| Popis: |
Polarimetric Synthetic Aperture Radar (SAR) backscatter from man-made structures in urban areas is quite different than backscatter from predominantly natural areas. Backscatter from natural areas is often reflection symmetric; i.e., characterized by near zero values for covariance matrix off-diagonal terms of the form 〈 S HV S HH ⁎ 〉, 〈 S HV S VV ⁎ 〉 and their conjugates. A new approach is proposed to detect scattering from non-reflection symmetric structures using circular-pol, RR-LL, correlation coefficients, | ρ |. This method creates a normalization term, | ρ 0 |, and then forms a ratio, | ρ |/| ρ 0 |. The normalization term, | ρ 0 |, contains the same diagonal terms of the covariance matrix. The 〈 S HV S HH ⁎ 〉 and 〈 S HV S VV ⁎ 〉 off-diagonal terms and their conjugates are purposely set to zero. The ratio, | ρ |/| ρ 0 |, is rewritten as a product of separable helicity (τ) and orientation angle ( θ ) dependencies. The mathematical form of the τ dependence is a resonant singularity, or pole, term. This pole significantly enhances returns from man-made, high helicity, non-reflection symmetric structures. These structures have values of τ near the resonance value at τ = ± 1. Natural scatterers possess very strong RR / LL symmetry (τ ≈ 0) and the pole response for them is correspondingly weak. The dependence of | ρ |/| ρ 0 | on the orientation angle ( θ ) is known from previous studies to be useful for measuring urban building alignments (relative to the azimuth direction) and measuring surface topography. The ratio | ρ |/| ρ 0 | reduces much of the un-needed image detail of backscatter variations from natural areas of different surface roughness. This image simplification further facilitates detection of localized man-made targets. |
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