[12] MTF is composed of tilt, hydrodynamic and velocity bunching

[12]. MTF is composed of tilt, hydrodynamic and velocity bunching modulations. According to Nunziata et al. [8], VB theory focuses on simple particle scattering. On the other hand, DS model focuses backscattering intensity from the surface. SAR image intensity of each facet is computed to generate numerical SAR images. However, DS model is not aimed to velocity bunching.SARAS [10], which is based on DS model, is developed in time domain to obtain SAR raw signals. They use PO to compute backscattering intensity of each computational grid. The scale of the computational grids is one-quarter of the resolution cell. SAR signals from the grids are calculated in this simulator.The beneficial features and some limitations of our simulator are described as follows.

The simulation process of obtaining microwave backscattering is similar to that of an actual SAR system. In our simulator, the pulse irradiation area is the calculation area. It is divided into computational grids that are smaller than the wavelength of the transmitted microwave to demonstrate accurate interaction between electromagnetic waves and ocean surface waves. PO is also used to calculate microwave backscattering. The time series of microwave backscattering as SAR raw signals is the summation of backscattered microwave from all computational grids in the pulse irradiation area. The position of the calculation area changes with microwave pulse and platform motions to obtain SAR raw signals for range and azimuth directions.One advantage of our simulator is that the phases of the received signals are based on Bragg scattering.

The backscattered microwaves from computational grids smaller than the microwave are emphasized in the Bragg resonant condition. Therefore the simulation adequately reproduces microwave backscattering from the ocean surface. In addition, our simulator can also obtain the time series of SAR raw signals while considering modulations caused by moving ocean waves. In order to understand sophisticated SAR imaging mechanism of ocean waves, we attempt to develop a simulator that generates numerical SAR images with regard to not only motion induced modulations Brefeldin_A but also scattering intensity based on Bragg scattering. Note that our simulation is not suitable for land SAR images because it ignores shadowing and multi scattering, which are important imaging factors for SAR images of land areas.

However, these are considered to be a minor scattering mechanism in ocean SAR images. In the ocean case, motion-induced modulation and microwave scattering on the sea surface are the key factors. Consequently, we focus on these factors in the SAR image simulation for moving ocean surfaces.This paper is organized as follows: firstly, we have simulated a stationary target case to confirm SAR signal processing.

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