No abstract

No abstract

No abstract

In the search for extremely reliable electromagnetic communication to submerged submarines, the question arose, * "What is the effect of the roughness and irregularity of the sea surface on the propagation of electromagnetic waves?" The purpose of this investigation is to obtain an engineering-understanding of the effect of the rough air-sea interface on electromagnetic signals used in communication to submerged submarines. The frequency of the electromagnetic wave is restricted to the3 ELF or VLF range. In the initial part of the investi-gaticin, the sea surface is assumed to .be a two-dimensional (constant in one variable or direction) sinusoidal surface; later a doubly,(three.-dimensional) sinusoidal surface is considered. The source of electromagnetic energy is assumed-to be a plane wave with arbitrary direction of propagation and: polarization. The fields on the air side of the sea surface are com-pited.with the aid of the assumptions that the sea is a p-ect .electric conductor and that the sea surface is only-sg+Eghtly-rough (,i.e., the maximum slope of the sea surface q-tis uch less than 1). The integral equations governing the tangential magnetic fields are formulated and solved. These-solutions show a variation of the tangential magnetic field '(of the otder of 2 db. frn the flat surface case) depending '7 .i I on polarization and direction of propagation of the incident plane wave. The fields in the sea are computed by assuming the tangential magnetic field is continuous through the air-sea interface. The method used in these calculations is a numerical one based on finite differences. Both from the numerical solutions and a heuristic theory of propagation in the sea, it is seen that the perturbation of the fields caused by the roughness of the sea surface decays rapidly with depth if the sea wave wavelength is less than or the order of magnitude of the skin depth of the sea at the frequency considered; if the sea wave wavelength is many orders of magnitude larger than the skin depth, there is little decay (at the depths considered) of the perturbation, so that the phase and amplitude of the fields in the sea vary with the height of the sea vert±cally above them.

In microwave remote sensing, it is desirable to select radar antenna polarizations that maximize the contrast between two classes ofscatterers or scatterer ensembles. A polarimetric radar measures complete polarization properties ofa target and then provides a vector description of the resulting scattered wave through various target matrices. Several optimization procedures for the completely and partially polarized cases have been proposed based on the theory of radar polarimetry. It is the purpose of this paper to present optimization procedures for the enhancement ofpolarimetric contrast between two timevarying targets and to extend the procedure to two spatially incoherent image pixel targets. The targets are now characterized by the time-averaged or spatially-avemged Kronecker matrices, from which one can obtain the associated Graves and Kennaugh matrices.The Graves matrices ofthe targets are used to find a tnmsmitter polarization to maximize the ratio of scattered power densities at the receiver. Using the Lagrange multiplier method, the maximization problem is cast into the form of a generalized Balois eigenvalue equation. The largest eigenvalue ofthe equation equals the maximal power ratio, and the optimal effective length ofthe transmitting antenna is proportional to the corresponding eigenvector. The Kennaugh matrices of the targets are employed to obtain the Kennaugh vectors of partially polarized scattered waves from the two targets. Each of the scattered Kemutugh vectors is decomposed into a completely polarized and an unpolarized part. It is well known that the power received from the unpolarized part is independent ofthe polarization characteristics ofthe receiving antenna. Then a receiver polarization is selected to maximize or minimize the completely polarized part scattered from the desired or the undesired target.As a numerical example, the optimal Stokes vectors of transmitting and receiving antennas are given to show the validity ofthe optimization procedures and how it can be applied to perfecting high resolution POL-SAR/SAL Image Feature Extraction.