Doppler spectra of electromagnetic fields scattered from two-dimensional fetch- and depth-limited nearshore sea surfaces

- A two-dimensional (2-D) fetch- and depth-limited sea surfaces model is proposed.
- The Doppler spectral features at various incident angles are investigated.
- The spectral feature is impacted most for large wind fetch and small water depth.
- Nonlinear effect impacts co-polarization results more greatly.

Doppler spectral signatures of sea echoes from two-dimensional (2-D) fetch- and depth-limited sea surfaces are investigated using the second-order small-slope approximation (SSA-II) model. For the description of 2-D nearshore sea surface, the revised choppy wave model (RCWM) is applied, which takes into account the wind fetch effect and water depth effect in nearshore marine environment. Comparisons of computed results in co-polarizations and cross polarization at various incident angles show that Doppler shift and spectral bandwidth can be greatly influenced by hydrodynamic modulation of waves in the large wind fetch and small water depth marine environment, which indicates that the hydrodynamic modulation induced by shoaling effect would be greatly enhanced in the situation of the nearshore shallow sea with a long wind fetch. The differences in variation trend between results in co-polarizations and cross polarization also reflect varying degrees of influence of aforementioned hydrodynamic modulation on different scattering mechanisms.