| Research Abstract |
This project is
1. to present a theory of wave scattering from a target in random media,
2. to formulate (2-1) the-scattering cross-section of a conducting cylinder in turbulent media, (2-2) the mean pulse waveform of received waves in a FM chirp radar, which waves passed through turbulence, (2-3) the reconstructed image in holographic radars, and (2-4) the iiacroscopic characteristics of discrete random media,
3. to analyze (2-1) to (2-4) numerically for some practical models and make clear the effects of random irregularities.
Subject 1 :
We present a general method applicable to most practical cases, by which method the wave scattering can be exactly analyzed as boundary value problems for a conducting target of arbitrary shape and size. That is, it can be solved through two independent analyses of current generators on the target in free space and of wave propagation in random media.
Subject 2 and 3 :
(3-1) In strong turbulence, the backscattering cross-section sigma becomes about two times compared with sigma in free space if the spatial coherence length l of waves on the target is very larger than the size a of target, but sigma takes very large values at the frequency bands close to the internal resonance frequencies of target. (3-2) A FM chirp radar system, one of satellite microwave sensing systems, is insusceptible to the atmospheric turbulence and the ionospheric turbulence. (3-3) Holographic images smeared due to turbulence can be reconstructed with negligible distortion by a spatial filtering of amplitudes of received waves. (3-4) The condition for many dielectric spheres to be randomly distributed for coherent waves is presented, and the effective dielectric constant and the coherence attenuation rate are precisely analyzed compared with the conventional results.
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