Estimation of vector surface currents beyond the region of overlap of dual-site HF radar : an implementation of the continuity equation

Bobby, Pradeep (2003) Estimation of vector surface currents beyond the region of overlap of dual-site HF radar : an implementation of the continuity equation. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/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 (5MB) [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. (Original Version)

Abstract

Knowledge of ocean surface currents is important for commercial and research reasons. High-frequency (HF) radar is a useful tool for measuring oceanographic phenomena because the frequencies involved can propagate for long distances across salt water, the radar wavelength is of similar magnitude to ocean wavelengths of significant energy, and a large expanse of water can be interrogated. -- Oceanographic information can be found from the Doppler plot of the electromagnetic energy reflecting from the ocean surface. The ocean, like any target, will have a radar cross section and it will depend on electromagnetic and hydrodynamic factors. Although the mechanism of interaction between radar and ocean waves is complex, it can be modelled and it has been found that there are many different portions of the cross section that depend on the order and location of the scatter or scatters. Several examples of simulated cross sections are presented at a variety of wind speeds, dominant wave directions and radar frequencies. The radar senses the component of the current projected along the radar look direction and the manifestation of this is a displacement of the first order spectral energy. -- When two or more radars illuminate the same area of ocean it is possible to construct a two-dimensional vector current. The geometrical method used to find the vector current will affect the accuracy of the values. The Cartesian method involves locating the range cell in Cartesian coordinates with respect to the centre of the baseline joining the radars. The Cylindrical method uses one of the radar sites as the coordinate system origin; the radial current is found automatically and the tangential component is proportional to the radial term of the other radar. HF radar systems are located at Cape Race and Bonavista and a series of simulations based on their geometry indicate that the Cartesian method is preferrable for the calculation of vector currents. -- Due to the limited dimensions of the dual-site coverage, it is desirable to find a way to increase the effective size of the overlap. An approach incorporating the continuity equation uses knowledge of vector currents within the overlap and radial currents outside of it to estimate tangential currents where only single-site data exists. Simulations indicate that the method should work for uniform currents and variable currents. The current magnitude and direction affect the utility of the technique. -- The continuity technique is used within the overlap with real radar data so that dual-site currents, calculated with the Cartesian method, can be used to verify the extrapolations. Regardless of whether the Cape Race or Cape Bonavista facilities is used as the reference for the calculations, the continuity technique yielded good approximations of vector current magnitude and direction for the first extension cell.

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