Sustained Ocean Surface Observation Using HF Radar: From Data to Societal Applications II

Dear Colleagues,

HF radars offer comprehensive, frequent, and detailed information at the interface of the ocean and the atmosphere. These shore-based remote sensing systems have thus evolved into indispensable instruments within operational oceanography, enabling fo the measurement of synoptic, high-frequency and high-resolution data from surface currents, waves, and winds over wide areas. Additionally, their practical applications span across various sectors.

The majority of HF radars deployed over the past two decades have primarily served research and development purposes. Throughout this timeframe, the technology has undergone extensive validation, and at present, HF radar technology has reached a mature stage, especially in terms of surface current data extraction. It is now acknowledged as a fundamental tool for researching and managing coastal environments.

By combining the high-resolution spatial and temporal data provided by HF radar velocities with other in situ or remote sensing measurements and models, our understanding of coastal dynamics can be significantly enhanced. Consequently, this technology can foster economic blue growth while minimizing environmental impacts in coastal areas. For example, HF radars have diverse applications, including monitoring oil spills, aiding in search and rescue efforts, tracking extreme wave events, providing meteorological support, managing marine environments, operating tsunami warning systems, monitoring coastal currents and waves, facilitating routine navigation, supporting commercial fishing, monitoring Harmful Algae Blooms (HABs), assessing marine energy resources, and studying climate change, among other applications.

This Special Issue is the second volume of a previous SI that focused on the societal applications that arise from this technology. It is important to note that the scope of the first Special Issue was more extensive, and therefore was aimed at not just HF radar products. In this new Special Issue, we wish to invite more papers that demonstrate emerging products derived from HF radars in an evolutionary manner, providing useful information not only on intermediate users but also end users (specialist or non-specialist sectors).

Dr. Silvia Piedracoba
Guest Editor

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• HF radar
• multiplatform observations
• circulation models
• products and applications
• downstream services
• open sea and coastal areas monitoring
• physical–biological interactions

• Sustained Ocean Surface Observation Using HF Radar: From Data to Societal Applications in Remote Sensing (14 articles)

Title: High-Resolution Sea Surface Target Detection Using Bi-Frequency HFSWR
Authors: Dragan Golubović; Miljko Erić; Nenad Vukmirović; Vladimir Orlić
Affiliation: 1. Vlatacom Institute of High Technologies, Belgrade, Serbia 2. University of Belgrade, School of Electrical Engineering, Belgrade, Serbia 3. University of Belgrade, School of Electrical Engineering and Innovation Center of the School of Electrical Engineering, Belgrade, Serbia
Abstract: The monitoring of the sea surface, whether it is the state of the sea or the position of targets (ships) is an up-to-date research topic. In order to determine localization parameters of ships, we propose a high- resolution algorithm for primary signal processing in High Frequency Surface Wave Radar (HFSWR) which operates at two frequencies. The proposed algorithm is based on a high-resolution estimate of the Range–Doppler (RD-HR) map formed at every antenna in the receive antenna array, which is an essential task, because the performance of the entire radar system depends on its estimation. We also propose a new focusing method allowing us to have only one RD-HR map in the detection process, which collects the information from both these carrier frequencies. The goal of the bi-frequency mode of operation is to improve the detectability of targets, because their signals are affected by different Bragg-line interference patterns at different frequencies, as seen on the RD-HR maps during the primary signal processing. Also, the effect of the sea (sea clutter) manifests itself in different ways at different frequencies. Some targets are masked (undetectable) at one frequency, but they become visible at another frequency. By exploiting this, we increase the probability of detection. The bi-frequency architecture (system model) for the localization of sea targets and the novel signal model were presented in the paper. The advantage of bi-frequency mode served as a motivation for testing the detectability of small boats, which is otherwise a very challenging task, primarily because such targets have a small radar reflective surface, they move quickly and often change their direction. Based on experimentally obtained results, it can be observed that the probability of detection of small boats can also be significantly improved by using a bi-frequency architecture.