A semiempirical model of the normalized radar cross‐section of the sea surface 1. Background model

Abstract

[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.

Investigation of Low-Grazing-Angle Microwave Backscattering From Threedimensional Breaking Sea Waves

“…The Ku band (14 GHz) composite backscattering including breakers is compared with the Kudryavtsev model [23] under 15 m/s wind speed in Figure 7. Both of the models predict the enhancement of HH polarization in LGA and yield similar results in moderate incidence angles.…”

“…The volume scatters on the sea surface are generally considered as the source of non-Bragg scattering. Based on the energy balance equation, Kudryavtsev et al [23] proposed a simplified scattering model…”

“…The large-scale breaking waves scattering was treated with the method of moment (MoM), Extended GO and three-dimensional multilevel fast-multipole algorithm (MLFMA). Kudryavtsev et al [23] calculated the distributed surface scattering with the two-scale method (TSM) and take into account the modulation of the non-Bragg scattering, which is proportional to the whitecap coverage of the surface. This scattering numerical model agrees with the measured data in specific sea conditions properly.…”

Incidence angle normalization of Wide Swath SAR data for oceanographic applications

“…The NRCS values can be correlated with wind speeds and are dependent on polarization, upwind or downwind direction and incidence angle [20]. This correlation is multivariable and remains an open question among the scientific community.…”

“…This procedure requires modeling and measurements of the normalized radar cross-section of the sea surface at several wind speeds [19][20][21][22] and wind directions [23].…”