Modeling and SAR imaging of the sea surface: A review of the state-of-the-art with simulations

Among other remote sensing technologies, synthetic aperture radar (SAR) has become firmly established in the practice of oceanographic research. Despite solid experience in this field, comprehensive knowledge and interpretation of ocean/sea and vessel wave signatures on radar images are still very challenging. This is not only due to the complex mechanisms involved in the SAR imaging of moving waves: Many technical parameters and scanning conditions vary for different SAR platforms, which also imposes some restrictions on the cross-analysis of their respective images. Numerical simulation of SAR images, on the other hand, allows the analysis of many radar imaging parameters including environmental, ship, or platform related. In this paper, we present a universal simulation framework for SAR imagery of the sea surface, which includes the superposition of sea-ship waves. This paper is the first attempt to cover exhaustively all SAR imaging effects for the sea waves and ship Kelvin wakes scene. The study is based on well proven concepts: the linear theory of sea surface modeling, Michell thin-ship theory for Kelvin wake modeling, and ocean SAR imaging theory. We demonstrate the role of two main factors that affect imaging of both types of waves: (i) SAR parameters and (ii) Hydrodynamic related parameters such as wind state and Froude number. The SAR parameters include frequency (X, C, and L-band), signal polarization (VV, HH), mean incidence angle, image resolution (2.5, 5 and 10 m), variation by scanning platform (airborne or spaceborne) of the range-to-velocity (R/V) ratio, and velocity bunching with associated shifting, smearing and azimuthal cutoff effects. We perform modeling for five wave frequency spectra and four ship models. We also compare spectra in two aspects: with Cox and Munk's probability density function (PDF), and with a novel proposed evaluation of ship wake detectability. The simulation results agree well with SAR imaging theory and the example of a real SAR image. The study gives a fuller understanding of radar imaging mechanisms for sea waves and ship wakes.

Automated summary

In this paper, a universal simulation framework for SAR imagery of the sea surface is presented, which includes the superposition of sea-ship waves. The study explores the impact of SAR parameters and hydrodynamic related parameters on the imaging of sea waves and ship wakes. The simulation results agree well with SAR imaging theory and provide a fuller understanding of radar imaging mechanisms for these phenomena.