[1] Multiscale composite models based on the Bragg theory are widely used to study the normalized radar cross-section (NRCS) over the sea surface. However, these models are not able to correctly reproduce the NRCS in all configurations and wind wave conditions. We have developed a physical model that takes into account, not only the Bragg mechanism, but also the non-Bragg scattering mechanism associated with wave breaking. A single model was built to explain on the same physical basis both the background behavior of the NRCS and the wave radar Modulation Transfer Function (MTF) at HH and VV polarization. The NRCS is assumed to be the sum of a Bragg part (two-scale model) and of a non-Bragg part. The description of the sea surface is based on the short wind wave spectrum (wavelength from few millimeters to few meters) developed by Kudryavtsev et al. [1999] and wave breaking statistics proposed by Phillips [1985]. We assume that non-Bragg scattering is supported by quasi-specular reflection from very rough wave breaking patterns and that the overall contribution is proportional to the white cap coverage of the surface. A comparison of the model NRCS with observations is presented. We show that neither pure Bragg nor composite Bragg model is able to reproduce observed feature of the sea surface NRCS in a wide range of radar frequencies, wind speeds, and incidence and azimuth angles. The introduction of the non-Bragg part in the model gives an improved agreement with observations. In Part 2, we extend the model to the wave radar MTF problem.

This paper describes a self‐consistent axisymmetric stationary MHD model of the Jovian magnetosphere, in which both the centrifugal force and the pressure gradients exerted on the plasma are taken into account. The outer boundary condition is chosen so as to represent the dayside (noon meridian). The plasma distribution within the magnetosphere is represented by two Maxwellian components: a cold plasma (several tens of eV) produced at the orbit of Io and diffusing outward under centrifugally driven interchange instability, and a hot (30 keV) low‐density plasma, originating from the outer regions of the magnetosphere and diffusing inward in response to it. Outside the Io torus, this process is assumed to be sufficiently rapid that the amount of particles of each population per unit flux tube is independent of distance. The self‐consistent solution to the model, with input parameters suitable for the Voyager 1 encounter, is presented and compared to observations. It is found to reproduce very satisfactorily the large‐scale features of the dayside magnetic field, plasma density, and plasma pressure, thus supporting the relevance of the plasma distribution that was assumed as input to the model. Among the main conclusions, the pressure gradients are found to constitute the major source of azimuthal currents, thus producing, at all distances, at least 68% of the total current (integrated over latitude) per unit radial distance. The centrifugal current is of secondary importance, although its distribution is more closely confined to the equator. Several runs of the model made with different outer boundary conditions have also permitted study of the compressibility of the magnetosphere, thus showing that due to the presence of high beta plasma within it, the Jovian magnetosphere is much more sensitive to variations of the solar wind pressure than is the terrestrial magnetosphere, in accordance with the observed large variability of the Jovian magnetopause location.

[1] Radar observations of the sea surface at C-Band and small incidence angles are used to investigate some properties of the surface slope probability density function (pdf). The method is based on the analysis of the variation of the radar cross-section with incidence angle, assuming a backscattering process following the Geometrical Optics theory. First, we assess the limit of this model in our experimental configuration by using simulations of radar cross-sections with a more accurate backscattering model, namely the Physical Optics model. We show that roughness properties with scales larger than 12 cm can be analyzed in our configuration (C-Band, incidence 7 to 16°). The radar data are then analyzed in terms of filtered mean square slope under the assumption of a Gaussian slope pdf. Dependence of the radar-derived mean square slopes (mss) with wind speed is analyzed, thanks to wind estimates obtained by using coincident observations of the same radar at larger incidence (around 32°). Furthermore an analysis of the anisotropy of the mean square slope is proposed. The results are discussed in comparison with those of Munk (1954a, 1954b), and with the mean square slopes derived from two surface models (Elfouhaily et al., 1997 andKudryavtsev et al., 2003). We find that the radar-derived values are in good agreement with Cox and Munk results, taking into account the filtering effect on radar-derived values. We also show that the surface model of Elfouhaily et al. yields good agreement for the omni directional mss, but a too large anisotropy of the mss. The model of Kudryavtsev provides a reasonable anisotropy of the mss, but overestimates the mss values in all directions. Finally, we propose an analysis of the radar data under a non-Gaussian assumption for the slope pdf, by applying the compound model suggested by Chapron et al. (2000) to our observations. To our knowledge, it is the first time that peakedness values are explicitly derived from radar observations, and documented as a function of azimuth and wind speed. We show that the peakedness (or kurtosis) of the slope pdf is not zero but weak (peakedness factor reaching about 0.20), and slightly increases with wind speed.Citation: Hauser, D., G. Caudal, S. Guimbard, and A. A. Mouche (2008), A study of the slope probability density function of the ocean waves from radar observations,

Simultaneous data were obtained bet-Various kinds of ground-based facilities also proween the SAFARI HF coherent radars and the EISCAT vide an access to the ionospheric electric field. incoherent scatter experiment in December 1953. Incoherent scatter radars measure most parameters

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[1] Multiscale composite models based on the Bragg theory are widely used to study the normalized radar cross section (NRCS) over the sea surface. However, these models are not able to correctly reproduce the NRCS in all configurations. In particular, even if they may provide consistent results for vertical transmit and receive (VV) polarization, they fail in horizontal transmit and receive (HH) polarization. In addition, there are still important discrepancies between model and observations of the radar modulation transfer function (MTF), which relates the modulations of the NRCS to the long waves. In this context, we have developed a physical model that takes into account not only the Bragg mechanism but also the non-Bragg scattering associated with radio wave scattering from breaking waves. The same model was built to explain both the background NRCS and its modulation by long surface wave (wave radar MTF problem). In part 1, the background NRCS model was presented and assessed through comparisons with observations. In this part 2, we extend the model to include a third underlying scale associated with longer waves (wavelength $10-300 m) to explain the modulation of the NRCS. Two contributions are distinguished in the model, corresponding to the so-called tilt and hydrodynamic MTF. Results are compared to observations (already published in the literature or derived from the FETCH experiment). As found, taking into account modulation of wave breaking (responsible for the non-Bragg mechanism) helps to bring the model predictions in closer agreement with observations. In particular, the large MTF amplitudes for HH polarization (much larger than for VV polarization) and MTF phases are better interpreted using the present model.

[1] In order to prepare the sea surface salinity (SSS) retrieval in the frame of the Soil Moisture and Ocean Salinity (SMOS) mission we conduct sensitivity studies to quantify uncertainties on simulated brightness temperatures (T b ) related to uncertainties on sea surface and scattering modeling. Using a two-scale sea surface emissivity model to simulate T b at L band (1.4 GHz), we explore the influence on estimated SSS of the parameterization of the seawater permittivity, of the sea wave spectrum, of the choice of the two-scale cutoff wavelength, and of adding swell to the wind sea. Differences between T b estimated with various existing permittivity models are up to 1.5 K. Therefore a better knowledge of the seawater permittivity at L band is required. The influence of wind speed on T b simulated with various parameterizations of the sea wave spectrum differs by up to a factor of two; for a wind speed of 7 m s À1 the differences on estimated SSS is several psu depending on the sea wave spectral model taken, so that sea spectrum is a major source of uncertainty in models. We find no noticeable effect on simulated T b when changing the two-scale cutoff wavelength and when adding swell to the wind sea for low to moderate incidence angles. The dependence of the wind-induced T b on SST and SSS being weak, we assess the error in SSS estimated assuming that the wind speed influence is independent of SST and SSS. We find errors on estimated SSS up to 0.5 psu for 20°C variation in SST. Therefore this assumption would induce regional biases when applied to global measurements.INDEX TERMS: 4275 Oceanography: General: Remote sensing and electromagnetic processes (0689); 4271 Oceanography: General: Physical and chemical properties of seawater; 0659 Electromagnetics: Random media and rough surfaces; KEYWORDS: microwave, radiometry, remote sensing, salinity, roughness Citation: Dinnat, E. P., J. Boutin, G. Caudal, and J. Etcheto, Issues concerning the sea emissivity modeling at L band for retrieving surface salinity,

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