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EE 529 EE 529 RemoteRemote SensingSensingTechniquesTechniques
IntroductionIntroduction
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Course ContentsCourse Contents
RadarRadar
Imaging SensorsImaging Sensors
Imaging AlgorithmsImaging Algorithms
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Course Contents (Course Contents (ContCont’’dd))
y
r
Simulated Raw Data
Processing
Simulated Images
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Course Contents (Course Contents (ContCont’’dd))
RadarRadar
Imaging SensorsImaging Sensors
Imaging AlgorithmsImaging Algorithms
Complex SceneComplex Scene
Real Image Simulated Image
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Course Contents (Course Contents (ContCont’’dd))
Surface ScatteringSurface Scattering
NonimagingSensors
NonimagingSensors
y
r
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PrerequisitesPrerequisites
Knowledge of DSP, EMT and MATLAB
BooksBooks
[1] Introduction to the Physics and Techniques of Remote Sensingby C. Elachi and J. J. van Zyl (Chapters 1, 2 and 6).
[2] Scattering, Natural Surfaces, and Fractals by G. Franceschettiand D. Riccio (Chapters 1 and 2).
[3] Digital Signal Processing Techniques and Applications in Radar Image Processing by B. Wang (Chapters 4, 5 and 6).
Course Contents (Course Contents (ContCont’’dd))
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Definition - Acquisition of information “remotely”- Components:
- Energy source- Interaction of energy with atmosphere- Interaction with object- Energy scattered Data storage by sensor- Transmission, reception and processing of data and display
Introduction to Introduction to RemoteRemote SensingSensing
SourceSource/Sensor
Object
Processor
Image
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Advantages- Large amount of area can be observed in a small time period- Data can be collected from locations that are difficult to access
Measurable variables-Topography-Soil moisture-Velocity of ocean waves-Condition and behavior of snow, sea ice, etc.
Introduction to Introduction to RemoteRemote SensingSensing ((ContCont’’dd))
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Applications - Agricultural monitoring- Cartography - Coastal erosion- Disaster monitoring- Soil characterization- Urban mapping- Oceanography- Pollution monitoring, etc.
Introduction to Introduction to RemoteRemote SensingSensing ((ContCont’’dd))
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System types- Passive and Active- Optical and Microwave- Imaging and Nonimaging
Passive systems - Detect naturally occurring radiation-UV, visible light, near infrared,
infrared- Receiver only - No independent illumination source- Measure the amount of emitted radiation- Examples are: Microwave radiometry, infrared imagery, aerial
photography, etc.
RemoteRemote SensingSensing SystemsSystems
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Active systems
- Emit radiation and analyze reflections- Use transmitter(s) and receiver(s)- Measure the amount of emitted radiation
and- The time of arrival made possible as the time of emitted
radiation can be known- Examples are: radar (real aperture and synthetic aperture
radars), altimetry, scatterometry, etc.
RemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
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Optical systems
- Started in the middle of nineteenth century with the advent of photography and used balloons, kites, etc. as platforms
- Later on used with aeroplanes and satellites
- Applications: - Geology- Hydrology- Disaster monitoring - Cartography- Study of crop types, etc.
RemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
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Optical systems
Some satellite based systems-IKONOS, LANDSAT, etc.Advantages:
- High resolution - “Normal” images- Comparatively inexpensive
Disadvantages/Limitations: - No night capability- Limited by weather
- Alternative: Microwave remote sensing
RemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
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Microwave systems
- Started with the development of radar
- Applications:- Cartography- Identification and monitoring of crops- Change and damage detection- Monitoring of landslides- Detection of snow cover
- Some examples are:- Airborne: ESAR, EMISAR, AIRSAR, etc.- Satellite: RADARSAT 1&2, TerraSAR-X, ERS, etc.
RemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
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Microwave systems
- Advantages: - Day and night capability - Independent of weather- Can give properties of conditions on and inside a surfaces
- Disadvantages: - Different from optical images requires image interpretation- Resolution not better than optical sensors
RemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
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Imaging systems Give information in form of imagesExamples: Aerial photography, Real Aperture Radar, Synthetic Aperture Radar, Radiometer, etc.
RemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
Optical Image
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Imaging systems Give information in form of imagesExamples: Aerial photography, Real Aperture Radar, Synthetic Aperture Radar, Radiometer, etc.
Nonimaging systemsGive information such as backscattering, height, etc.Examples: Radiometer, Scatterometer, Altimeter, etc.
RemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
Optical Image
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RemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
High Resolution Optical ImageLow Resolution Optical Image
LowLow resolutionresolution givesgives lessless informationinformation
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Passive system
OpticalRemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
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RemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
Active system
Microwave
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Microwave
Active system Passive system
OpticalRemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
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RemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
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RemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
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RemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
Active Microwave Imaging systems
Real Aperture Radar (RAR), Synthetic Aperture Radar (SAR) – Strip of ground parallel to and offset to the side of the platform is imaged, hence the name Side Looking Radar
RAR – Incoherent processingSAR – Coherent processing, better
resolution than RAR y (A
zim
uth)
r (Range)
Sensor
Low resolution: Large pixel size
High resolution: Small pixel size
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RemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))
Nonimaging systems
Altimeter – Measures heightScatterometer – Measures backscattered energy as a function of incidence
angle
Altimeter Scatterometer
ct/2
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Energy Source
Plane waves
E: Electrical fieldM: Magnetic field
( )( )( )
⎪⎩
⎪⎨
⎧
=−−=−−=
=0E
kztcosEEkztcosEE
t,zE
z
yy0y
xx0x
δωδω
r
λπ2
=k
MicrowaveMicrowave RemoteRemote SensingSensing
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Polarization: Spatial orientation of the electrical oscillation plane
Vertical or Horizontal Polarization
Change of amplitude and polarization gives useful information
( )( )( )
⎪⎩
⎪⎨
⎧
=−−=−−=
=0E
kztcosEEkztcosEE
t,zE
z
yy0y
xx0x
δωδω
r
λπ2
=k
MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
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Interaction with atmosphere
-Scattering- Rayleigh: Particle size < wavelength- Mie: Particle size ≈ wavelength - Nonselective: Particle size > wavelength
-Absorption- Blocking of transmission of energy by molecules in the atmosphere- Limits the use for remote sensing
λπrx 2
=
MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
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Available frequency bands
Use limited by transparency of the Earth’s atmosphere
MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
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MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
Interaction with object
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For a single wavelength, a surface appears smoother as the incidence angle increases.
Horizontal smooth surfaces that reflect nearly all the incidence energy away from the radar arecalled specular reflectors. These surfaces, such as calm water or paved roads appear dark onradar images.
Rough surfaces scatter incident microwave energy in many directions. This is known as diffusereflection. Vegetated surfaces cause diffuse reflectance and result in a brighter tone on radar images.
MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))Interaction with object
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Surface Roughness is determined with respect to radar wavelength and incidence angle.
Surfaces will appear to have a greater or lesser degree of roughness, depending on the radar bandwidth used for imaging.
Surface roughness influences the reflectivity of microwave energy. On radar images, roughsurfaces appear brighter than smoother surfaces composed of the same material.
Smooth surfaceSpecular reflection
No return
Intermediate roughnessModerate return
Rough surfaceDiffuse scattering
Strong return
MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))Interaction with object
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Frequency bands used for microwave remote sensing applications
P L S C X K Q V W
f (GHz)0.39 1.55 3.90 5.75 10.9 36.0 46.0 56.0
0.3 1.0 3.0 10.0 30.0 100.0
λ (cm)100 30 10 3 1 0.3
P L S C X K Q V W
f (GHz)0.39 1.55 3.90 5.75 10.9 36.0 46.0 56.0
0.3 1.0 3.0 10.0 30.0 100.0
λ (cm)100 30 10 3 1 0.3
Different achievable spatial resolutions depending on bandwidth (BW)
fc /=λ
MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
cf
f
BW
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Resolution in two dimensions for different sensors
10m 3m 1m 10cm
ENVISAT / ASAR
ERS 1&2 RADARSAT 1 RADARSAT 2
ALOS SENTINEL-1 Cosmo-Skymed SAR-Lupe
HJ-1-C TerraSAR-X
FGAN - PAMIR
ONERA - RAMSES
ONERA - SETHI
MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
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P L S C X K Q V W
f (GHz)0.39 1.55 3.90 5.75 10.9 36.0 46.0 56.0
0.3 1.0 3.0 10.0 30.0 100.0
λ (cm)100 30 10 3 1 0.3
P L S C X K Q V W
f (GHz)0.39 1.55 3.90 5.75 10.9 36.0 46.0 56.0
0.3 1.0 3.0 10.0 30.0 100.0
λ (cm)100 30 10 3 1 0.3
Different sensitivity to geo-physical parameters (moisture, …)Different penetration depths into volumes
MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))Radiation-Object Interaction
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Resolution: 5m
L-Band
MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
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Resolution: 2.5m
X-Band
MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
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Radiometry
Sensor measures the power of the reflected signal, which determines the brightness of each element (pixel) in the image. Different surface features exhibit different scattering characteristics:
• Urban areas: very strong backscatter• Forest: medium backscatter• Calm water: smooth surface, low backscatter• Rough sea: increased backscatter due to wind and current effects
MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
High
Low
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MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
Sensor
Scattering by a scene
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MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
Sensor
Scattering by a scene
Raw data contains amplitude and phase
Processing/Imaging generates an image containing both amplitude and phase
50 100 150 200 250 300
200
400
600
800
1000
120015.5
16
16.5
17
17.5
18
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MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
High
Low
Optical Image SAR Image
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MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
E-SAR
Sensor ParametersFrequency: 1.3 GHzBandwidth: 100MHz
Scattering Mechanisms
Optical Image
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MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
Optical Image Raw Data
Sensor
Acquistion
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MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
Raw Data
SAR Image
y
r
Simulated raw data
Processing
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MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
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Raw Data SAR Image
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MicrowaveMicrowave RemoteRemote SensingSensing ((ContCont’’dd))
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Optical Image SAR Image
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Remote Sensing
Types of remote sensing systems
Microwave remote sensing-Imaging and nonimaging
Scattering mechanisms
SAR images
SummarySummary