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HF Surface Wave Radar: Improving Performance and Extending Capabilities

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A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Environmental Remote Sensing".

Deadline for manuscript submissions: 26 May 2024 | Viewed by 5356

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Prof. Dr. Lucy Wyatt

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Guest Editor

School of Mathematics and Statistics, The University of Sheffield, Hicks Building, Hounsfield Road, SHEFFIELD S3 7RH, UK
Interests: HF radar; ocean surface waves; currents and winds; Signal processing; remote sensing

Prof. Dr. Stuart Anderson

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Guest Editor

Physics Department, University of Adelaide, Adelaide, Adelaide, SA 5007, Australia
Interests: radiowave propagation; electromagnetic scattering; oceanography and ionospheric physics; focusing on applications to HF radar
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Dear Colleagues,

HF radars are now widely used in coastal observing systems to monitor surface currents, from the coast to over 100 km offshore. Measurements of ocean waves and inferred winds have also been carried out with these systems, although these are not routinely available from most operational systems. The radar echoes containing the desired information must compete with external noise, which may originate from natural or anthropogenic sources, and unwanted echoes, including echoes from ships and plasma irregularities in the ionosphere. In some parts of the world, the performance of these systems is also being threatened by the push for offshore wind energy, because wind turbines impose a broad spectral modulation on the radar signals and thereby corrupt oceanographic and meteorological measurements.

Some of the factors that impose limits to radar performance are beyond our control, but others may be self-inflicted. For instance, the radar technology being used may be inappropriate in its design or its deployment, the quality of the radar data obtained may be degraded by signal treatment schemes that are suboptimum, and the methods used to extract MetOcean data from the inevitably noisy sea echo signatures may not be sufficiently robust.

We hope that some of these limitations will be explored and, where possible, solutions offered, in papers submitted to this Special Issue. These could include new radar technologies and deployment principles, new signal processing approaches, and new inverse methods. We also invite papers that review existing techniques that address some of these issues but are not yet widely applied. Beyond these advances, we would be delighted to receive descriptions of other problems encountered by radar users that have limited robust and accurate data delivery, to suggest future research directions.

Prof. Dr. Lucy Wyatt
Prof. Dr. Stuart Anderson
Guest Editors

Manuscript Submission Information

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Keywords

HF radar
radar systems
signal processing
inverse methods
currents
waves
winds
MetOcean

Published Papers (4 papers)

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Research

27 pages, 5910 KiB

Open AccessArticle

Developments in Scope and Availability of HF Radar Wave Measurements and Robust Evaluation of Their Accuracy

by Lucy R. Wyatt and J. J. Green

Remote Sens. 2023, 15(23), 5536; https://doi.org/10.3390/rs15235536 - 28 Nov 2023

Cited by 1 | Viewed by 689

Abstract

HF radar systems form part of many operational coastal monitoring systems providing near-real-time surface currents for many useful applications. Although wave measurements have been possible with these systems for many years, they have not yet been adopted widely for operational monitoring because they have not been thought to be sufficiently accurate or reliable. However, the value of such data is beginning to be appreciated, and this is motivating more work on wave measurement with HF radar systems with many more papers on accuracy assessment and data availability appearing in the literature. In this paper, the wave measurement capability, limitations, and differences between different radar types are reviewed, and methods to assess accuracy are discussed and applied to phased array HF radar data obtained from the University of Plymouth WERA radars using the Seaview Software inversion method during April and November 2012 compared with directional buoy data. Good accuracy over a range of different wave parameters will be demonstrated. Newly available single-radar inversions are shown to be less accurate than dual-radar inversions, although they still provide useful data, and ways to improve performance are discussed. Swell and wind–sea components in the directional spectra are identified, and qualitative agreement with buoy peak parameters is demonstrated. Recommendations are given on statistical methods for the validation of wave parameters. Full article

(This article belongs to the Special Issue HF Surface Wave Radar: Improving Performance and Extending Capabilities)

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21 pages, 10926 KiB

Open AccessArticle

Quantitative Assessment of Sea Surface Salinity Estimates Using a High-Frequency Radar in Ise Bay, Japan

by Yu Toguchi and Satoshi Fujii

Remote Sens. 2023, 15(12), 3088; https://doi.org/10.3390/rs15123088 - 13 Jun 2023

Cited by 1 | Viewed by 1065

Abstract

Changes in sea surface salinity (SSS) caused by the discharge of freshwater plumes from rivers affect the marine environment in estuaries; therefore, monitoring SSS is essential for understanding the changes in physical phenomena within coastal ecosystems induced by river plume discharge. Previous studies showed that salinity could be estimated using a very-high-frequency radar; however, this method was only validated over a short period and few qualitative evaluations were performed. Therefore, to verify quantitative assessments of SSS estimates for practical use, we estimated SSS using the Doppler spectrum of a 24.5-MHz phased-array high-frequency (HF) radar installed in Ise Bay, Japan, and data of approximately 1 year were used for verification. The radar-estimated SSS map was consistent with the velocity field and salinity distribution reported in previous studies. The root mean square error (RMSE) of the SSS estimate for 1-h radar data compared with in situ observations was 4.42 psu when the effect of wind on the received power was removed and 5.04 psu when it was not. For the daily (25-h) average, the RMSE when the effect of wind was considered was 3.32 psu. These results were considered sufficiently applicable in closed coastal areas such as Ise Bay, where the SSS decreases rapidly by 10 psu or more due to river flooding. The results revealed that the HF radar, which can continuously measure sea surface velocity and SSS with a high spatiotemporal resolution, can be a useful tool for providing a deeper understanding of the physical and environmental phenomena that are greatly affected by river water discharge. Full article

(This article belongs to the Special Issue HF Surface Wave Radar: Improving Performance and Extending Capabilities)

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20 pages, 6072 KiB

Open AccessArticle

First Open-Coast HF Radar Observations of a 2-Phase Volcanic Tsunami, Tonga 2022

by Belinda Lipa, Donald Barrick, Chad Whelan, Marcel Losekoot and Hardik Parikh

Remote Sens. 2023, 15(9), 2325; https://doi.org/10.3390/rs15092325 - 28 Apr 2023

Cited by 1 | Viewed by 1370

Abstract

We describe results from coastal radar systems that observed anomalous current flows generated by the volcanic eruption in the Tongan archipelago on 15 January 2022 UTC, reporting the first radar detection of a volcanic tsunami. The eruption caused small tsunamis along the western U.S. Coast, generating some damage in a few harbors. The highest tsunami signal in U.S. tide gauge data from the California coast occurred at Arena Cove, with significant heights detected at Port San Luis and Crescent City. We analyze correlated wave orbital velocity detections by High Frequency (HF) radars along the coast between Gerstle Cove and Santa Barbara. Signals observed by the radars indicate that the event had two phases, each with its own distinct genesis: an initial weak surface disturbance, most likely generated by the wave of atmospheric pressure that moved outward from the blast source at just below the speed of sound, followed by a stronger disturbance that arrived approximately 3.5 h later, matching the arrival time for a wave moving entirely through the water from the volcano to the U.S. West Coast. We conclude that this phase consists of a conventional water wave tsunami and weaker waves generated by the pulse. We also report the detection of a small pulse-generated event off the west coast of Florida. Radar observations are compared with water level measurements at nearby tide gauges and a DART buoy, and with observations of barometric pressure. We point out that a Proudman near-resonance at the Tonga Trench is unlikely to explain the second phase observations. Comparison with tide gauge signals at San Francisco, generated by the Krakatoa eruption in 1883, support our conclusions. Full article

(This article belongs to the Special Issue HF Surface Wave Radar: Improving Performance and Extending Capabilities)

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17 pages, 4548 KiB

Open AccessArticle

Observations of Ionospheric Clutter at Near Equatorial High Frequency Radar Stations

by Thomas M. Cook, Eric J. Terrill, Carlos Garcia-Moreno and Sophia T. Merrifield

Remote Sens. 2023, 15(3), 603; https://doi.org/10.3390/rs15030603 - 19 Jan 2023

Viewed by 1268

Abstract

The temporal variation of received clutter and noise at a pair of oceanographic high frequency radars (HFR) operating near the geomagnetic equator in the Republic of Palau is investigated. Oceanographic HFRs process range-gated Doppler spectra from groundwave signals that are backscattered from the ocean’s surface to derive maps of ocean currents. The range performance of the radars exhibited a regular diurnal signal which is determined to be a result of both ionospheric clutter and noise. The increased Clutter plus Noise Floor (C+NF) decreases the Signal to Clutter plus Noise Ratio (SCNR) which, in turn, reduces the range and quality of ocean surface current measurement. Determining the nature and origin of this degradation is critical to QA/QC of existing HFR deployments as well as performance predictions of future installations. Nighttime impacts are most severe and negatively affect ocean surface current measurements as low SCNR is found to extend across the Doppler spectra at all ranges, challenging the ability of HFR to map the ocean surface current. Daytime degradation is less severe and presents itself in a way consistent with independent observations of ionospheric clutter, specifically the diurnal temporal pattern and range where the C+NF features occur. A timeseries analysis of SCNR and C+NF is pursued to understand this relationship using received range-dependent Doppler spectra and C+NF features using image segmentation techniques. Clutter plus noise features are classified into daytime, nighttime, and no-noise feature types. The diurnal structure and variability of these features are examined, and the occurrences of each feature type are calculated. The occurrences are compared with space weather indices including a measure of geomagnetic activity, namely the EE (Equatorial Electro Jet) index (determined from magnetometers measuring the earth’s magnetic field), as well as solar impacts using the F10.7 solar radio clutter index to assess the relationship of ionospheric conditions with HFR ocean surface current measurement. Full article

(This article belongs to the Special Issue HF Surface Wave Radar: Improving Performance and Extending Capabilities)

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