G3-1 - bilişim teknolojileri enstitüsü

Transkript

01.07.2014
UYGU 2104 – Uydu Yer Gözlem Uygulamaları Yaz Okulu
TÜBİTAK
Introduction to
Microwave Remote Sensing
Mehmet Kurum
TÜBİTAK BİLGEM
Bilişim Teknolojileri Enstitüsü
WED.AM1
Uydu Yer Gözlem Uygulamaları Yaz Okulu | 23-27 Haziran 2014 | T ÜBİTAK Gebze Yerleşkesi
Content
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PART I – Fundamentals
Reference Books
Motivation
•
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brightness temperature and emissivity
Radiometer systems
•
antenna concepts, arrays
Passive microwave remote sensing and radiometry
•
Lossless, lossy media, layered media
Antenna systems in microwave remote sensing
•
Why microwaves for remote sensing?
Plane wave propagation, reflection, refraction, and attenuation
system noise, Dicke radiometer
Radar systems
•
range equation, Doppler effects, fading
PART II – Specific Examples (Friday)
Scattering and emission from natural targets
•
surface scatter, volume scatter, the sea, ice, snow, vegetation
Microwave remote sensing applications
•
sea ice, oceans, vegetation, etc.
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References
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Fundamental Books
Fundemental Books – Ulaby et. al.
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Ulaby, F. T., R. K. Moore, and A.K. Fung, Microwave Remote Sensing: Active and Passive, Vol. I
-- Microwave Remote Sensing Fundamentals and Radiometry, Addison-Wesley, Advanced Book
Program, Reading, Massachusetts, 1981, 456 pages.
Ulaby, F. T., R. K. Moore, and A.K. Fung, Microwave Remote Sensing: Active and Passive, Vol. II
-- Radar Remote Sensing and Surface Scattering and Emission Theory, Addison-Wesley,
Advanced Book Program, Reading, Massachusetts, 1982, 609 pages.
Ulaby, F. T., R. K. Moore, and A. K. Fung, Microwave Remote Sensing: Active and Passive, Vol.
III -- Volume Scattering and Emission Theory, Advanced Systems and Applications, Artech
House, Inc., Dedham, Massachusetts, 1986, 1100 pages
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Books – Ulaby and Long
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Ulaby and Long, Microwave Radar and Radiometric Remote Sensing, University of Michigan
Press, 2014, 1116 pages.
Books – Tsang et. al.
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L. Tsang, J. A. Kong, and R. Shin, Theory of Microwave Remote Sensing, Wiley-Interscience, New
York, 1985.
L. Tsang, J.A. Kong, and K.H. Ding, Scattering of Electromagnetic Waves, Vol. 1:Theory and
Applications , Wiley Interscience, 2000, 426 pages.
L. Tsang, J.A. Kong, K.H. Ding and C.O. Ao, Scattering of Electromagnetic Waves, Vol. 2:
Numerical Simulations, Wiley Interscience, 2001, 705 pages.
L. Tsang and J.A. Kong, Scattering of Electromagnetic Waves, Vol. 3: Advanced Topics, Wiley
Interscience, 2001, 413 pages.
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Books - Ishimaru
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Akira Ishimaru, Wave Propagation and Scattering in Random Media: Single scattering and
transport theory, Academic Press, 1978 - 572 pages
Akira Ishimaru, Wave Propagation and Scattering in Random Media: Multiple Scattering,
Turbulence, Rough Surfaces, and Remote Sensing, Academic Press, 1978 - 250 pages
Akira Ishimaru, Wave Propagation and Scattering in Random Media, Wiley-IEEE Press, 1999 600 pages
Books - Fung
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Adrian K. Fung, Microwave Scattering and Emission Models and their Applications, Artech
House Remote Sensing, 1994 - 592 pages
Adrian K. Fung , K. S. Chen, Microwave Scattering and Emission Models for Users, Artech House
Remote Sensing, 2009 - 430 pages
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Books - Elachi
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C. Elachi, Introduction To The Physics and Techniques of Remote Sensing, Wiley-Interscience,
New York, 1987, 432 pages.
C. Elachi, F. T. Ulaby, Radar Polarimetry for Geoscience Applications, Artech House, 1990, 388
pages.
Books - Matzler
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C. Matzler, Thermal Microwave Radiation: Applications for Remote Sensing , The Institution of
Engineering and Technology, 2006 - 584 pages
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Content
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Motivation
Why Microwaves for Remote Sensing?
Emission Spectrum, Atmospheric Tranmissivity
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Microwave Atmospheric Window
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Microwave remote sensing
background
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Optical remote sensing has been around a long time
•
•
•
•
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Uses the visible part of the electromagnetic spectrum
Instrumentation includes the human eye, cameras, telescopes
Has problems with clouds, rain, fog, snow, smoke, smog, etc.
Cannot penetrate soil, vegetation, snowpack, ice
Relies on ambient light sources (e.g., sunlight)
Microwave remote sensing is less than 100 years old
•
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Uses the microwave and RF parts of the spectrum
Instrumentation includes radars and radiometers
Is largely immune to clouds, precipitation, smoke, etc.
Penetrates sand, soil, rock, vegetation, dry snow, ice, etc.
Does not rely on sunlight – radar provides its own illumination,
radiometers use the target’s thermal emission
Data from microwave sensors complement data from
optical sensors
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Microwave Sensors
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Microwave Sensors
Active (Radars)
Real Aperture
Synthetic Aperture (SAR)
Passive (Radiometers)
Real Aperture
Synthetic Aperture
(Interferomters)
Scatteromters
Altimeters
Weather Radars
Basic elements of a remote sensing
radar instrument
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Key elements of a microwave
radiometer
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0.3 - 300 GHz ( wavelength 1 m - 1 mm )
Active
Passive
(Radiation or TB [K])
Radiometers
TB = e T
Where e is emissivity and T
is physical temperature
(Backscattering σ0 [dB ])
Radar
depends on dielectric
properties of soil,
geometric properties and
system parameters.
σ0
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Application of Remote Sensing
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Atmosphere(e.g. temperature, water vapour, rain
intensity, etc.)
Sea(e.g. winds, salinity, etc.)
Ice (e.g. depth, age, etc.)
Land (e.g. soil moisture, crop biomass, forest
biomass, classification)
Basic Rationale for Applications
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Instrument outputs may be related to surface
variables
The relationship defines a “model”
Physical models
Empirical models
Combinations
Forward
Microwave
Measurements
Model
Target
Parameters.
Inversion
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Steps
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Adopting a convenient instrument (suitable selection of
frequency, look angle, revisit time, etc.)
Developing a reliable model (direct problem)
surface variables -> instrument outputs
Retrieval (inverse problem)
instrument outputs -> surface variables
Forward
Microwave
Measurements
Model
Target
Parameters.
Inversion
Radiometric Sensitivity
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The arrows indicate the SMMR frequencies. The signs have been chosen to be positive
in the frequency range of primary importance to the given parameter [from Wilheit et al.,
1980].
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Main physical processes
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Surface Scattering
Sea, bare soil, etc.
Volume Scattering
vegetation, snow, etc.
Passive Microwave Applications
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Soil moisture
Snow water equivalent
Sea/lake ice extent, concentration and type
Sea surface temperature
Atmospheric water vapor
Surface wind speed
only over the oceans
Cloud liquid water
Rainfall rate
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Imaging Radar Applications
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Environmental Monitoring
Vegetation mapping
Monitoring vegetation regrowth, timber yields
Detecting flooding underneath canopy, flood plain mapping
Assessing environmental damage to vegetation
Hydrology
Soil moisture maps and vegetation water content monitoring
Snow cover and wetness maps
Measuring rain-fall rates in tropical storms
Oceanography
Monitoring and routing ship traffic
Detection oil slicks (natural and man-made)
Measuring surface current speeds
Sea ice type and monitoring for directing ice-breakers
Applications to Forestry
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National agencies/companies
Clear cut mapping / regeneration assessment
Disturbances
Infrastructure mapping / operations support
Forest inventory / biomass estimation
Vegetation density
Species inventory
Environmental Monitoring
Deforestation
Species inventory/ habitat mapping
Watershed protection
Coastal protection
Forest health and vigour
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Examples of SAR Applications
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Frequency Band
Ka
Ku
X
C
S
L
P
Frequency [GHz]
40-25
17.6-12
12-7.5
7.5-3.75
3.75-2
2-1
0.5-0.25
Wavelength [cm]
0.75-1.2
1.7-2.5
2.5-4
4-8
8-15
15-30
60-120
Foliage Penetration
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Subsurface Imaging
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Biomass Estimation
Agriculture
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Ocean
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Ice
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Subsidance Monitoring
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Snow monitoring
VHR Imaging
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Hydrological Applications
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The availability of soil moisture data on a global basis is
required to better assist the water, energy, and
biogeochemistry communities.
Weather
& Climate
Forecasting
Drought Early
Warning and
Decision
support
Floods &
Landslides
Agricultural
Productivity
Human
Health
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Evolution of Soil Moisture Mapping
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Soil Moisture Sensing Technology
Broad science, high spatial
resolution, higher sensitivity (10 km)
Improved global mapping
(50 km)
SMAP
SMOS
AMSR
Large scale mapping and integrated
hydrologic research (1 km)
ESTAR
Exploration of spatial/temporal
concepts (100 m)
PBMR
Field
Experiments
1970s
1980s
Limited global mapping,
demonstrate feasibility (50km)
Ground and aircraft development
verification of theory (1 m)
1990s
2000s
2010s
Time Period
L-Band Soil Moisture Space Missions
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[scheduled to launch November in 2014]
[launched in November, 2009]
SMOS:
Soil
Moisture
and Ocean
Salinity
Mission
A combined L-band
radiometer and high-resolution radar
to produce a global 10 km
surface soil moisture data product
An L-band, 2-dimensional
interferometric radiometer design
providing a resolution of 50 km
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Ground and Airborne Observations
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Calibration / validation of satellite
measurements during the mission
Refinement of current algorithm
parameterizations to improve the accuracy
of microwave moisture retrievals
Acquisition of long-term measurements
to assess seasonal to year-round changes
Examination of “specific” scenes such
as
the continuum of trees from small orchards to
mature forests to extend accurate soil moisture
retrievals to denser land covers
Improved understanding of spatial
scaling and scene heterogeneity issues
Content
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EM theory and its application to microwave
remote sensing
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EM theory and its application to
microwave remote sensing
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Plane wave propagation
Lossless media
Lossy media
Polarization
Fresnel reflection and transmission
Layered media
EM spectra, bands, and energy sources
Plane Wave Propagation
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Plane wave propagation through lossless and
lossy media is fundamental to microwave remote
sensing.
Consider the wave equation and plane waves in
homogeneous unbounded, lossless media
Plane waves – constant phase and amplitude in the
plane
Homogeneous – electrical and magnetic parameters
do not vary with throughout the medium
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Maxwell’s equations
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Beginning with Maxwell’s equations
∂H
∂t
∂E
∇×H = ε
∂t
∇×E = −µ
Fraday’s
Ampere’s
Assuming a homogeneous, source-free medium leads to
the homogeneous wave equation
∇ 2E = µ ε
∂2 E
∂ t2
where
E is the electric field vector (V/m) [note that bolded symbols denote
vectors]
µ is the medium’s magnetic permeability (H/m) [H: Henrys]
ε is the medium’s permittivity (F/m) [F: Farads]
Solution to Wave Equation
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Assuming sinusoidal time dependence
{
E(r, t ) = Re E(r ) e jωt
}
where ω is the radian frequency (rad/s)
r is the displacement vector
and Re{⋅} is the real operator
E(r,t) satisfies the wave equation if
∇ 2E(r ) + ω2µ ε E(r ) = 0
Using phasor representation (i.e., e.jωt is understood) and
assuming a rectangular coordinate system, the solution
has the general form of
E(r ) = E 0 exp [± j (k x x + k y y + k z z )]
where E0 is a constant vector and
k 2 ≡ ω2 µ ε = k 2x + k 2y + k 2z
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Propagation Vector
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A more compact form results from letting
k = xˆ k x + yˆ k y + zˆ k z
where k is the propagation vector, and
k = |k| is called the wave number (rad/m)
resulting in
E(r ) = E 0 exp [± j k ⋅ r ]
Finally reintroducing the time dependence and expressing
only the real-time field component yields
E(r, t ) = E 0 cos (ω t ± k ⋅ r )
This equation represents two waves propagating in
opposite directions defined by the propagation vector k
Time and Space Phase Components
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The time phase component is characterized by ω where
ω = 2πf = 2π T
f is the frequency (Hz) and T is the time period (s).
Similarly the space phase component depends on k where
k = 2π λ = ω µε
λ is the space period (m), or wavelength, in the medium
which can also be expressed as
(
λ =1 f µε
)
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Phase Velocity
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Consider now the electric field’s phase for a positivetraveling wave, i.e., ωt – kz.
A surface on which this phase is constant requires
ω t − k z = constant
For any given time t, this surface represents a plane
defined by z = constant, on which both the phase and
amplitude are constant. As time progresses, this plane of
constant phase and amplitude advances along the z axis,
hence the name uniform plane wave.
The rate at which this plane advances along the z axis
is called the phase velocity, v (m/s)
dz ω
1
v=
= =
dt k
µε
Orthogonality of the E, H, and k vectors
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Given an uniform plane E-field solution to the wave
equation, the H-field is found using Maxwell’s equations
∇×E = − µ
∂H
∂t
From the E-field component in the x-axis direction, Ex, is
found the H-field component in the y-axis direction, Hy, as
H y (z , t ) =
k
ωµ
E x 0 cos (ω t − k z ) =
E x0
η
cos (ω t − k z )
where η is the intrinsic impedance (Ω) of the medium
η =ωµ k = µ ε
Note that Ex and Hy are related through the intrinsic impedance similar
to how voltage and current in a circuit are related through Ohm’s law.
Note also the orthogonality of the E, H, and k vectors.
E = xˆ E x , H = yˆ H y ,
k = zˆ k
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Polarization
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Pottier
Polarization Handeness
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ROTATION SENSE: LOOKING INTO THE DIRECTION OF THE WAVE
PROPAGATION
ANTI-CLOCKWISE ROTATION
LEFT HANDED POLARISATION
CLOCKWISE ROTATION
RIGHT HANDED POLARISATION
Pottier
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Polarization State - Examples
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Horizontal
Left-hand Circular
Vertical
Right-hand Circular
Pottier
Polarization State - Examples
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Plane waves in a lossy medium
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A lossy medium is characterized by its permeability, µ,
permittivity, ε, and conductivity, σ (S/m) [S: Siemens].
Maxwell’s equations for a source-free medium become
∂H
∂E
∇×E = − µ
,
∇×H = σ E + ε
∂t
∂t
And the corresponding wave equation remains
∇ 2E(r ) + k 2 E(r ) = 0
where the wave number is
k = − j ω µ (σ + j ω ε )
Note that for a lossless medium, k is purely real when
σ = 0 and both µ and ε are real
k=
ω2 µ ε
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For a lossy medium k is complex
k = − j ω µ (σ + j ω ε )
due to σ ≠ 0 or either µ or ε are complex
µ = µ ′ − j µ ′′
ε = ε ′ − j ε ′′
For lossless media the imaginary parts of the permeability
and permittivity are zero.
Non-zero imaginary terms (µ″ > 0 and ε″ > 0) represent
mechanisms for converting a portion of the
electromagnetic wave’s energy into heat, resulting in a
loss of wave energy.
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Consider the complex electric field plane wave
propagation along the positive z axis
E(z , t ) = E 0 e j (ω t − k z )
whereas for the lossless case k was real, in a lossy
medium k is complex and is related to the propagation
factor or propagation constant, γ (1/m), by
γ = j k = j − j ω µ (σ + j ω ε )
γ =α + j β
such that
E( z ) = E 0e − j k z = E 0e −γ z = E 0 e −(α + j β ) z
where α and β are real quantities and α is the attenuation
constant (Np/m) and β is the phase constant (rad/m)
[Np = Neper]
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Clearly for a wave travelling along the +z axis
E( z ) = E 0 e − α z e − j β z
as z increases, the magnitude of the electric field
decreases.
The real time expression for the x-axis field component is
E x ( z , t ) = E x 0 e −α z cos (ω t − β z )
The attenuation constant is the real part of jk
α = Re
{
}
j ω µ (σ + j ω ε ) ,
Np/m
The phase constant is the imaginary part of of jk
β = Im
{
}
j ω µ (σ + j ω ε ) ,
rad/m
Note: (Neper/m) × 8.686 (dB/Neper) = (dB/m)
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Pure Water
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1
Pure Water and Seawater
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1
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Dry Snow
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Soil
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Corn Leaves
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Corn Leaves
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Fresnel reflection and transmission
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Properties of interest include reflection, refraction, transmission
Perpendicular (horizontal) case
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Reflection coefficient (relates to field strength)
(sometimes represented by Γ, ρ, or r).
R⊥ ≡
Er
n cos θ i − n2 cos θ t
= 1
Ei
n1 cos θ i + n2 cos θ t
= −
sin (θ i − θ t )
=
sin (θ i + θ t ) θ ≠ 0
i
η 2 cos θ i − η 1 cos θ t
η 2 cos θ i + η 1 cos θ t
Transmission coefficient (relates to field strength)
T⊥ ≡
=
2 n1 cosθ i
Et
=
Ei
n1 cosθ i + n 2 cosθ t
2 sin θ t cos θ i
sin (θ i + θ t )
=
θi ≠ 0
2 η 2 cos θ i
η 2 cos θ i + η 1 cos θ t
Note that 1 + R ⊥ = T⊥
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Perpendicular (horizontal) case
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Reflectivity (relates to power or intensity)
Γ⊥ = R⊥
2
Transmissivity (relates to power or intensity)
(sometimes represented by T)
ϒ⊥ =
or
Re{(cos θ t ) / η 2 }
T⊥
Re{(cos θ i ) / η1}
2
ϒ ⊥ = 1 − Γ⊥
Note that Γ⊥+ϒ⊥= 1 which satisfies the
conservation of energy
Parallel (vertical) case
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Reflection coefficient (relates to field strength)
R// ≡
=
Er
n cos θ i − n1 cos θ t
= 2
Ei
n2 cos θ i + n1 cos θ t
η 1 cos θ i − η 2 cos θ t
tan (θ i − θ t )
=
tan (θ i + θ t ) θ ≠ 0 η 1 cos θ i + η 2 cos θ t
i
Transmission coefficient (relates to field
strength)
T// ≡
=
Et
2 n2 cos θ i
=
Ei n2 cos θ i + n1 cos θ t
2 η 1 cos θ i
2 sin θ t cos θ i
=
sin (θ i + θ t ) cos(θ i − θ t ) θ ≠ 0 η 1 cos θ i + η 2 cos θ t
i
Note that 1 + R // = T//
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Parallel (vertical) case
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Reflectivity (relates to power or intensity)
Γ// = R //
2
Transmissivity (relates to power or intensity)
ϒ // =
Re{η 2 cos θ t }
Re{η 1 cos θi }
T//
2
or
ϒ // = 1 − Γ//
Note that Γ//+ϒ//= 1 which satisfies the
conservation of energy
Reflectivity for Water, Wet Soil, and Dry Soil
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Layered Madia
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Reflection and Transmission for an n-layer medium
Layered Madia – Forest Floor
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Effective dielectric constants of
Soil, humus, and litter layers
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HUMUS
MINERAL SOIL
(LOAMY SAND)
Bulk dielectric - Real Part
LITTER
Mineral Soil
Humus
Litter
Shallow Lake Ice Trends
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Play video
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Content
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Antennas
Antennas
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Role of antennas
Theory
Antenna types
Characteristics
Radiation pattern – beamwidth, pattern solid angle
Directivity, gain, effective area
Bandwidth
Friis’ transmission formula
Implementations
Dipole, monopole, and ground planes
Horn
Parabolic reflector
Arrays
Terminology
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The role of antennas
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Antennas serve four primary functions
Spatial filter
directionally-dependent sensitivity
Polarization filter
polarization-dependent sensitivity
Impedance transformer
transition between free space and transmission line
Propagation mode adapter
from free-space fields to guided waves
(e.g., transmission line, waveguide)
Spatial filter
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Antennas have the property of being more sensitive in one direction
than in another which provides the ability to spatially filter signals from
its environment.
Directive antenna.
Radiation pattern of directive antenna.
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Polarization filter
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Antennas have the property of being more sensitive to one
polarization than another which provides the ability to filter
signals based on its polarization.
Incident
E-field
vector
r
E = ẑ E 0
Dipole antenna
r r
V = h⋅E
r
h = ẑ h
+
_
V = h E0
r r
V = h⋅E
r
h = ẑ h
r
E = ŷ E 0
z
y
x
In this example, h is the antenna’s
effective height whose units are
expressed in meters.
Impedance transformer
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Intrinsic impedance of free-space, E/H
η0 = µ0 ε 0
= 120 π
≅ 376.7 Ω
Characteristic impedance of transmission line, V/I
A typical value for Z0 is 50 Ω.
Clearly there is an impedance mismatch that must be
addressed by the antenna.
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Propagation mode adapter
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During both transmission and receive operations the antenna
must provide the transition between these two propagation
modes.
Antenna Types
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Antennas include wire and aperture types.
Wire types include dipoles, monopoles, loops, rods, stubs,
helicies, Yagi-Udas, spirals.
Aperture types include horns, reflectors, parabolic, lenses.
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Radiation pattern
UYGU 2014
TÜBİTAK
Radiation pattern – variation of the field intensity of an
antenna as an angular function with respect to the axis
Three-dimensional representation of the radiation
pattern of a dipole antenna
Radiation Pattern - Characterstics
73
UYGU 2014
TÜBİTAK
74
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01.07.2014
Beamwidth and beam solid angle
UYGU 2014
TÜBİTAK
The beam or pattern solid angle, Ωp [steradians or sr] is defined as
Ω p = ∫∫ Fn (θ , φ ) d Ω
4π
where dΩ is the elemental solid angle given by
d Ω = sin θ dθ dφ
75
UYGU 2014
TÜBİTAK
Directivity – the ratio of the radiation intensity in a given direction from the
antenna to the radiation intensity averaged over all directions.
[unitless]
Maximum directivity, Do, found in the direction (θ, φ) where Fn= 1
and
or
Given Do, D can be found
76
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UYGU 2014
TÜBİTAK
Gain – ratio of the power at the input of a loss-free isotropic antenna to the
power supplied to the input of the given antenna to produce, in a given
direction, the same field strength at the same distance
Of the total power Pt supplied to the antenna, a part Po is radiated out into space
and the remainder Pl is dissipated as heat in the antenna structure. The
radiation efficiency ηl is defined as the ratio of Po to Pt
ηl =
Po
Pt
Therefore gain, G, is related to directivity, D, as
G (θ , φ ) = ηl D(θ , φ )
And maximum gain, Go, is related to maximum directivity, Do, as
Go = ηl Do
77
UYGU 2014
TÜBİTAK
Effective area – the functional equivalent area from which an antenna
directed toward the source of the received signal gathers or absorbs the
energy of an incident electromagnetic wave
It can be shown that the maximum directivity Do of an antenna is related to an
effective area (or effective aperture) Aeff, by
D0 =
4π
4π
Aeff = 2 ηa Ap
2
λ
λ
where Ap is the physical aperture of the antenna and ηa = Aeff / Ap is the
aperture efficiency (0 ≤ ηa ≤ 1)
Consequently
Aeff =
λ2
λ2
≅
Ω p β xz β yz
[m2]
For a rectangular aperture with dimensions lx and ly in the x- and y-axes, and
an aperture efficiency ηa = 1, we get
β xz ≅ λ l x
[rad]
β yz ≅ λ l y
[rad]
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01.07.2014
Bandwidth
UYGU 2014
TÜBİTAK
The antenna’s bandwidth is the range of operating
frequencies over which the antenna meets the operational
requirements, including:
Spatial properties (radiation characteristics)
Polarization properties
Impedance properties
Propagation mode properties
Most antenna technologies can support operation over a
frequency range that is 5 to 10% of the central frequency
(e.g., 100 MHz bandwidth at 2 GHz)
To achieve wideband operation requires specialized
antenna technologies
(e.g., Vivaldi, bowtie, spiral)
ComRAD - Dual band Antenna
79
UYGU 2014
TÜBİTAK
Radar
Band
1.25GHz
Radiometer
Band
1.413GHz
80
40
01.07.2014
RADIOMETER BAND (1403-1424MHz)
UYGU 2014
TÜBİTAK
RADAR BAND (1200-1300MHz)
81
UYGU 2014
TÜBİTAK
82
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01.07.2014
Antenna arrays
UYGU 2014
TÜBİTAK
Antenna array composed of several similar radiating
elements (e.g., dipoles or horns).
Element spacing and the relative amplitudes and phases
of the element excitation determine the array’s radiative
properties.
Linear array examples
Two-dimensional array of
microstrip patch antennas
Antenna arrays
83
UYGU 2014
TÜBİTAK
84
42
01.07.2014
Antenna arrays
UYGU 2014
TÜBİTAK
Soil Moisture Ocean Salinity
Sentinel 1a
Antennas- Summary
85
UYGU 2014
TÜBİTAK
Antennas play an important role in microwave remote
sensing systems.
There are both art and science aspects to antennas.
Antenna arrays enable the radiation characteristics to be
changed electronically (i.e., very rapidly) unlike
conventional mechanically-steered antennas.
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Antennas - Terminology
UYGU 2014
TÜBİTAK
Antenna – structure or device used to collect or radiate electromagnetic waves
Array – assembly of antenna elements with dimensions, spacing, and illumination sequency such
that the fields of the individual elements combine to produce a maximum intensity in a particular
direction and minimum intensities in other directions
Beamwidth – the angle between the half-power (3-dB) points of the main lobe, when referenced to
the peak effective radiated power of the main lobe
Directivity – the ratio of the radiation intensity in a given direction from the antenna to the radiation
intensity averaged over all directions
Effective area – the functional equivalent area from which an antenna directed toward the source of
the received signal gathers or absorbs the energy of an incident electromagnetic wave
Efficiency – ratio of the total radiated power to the total input power
Far field – region where wavefront is considered planar
Gain – ratio of the power at the input of a loss-free isotropic antenna to the power supplied to the
input of the given antenna to produce, in a given direction, the same field strength at the same
distance
Isotropic – radiates equally in all directions
Main lobe – the lobe containing the maximum power
Null – a zone in which the effective radiated power is at a minimum relative to the maximum effective
radiation power of the main lobe
Radiation pattern – variation of the field intensity of an antenna as an angular function with respect
to the axis
Radiation resistance – resistance that, if inserted in place of the antenna, would consume that same
amount of power that is radiated by the antenna
Side lobe – a lobe in any direction other than the main lobe
Content
87
UYGU 2014
TÜBİTAK
Radiometry – remote sensing via
microwave emission
88
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01.07.2014
Radiometry – remote sensing via
microwave emission
UYGU 2014
TÜBİTAK
Thermal radiation
Blackbody radiation and Planck’s law
Stefan-Boltzmann law
Emissivity, graybodies, selective radiators
Rayleigh-Jeans approximation
Temperature
Brightness temperature
Apparent temperature
Antenna temperature
Radiative transfer
Extinction (absorption and scattering)
Emission
Apparent temperature of terrain
89
UYGU 2014
TÜBİTAK
Using classical physics (mechanics), theories were put forth
by Wilhelm Wien (1893) and Lord Rayleigh (1900) that, in a
piecemeal fashion, agreed well with experimentally
measured radiative emissions.
While the Wein law was valid for shorter (optical)
wavelengths, the Rayleigh law was valid for longer
wavelengths.
In 1905 Lord Rayleigh and Sir James Jeans offered a more
complete theory was presented (Rayleigh-Jeans law) that
again only agreed well with experimental measurements at
long wavelengths.
Max Planck’s blackbody radiation law (1901) accurately
predicted the spectral intensity of electromagnetic radiation at
all frequencies or wavelengths by incorporating quantum
theory.
90
45
01.07.2014
UYGU 2014
TÜBİTAK
Notation for radiometric quantities
91
UYGU 2014
TÜBİTAK
92
46
01.07.2014
Planck’s blackbody radiation law
UYGU 2014
TÜBİTAK
A blackbody is an idealized, perfectly opaque material that absorbs all the
incident radiation at all frequencies, reflecting none.
To maintain thermal equilibrium, a blackbody is also a perfect emitter.
Bf =
where
2h f 3 h f
e
c2
(
kT
)
−1
−1
Bf = Blackbody spectral brightness, W m-2 sr-1 Hz-1
h = Planck’s constant = 6.63 × 10-34 J s
f = frequency, Hz
k = Boltzmann’s constant = 1.38 × 10-23 J K-1
T = absolute temperature, K
c = speed of light, 3 × 108 m s-1
Note: Only two variables: frequency, f, and temperature, T.
Temperature dependence of emission
93
UYGU 2014
TÜBİTAK
94
47
01.07.2014
Solar spectral irradiance
UYGU 2014
TÜBİTAK
Emissivity, graybodies, selective radiators
95
UYGU 2014
TÜBİTAK
Blackbodies transform heat into electromagnetic
energy with perfect efficiency.
Natural targets generally have lower efficiencies and are
sometimes called graybodies.
This reduced efficiency is termed emissivity, e, and is
defined as the ratio of the observed brightness relative to
that of a blackbody at the same temperature.
e(θ , φ ) = B(θ , φ ) Bbb
Since Β(θ, φ) ≤ Bbb, then 0 ≤ e(θ, φ) ≤ 1
A selective radiator denotes a case where emissivity is
frequency or wavelength dependent, e(f) or e(λ).
96
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01.07.2014
Emissivity, graybodies, selective
radiators
UYGU 2014
TÜBİTAK
Relating brightness to received power
97
UYGU 2014
TÜBİTAK
To allow for spectrally-dependent
brightness, we introduce spectral
brightness, Bf (θ, φ).
Thus the total power received
by the aperture over a bandwidth ∆f, extending from
frequency f to f+∆f is
P=
Ar
2
∫
f + ∆f
f
∫∫π B (θ , φ ) F (θ , φ ) dΩ df
f
n
4
where the ½ term reflects the fact that only half of the incident
power is detected due to the polarization selectivity of the
antenna.
98
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01.07.2014
Relating power and temperature (1/3)
UYGU 2014
TÜBİTAK
From the Rayleigh-Jeans law we know that brightness and temperature
are linearly related at RF and microwave frequencies.
2 f 2 k T 2kT
Bf =
= 2
c2
λ
To apply this to radiometric measurements, consider the experiment
illustrated below.
99
UYGU 2014
TÜBİTAK
For a blackbody enclosure at temperature T
Pbb =
Ar
2
∫
f + ∆f
f
∫∫π
2kT
Ar
∫∫π F (θ , φ ) dΩ
Fn (θ , φ ) dΩ df
λ2
4
For narrowband operation, we assume Bf ~ constant over ∆f permitting
Pbb = k T ∆f
λ2
n
4
From antenna theory we know that
∫∫π F (θ , φ ) dΩ = Ω
n
p
= λ2 Ar
4
100
50
01.07.2014
UYGU 2014
TÜBİTAK
So
Pbb = k T ∆f
which agrees exactly with the noise power from a resistor at temperature T
Pn = k T ∆f
Therefore the power-temperature relationship permits us to speak of
temperatures rather than power or brightness.
Example: for T = 300 K and ∆f = 1 MHz, P = k T ∆f = 4.1 fW (4.1 × 10-15 W) or
-144 dBW (dB relative to 1 W) or -114 dBm (dB relatice to 1 mW).
If R = 50 Ω, then the output voltage will be Vrms = √(R P) = 450 nV.
If R = 1000 Ω, then Vrms = 2 µV.
Brightness temperature
101
UYGU 2014
TÜBİTAK
Having related received power, P, to temperature
P = k T ∆f
and recognizing that emissivity, e, reduces an object’s
brightness, leads us to define an equivalent brightness
temperature, TB
e(θ , φ ) =
TB (θ , φ )
or
T
TB (θ , φ ) = T e(θ , φ )
where T is the absolute physical temperature.
102
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01.07.2014
Apparent temperature
UYGU 2014
TÜBİTAK
Bi (θ , φ ) =
2k
λ2
TAP (θ , φ ) ∆f
Antenna temperature
103
UYGU 2014
TÜBİTAK
The antenna radiometric
temperature, TA, is the resistorequivalent temperature that would
deliver the same output power.
Pn = k TA ∆f = P
P=
Ar
2
2k
∫∫π λ
2
TAP (θ , φ ) ∆f Fn (θ , φ ) dΩ
4
With TAP and TA related as
TA =
Ar
λ2
∫∫π T (θ , φ ) F (θ ,φ ) dΩ
AP
n
4
104
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01.07.2014
Radiative Transfer
UYGU 2014
TÜBİTAK
Change in Intensity = - Extinction + Emission + Scattering into Beam
Smooth surface scattering and emission
105
UYGU 2014
TÜBİTAK
Specular reflection from a smooth,
planar surface (Fresnel reflection)
Pr (θ1 ; p ) = Γ(θ1 ; p ) Pi (θ1 ; p )
where
Pi = incident power
Γ = specular reflectivity
Pr = reflected power
θ1 = incidence angle
p = polarization state (p = h or v)
For the specular surface it can be shown that the emissivity is
related to the reflectivity as
e (θ1 ; p ) = 1 − Γ(θ1 ; p )
106
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01.07.2014
Rough surface scattering and emission
UYGU 2014
TÜBİTAK
Scattering from a rough surface is
characterized by the bistatic
scattering cross-section per unit
area σ°(θ0, φ0; θs, φs, p0, ps) [unitless]
where
(θ0, φ0) = direction of incident power
(θs, φs) = direction of scattered power
(p0, ps) = polarization state of incident and scattered fields
The emissivity of a rough surface is
e(θ 0 , φ0 ; p ) =1 −
1
[σ °(θ 0 , φ0 ;θ s , φs ; p0 , p0 )
4 π cos θ 0 ∫
+ σ °(θ 0 , φ0 ;θ s , φs ; p0 , ps )] dΩ s
Brightness temperature of a specular sea surface
107
UYGU 2014
TÜBİTAK
108
54
01.07.2014
Soil emissivity, roughness
UYGU 2014
TÜBİTAK
Angular patterns of the emissivity measured at 1.4 GHz for three bare-soil fields with
different surface roughnesses [Newton and Rouse, 1980].
Effect of vegetation
109
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TÜBİTAK
Angular plots of the h-polarized emissivity for (a) a dry soil surface and (b) a very wet
soil surface, covered with vegetation of nadir optical thickness t0. The soil surface is
perfectly smooth.
110
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01.07.2014
Effect of Moisture
UYGU 2014
TÜBİTAK
Variation of h-polarized emissivity with soil moisture content for (a) a smooth soil
surface and (b) a moderately rough soil surface.
Ocean Salinity
111
UYGU 2014
TÜBİTAK
112
56
01.07.2014
Sea Ice
UYGU 2014
TÜBİTAK
Incoherent emissivity of sea ice as a function of ice thickness at multiple frequencies.
Content
113
UYGU 2014
TÜBİTAK
Radiometer systems
114
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01.07.2014
Radiometer systems
UYGU 2014
TÜBİTAK
Equivalent noise temperature
Characterization of noise
Noise of a cascaded system
Noise characterization of an attenuator
Equivalent-system noise power at the antenna terminals
Equivalent noise temperature of a superheterodyne receiver
Radiometer operation
Effects of gain variations
Dicke radiometer
Examples of developed radiometers
Synthetic-aperture radiometers
Radiometer Systems
115
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TÜBİTAK
A radiometer is a very sensitive microwave receiver that
outputs a voltage, Vout, that is related to the antenna
temperature, TA.
Based on the output voltage, the radiometer estimates TA
with finite uncertainty, ∆T, which is referred to as the
radiometer’s sensitivity or radiometric resolution.
Radiometric resolution is a key parameter that
characterizes the radiometer’s performance.
An understanding of the factors affecting radiometer’s
performance characteristics requires an understanding of
noise, radiometer design, and calibration techniques
116
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01.07.2014
Thermal Noise
UYGU 2014
TÜBİTAK
Thermal noise is characterized with a zero mean, 〈Vn〉 = 0,
and is has equal power content at all frequencies, hence it
is often called white noise.
For a conductor with resistance R connected to an ideal
filter with bandwidth B, the output noise power Pn is
Pn = k T B
where k is Boltzmann’s constant (1.38 × 10-23 J K-1), T is the
absolute temperature (K).
Equivalent noise temperature
117
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TÜBİTAK
Now replace the noisy resistor with an antenna with
radiometric antenna temperature TA′.
TA′ is the antenna weighted apparent temperature that includes the
self-emission of the lossy antenna.
If the same average power is delivered into the matched
load, then we can relate TA′ to the thermodynamic
temperature T of the resistor.
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01.07.2014
Combined Radar Radiometer
UYGU 2014
TÜBİTAK
ComRAD Radiometer Blok Diagram
119
UYGU 2014
TÜBİTAK
120
60
01.07.2014
Temperature Monitoring
UYGU 2014
TÜBİTAK
Side-view
Top-view
Aluminum
plate
FAN
Radar-SW
Thermo-Electric Module
Cold
30dB-Amp
60dB-Amp
Hot Controller
Cal-SW
Locations of the thermistors on the board
The temperature data is
obtained via the Keithley
Multimeter with the 20
channel interface card
installed.
TS91 Series negative
temperature coefficient (NTC)
Thermistors are used.
Temperature Stability Test
121
UYGU 2014
TÜBİTAK
122
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01.07.2014
Radiometric Linearity
UYGU 2014
TÜBİTAK
Radiometer Internal Calibration
123
UYGU 2014
TÜBİTAK
xh
ic
xh
xa
TB
xa
Vout
ih
xc
xc
# samples
Vout
Maury Microwave Corporation
Known Calibration Source
7mm Noise Calibration System
124
62
01.07.2014
Antenna and Transmission Line
UYGU 2014
TÜBİTAK
Antenna Upgrade
125
UYGU 2014
TÜBİTAK
126
63
01.07.2014
Simplified Radiometer Schematic
UYGU 2014
TÜBİTAK
Receiver
T0
TA
αR
αS
TA′
G
VA
TR
TC
TH
Cold
Hot
Temperature Controlled Radiometer Enclosure
Radiometer Calibration
127
UYGU 2014
TÜBİTAK
External
Calibration
AMBIENT MICROWAVE ABSORBER TARGET
Periodic Internal
Calibration
COLD SKY TARGET
128
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01.07.2014
Content
UYGU 2014
TÜBİTAK
Radar systems
Radar systems
129
UYGU 2014
TÜBİTAK
Radar measurements
Radar equation
Range resolution
Doppler shift and velocity resolution
Signal fading
Spatial discrimination
Radar system types
Side-looking airborne radar (SLAR)
Synthetic-aperture radar (SAR)
Inverse SAR
Interferometers
Scatterometers
Scattering mechanisms and characteristics
130
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01.07.2014
A brief overview of radar
UYGU 2014
TÜBİTAK
Radar – radio detection and ranging
Developed in the early 1900s (pre-World War II)
• 1904 Europeans demonstrated use for detecting ships in fog
• 1922 U.S. Navy Research Laboratory (NRL) detected wooden ship on Potomac River
• 1930 NRL engineers detected an aircraft with simple radar system
World War II accelerated radar’s development
• Radar had a significant impact militarily
• Called “The Invention That Changed The World” in two books by
Robert Buderi
Radar’s has deep military roots
• It continues to be important militarily
• Growing number of civil applications
• Objects often called ‘targets’ even civil applications
Radar System
131
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TÜBİTAK
Like a radiometer, radar systems use very sensitive
receivers to output a voltage that contains information
about the target.
Unlike a radiometer, the signal that the radar receives does
not originate from the target (emission), rather it is a
scattered version of a signal transmitted by the radar.
Therefore the characteristics of the signal received by
radar may be fundamentally different from the
radiometer signal
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01.07.2014
Radar System
UYGU 2014
TÜBİTAK
Radar is an acronym for radio detection and ranging.
Detection addresses the question of whether a target is
present or changing.
Ranging, the ability to measure the range to a target, is
possible as radar provides its own illumination (the
transmitter) unlike a radiometer that provides no range
information
Radar System
133
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TÜBİTAK
The transmitted radar signal may be coherent, polarized,
and modulated in frequency, phase, amplitude, and
polarization.
In addition, the transmit antenna determines the spatial
distribution of the transmitted signal.
While radar system measures only the received signal
voltage as a function of time, signal analysis enables the
extraction of new information about the target including
location,
velocity,
composition,
structure,
rotation,
vibration, etc.
Radar images of 3.5-km asteroid 1999 JM8 at a range of
8.5x106 km with ~ 30-m spatial resolution
134
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01.07.2014
Basic Geometry – Radar Equation
UYGU 2014
TÜBİTAK
Pr =
Pt Gt Ar
[A (1 − f a ) Gts ] , W
(4 π Rt Rr ) 2 rs
Radar Scattering Cross Section
135
UYGU 2014
TÜBİTAK
The terms associated with the scatterer may be combined
into a single variable, σ, the radar scattering cross section
(RCS).
σ = Ars (1 − f a ) Gts , m 2
The RCS value will depend on the scatterer’s shape and
composition as well as on the observation geometry.
For bistatic observations
σ (θ 0 , φ0 ; θ s , φs ; p0 , ps ) , m 2
where
(θ0, φ0) = direction of incident power
(θs, φs) = direction of scattered power
(p0, ps) = polarization state of incident
and scattered fields
136
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01.07.2014
Radar equation – Monostatic
UYGU 2014
TÜBİTAK
In monostatic radar systems the transmit and receive
antennas are collocated (placed together, side-by-side) such that
θ0 = θs, φ0 = φs, and Rt = Rr so that the RCS becomes
σ (θ , φ ; p0 , ps ) , m 2
The radar range equation for the monostatic case is
Pr =
Pt Gt Ar
(4 π R )
2 2
σ,W
Radar equation – Monostatic
137
UYGU 2014
TÜBİTAK
If the same antenna or identical antennas are used in a
monostatic radar system then
Gt = Gr = G and At = Ar = A
and recognizing the relationship between A and G
4π A
λ2 G
and G = 2
4π
λ
we can write
A=
Pt G 2 λ2 σ
Pt A2 σ
Pr =
=
(4 π ) 3 R 4 4 π λ2 R 4
138
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01.07.2014
Radar equation for extended targets
UYGU 2014
TÜBİTAK
The preceding development considered
point target with a simple RCS, σ.
The point-target case enables simplifying
assumptions in the development.
Gain and range are treated as constants
Now consider the case of extended targets
including surfaces and volumes.
The backscattering characteristics of
a surface are represented by the
scattering coefficient, σ°,
σ° =σ A
where A is the illuminated area.
σ °(θ , φ ; p0 , ps ) , unitless
Radar equation for extended targets
139
UYGU 2014
TÜBİTAK
For homogeneous extended area targets (e.g., grass, bare soil, forest,
water, sand, snow, etc.) σ° ≅ constant (though still dependent on θ, φ, and polarization).
Substituting this relationship leads to
λ2 Pt G 2 σ ° ∆A
(4 π ) 3 R 4
where ∆A is determined by the system’s spatial resolution.
The scattering coefficient, σ°, contains target information.
Pr =
Soil moisture
Surface wind speed and direction over water
Ground surface roughness
Water equivalent content of a snowpack
Therefore the accuracy and precision of σ° measurements
are important.
140
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01.07.2014
ComRAD : Radar Blok Diagram
UYGU 2014
TÜBİTAK
Radiometer
T
400
SW
D. Coupler
SW
H
R
PreAmp
SW 501
SW
201
V
D. Coupler
Antenna
Network Analyzer
Switch Box
100
SW
SW
Radiometer
141
UYGU 2014
TÜBİTAK
HH - POL
Radiometer
400
T
SW
SW
R
SW
201
D. Coupler
SW
H
PreAmp
SW 501
V
D. Coupler
Antenna
Network Analyzer
Switch Box
100
SW
Radiometer
142
71
01.07.2014
UYGU 2014
TÜBİTAK
HV - POL
Radiometer
T
400
SW
D. Coupler
SW
H
R
PreAmp
SW 501
SW
201
V
D. Coupler
Antenna
Network Analyzer
Switch Box
100
SW
SW
Radiometer
143
UYGU 2014
TÜBİTAK
VV - POL
Radiometer
400
T
SW
SW
R
SW
201
D. Coupler
SW
H
PreAmp
SW 501
V
D. Coupler
Antenna
Network Analyzer
Switch Box
100
SW
Radiometer
144
72
01.07.2014
UYGU 2014
TÜBİTAK
VH - POL
Radiometer
T
400
SW
D. Coupler
SW
H
R
PreAmp
SW 501
SW
201
V
D. Coupler
Antenna
Network Analyzer
Switch Box
100
SW
SW
Radiometer
145
UYGU 2014
TÜBİTAK
Internal Cal
Radiometer
400
T
SW
SW
R
SW
201
D. Coupler
SW
H
PreAmp
SW 501
V
D. Coupler
Antenna
Network Analyzer
Switch Box
100
SW
Radiometer
146
73
01.07.2014
Radar Calibration
UYGU 2014
TÜBİTAK
Translating the received signal power into a target’s radar
characteristics (cross section or attenuation) requires
radiometric accuracy.
From the radar range equation for an extended target
λ2 Pt G 2 σ ° ∆A
Pr =
(4 π ) 3 R 4
we know that the factor affecting the received signal power
include the transmitted signal power, the antenna gain, the
range to the target, and the resolution cell area.
Uncertainty in these parameters will contribute to the
overall uncertainty in the target’s radar characteristics.
Calibration targets
147
UYGU 2014
TÜBİTAK
Radiometric calibration of the entire radar system may
require external reference targets such as spheres,
dihedrals, trihedrals, Luneberg lens, or active calibrators.
148
74
01.07.2014
RCS of some common shapes
UYGU 2014
TÜBİTAK
Radar Calibration
149
UYGU 2014
TÜBİTAK
150
75
01.07.2014
ComRAD : Radar Calibration
UYGU 2014
TÜBİTAK
151
UYGU 2014
TÜBİTAK
152
76
01.07.2014
UYGU 2014
TÜBİTAK
Circular Plate
153
UYGU 2014
TÜBİTAK
Dihedral in Horizontal position
154
77
01.07.2014
UYGU 2014
TÜBİTAK
Dihedral in Vertical position
155
UYGU 2014
TÜBİTAK
Dihedral rotated in 45 degrees in CCW
156
78
01.07.2014
UYGU 2014
TÜBİTAK
Dihedral rotated in 45 degrees in CW
157
http://bte.bilgem.tubitak.gov.tr/tr/uygu-yo2014
[email protected]
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G3-1 - bilişim teknolojileri enstitüsü

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G5-1-2 - bilişim teknolojileri enstitüsü

Lecture Notes File

SIU 2010

ÖZGEÇMİŞ 1. Adı Soyadı: Ahmet Emre TEKELİ 2. Doğum Tarihi ve

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