The influence of a surface-active substance (SAS) film on the Doppler spectrum width at small incidence angles is theoretically investigated for the first time for microwave radars with narrow-beam and knife-beam antenna patterns. It is shown that the requirements specified for the antenna system depend on the radar motion velocity. A narrow-beam antenna pattern should be used to detect slicks by an immobile radar, whereas radar with a knife-beam antenna pattern is needed for diagnostics from a moving platform. The study has revealed that the slick contrast in the Doppler spectrum width increases as the radar wavelength diminishes, thus it is preferable to utilize wavelengths not larger than 2 cm for solving diagnostic problems. The contrast in the Doppler spectrum width is generally weaker than that in the radar backscattering cross section; however, spatial and temporal fluctuations of the Doppler spectrum width are much weaker than those of the reflected signal power. This enables one to consider the Doppler spectrum as a promising indicator of slicks on water surface.

Improvement of methods for satellite monitoring of the world ocean state is one of the most important areas of the remote sensing because of the influence the oceans have on the Earth's climate. Currently, only one parameter is measured on a regular basis on a global scale: the significant wave height which is obtained from spaceborne radar altimeter data. It is known that at small incidence angles within the framework of Kirchhoff approximation, the backscattering radar cross section depends mainly on the mean square slope (mss) of the sea surface; therefore, this parameter can be measured. The performed studies lead to the improvement of the methods for processing the data from a precipitation radar. We demonstrate that the mss of the large‐scale (compared to the radar wavelength) sea waves can be restored within the swath, that is, about 115 km wide. The aim of this work is to communicate these new possibilities to the broad research community involved in the studies of the oceans. In this paper, a review of the results is performed and the prospects for global monitoring are first shown. On the basis of the precipitation radar data, it becomes possible to measure global fields of sea wave slopes, which in turn will help scientists to analyze the processes of air‐sea interaction. Availability of this new mss parameter essentially doubles the amount of available descriptors of sea waves, which will advance the understanding of the processes occurring in the oceans.

The use of a nadir altimeter radar with a rotating knife-beam antenna pattern isconsidered for improved measurements of the sea surface wind and wave parameters over awide swath. Theoretical calculations suggest the antenna beam rotating about the verticalaxis is able to provide wide swath of order 250-350 km. Processing of the signals using timeor Doppler sampling techniques results in the division of the antenna footprint intoelementary scattering cells of the order of 14x14 km. The theoretical algorithms developedhere indicate that the system may be used to retrieve the variance of large-scale slopes, thedirection of wave propagation and the wind speed in each cell. The possibility of measuringsignificant wave height is also analyzed. The combination of linear motion of the radar andthe rotation of the knife-beam antenna can be exploited to build up a two-dimensional mapof the surface, which enables better understanding of wave processes and to study theirstructure and temporal dynamics using repeated observations.

The total mean square slope (mss) of large-scale (in comparison with the scale of radar wavelengths) ocean waves can describe the roughness of the ocean surface. This important parameter has found many applications and can be determined by the dependence of large-scale mss on azimuthal angles. The Surface Waves Investigation and Monitoring instrument onboard the China France Oceanography Satellite (CFOSAT) can provide a 2-D normalized backscattering radar cross section (NRCS) for 2-D global ocean-surface wave detection. In this article, the 2-D NRCS is used to calculate the total large-scale mss via two methods. The first method is constructed from regression, while the second scheme is derived from a three-solution method. Finally, the total large-scale mss is calculated using these methods, and the map of the distribution of the global total mss is presented for the first time. Our results show that the two sources of total large-scale mss obtained are consistent with each other. CFOSAT can provide a 2-D total large-scale mss map and be used as a new data resource for global applications.