A new form for the spectrum of the ocean surface vertical displacements is derived for the case of nonfully developed states. The gravity range is expressed as a function of the fetch x and the significant slope /spl conint/ as well. The capillary-gravity range is assumed dependent on the wind friction velocity only. Recent wavenumber spectrum measurements in this spectral domain and ocean conditions are analyzed. Toba's spectral shape is shown to represent correctly these experimental data when updated with an equivalent amplitude factor. An expression for this factor is proposed. It is weakly wind friction velocity dependent, as observed by Mitsuyasu in the late 1970s. The proposed spectrum is then combined with a boundary perturbation model for electromagnetic scattering computations. Empirical scattering models and radar data collocated with assumed ground-truth data are used for comparison. This is shown to give consistent results for both C- and Ku-bands as well as large ranges of wind speeds and incidence angles. Comparisons of backscattering coefficients computed using other sea spectra from the literature are presented. The significant slope is found to be an important factor for scattering at low incidence angles. The proposed spectrum thus constitutes a useful basis for physically based inversion algorithms.

A radiative transfer model is described for the evaluation of the brightness temperatures measured by microwave radiometers above the oceans. For observations at an incidence angle around 50/spl deg/ from the local vertical, a crude approximation of this model is providing the basis for a wind-independent inversion algorithm for the retrieval of atmospheric integrated water vapor and cloud liquid water. The algorithm is applied to special sensor microwave imager (SSM/I) data, and the results compared with estimates from the ECMWF climatological model and from the algorithms specifically developed for SSM/I. A short discussion on the accuracy of the algorithm is also provided.

This paper is concerned with the notions of the Mueller matrix and the Kennaugh (or Stokes scattering) matrix, that are commonly used in the field of radar polarimetry. Although these two matrices are quite similar, there exists a basic difference between them that seems to have been overlooked by a number of researchers, resulting in a great deal of confusion. An attempt is made to clarify this point and to present the basic relationships of radar polarimetry in a compact form.>

The phase calibration problem for polarimetric radars is discussed. More specifically, the assumption that the copolar vertical and horizontal returns from a slightly rough surface are in phase is critically reviewed. It is concluded by means of a theoretical analysis that the phase difference for moist soil targets can reach up to 10/spl deg/ at 15 GHz and for incidence angles of 50/spl deg/. However the assumption of zero phase difference is a good approximation for dry soils, lower frequencies, and low incidence angles.>

A method extending the Kirchhoff classical approach for mobile maritime satellite communications is presented. Carrier to specular and carrier to multipath ratios are evaluated from scattering by the rough sea surface calculations using the boundary perturbation method. They are compared with experimental results and with other experimental models. The results illustrate the limited effects of the wind speed and significant wave height, the important dependence on the elevation angle and the very large effects of the ship motions.>

A unified approach for combining active and passive microwave measurements for remote sensing applications is described. A synergic inversion technique has been developed and applied to the retrieval of geophysical parameters of the ocean surface and of the atmosphere. It is based on the combination of radiometric and radar measurements at the electromagnetic and cell level and not only on the correction of radar measurements by radiometric measurements, or conversely. Such a combination is performed through a common quantity: the bistatic scattering coefficient of the observed surface. This is used in a direct model to simulate combined measurements from active and passive sensors. It requires a rather complete and accurate calculation of the scattering of microwaves by the rough sea surface.>

In the above paper (ibid., vol. COM-27, pp. 502-509, Feb. 1979) L.S. Lee proposes a method to compensate for the rain-induced cross polarization in a dual-polarization zation link. This method is based on a model of Chu, in which the effect of rain on two orthogonal linear polarizations, along unit vectors is represented by a given matrix. The idea is that the medium is characterized by two orthogonal axes which are, the eigenvectorsof the matrix. If these vectors are used as a new basis, the matrix takes the diagonal form. The compensation is obtained by rotating the emitted linear polarizations of an angle, which is necessary to align them with the eigenvectors. The Lee claims that a similar compensation is applicable to the case of circular polarizations. It is here shown that the two signals are linearly polarized along the principal axes given by the eigenvectors. This means that the antenna does not radiate circular polarizations in space, but linear ones as a result of the addition in each channel of two equal and opposite circularly polarized signals. The proposed compensation actually is an elegant method to perform the rotation of the linear polarizations by first transforming them to circular polarizations, then introducing a phase shift, and finally converting them back to linear polarizations.