types of sensors :
Across track Scanners:
Image is acquired by pixel by pixel

Types of sensors :
2. Non imaging sensors:
• These sensors do not form the image
• These are used to record spectral
quantity or parameter as a function of
time
Ex: temperature measurement, study of
atmosphere

Types of sensors :
Image Plane Scanning:
Lens is used after the
scan mirror to focus
the light on the
detector

Types of sensors :
Object Plane Scanning:
Lens is placed before
the scan mirror to
focus the light on
the detector

CHARECTERISTICS OF SENSORS
1. Spatial resolution
2. Spectral resolution
3. Radiometric resolution
4. Temporal resolution

Spatial resolution
• It refers to the size of the
smallest possible object
that can be detected
• It depends on the
Instantaneous Field Of
View (IFOV) and the
height of the satellite
orbit
• It tells the pixel size on
the ground surface

Spatial resolution

Spectral resolution
• It describes the ability of a sensor to define fine
wavelength ranges
• Sand is appear as coarser in finer wavelength bands

Radiometric resolution
• It describes the ability of sensor to discriminate very
slight differences in energy
• The number of brightness levels depends upon the
number of bits used

Radiometric resolution

Temporal resolution
It refers to how often it records imagery of a
particular area, which means the frequency
of repetitive coverage

UNIT-3.pptx GIS INFORMATION SYSTEMFOR COMPUTING

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