Measurement of Ocean Wave Directional Spectra Using Airborne HF/VHF Synthetic Aperture Radar: A Theoretical Evaluation

Currently, images obtained with microwave synthetic aperture radars (SARs) are widely used for measuring directionality of ocean waves on a global and continuous scale. However, with all the advantages of the microwave SAR systems, the effectiveness of wave spectrum retrieval from SAR images is still debated. In this paper, we demonstrate how the directional spectrum of relatively long sea waves can be measured using aperture synthesis method in conjunction with relatively low radio frequencies (HF and VHF bands). This approach has advantages over HF ground-based radars used for ocean wave studies in coastal zones. In this paper, we theoretically evaluate this technique for the system mounted on aircraft. A favorable combination of the parameters for both ocean surface waves and HF electromagnetic waves allows an accurate analytical description of scattering from the sea surface based on the first approximation of the small perturbation method. In this case, scattered electromagnetic field becomes a linear functional of sea surface wave elevations. An analysis of the signal processing pertaining to this situation is presented, and a practical example is discussed. The proposed approach can be used even in the case when the radar platform is moving nonsteadily and/or along the curvilinear trajectory.