Interoperability of Direction-Finding and Beam-Forming High-Frequency Radar Systems: An Example from the Australian High-Frequency Ocean Radar Network

Simone Cosoli,Stuart De Vos

doi:10.3390/rs11030291

Abstract

Direction-finding SeaSonde (4.463 MHz; 5.2625 MHz) and phased-array WEllen RAdar WERA (9.33 MHz; 13.5 MHz) High-frequency radar (HFR) systems are routinely operated in Australia for scientific research, operational modeling, coastal monitoring, fisheries, and other applications. Coverage of WERA and SeaSonde HFRs in Western Australia overlap. Comparisons with subsurface currents show that both HFR types agree well with current meter records. Correlation (R), root-mean-squares differences (RMSDs), and mean bias (bias) for hourly-averaged radial currents range between R = (−0.03, 0.78), RMSD = (9.2, 30.3) cm/s, and bias = (−5.2, 5.2) cm/s for WERAs; and R = (0.1, 0.76), RMSD = (17.4, 33.6) cm/s, bias = (0.03, 0.36) cm/s for SeaSonde HFRs. Pointing errors (θ) are in the range θ = (1°, 21°) for SeaSonde HFRs, and θ = (3°, 8°) for WERA HFRs. For WERA HFR current components, comparison metrics are RU = (−0.12, 0.86), RMSDU = (12.3, 15.7) cm/s, biasU = (−5.1, −0.5) cm/s; and, RV = (0.61, 0.86), RMSDV = (15.4, 21.1) cm/s, and biasV = (−0.5, 9.6) cm/s for the zonal (u) and the meridional (v) components. Magnitude and phase angle for the vector correlation are ρ = (0.58, 0.86), φ = (−10°, 28°). Good match was found in a direct comparison of SeaSonde and WERA HFR currents in their overlap (ρ = (0.19, 0.59), φ = (−4°, +54°)). Comparison metrics at the mooring slightly decrease when SeaSonde HFR radials are combined with WERA HFR: scalar (vector) correlations for RU, V, (ρ) are in the range RU = (−0.20, 0.83), RV = (0.39, 0.79), ρ = (0.47, 0.72). When directly compared over the same grid, however, vectors from WERA HFR radials and vectors from merged SeaSonde–WERA show RU (RV) exceeding 0.9 (0.7) within the HFR grid. Despite the intrinsic differences between the two types of radars used here, findings show that different HFR genres can be successfully merged, thus increasing current mapping capability of the existing HFR networks, and minimising operational downtime, however at a likely cost of slightly decreased data quality.

Highlights

Shore-based high-frequency radar (HFR) systems, operating in the frequency range between 3–30 MHz, are extensively used to remotely sense ocean currents in coastal areas, and for operational purposes [1]
Separate intermediate range (13.5 MHz) WERA and long-range (5.2675 MHz) SeaSonde High-frequency radar (HFR) stations are located at Coffs Harbor (COF) and Newcastle (NEWC), New South Wales (NSW)
For WERA HFR systems, comparison metrics are in relatively good agreement with previously reported findings in different ocean regions, but poorer compared to a previous validation in the same area for a different time period [34]

Summary

Introduction

Shore-based high-frequency radar (HFR) systems, operating in the frequency range between 3–30 MHz, are extensively used to remotely sense ocean currents in coastal areas, and for operational purposes [1]. Extensive analyses have proven the general reliability and limitations of HFR systems, including their ability to record oceanographic features at different spatial and temporal scales, their usefulness for the validation of numerical circulation models, and the potential for search and rescue purposes [7,8,9,10,11,12,13,14,15,16,17]. SeaSonde systems transmit a frequency-modulated interrupted continuous wave (FMICW) pulse from an omnidirectional vertical antenna and use a compact antenna system (two orthogonal loops and a monopole element) in combination with a direction-finding algorithm to resolve the azimuth of the incoming signal on a polar grid [21]. Separate transmit and receive elements are required, typically spaced one radar wavelength apart

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Conclusion