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Transcript of CHARACTERISTICS OF OPTICAL SENSORS Course: Introduction to RS & DIP Mirza Muhammad Waqar Contact:...
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CHARACTERISTICS OF OPTICAL SENSORS
Course: Introduction to RS & DIP
Mirza Muhammad WaqarContact:
[email protected]+92-21-34650765-79 EXT:2257
RG610
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Outlines
Earth Observation Remote Sensing Physical Basis of Remote Sensing Platform Sensor Characteristics of Optical Sensor Color Composite
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Remote Sensing
Celestial RS Terrestrial RS
Meteorological
Telecommunication
Earth Observation
Optical ThermalMicrowav
e
Earth Observation Remote Sensing
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Physical Basis of Remote Sensing
Physical Basis of Remote Sensing
ConclusionInterpretatio
nObservation
Source of illumination
EM Radiations
TargetTraveling
Path
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Platform
PlatformCherry Lifter
Balloons Air Crafts Space Craft
Low Altitude
2 Km
Medium Altitude 2-10 Km
High Altitude
10-13 Km
Low Altitude200-00
Km
Medium Altitude 500-900
Km
High Altitude36k-45k
Km
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Sensors
Active
Passive
Non-Imaging
Imaging
Non-Imaging
Framing
Non-Framing
Sensor
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Sensor Type
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Passive vs Active Remote Sensing
Passive Remote Sensing Active Remote Sensing
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1. Discrete Detectors and scanning mirrors-MSS, TM, ETM+, GOES, AVHRR, SeaWiFS, AMS, ATLAS
2. Linear Arrays-SPOT, IRS, IKONOS, ORBIMAGE, Quickbird, ASTER, MISR
3. Liner and area arrays-AVIRIS, CASI, MODIS, ALI, Hyperion, LAC
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1. Pixel
2. Spectral Bandwidth
3. Instantaneous Field of View (IFOV)
4. Field of View (FOV)
5. Dwell Time
6. Altitude
7. Resolution
8. Satellite Orbits
Characteristics of Optical Sensor
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Pixels
Pixel is picture element
It contains Address (latitude & longitude) Digital Numbers Size
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Spectral Bandwidth of the Detector
The signal is stronger for detectors that respond to a broader bandwidth of energy.
For example, a detector that is sensitive to the entire visible range will receive more energy than a detector that is sensitive to a narrow band. Such as visible red.
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Instantaneous Field of View (IFOV)
The instantaneous field of view (IFOV) of any detector is the solid angle through which a detector is sensitive to radiation.
Both the physical size of the sensitive element of the detector and the effective focal length of the scanner optics determine the IFOV.
IFOV is defined as the angle which corresponds to the sampling unit. Information within an IFOV is represented by a pixel in the image.
A small IFOV is required for high spatial resolution but also restricts the signal strength.
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Instantaneous Field of View (IFOV)
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Field of View (FOV)
The maximum angle of view which a sensor can effectively detect the electromagnetic energy, is called the Field of View (FOV).
The width on the ground corresonding to the FOV is called the Swath Width.
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Field of View (FOV)
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Dwell Time
The time required for the detector IFOV to sweep across a ground resolution cell is the dwell time.
A longer dwell time allows more energy to exposure to the detector, which creates a stronger signal.
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Altitude
For a given ground resolution cell, the amount of energy reaching the detector is inversely proportional to the square of the distance.
A greater altitudes the signal strength is weaker.
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1. Spatial Resolution2. Spectral Resolution3. Radiometric Resolution4. Temporal Resolution
Resolutions –Key to Check Image Quality
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Spatial Resolution
The spatial resolution of a satellite image is based on the pixel size or picture element.
Can only identify objects which are larger than the pixel size.
To accurately determine size and shape, object must be a few pixels long and wide.
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Satellite Resolution
SPOT – 5 (Pan)
SPOT – 5 (XS)
LANDSAT TM
LANDSAT MSS
NOAA
IRS-1C (Pan)
Quick Bird (Pan)
2.5 m
10 m
30 m
80 m
1 km
5,8 m
0.6 m
Spatial Resolution
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Landsat MSS
80 m x 80 m Approximately the size of a hockey field
General Detail
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Landsat ETM+
30 m x 30 m approximately 1/3rd of a hockey field
Local Detail
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Point Detail
ASTER
15 m x 15m
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Quickbird (0.6 x 0.6 m)
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Spectral Resolution
The finer the spectral resolution the narrower the
wavelength range for a particular channel or band.
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• Example: Black and white image
- Single sensing device
- Intensity is sum of intensity of all visible wavelengths
Can you tell the color of the platform top?
How about her sash?
0.4 mm 0.7 mm
Black & White Images
Blue + Green + Red
Spectral Resolution
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• Example: Color image
- Color images need least three sensing devices, e.g., red, green, and blue; RGB
Using increased spectral resolution (three sensingwavelengths) adds information
In this case by “sensing” RGB can combine toget full color rendition
0.4 mm 0.7 mm
Color Images Blue Green Red
Spectral Resolution
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Spectral Response Differences
TM Band 3 (Red)
TM Band 4 (NIR)
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Spectral Data
On the basis of spectral resolution we can divide data as follows:
1. Panchromatic Data2. Multispectral Data3. Hyperspectral Data
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Hyperspectral Data
Multispectral Data
Panchromatic Data
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Radiometric Resolution
The radiometric characteristics describe the actual information content in an image.
The radiometric resolution of an imaging system describes its ability to discriminate very slight differences in energy
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• Number of Shades or brightness levels at a given wavelength
• Smallest change in intensity level that can be detected by the sensing system
Radiometric Resolution
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Radiometric Resolution
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Temporal Resolution
Each satellite revisits the same area after certain time period, which is called Temporal Resolution.
Note that the Earth is also rotating to the East, means satellite does not pass over the same path next time.
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Temporal Resolution
It is the revisit frequency of the satellite More frequency => More Temporal resolution Different for every satellite Varies with the altitude of satellite Temporal resolution is high for upper latitude but
lower for equator The temporal resolution of stereo satellite vary.
Animation in comment box
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High altitude satellite => High temporal resolution (3-4 days)
For frequent coverage => Satellite to satellite transfer coverage Data is not on same scale
Temporal Resolution
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1. Geostationary Orbit
2. Polar Orbit
3. Sun Synchronous Orbit
Satellite Orbits
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Satellite Orbit Determines...
1. What part of the globe can be viewed.2. The size of the field of view.3. How often the satellite can revisit the same
place.4. The length of time the satellite is on the sunny
side of the planet.
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Satellite Orbits
A satellite follows a generally elliptical orbit around the earth.
The time taken to complete one revolution of the orbit is called the orbital period.
The satellite traces out a path on the earth surface, called its ground track, as it moves across the sky.
As the earth below is rotating, the satellite traces out a different path on the ground in each subsequent cycle.
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Repeat Cycle
Remote sensing satellites are often launched into special orbits such that the satellite repeats its path after a fixed time interval. This time interval is called the repeat cycle of the
satellite.
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Geostationary Orbit
If a satellite follows an orbit parallel to the equator in the same direction as the earth's rotation and with the same period of 24 hours.
The satellite will appear stationary with respect to the earth surface. This orbit is a geostationary orbit.
Satellites in the geostationary orbits are located at a high altitude of 36,000 km.
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Near Polar Orbit
A near polar orbit is one with the orbital plane inclined at a small angle with respect to the earth's rotation axis.
A satellite following a properly designed near polar orbit passes close to the poles and is able to cover nearly the whole earth surface in a repeat cycle.
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Sun Synchronous Orbit
Earth observation satellites usually follow the sun synchronousorbits.
A sun synchronous orbit is a nearpolar orbit whose altitude is such that the satellite will alwayspass over a location at a given latitude at the same local solartime.
In this way, the same solarillumination condition (except for seasonal variation) can be achieved for the images of a given location taken by the satellite.
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Color Composite
True Color Composite Natural color composite displays combination of
visible red, green & blue bands (Landsat bands 3, 2 and 1 ).
False Color Composite False-color represent multispectral
image produce by using bands other than visible red, green & blue.(Landsat bands 7,4,2 or 4,3,2)
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Band CombinationTM Band – 2
Green
TM Band - 4 NIR
TM Band - 7 FIR
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Band Combinations
3,2,1
4,3,2
5,4,3
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Questions & Discussion