Improved Detection of the First-Order Region for Direction-Finding HF Radars Using Image Processing Techniques

Abstract

For direction-finding high-frequency (HF) radar systems, the correct separation of backscattered spectral energy due to Bragg resonant waves from that due to more complex double-scattering represents a critical first step toward attaining accurate estimates of surface currents from the range-dependent radar backscatter. Existing methods to identify this ''first order'' region of the spectra, generally sufficient for lower-frequency radars and low-velocity or low-surface gravity wave conditions, are more likely to fail in higher-frequency systems or locations with more variable current, wave, or noise regimes, leading to elevated velocity errors. An alternative methodology is presented that uses a single and globally relevant smoothing length scale, careful pretreatment of the spectra, and marker-controlled watershed segmentation, an image processing technique, to separate areas of spectral energy due to surface currents from areas of spectral energy due to more complex scattering by the wave field or background noise present. Applied to a number of HF radar datasets with a range of operating frequencies and characteristic issues, the new methodology attains a higher percentage of successful first-order identification, particularly during complex current and wave conditions. As operational radar systems continue to expand to more systematically cover areas of high marine traffic, close approaches to ports and harbors, or offshore energy installations, use of this type of updated methodology will become increasingly important to attain accurate current estimates that serve both research and operational interests.

Real-time quality assurance and quality control for a high frequency radar network

“…We currently use the SeaSonde software to delineate the first order region of the spectra. Alternative methods (Kirincich, 2017;Rodriguez-Alegre, 2022) utilize image processing techniques and machine learning to draw this boundary and we are evaluating the impact of this new methodology. If a more efficient methodology for extracting the first order Bragg region becomes available, radial maps can be reprocessed using spectra which are archived at each operator's institution.…”

Best Practices on High Frequency Radar Deployment and Operation for Ocean Current Measurement

“…These considerations apply especially for DF systems, where the power spectra contain the contributions from all the azimuthal directions. In some cases the application of advanced methods for FOLs detection can improve the quality of the data (Kirincich, 2017).…”

First-Order Peaks Determination for Direction-Finding High-Frequency Radar

“…However, the process of optimizing the values of the six user-defined parameters is complicated, because some parameters have only a minor effect (i.e., nsm) and others (noisefact, flim) have overlapping effects [16]. Recently, to reduce the complexity of FOPs determination for broad-beam DF HFR, Kirincich [16] proposed an image-processing-based (IPB) FOPs determination method, which needs three userdefined parameters. Therefore, this IPB method reduces input parameters and simplifies the parameter tuning process.…”

“…Therefore, this IPB method reduces input parameters and simplifies the parameter tuning process. To assess the performance of this IPB method, Kirincich [16] compared this IPB method with the SeaSonde method by visually inspecting the FOPs determination results and evaluating the accuracy of radar-derived radial velocities. The radial velocities evaluation is convincing, whereas the visual inspection is not objective enough as well as time and labor consuming.…”

“…The performance of the SSB method is checked by comparing the FOPs determination results from the SSB method with those from the SeaSonde method. The method of assessing the performance of the SSB method is totally different from the visual inspection method used in [16]. In this study, we analyze the boundaries and the number of solutions of the determined FOPs.…”