Bistatic high frequency radar ocean surface cross section for an antenna on a floating platform

Ma, Yue (2017) Bistatic high frequency radar ocean surface cross section for an antenna on a floating platform. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Land-based high frequency surface wave radar (HFSWR) is an established sensor for ocean remote sensing. Placing an HFSWR on a floating platform has the advantage of mobility. However, antenna motion will distort the Doppler spectrum, which is used to extract ocean information and to detect the signatures of targets. In this thesis, significant effort has been expended on establishing radar cross section (RCS) models for a fixed receiver and a transmitter on a floating platform, analyzing the effect of the antenna motion, and developing a motion compensation method to eliminate the effect of the platform motion. The first- and second-order monostatic RCSs of the ocean surface for the case of a pulsed dipole source on a floating platform have been previously derived in the literature, with the assumption that the platform motion is a single-frequency sinusoid. Following that work, the research in this thesis is extended to the bistatic case. The effect of platform motion on simulated Doppler spectra is considered for a variety of sea states. It is shown that the resulting motion-induced peaks are symmetrically distributed in the Doppler spectrum. Following this work, the corresponding bistatic RCS models for a frequency modulated continuous waveform (FMCW) source are derived. Results show that the sidelobe level for an FMCW source is reduced with increasing extent of range bin. To mimic real world scenarios, platform motion is next modelled as a combination of two cosine functions, based on existing research of realistic horizontal motions of moored floating platforms. RCSs incorporating a dual-frequency platform motion model are then developed. These can be extended to a general form incorporating a multi-frequency platform motion. It is found that the platform motion can be viewed as a modulator of the radar frequencies, with the modulation indices related to the amplitudes of the platform motion. Finally, to mitigate the effect of platform motion on the Doppler spectra, a motion compensation method is proposed. This motion compensation method can be achieved by a deconvolution process. Calculations involving a RCS model, incorporating external noise, for an antenna on a floating platform are conducted in order to simulate field data and to examine this motion compensation method. The external noise is characterized as a white Gaussian zero-mean process. By using this newly-developed RCS model with external noise, motion compensation results under different sea states and signal-to-noise ratios (SNRs) are examined. The outcomes indicate that an iterative Tikhonov regularized deconvolution technique is superior to other compensation methods implemented in this study.

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