Abstract
The high-frequency radars (HFRs) receiving the sea echoes backscattered from the fluctuating ocean surface to remotely sense ocean surface currents are a popular and powerful tool in oceanic observation. Dominant error source in current measurement for HFR systems has been recognized to be the direction of arrival (DOA) determination of the sea echoes. To eliminate this error and therefore improve the performance of direction-finding HFR system in current measurement, we have investigated a dual monopole-cross-loop (MCL) antenna array in current observation. Simulations indicated that the dual MCL antenna array has a better performance than the conventional single MCL antenna system in current mapping, especially for the complex current profile. And comparisons of radar field data and buoy measurements suggested that the RMSE value was larger than 15 cm/s for the conventional MCL antenna. But it decreased to 12.64 cm/s for the dual MCL antenna array. Moreover, the temporal coverage rate also showed the benefit of using this antenna system in current mapping. The results demonstrated that it is advisable to adopt the dual MCL antenna array in operational applications.
Highlights
The high-frequency radars (HFRs) operating at a frequency range of 3 MHz to 30 MHz have been extensively used to provide ocean surface current in real time [1]
Stoica and Nehorai [13] have proven that the estimated direction of arrival (DOA), θ, in multiple signal classification (MUSIC) for arbitrary antenna system is a Gaussian distribution with a mean value being equal to the actual DOA, θ, and the variance given by var θ bH θ b signal-to-noise ratio (SNR)
Taking the occupation of space of an antenna system into consideration, we suggest that an MCL antenna array composed of two or three MCL elements is an optimal scheme in practice
Summary
The HFRs operating at a frequency range of 3 MHz to 30 MHz have been extensively used to provide ocean surface current in real time [1]. Beam forming radars electronically steer a linear phased array of receiving antennas toward a patch of the ocean surface This type of radar can provide an excellent angular resolution to separate the sea echoes scattered from different patch efficiently but with a cost of occupying a large space in practice, while the direction-finding method is usually adopted by transportable radar systems, which are equipped with a MCL antenna comprising one monopole and two loops [6]. These radars exploit the directional properties of the conventional MCL antenna to determine bearing using the multiple signal classification (MUSIC) [7] algorithm. This performance improvement of the dual MCL antenna array relative to the conventional MCL antenna is confirmed by the field experiment
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