Abstract
Azimuth cutoff is an inherent disadvantage of synthetic aperture radar (SAR) waves observation. The waves shorter than some certain wavelength (azimuth cutoff) cannot be imaged in original form (structures) by SAR. For a single SAR observation, the problem of the azimuth cutoff for ocean waves can be resolved to some extent by cooperative observations of SAR satellites. Multiple SAR satellites are required to achieve simultaneous observation of an ocean area to obtain multiview SAR ocean wave synchronization data. Currently, these data cannot be acquired from in-orbit SARs. In this study, imaging simulations of multiview SAR ocean wave synchronization data based on small SAR satellites were carried out for the first time with X-band, 4-m resolution, stripmap mode and Single Look Complex (SLC) product. The Max Planck Institute (MPI) method was used to obtain the optimum wave spectrum of the synchronous data. The influencing factors of the azimuth cutoff wavelength were analyzed by using measured and simulated SAR data. The analysis results were used to develop a novel multiview wave spectrum data fusion method for azimuth cutoff compensation. The azimuth cutoff compensation effect was evaluated by comparing the inversion results before and after data fusion: the azimuth cutoff decreased by 9.76% on average, the root mean square error (RMSE) of the significant wave height is 0.06m, and RMSE of the mean wave period is 0.58s. The azimuth cutoff compensation method can be applied to SAR data for medium and low sea states (that is, wind speeds of 5-15 m/s). These results show that the proposed method of multiview wave spectrum data fusion effectively compensates for azimuth cutoff.
Highlights
Ocean waves are typically generated by local winds and can be categorized as wind sea waves and swells
The simulation of multiview Synthetic aperture radar (SAR) wave synchronization data consists of the following steps: simulation of the wave spectrum, simulation of the ocean surface, calculation of the backscattering coefficient, generation of echo signals, SAR imaging of ocean waves, and synchronization of the ocean wave data [20], [21]
The results show that in this case, the real SAR data could not be used to correlate the azimuth cutoff and the azimuth angle because the factors affecting the azimuth cutoff, such as wind speed and significant wave height, were not consistent
Summary
Ocean waves are typically generated by local winds and can be categorized as wind sea waves and swells. Additional sources of wave generation are tides, currents, internal waves, thalassogenic movement, changes in atmospheric pressure, the uneven distribution of seawater density, etc. The mechanism of the formation and evolution of ocean waves has become an important research field in oceanography. Synthetic aperture radar (SAR) is an effective means of observing large areas of ocean waves to obtain a two-dimensional (2D) ocean wave spectrum [1]. Recently the X-band radar are widely used on wave observation [2], [3]. Compared with other remote sensing methods, such as altimetry and wave spectrometry, SAR has
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