An algorithm for the extraction of ocean surface current velocity from bistatic HF groundwave radar data: a simulation

Jin, Qiu (2007) An algorithm for the extraction of ocean surface current velocity from bistatic HF groundwave radar data: a simulation. Masters thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (40MB)

Abstract

More than seventy percent of our earth surface is covered by ocean. The conditions at sea will not only influence our climate, but also affect human activities such as offshore oil drilling, fisheries, etc. Monitoring ocean surface information, such as surface current, wave and wind conditions, becomes more and more important. High frequency (HF) ground wave radar is proven to be a very useful tool for measuring ocean surface current. The ability of the HF signal to travel beyond the line-of-sight because of the high conductivity of seawater enables the radar to be used to survey and obtain the ocean surface current maps over a large ocean area. The longer radio wavelength also allows measurements to be conducted under all weather conditions. In addition, the features of near real-time measurement and high spatial and temporal resolutions make this method more attractive than conventional techniques, such as are available from surface current meters and drifter buoys. -- The component of the current velocity along the radar look direction can be extracted from the first-order Doppler shift of the electromagnetic wave scattered from the ocean surface. In order to obtain a current vector, at least two projections along different directions should be known. This can be achieved by two widely separated monostatic radar installations, each of which contains a co-located transmitter and receiver. Another, potentially more cost effective, approach is by means of a pair of bistatic and monostatic receivers sharing the same radar transmitter. In this configuration the projections of the current along two different directions can be found and thus the current velocity can be obtained without significantly losing potential coverage. Here, an algorithm is developed to examine the relevant issues of this new approach of surface current measurements. More specifically, the scatter patch in this model is chosen to be along a constant bistatic angle curve. The simulated bistatic and monostatic radar received time series data are processed by averaging fifteen 512-point fast Fourier transforms with 50 percent overlap to yield the Doppler spectrum (power spectral density (PSD)). The first-order Doppler shifts are obtained by comparing the centroid frequencies of the spectral peak regions with their theoretical positions determined by the Bragg scatter mechanism. The current components are obtained from these Doppler offsets. The error analysis is carried out by means of the concept of geometric dilution of precision (GDOP). -- While no consideration is given to the significant problem of sidelobes in the antenna patterns, zero-mean Gaussian noise from external sources is added to simulate pulsed HF radar clutter from the ocean surface. Deep water is assumed when the monostatic and bistatic radar data are simulated. The combination of clutter PSDs and noise makes the simulated radar data more realistic.

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