EE 529 Remote Sensing Techniques Remote Sensing... · [1] Introduction to the Physics and Techniques of Remote Sensing by C. Elachi and J. J. van Zyl (Chapters 1, 2 and 6). [2] Scattering,

EE 529 EE 529 RemoteRemote SensingSensingTechniquesTechniques

IntroductionIntroduction

Course ContentsCourse Contents

RadarRadar

Imaging SensorsImaging Sensors

Imaging AlgorithmsImaging Algorithms

Course Contents (Course Contents (ContCont’’dd))

y

r

Simulated Raw Data

Processing

Simulated Images


RadarRadar

Imaging SensorsImaging Sensors

Imaging AlgorithmsImaging Algorithms

Complex SceneComplex Scene

Real Image Simulated Image


Surface ScatteringSurface Scattering

NonimagingSensors

NonimagingSensors

y

r

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).


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

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))

Applications - Agricultural monitoring- Cartography - Coastal erosion- Disaster monitoring- Soil characterization- Urban mapping- Oceanography- Pollution monitoring, etc.

Introduction to Introduction to RemoteRemote SensingSensing ((ContCont’’dd))

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

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))

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.


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


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.


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


Imaging systems Give information in form of imagesExamples: Aerial photography, Real Aperture Radar, Synthetic Aperture Radar, Radiometer, etc.


Optical Image

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.


Optical Image


High Resolution Optical ImageLow Resolution Optical Image

LowLow resolutionresolution givesgives lessless informationinformation

Passive system

OpticalRemoteRemote SensingSensing SystemsSystems ((ContCont’’dd))


Active system

Microwave

Microwave

Active system Passive system

OpticalRemoteRemote 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


Nonimaging systems

Altimeter – Measures heightScatterometer – Measures backscattered energy as a function of incidence

angle

Altimeter Scatterometer

ct/2

Energy Source

Plane waves

E: Electrical fieldM: Magnetic field

( )( )( )

⎪⎩

⎪⎨

⎧

=−−=−−=

=0E

kztcosEEkztcosEE

t,zE

z

yy0y

xx0x

δωδω

r

λπ2

=k

MicrowaveMicrowave RemoteRemote SensingSensing

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))

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

=


Available frequency bands

Use limited by transparency of the Earth’s atmosphere



Interaction with object

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

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

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


cf

f

BW

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


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

Resolution: 5m

L-Band


Resolution: 2.5m

X-Band


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


High

Low


Sensor

Scattering by a scene


Sensor

Scattering by a scene

Raw data contains amplitude and phase

Processing/Imaging generates an image containing both amplitude and phase

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High

Low

Optical Image SAR Image


E-SAR

Sensor ParametersFrequency: 1.3 GHzBandwidth: 100MHz

Scattering Mechanisms

Optical Image


Optical Image Raw Data

Sensor

Acquistion


Raw Data

SAR Image

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Processing


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Raw Data SAR Image

Processing


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Optical Image SAR Image

Remote Sensing

Types of remote sensing systems

Microwave remote sensing-Imaging and nonimaging

Scattering mechanisms

SAR images

SummarySummary

Documents

EE 529 Remote Sensing Techniques Remote Sensing... · [1] Introduction to the Physics and Techniques of Remote Sensing by C. Elachi and J. J. van Zyl (Chapters 1, 2 and 6). [2] Scattering,