Sar polarimetric data analysis for identification of ships

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Sar polarimetric data analysis for identification
of ships
India Geospatial Forum 14th International
Conference February 07-09, 2012, Gurgaon
S. Swarajya lakshmi ADRIN, Dept. of Space, Govt.
of India
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Objectives

• Exploitation of polarimetric SAR data for
  detection of ships
• Understanding the scattering mechanisms of ships
  through decomposition
• Feasibility for deriving additional information
  for identification and classification of ships

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Polarization Combinations
VV
HH
HV
VH
pq p transmit q -receive
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Polarimetry Information Content

• As compared to single-polarization SAR,
  polarimetric SAR provides additional information
  on
• Type of scatterer Trihedral, dihedral, dipole
  etc.
• Orientation of the scatterer about the radar line
  of sight
• Ellipticity degree of scatterer symmetry
• Entropy significance of the polarimetric
  information
• Therefore, enables better characterization of
  the target

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Scattering Mechanisms
T11 hhvv2
T22 hh-vv2
T332hv2
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Polarimetric Signature
Horizontal Polarization ? 0º or 180º Vertical
Polarization ? 90º
Pedestal Height
Circular Polarization
Elliptical Polarization
Linear Polarization
Vertical Polarization
Linear Polarization ?
0º Elliptical Polarization -45º lt ? lt 0º
and 0º lt ? lt 45º Circular
Polarization ? -45º or 45º
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Materials Methods
Data Used
Radarsat 2 Radarsat 2
Acquisition Type Fine Quad Polarisation
Product Type SLC
Date 22-02-2009
Pixel Spacing 4.733m
Swath 25km
Approximate Resolution Range 12m Azimuth 8m
Incidence Angle 20 41 degrees
Software Used POLSAR of ESA
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Methodology
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Steps Involved

• Input SLC data
• Sinclair Matrix Shh, Shv, Svh, Svv
• Extracting Different Target Descriptors
• Stokes matrix, Covariance Matrix, Cherence Matrix
• Speckle Filtering
• Polarimetric Parameter Extraction
• Total Power, Entropy, Alpha, Anisotropy,
  Degree of Polarisation, Eigen Analysis parameters
  etc.
• Extracting Polarimetric signatures
• Polarimetric Synthesis
• Polarimetric Decomposition and Classification
• Separation of Land and Water
• Identification of anomalies in water
• Identification of ships
• Further characterisation of ships with respect to
  polarimetric parameters

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Entropy

• Eigen Values Three eigen values of the 3x3
  Coherency matrix ?i represent the intensities of
  the three main scattering mechanisms
• Probabilities Pi of each scattering mechanism
• Entropy (H)
• This is a measure of the dominance of a given
  scattering mechanism within a resolution cell.
• Entropy ranging from 0 to 1, represents the
  randomness of a scattering medium
• from isotropic scattering (H0)
• to totally random scattering
  (H1)

Where,
ENTROPY
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Alpha
 
If the Entropy is close to 0, the alpha angle
provides the nature or type of the dominant
scattering mechanism for that resolution cell.
For example it will identify if the scattering
is volume, surface or double bounce.
anisotropic odd bounce
anisotropic even bounce
? 90?
? 45?
? 0?
Isotropic odd bounce
Isotropic even bounce
Multiple
ALPHA
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Anisotropy (A)
This is the measure of how homogeneous a target
is relative to the radar look direction. For
example, the Amazon forest is a very
homogeneous target and would have a low
anisotropy value. In contrast, row crops would
have a high anisotropy value.
A indicates the distribution of the two less
significant eigenvalues
Anisotropy becomes 0 if both scattering
mechanisms are of an equal proportion values
of A gt 0 indicates increasing amount of
anisotropic scattering.
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Target Decomposition

• Analysis methods whereby individual scattering
  components that have meaningful physical
  interpretation can be identified in the received
  signal.
• Scattering matrix is decomposed into sub-matrices
  so that Individual component have physical
  meaning gt Surface scatterer, double bounce,
  volume scattering

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H-Alpha Scattering Plane
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Classified image depicting water and ships
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Class description
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Scattering Mechanisms with respect to the ships
identified
Turbulence of water
Boundary between water metallic ship body
Ship structure
Objects causing strong double bounce scattering
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Polarimetric signatures
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Polarimetric signatures ship
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Proportion () of pixels for each class of
scattering
Class Ship 1 2 3 4 5 6 7 8
1 3 9 5 60 21 - 4 1
2 4 5 8 50 21 - 6 7
3 2 8 5 56 18 - 6 5
4 4 12 6 56 15 - 4 4
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Proportion () of pixels for each class of
scattering
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Derived Information on Ship Measurements
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Conclusions Way Forward

• Typical scattering mechanisms were observed to be
  associated with the ships, which could be used
  towards automated detection and characterization
  of ships.
• Potential of the polarimetric data cold be
  further explored with multi-parametric
  decomposition schemes and tested with a wide
  variety of ships.

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THANKS FOR YOUR KIND ATTENTION