In this paper, numerical simulations of the scattering from time‐dependent realizations of one‐dimensional ocean surface waves are described. A new technique is used that allows efficient generation of ocean surface realizations that preserve the dominant nonlinear hydrodynamic characteristics. Thus unique scattering effects of real ocean surface waves can be explored. Until very recently, numerical simulations of rough‐surface scattering were used mainly to test and/or improve theoretical models that predict the average bistatic scatter cross section. We carry the simulations further by generating Doppler spectra from dynamically evolving surface realizations. Doppler spectra of signals scattered from the ocean surface are affected by both hydrodynamic nonlinearities and higher‐order scatter terms. The simulated Doppler spectra from nonlinear surface realizations reproduce the measured characteristics of ocean and wave‐tank data for low and high wind conditions. We also show that the results are essentially reproduced by the second‐order Kirchhoff approximation.

Th e frac tional d eviation of nose whi s tle r group delay from th e ze ro-tempe rature model has bee n calc ulat ed ass umin g a Maxwellian magne tos phere and a gyrofre qu e ncy electron de nsit y di s tributio n; i. e., th e electro n d e ns it y vari es as th e inverse c ube with di s tan ce from th e e arth 's ce nte r. Th e the rm a l c orrec ti on to th e ze ro-te mpe rature gro up refract ive ind ex has bee n in se r\ed int o the nose-whi stle r g roup d e lay int egra l to de te rmin e th e modifi ed group de lay. S ignifi ca nt dev ia tion s from th e ze rote mpera ture group de lay for frequ e nc ies a bov e th e nflse fre qu e ncy have bee n ca lcul a ted . S in ce dev ia tion s from th ,.. ze ro -te mpe rature di s pe rs ion o f a few pe rce nt a re rea di ly di s c e rnibl e_ noSe whi s tl er data s lwuld pro vide a t lea s t an es tim a te of th e uppe r bound on mag ne tos piJ e rl' te mpe ra ture. T we nt ythree whi s tl e rs have bee n a nal yzed a nd all uppe r bound on magne tos plwrc te mpe rat li n' of 2(1 0. 1 ) OK has bet'n de te rmined.' >

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The bistatic radar cross section of an underdense, inhomogeneous turbulent plasma was measured at X-band and the results were compared with a theoretical model. The turbulent plasma was formed by seeding a premixed ethylene-oxygen flame in a combustion chamber and exhausting it through an expansion nozzle into a low-pressure vessel. Electrostatic probes, biased for ion collection, were used to map the variation of the mean and rms electron density throughout the turbulent regions and to measure the·correlation coefficient of the plasma fluctuations. A theoretical scattering model was constructed using the Born approximation and the results of the diagnostic measurement program. Good agreement between theory and experiment has been obtained for the dependence of cross section on bistatic angle and for the spectrum of fluctuations of the scattered microwave signal. The predicted cross section underestimates the measured cross section by 6 to 11 dB when the measured cross sec· tions are in the range from 10-s to 10-• m2• The measured cross section was observed to have a square-law dependence on electron density in agreement with the Born model for densities up to one percent of the critical electron density. For densities beyond this, the Born approximation breaks down and the cross-section dependence becomes linear.

A pair of diagnostic techniques for the measurement of the statistical properties of the ionized particles of an equilibrium turbulent plasma have been developed including an electrostatic probe and a high-resolution microwave probe. The turbulent plasma is formed by seeding a premixed ethylene-oxygen flame in a combustion chamber and then exhausting through an expansion nozzle into a low-pressure vessel. The power spectral density of the fluctuations of the electrons and ions is measured. The electron and ion fluctuations are observed to have the identical spectrum. The ion density correlations in space and space-time have been measured throughout the plasma volume. The distribution of the mean and rms values of the electron density throughout the volume is also presented. It is concluded that on the axis of the hot jet exhaust the turbulent eddy pattern is approximately isotropic and frozen.