| Polarimetric information in scattered signals from Radar target, as well asamplitude, phase, Doppler frequency and waveform of target echo is very valuableinformation which is significantly potential in numerous research fields includinganti-active jamming, clutters jamming, signal filtering and enhancement, targetdetection and recognition. The geometrical and physical parameters of rough surfacecan be extracted from polarimetric scattered information which has the importantapplied value on microwave remote sensing research in natural land and seabackground.According to electromagnetic wave scattering theory in natural background,polarimetric scattering properties of electromagnetic waves from rough land and seasurface are emphasisly studied in this thesis including polarimetric scattering fromtwo-dimensional rough surface characterized by textures, one-order and two-orderpolarimetric scattering from barchan dune, polarimetric scattering from two-dimensional improved sea fractal surface, composite polarimetric scattering from seasurface and cubic target. The main works are as follows:1. The obvious textures can be observed when the ratio of two correlation lengths isenough great. The relationship between the Cartesian coordinate system and thelocal coordinate system of facets is derived by the discrete rough surface. Newpolarimetric scattering model is yielded by the integration of the gradients in thelocal coordinate system with Kirchhoff Approximation (KA). The influence ofcorrelation lengths, texture angle and root-mean-square height on polarimetricscattering cross section from Gaussian and Lorentzian rough surface is presented bynumerical sumulation.2. Barchans are the most common terrain in desert district. Double scattering field isderived by means of first Geometrical Optics (GO) and second Physical Optics (PO)based on Ray Tracing(RT). Numerical results show second scattering plays animportant role in some angle range. When the electromagnetic wave incident to theflee, the co-polarized RCS is greater at great incident angle than the one in otherincident directions and the cross-polarized RCS reach the peak when the incidentangle is adjacent to the repose angle of the dune.3. The sea surface model is dependent on wind speed and wind direction. Theinfluence of wind speed, wind direction, fractal dimension and radar frequency onpolarimetric RCS are presented by vector calculation with KA. HH and HV monostatic RCS is the maximum on downwind or upwind direction and is theminimum on crosswind direction when the wind speed is greater. Whateverpolarization, the monostatic RCS increases with the incident frequency. Theco-polarized RCS reaches the maximum on the mirror direction and the minimumon the cross-side direction which is opposite to the cross-polarized RCS. Severalhemispheres of unit radius, where the latitude and the longitude is represented asscattering angle and azimuth angle, respectively, show that the cross-polarizedscattering coefficients in some directions are greater than the co-polarizedscattering coefficients, even than the one in the backscattering direction.4. The electromagnetic polarimetric composite backscattering by a dihedral cornerreflector (DCR) composed of a two-dimensional sea rough surface and a cuboidaltarget on it is analyzed. The polarimetric composite backscattering is calculatedwith different sizes of the target. The numerical results show that the backscatterenhancement of the copolarized RCS is more obvious with the increment of heightand width of the target which are the key factor to the cross-polarized RCS as well.The height and width of the target can be retrieved from the higher HH RCS andthe range of unequal cross-polarized RCS in the sea clutters with scattered resultsof the composite dihedral corner. Moreover, the length of the cuboidal target can beextracted with the span of the less co-polarized RCS. |
PDF Full Text Request