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Emery, Brian, Anthony Kirincich y Libe Washburn. "Direction Finding and Likelihood Ratio Detection for Oceanographic HF Radars". Journal of Atmospheric and Oceanic Technology 39, n.º 2 (febrero de 2022): 223–35. http://dx.doi.org/10.1175/jtech-d-21-0110.1.
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Abstract Previous work with simulations of oceanographic high-frequency (HF) radars has identified possible improvements when using maximum likelihood estimation (MLE) for direction of arrival; however, methods for determining the number of emitters (here defined as spatially distinct patches of the ocean surface) have not realized these improvements. Here we describe and evaluate the use of the likelihood ratio (LR) for emitter detection, demonstrating its application to oceanographic HF radar data. The combined detection–estimation methods MLE-LR are compared with multiple signal classification method (MUSIC) and MUSIC parameters for SeaSonde HF radars, along with a method developed for 8-channel systems known as MUSIC-Highest. Results show that the use of MLE-LR produces similar accuracy, in terms of the RMS difference and correlation coefficients squared, as previous methods. We demonstrate that improved accuracy can be obtained for both methods, at the cost of fewer velocity observations and decreased spatial coverage. For SeaSondes, accuracy improvements are obtained with less commonly used parameter sets. The MLE-LR is shown to be able to resolve simultaneous closely spaced emitters, which has the potential to improve observations obtained by HF radars operating in complex current environments. Significance Statement We identify and test a method based on the likelihood ratio (LR) for determining the number of signal sources in observations subject to direction finding with maximum likelihood estimation (MLE). Direction-finding methods are used in broad-ranging applications that include radar, sonar, and wireless communication. Previous work suggests accuracy improvements when using MLE, but suitable methods for determining the number of simultaneous signal sources are not well known. Our work shows that the LR, when combined with MLE, performs at least as well as alternative methods when applied to oceanographic high-frequency (HF) radars. In some situations, MLE and LR obtain superior resolution, where resolution is defined as the ability to distinguish closely spaced signal sources.
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Zhu, Langfeng, Fan Yang, Yufan Yang, Zhaomin Xiong y Jun Wei. "Designing Theoretical Shipborne ADCP Survey Trajectories for High-Frequency Radar Based on a Machine Learning Neural Network". Applied Sciences 13, n.º 12 (16 de junio de 2023): 7208. http://dx.doi.org/10.3390/app13127208.
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A machine learning neural network-based design for shipborne ADCP navigation is proposed to improve the quality of high-frequency radar measurements. In traditional inversion algorithms for HF radars, sea surface velocity is directly extracted from electromagnetic echoes without constraints from oceanographic processes. Hence, we incorporated oceanographic information from observational data into seabed radar inversion results via an LSTM neural network model to enhance data accuracy. Through a series of numerical simulation experiments, we showed improved data accuracy and feasibility by incorporating both fixed-point and navigation observational data. The results indicate a significant reduction in (related) errors. This study has implications for guiding future navigation observations.
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Washburn, Libe, Eduardo Romero, Cyril Johnson, Brian Emery y Chris Gotschalk. "Measurement of Antenna Patterns for Oceanographic Radars Using Aerial Drones". Journal of Atmospheric and Oceanic Technology 34, n.º 5 (mayo de 2017): 971–81. http://dx.doi.org/10.1175/jtech-d-16-0180.1.
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AbstractA new method is described employing small drone aircraft for antenna pattern measurements (APMs) of high-frequency (HF) oceanographic radars used for observing ocean surface currents. Previous studies have shown that accurate surface current measurements using HF radar require APMs. The APMs provide directional calibration of the receive antennas for direction-finding radars. In the absence of APMs, so-called ideal antenna patterns are assumed and these can differ substantially from measured patterns. Typically, APMs are obtained using small research vessels carrying radio signal sources or transponders in circular arcs around individual radar sites. This procedure is expensive because it requires seagoing technicians, a vessel, and other equipment necessary to support small-boat operations. Furthermore, adverse sea conditions and obstacles in the water can limit the ability of small vessels to conduct APMs. In contrast, it is shown that drone aircraft can successfully conduct APMs at much lower cost and in a broader range of sea states with comparable accuracy. Drone-based patterns can extend farther shoreward, since they are not affected by the surfzone, and thereby expand the range of bearings over which APMs are determined. This simplified process for obtaining APMs can lead to more frequent calibrations and improved surface current measurements.
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Ilcev, Dimov Stojce. "Introduction to Coastal HF Maritime Surveillance Radars". Polish Maritime Research 26, n.º 3 (1 de septiembre de 2019): 153–62. http://dx.doi.org/10.2478/pomr-2019-0056.
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Abstract This paper presents the main technical characteristics and working performances of coastal maritime surveillance radars, such as low-power High-Frequency Surface Wave Radars (HFSWR) and Over the Horizon Radars (OTHR). These radars have demonstrated to be a cost-effective long-range early-warning sensor for ship detection and tracking in coastal waters, sea channels and passages. In this work, multi-target tracking and data fusion techniques are applied to live-recorded data from a network of oceanographic HFSWR stations installed in Jindalee Operational Radar Network (JORN), Wellen Radar (WERA) in Ligurian Sea (Mediterranean Sea), CODAR Ocean Sebsorsin and in the German Bight (North Sea). The coastal Imaging Sciences Research (ISR) HFSWR system, Multi-static ISR HF Radar, Ship Classification using Multi-Frequency HF Radar, Coastal HF radar surveillance of pirate boats and Different projects of coastal HF radars for vessels detecting are described. Ship reports from the Automatic Identification System (AIS), recorded from both coastal and satellite Land Earth Stations (LES) are exploited as ground truth information and a methodology is applied to classify the fused tracks and to estimate system performances. Experimental results for all above solutions are presented and discussed, together with an outline for future integration and infrastructures.
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Emery, Brian y Libe Washburn. "Uncertainty Estimates for SeaSonde HF Radar Ocean Current Observations". Journal of Atmospheric and Oceanic Technology 36, n.º 2 (1 de febrero de 2019): 231–47. http://dx.doi.org/10.1175/jtech-d-18-0104.1.
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Abstract HF radars typically produce maps of surface current velocities without estimates of the measurement uncertainties. Many users of HF radar data, including spill response and search and rescue operations, incorporate these observations into models and would thus benefit from quantified uncertainties. Using both simulations and coincident observations from the baseline between two operational SeaSonde HF radars, we demonstrate the utility of expressions for estimating the uncertainty in the direction obtained with the Multiple Signal Classification (MUSIC) algorithm. Simulations of radar backscatter using surface currents from the Regional Ocean Modeling System show a close correspondence between direction of arrival (DOA) errors and estimated uncertainties, with mean values of 15° at 10 dB, falling to less than 3° at 30 dB. Observations from two operational SeaSondes have average DOA uncertainties of 2.7° and 3.8°, with a fraction of the observations (10.5% and 7.1%, respectively) having uncertainties of >10°. Using DOA uncertainties for data quality control improves time series comparison statistics between the two radars, with r2=0.6 increasing to r2=0.75 and RMS difference decreasing from 15 to 12 cm s−1. The analysis illustrates the major sources of error in oceanographic HF radars and suggests that the DOA uncertainties are suitable for assimilation into numerical models.
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Chernyshov, Pavel, Katrin Hessner, Andrey Zavadsky y Yaron Toledo. "On the Effect of Interferences on X-Band Radar Wave Measurements". Sensors 22, n.º 10 (18 de mayo de 2022): 3818. http://dx.doi.org/10.3390/s22103818.
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X-band radars are in growing use for various oceanographic purposes, providing spatial real-time information about sea state parameters, surface elevations, currents, and bathymetry. Therefore, it is very appealing to use such systems as operational aids to harbour management. In an installation of such a remote sensing system in Haifa Port, consistent radially aligned spikes of brightness randomly distributed with respect to azimuth were identified. These streak noise patterns were found to be interfering with the common approach of oceanographic analysis. Harbour areas are regularly frequented with additional electromagnetic transmissions from other ship and land-based radars, which may serve as a source of such interference. A new approach is proposed for the filtering of such undesirable interference patterns from the X-band radar images. It was verified with comparison to in-situ measurements of a nearby wave buoy. Regardless of the actual source of the corresponding pseudo-wave energy, it was found to be crucial to apply such filtration in order to improve the performance of the standard oceanographic parameter retrieval algorithm. This results in better estimation of the mean sea state parameters towards lower values of the significant wave height. For the commercial WaMoSII system this enhancement was clearly apparent in the improvement of the built-in quality control criteria marks. The developed prepossessing procedure improves the robustness of the directional spectra estimation practically eliminating pseudo-wave energy components. It also extends the system’s capability to measure storm events earlier on, a fact that is of high importance for harbour operational decision making.
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Horstmann, Jochen, Jan Bödewadt, Ruben Carrasco, Marius Cysewski, Jörg Seemann y Michael Streβer. "A Coherent on Receive X-Band Marine Radar for Ocean Observations". Sensors 21, n.º 23 (25 de noviembre de 2021): 7828. http://dx.doi.org/10.3390/s21237828.
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Marine radars are increasingly popular for monitoring meteorological and oceanographic parameters such as ocean surface wind, waves and currents as well as bathymetry and shorelines. Within this paper a coherent on receive marine radar is introduced, which is based on an incoherent off the shelf pulsed X-band radar. The main concept of the coherentization is based on the coherent on receive principle, where the coherence is achieved by measuring the phase of the transmitted pulse from a leak in the radar circulator, which then serves as a reference phase for the transmitted pulse. The Doppler shift frequency can be computed from two consecutive pulse-pairs in the time domain or from the first moment of the Doppler spectrum inferred by means of a short time Fast Fourier Transform. From the Doppler shift frequencies, radial speed maps of the backscatter of the ocean surface are retrieved. The resulting backscatter intensity and Doppler speed maps are presented for horizontal as well as vertical polarization, and discussed with respect to meteorological and oceanographic applications.
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Kaeppler, Stephen R., Ethan S. Miller, Daniel Cole y Teresa Updyke. "On the use of high-frequency surface wave oceanographic research radars as bistatic single-frequency oblique ionospheric sounders". Atmospheric Measurement Techniques 15, n.º 15 (10 de agosto de 2022): 4531–45. http://dx.doi.org/10.5194/amt-15-4531-2022.
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Abstract. We demonstrate that bistatic reception of high-frequency oceanographic radars can be used as single-frequency oblique ionospheric sounders. We develop methods that are agnostic of the software-defined radio system to estimate the group range from the bistatic observations. The group range observations are used to estimate the virtual height and equivalent vertical frequency at the midpoint of the oblique propagation path. Uncertainty estimates of the virtual height and equivalent vertical frequency are presented. We apply this analysis to observations collected from two experiments run at two locations in different years, but utilizing similar software-defined radio data collection systems. In the first experiment, 10 d of data were collected in March 2016 at a site located in Maryland, USA, while the second experiment collected 20 d of data in October 2020 at a site located in South Carolina, USA. In both experiments, three Coastal Oceanographic Dynamics and Applications Radars (CODARs) located along the Virginia and North Carolina coast of the US were bistatically observed at 4.53718 MHz. The virtual height and equivalent virtual frequency were estimated in both experiments and compared with contemporaneous observations from a vertical incident digisonde–ionosonde at Wallops Island, VA, USA. We find good agreement between the oblique CODAR-derived and WP937 digisonde virtual heights. Variations in the virtual height from the CODAR observations and the digisonde are found to be nearly in phase with each other. We conclude from this investigation that observations of oceanographic radar can be used as single-frequency oblique incidence sounders. We discuss applications with respect to investigations of traveling ionospheric disturbances, studies of day-to-day ionospheric variability, and using these observations in data assimilation.
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He, Shuqin, Hao Zhou, Yingwei Tian y Wei Shen. "Ionospheric Clutter Suppression with an Auxiliary Crossed-Loop Antenna in a High-Frequency Radar for Sea Surface Remote Sensing". Journal of Marine Science and Engineering 9, n.º 11 (23 de octubre de 2021): 1165. http://dx.doi.org/10.3390/jmse9111165.
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Ionospheric clutter is one of the main problems for high-frequency surface wave radars (HFSWRs), as it severely interferes with sea surface state monitoring and target detection. Although a number of methods exist for ionospheric clutter suppression, most are suitable for radars with a large-sized array and are inefficient for small-aperture radars. In this study, we added an auxiliary crossed-loop antenna to the original compact radar antenna, and used an adaptive filter to suppress the ionospheric clutter. The experimental results of the HFSWRs data indicated that the suppression factor of the ionospheric clutter was up to 20 dB. Therefore, the Bragg peaks that were originally submerged by the ionospheric clutters could be recovered, and the gaps in the current maps can, to a large extent, be filled. For an oceanographic radar, the purpose of suppressing ionospheric clutter is to extract an accurate current speed; the radial current fields that were generated by our method showed an acceptable agreement with those generated by GlobCurrent data. This result supports the notion that the ionospheric suppression technique does not compromise the estimation of radial currents. The proposed method is particularly efficient for a compact HFSWRs, and can also be easily used in other types of antennas.
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Emery, Brian M. "Evaluation of Alternative Direction-of-Arrival Methods for Oceanographic HF Radars". IEEE Journal of Oceanic Engineering 45, n.º 3 (julio de 2020): 990–1003. http://dx.doi.org/10.1109/joe.2019.2914537.
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Roarty, Hugh, Scott Glenn, Josh Kohut, Donglai Gong, Ethan Handel, Erick Rivera, Teresa Garner et al. "Operation and Application of a Regional High-Frequency Radar Network in the Mid-Atlantic Bight". Marine Technology Society Journal 44, n.º 6 (1 de noviembre de 2010): 133–45. http://dx.doi.org/10.4031/mtsj.44.6.5.
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AbstractThe Mid-Atlantic Regional Coastal Ocean Observing System (MARCOOS) High-Frequency Radar Network, which comprises 13 long-range sites, 2 medium-range sites, and 12 standard-range sites, is operated as part of the Integrated Ocean Observing System. This regional implementation of the network has been operational for 2 years and has matured to the point where the radars provide consistent coverage from Cape Cod to Cape Hatteras. A concerted effort was made in the MARCOOS project to increase the resiliency of the radar stations from the elements, power issues, and other issues that can disable the hardware of the system. The quality control and assurance activities in the Mid-Atlantic Bight have been guided by the needs of the Coast Guard Search and Rescue Office. As of May 4, 2009, these quality-controlled MARCOOS High-Frequency Radar totals are being served through the Coast Guard’s Environmental Data Server to the Coast Guard Search and Rescue Optimal Planning System. In addition to the service to U.S. Coast Guard Search and Rescue Operations, these data support water quality, physical oceanographic, and fisheries research throughout the Mid-Atlantic Bight.
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Hardman, Rachael L., Lucy R. Wyatt y Charles C. Engleback. "Measuring the Directional Ocean Spectrum from Simulated Bistatic HF Radar Data". Remote Sensing 12, n.º 2 (18 de enero de 2020): 313. http://dx.doi.org/10.3390/rs12020313.
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HF radars are becoming important components of coastal operational monitoring systems particularly for currents and mostly using monostatic radar systems where the transmit and receive antennas are colocated. A bistatic configuration, where the transmit antenna is separated from the receive antennas, offers some advantages and has been used for current measurement. Currents are measured using the Doppler shift from ocean waves which are Bragg-matched to the radio signal. Obtaining a wave measurement is more complicated. In this paper, the theoretical basis for bistatic wave measurement with a phased-array HF radar is reviewed and clarified. Simulations of monostatic and bistatic radar data have been made using wave models and wave spectral data. The Seaview monostatic inversion method for waves, currents and winds has been modified to allow for a bistatic configuration and has been applied to the simulated data for two receive sites. Comparisons of current and wave parameters and of wave spectra are presented. The results are encouraging, although the monostatic results are more accurate. Large bistatic angles seem to reduce the accuracy of the derived oceanographic measurements, although directional spectra match well over most of the frequency range.
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Flores-Vidal, X., P. Flament, R. Durazo, C. Chavanne y K. W. Gurgel. "High-Frequency Radars: Beamforming Calibrations Using Ships as Reflectors*". Journal of Atmospheric and Oceanic Technology 30, n.º 3 (1 de marzo de 2013): 638–48. http://dx.doi.org/10.1175/jtech-d-12-00105.1.
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Abstract Linear array antennas and beamforming techniques offer some advantages compared to direction finding using squared arrays. The azimuthal resolution depends on the number of antenna elements and their spacing. Assuming an ideal beam pattern and no amplitude taper across the aperture, 16 antennas in a linear array spaced at half the electromagnetic wavelength theoretically provide a beam resolution of 3.5° normal to the array, and up to twice that when the beam is steered within an azimuthal range of 60° from the direction normal to the array. However, miscalibrated phases among antenna elements, cables, and receivers (e.g., caused by service activities without recalibration) can cause errors in the beam-steering direction and distortions of the beam pattern, resulting in unreliable ocean surface current and wave estimations. The present work uses opportunistic ship echoes randomly received by oceanographic high-frequency radars to correct an unusual case of severe phase differences between receiver channels, leading to a dramatic improvement of the surface current patterns. The method proposed allows for simplified calibrations of phases to account for hardware-related changes without the need to conduct the regular calibration procedure and can be applied during postprocessing of datasets acquired with insufficient calibration.
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Kantha, Lakshmi y Hubert Luce. "Mixing Coefficient in Stably Stratified Flows". Journal of Physical Oceanography 48, n.º 11 (noviembre de 2018): 2649–65. http://dx.doi.org/10.1175/jpo-d-18-0139.1.
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AbstractTurbulent mixing in the interior of the oceans is not as well understood as mixing in the oceanic boundary layers. Mixing in the generally stably stratified interior is primarily, although not exclusively, due to intermittent shear instabilities. Part of the energy extracted by the Reynolds stresses acting on the mean shear is expended in increasing the potential energy of the fluid column through a buoyancy flux, while most of it is dissipated. The mixing coefficient χm, the ratio of the buoyancy flux to the dissipation rate of turbulence kinetic energy ε, is an important parameter, since knowledge of χm enables turbulent diffusivities to be inferred. Theory indicates that χm must be a function of the gradient Richardson number. Yet, oceanic studies suggest that a value of around 0.2 for χm gives turbulent diffusivities that are in good agreement with those inferred from tracer studies. Studies by scientists working with atmospheric radars tend to reinforce these findings but are seldom referenced in oceanographic literature. The goal of this paper is to bring together oceanographic, atmospheric, and laboratory observations related to χm and to report on the values deduced from in situ data collected in the lower troposphere by unmanned aerial vehicles, equipped with turbulence sensors and flown in the vicinity of the Middle and Upper Atmosphere (MU) radar in Japan. These observations are consistent with past studies in the oceans, in that a value of around 0.16 for χm yields good agreement between ε derived from turbulent temperature fluctuations using this value and ε obtained directly from turbulence velocity fluctuations.
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Georges, T. M. y G. D. Thome. "An Opportunity for Long-Distance Oceanographic and Meteorological Monitoring Using Over-the-Horizon Defense Radars". Bulletin of the American Meteorological Society 71, n.º 12 (diciembre de 1990): 1739–45. http://dx.doi.org/10.1175/1520-0477(1990)071<1739:aofldo>2.0.co;2.
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Cook, Thomas M., Eric J. Terrill, Carlos Garcia-Moreno y Sophia T. Merrifield. "Observations of Ionospheric Clutter at Near Equatorial High Frequency Radar Stations". Remote Sensing 15, n.º 3 (19 de enero de 2023): 603. http://dx.doi.org/10.3390/rs15030603.
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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.
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Kohut, Josh, Kim Bernard, William Fraser, Matthew J. Oliver, Hank Statscewich, Peter Winsor y Travis Miles. "Studying the Impacts of Local Oceanographic Processes on Adélie Penguin Foraging Ecology". Marine Technology Society Journal 48, n.º 5 (1 de septiembre de 2014): 25–34. http://dx.doi.org/10.4031/mtsj.48.5.10.
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AbstractWe are conducting a multi-platform field study to investigate the impact of local physical processes on Adélie penguin foraging ecology in the vicinity of Palmer Deep off Anvers Island, Western Antarctic Peninsula (WAP). Guided by real-time remotely sensed surface current measurements of convergence derived from a network of high-frequency radars (HFRs), we adaptively sample the distribution and biomass of phytoplankton and Antarctic krill, which influence Adélie penguin foraging ecology, to understand how local oceanographic processes structure the ecosystem. The recent application of ocean observing and animal telemetry technology over Palmer Deep has led to new understanding and many new questions related to polar ecosystem processes. The HFR coastal surface current mapping network is uniquely equipped to resolve local circulation patterns over Palmer Deep. The surface current measurements enable identification of regions of convergence and divergence in real time. Guided by these maps, our field study adaptively samples the measured convergence and divergence zones within the context of semi-diurnal and diurnal mixed tidal regimes. The in situ sampling includes (a) a mooring deployment, (b) multiple underwater glider deployments, (c) small boat acoustic surveys of Antarctic krill, and (d) penguin ARGOS-linked satellite telemetry and temperature-depth recorders (TDRs). The combination of real-time surface convergence maps with adaptive in situ sampling introduces HFR to the Antarctic in a way that allows us to rigorously and efficiently test the influence of local tidal processes on top predator foraging ecology.
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Martinez-Pedraja, J., L. K. Shay, B. K. Haus y C. Whelan. "Interoperability of SeaSondes and Wellen Radars in Mapping Radial Surface Currents". Journal of Atmospheric and Oceanic Technology 30, n.º 11 (1 de noviembre de 2013): 2662–75. http://dx.doi.org/10.1175/jtech-d-13-00022.1.
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Abstract A dual-station high-frequency (HF) Wellen Radar (WERA) transmitting at 16 MHz has observed near-real-time surface currents over an approximate range of 100 km across the Florida Straits since July 2004. During a 10-day period in April 2005 (15–25 April), a pair of 12.6-MHz SeaSondes (SS) were deployed south of the WERAs sites by NOAA's Center for Operational Oceanographic Products and Services (CO-OPS). The resulting SS grid overlapped the southern portion of the WERA domain. During the same period of time, a bottom-mounted acoustic Doppler current profiler (ADCP) acquired subsurface current measurements within these HF radar grids starting at 14 m below the surface in water of 86-m depth. The interoperability of beam-forming (WERA) and direction-finding (SS) HF radar technologies was examined. Comparisons of radial and vector currents for an 8-day concurrent time series suggested good agreement in current direction over both domains, where the surface currents' magnitudes were a maximum of 1.2 m s−1. In the core of the radar domains consisting of 108 cells, hourly vector currents were obtained by combining WERA and SS radials. Generally, this can be done in a relatively straightforward manner, considering the geometric dilution of precision (GDOP). A second key issue is downscaling the SS measurements from a 3-km grid to a 1.1-km grid to match the WERA output. This enhanced grid spacing is important along the western flank of the Florida Current, where energetic, small-scale surface features have been observed.
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Bentz, Cristina Maria y Josemá Oliveira de Barros. "A MULTI-SENSOR APPROACH FOR OIL SPILL AND SEA SURFACE MONITORING, IN SOUTHEASTERN BRAZIL". International Oil Spill Conference Proceedings 2005, n.º 1 (1 de mayo de 2005): 703–6. http://dx.doi.org/10.7901/2169-3358-2005-1-703.
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ABSTRACT Since May 2001 PETROBRAS is using spaceborne multi-sensor remote sensing for its sea surface monitoring program at the Campos, Santos and Espirito Santo Basins, southeastern Brazilian coast. This area is presently responsible for about 80% of all the Brazilian oil and gas production. Ocean color (SeaWiFS and MODIS), thermal infrared (NOAA/AVHRR), scatterometer (QuikSCAT) and Synthetic Aperture Radar (RADARSAT-1 and ENVISAT) data were integrated in order to detect and characterize different sorts of marine pollution and meteo-oceanographic phenomena. The near real time processing and delivery of the SAR data allowed the timely in-situ verification and sampling of the remotely detected events. Satellite sensors operating in the visible part of the spectrum are used to monitor ocean color variations and associated biomass changes. Thermal infrared radiometers are ideal to monitor features like oceanic fronts and upwelling plumes. However, the major limitation for both types of sensors is the extensive and persistent presence of clouds in the monitored area. Fortunately, microwave sensors such imaging spaceborne Synthetic Aperture Radars (SAR) permit the acquisition of oceanic scenes, regardless cloud coverage. With the spaceborne SAR systems available it is possible to have almost a daily synoptic view of large areas with suitable spatial resolution for the detection of different natural and men-made events. The integrated analysis of these dataset presents an important decision tool for emergencies, as well for the elaboration of contingency plans and evaluation of the oil industry activity impacts.
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Cosoli, Simone. "Implementation of the Listen-Before-Talk Mode for SeaSonde High-Frequency Ocean Radars". Journal of Marine Science and Engineering 8, n.º 1 (19 de enero de 2020): 57. http://dx.doi.org/10.3390/jmse8010057.
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The International Telecommunication Union (ITU) Resolution 612, in combination with Report ITU-R M2.234 (11/2011) and Recommendation ITU-R M.1874-1 (02/2013), regulates the use of the radiolocation services between 3 and 50 MHz to support high frequency oceanographic radar (HFR) operations. The operational frame for HFR systems include: band sharing capabilities, such as synchronization of the signal modulation; pulse shaping and multiple levels of filtering, to reduce out-of-band interferences; low radiated power; directional transmission antenna, to reduce emission over land. Resolution 612 also aims at reducing the use of spectral bands, either through the application of existing band-sharing capabilities, the reduction of the spectral leakage to neighboring frequency bands, or the development and implementation of listen-before-talk (LBT) capabilities. While the LBT mode is operational and commonly used at several phased-array HFR installations, the implementation to commercial direction-finding systems does not appear to be available yet. In this paper, a proof-of-concept is provided for the implementation of the LBT mode for commercial SeaSonde HFRs deployed in Australia, with potential for applications in other networks and installations elsewhere. Potential critical aspects for systems operated under this configuration are also pointed out. Both the receiver and the transmitter antennas may lose efficiency if the frequency offset from the resonant frequency or calibration pattern are too large. Radial resolution clearly degrades when a dynamical adaptation of the bandwidth is performed, which results in non-homogeneous spatial resolution and reduction of the quality of the data. A recommendation would be to perform the LBT-adapt scans after a full measurement cycle (1-h or 3-h, depending on the system configuration) is concluded. Mutual cross-interference from clock offsets between two HFR systems may bias the frequency scans when the site computers controlling data acquisitions are not properly time-synchronized.
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Specht, Mariusz, Cezary Specht, Oktawia Lewicka, Artur Makar, Paweł Burdziakowski y Paweł Dąbrowski. "Study on the Coastline Evolution in Sopot (2008–2018) Based on Landsat Satellite Imagery". Journal of Marine Science and Engineering 8, n.º 6 (24 de junio de 2020): 464. http://dx.doi.org/10.3390/jmse8060464.
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The coastline is the boundary between the water surface in a reservoir or watercourse and the land, which is characterised by high instability and functional diversity. For these reasons, research on coastal monitoring has been conducted for several decades. Currently, satellite images performed with synthetic aperture radars (SARs) are used to determine its course and variability together with high-resolution multispectral imagery from satellites such as IKONOS, QuickBird, and WorldView, or moderate-resolution multispectral images from Landsat satellites. This paper analysed the coastline variability in Sopot (2008–2018) based on Landsat satellite imagery. Furthermore, based on multispectral images obtained, it was determined how the beach surface in Sopot changed. Research has shown that the coastline keeps moving away from the land every year. This was particularly noticeable between 2008 and 2018 when the coastline moved on average 19.1 m towards the Baltic Sea. Moreover, it was observed that the area of the sandy beach in Sopot increased by 14 170.6 m2, which translates into an increase of 24.7% compared to 2008. The probable cause of the continuous coastline shift towards the sea and the increase of the beach surface is the oceanographic phenomenon called tombolo, which occurred in this area as a result of the construction of a yacht marina near the coast.
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Weissman, D. E., B. W. Stiles, S. M. Hristova-Veleva, D. G. Long, D. K. Smith, K. A. Hilburn y W. L. Jones. "Challenges to Satellite Sensors of Ocean Winds: Addressing Precipitation Effects". Journal of Atmospheric and Oceanic Technology 29, n.º 3 (1 de marzo de 2012): 356–74. http://dx.doi.org/10.1175/jtech-d-11-00054.1.
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Abstract Measurements of global ocean surface winds made by orbiting satellite radars have provided valuable information to the oceanographic and meteorological communities since the launch of the Seasat in 1978, by the National Aeronautics and Space Administration (NASA). When Quick Scatterometer (QuikSCAT) was launched in 1999, it ushered in a new era of dual-polarized, pencil-beam, higher-resolution scatterometers for measuring the global ocean surface winds from space. A constant limitation on the full utilization of scatterometer-derived winds is the presence of isolated rain events, which affect about 7% of the observations. The vector wind sensors, the Ku-band scatterometers [NASA’s SeaWinds on the QuikSCAT and Midori-II platforms and Indian Space Research Organisation’s (ISRO’s) Ocean Satellite (Oceansat)-2], and the current C-band scatterometer [Advanced Wind Scatterometer (ASCAT), on the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT)’s Meteorological Operation (MetOp) platform] all experience rain interference, but with different characteristics. Over this past decade, broad-based research studies have sought to better understand the physics of the rain interference problem, to search for methods to bypass the problem (using rain detection, flagging, and avoidance of affected areas), and to develop techniques to improve the quality of the derived wind vectors that are adversely affected by rain. This paper reviews the state of the art in rain flagging and rain correction and describes many of these approaches, methodologies, and summarizes the results.
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Gilmore, Grant R., Andrew M. Clark y John Cooke. "Technologies for Sustained Biological Resource Observations with Potential Applications in Coastal Homeland Security". Marine Technology Society Journal 37, n.º 3 (1 de septiembre de 2003): 134–41. http://dx.doi.org/10.4031/002533203787537159.
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Of all the classical oceanographic disciplines, we are probably least well equipped to further the understanding of biological oceanography through the data that will be provided by an Integrated Sustained Ocean Observing System (IOOS). What's more, some of the same federal agencies that would normally be approached to invest in the development of new sensor systems for IOOS biological applications are now faced with more pressing priorities—homeland security among them—all competing for the same limited resources. This paper introduces some technologies and applications that are capable of conducting sustained biological oceanographic observations and how these technologies may be used for ocean biological resource assessment while simultaneously helping to secure our nation's borders. Particular emphasis is given to passive acoustic systems that may be employed both to monitor biota as well as anthropogenic activity. Also discussed are potential dual use applications in both oceanography and USCG mission execution, including High Frequency Surface Wave Radar (HFSWR). Finally, a number of existing and emerging telemetry techniques and systems are described that may provide the extensive data connectivity for the offshore sensors required of the IOOS, as well as improve coastal security.
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Silva, Murilo Teixeira, Weimin Huang y Eric W. Gill. "Bistatic High-Frequency Radar Cross-Section of the Ocean Surface with Arbitrary Wave Heights". Remote Sensing 12, n.º 4 (18 de febrero de 2020): 667. http://dx.doi.org/10.3390/rs12040667.
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The scattering theory developed in the past decades for high-frequency radio oceanography has been restricted to surfaces with small heights and small slopes. In the present work, the scattering theory for bistatic high-frequency radars is extended to ocean surfaces with arbitrary wave heights. Based on recent theoretical developments in the scattering theory for ocean surfaces with arbitrary heights for monostatic radars, the electric field equations for bistatic high-frequency radars in high sea states are developed. This results in an additional term related to the first-order electric field, which is only present when the small-height approximation is removed. Then, the radar cross-section for the additional term is derived and simulated, and its impact on the total radar cross-section at different radar configurations, dominant wave directions, and sea states is assessed. The proposed term is shown to impact the total radar cross-section at high sea states, dependent on radar configuration and dominant wave direction. The present work can contribute to the remote sensing of targets on the ocean surface, as well as the determination of the dominant wave direction of the ocean surface at high sea states.
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Vivekanandan, J., W. C. Lee, E. Loew, J. L. Salazar, V. Grubišić, J. Moore y P. Tsai. "The next generation airborne polarimetric Doppler weather radar". Geoscientific Instrumentation, Methods and Data Systems 3, n.º 2 (21 de julio de 2014): 111–26. http://dx.doi.org/10.5194/gi-3-111-2014.
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Abstract. Results from airborne field deployments emphasized the need to obtain concurrently high temporal and spatial resolution measurements of 3-D winds and microphysics. A phased array radar on an airborne platform using dual-polarization antenna has the potential for retrieving high-resolution, collocated 3-D winds and microphysical measurements. Recently, ground-based phased array radar (PAR) has demonstrated the high time-resolution estimation of accurate Doppler velocity and reflectivity of precipitation and clouds when compared to mechanically scanning radar. PAR uses the electronic scanning (e-scan) to rapidly collect radar measurements. Since an airborne radar has a limited amount of time to collect measurements over a specified sample volume, the e-scan will significantly enhance temporal and spatial resolution of airborne radar observations. At present, airborne weather radars use mechanical scans, and they are not designed for collecting dual-polarization measurements to remotely estimate microphysics. This paper presents a possible configuration of a novel airborne phased array radar (APAR) to be installed on an aircraft for retrieving improved dynamical and microphysical scientific products. The proposed APAR would replace the aging, X-band Electra Doppler radar (ELDORA). The ELDORA X-band radar's penetration into precipitation is limited by attenuation. Since attenuation at C-band is lower than at X-band, the design specification of a C-band airborne phased array radar (APAR) and its measurement accuracies are presented. Preliminary design specifications suggest the proposed APAR will meet or exceed ELDORA's current sensitivity, spatial resolution and Doppler measurement accuracies of ELDORA and it will also acquire dual-polarization measurements.
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Svilicic, Boris, Igor Rudan, Vlado Frančić y Djani Mohović. "Towards a Cyber Secure Shipboard Radar". Journal of Navigation 73, n.º 3 (7 de noviembre de 2019): 547–58. http://dx.doi.org/10.1017/s0373463319000808.
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This paper presents a comparative cyber security resilience estimation of shipboard radars that are implemented on two oil/chemical tankers certified as SOLAS ships. The estimated radars were chosen from the same manufacturer, but belonged to different generations. The estimation was conducted by means of ships' crew interviews and computational testing of the radars using a widely deployed vulnerability scanning software tool. The identified cyber threats were analysed qualitatively in order to gain a holistic understanding of cyber risks threatening shipboard radar systems. The results obtained experimentally indicate that potential cyber threats mainly relate to maintenance of the radars' underlying operating system, suggesting the need for regulatory standardisation of periodic cyber security testing of radar systems.
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Anderson, Stuart. "Remote Sensing of the Polar Ice Zones with HF Radar". Remote Sensing 13, n.º 21 (31 de octubre de 2021): 4398. http://dx.doi.org/10.3390/rs13214398.
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Radars operating in the HF band are widely used for over-the-horizon remote sensing of ocean surface conditions, ionospheric studies and the monitoring of ship and aircraft traffic. Several hundreds of such radars are in operation, yet only a handful of experiments have been conducted to assess the prospect of utilizing this technology for the remote sensing of sea ice. Even then, the measurements carried out have addressed only the most basic questions: is there ice present, and can we measure its drift? Recently the theory that describes HF scattering from the dynamic sea surface was extended to handle situations where an ice cover is present. With this new tool, it becomes feasible to interpret the corresponding radar echoes in terms of the structural, mechanical, and electrical properties of the ice field. In this paper we look briefly at ice sensing from space-borne sensors before showing how the persistent and synoptic wide area surveillance capabilities of HF radar offer an alternative. The dispersion relations of different forms of sea ice are examined and used in a modified implementation of the electromagnetic scattering theory employed in HF radar oceanography to compute the corresponding radar signatures. Previous and present-day HF radar deployments at high latitudes are reviewed, noting the physical and technical challenges that confront the implementation of an operational HF radar in its ice monitoring capability.
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Roarty, Hugh J., Erick Rivera Lemus, Ethan Handel, Scott M. Glenn, Donald E. Barrick y James Isaacson. "Performance Evaluation of SeaSonde High-Frequency Radar for Vessel Detection". Marine Technology Society Journal 45, n.º 3 (1 de mayo de 2011): 14–24. http://dx.doi.org/10.4031/mtsj.45.3.2.
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AbstractHigh-frequency (HF) surface wave radar has been identified to be a gap-filling technology for Maritime Domain Awareness. Present SeaSonde HF radars have been designed to map surface currents but are able to track surface vessels in a dual-use mode. Rutgers and CODAR Ocean Sensors, Ltd., have collaborated on the development of vessel detection and tracking capabilities from compact HF radars, demonstrating that ships can be detected and tracked by multistatic HF radar in a multiship environment while simultaneously mapping ocean currents. Furthermore, the same vessel is seen simultaneously by the radar based on different processing parameters, mitigating the need to preselect a fixed set and thereby improving detection performance.
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LAMY, JÉRÔME. "THE BIRTH OF SPACE OCEANOGRAPHY: TECHNOLOGICAL QUESTIONS AND CLIMATOLOGICAL OPPORTUNITY (UNITED STATES, FRANCE, 1950–1980)". Earth Sciences History 38, n.º 1 (1 de abril de 2019): 124–36. http://dx.doi.org/10.17704/1944-6178-38.1.124.
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ABSTRACT This article analyzes the formation of space oceanography as a scientific specialty, in France and in the United States. Throughout much of its history, oceanography has relied upon a broad range of instrumentation (bathyscaphes, tide gauges, and so forth). The importance of instrumentation meant that many of the exchanges during major scientific meetings in the 1960s focused on engineering problems. As a result, institutional investments by NASA and the French space agency, the Centre National d'Études Spatiales (CNES) supported advances in instrumentation. The emergence of the climate change issue made it possible to merge several factors (technical, geopolitical, and institutional) into the specialty of space oceanography. The birth of a scientific specialty requires the conjunction of several determining factors: a powerful disciplinary basis, a technological innovation resulting in major advances, and scientific politicians capable of tackling new problems. The development of space oceanography provides an excellent example of the origin of a new scientific specialty. The purpose of this article is to trace the history of the combination of the technical and scientific factors that resulted in the origin of space oceanography. This article will focus on specific events that led to the origin of space oceanography, in particular on a series of meetings organized by researchers interested in very specific technical questions. Many of the classical questions of oceanography could be addressed and dealt with by developing and using new instruments (e.g. radar altimeters). To document how the specialty of space oceanography developed, I propose to follow American and French examples of the transformations induced by space oceanography. Such a comparison makes it possible to measure the differential scientific ‘maturity’ of a nascent speciality. The emergence of climate change research, starting in the 1970s, reorganized many of the oceanographic research questions and legitimized the extension of the discipline into geospatial research. One goal of this article is to understand how this development of science policy influenced interactions between different disciplines.
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Ward, N. "The Future of Radar Beacons". Journal of Navigation 50, n.º 2 (mayo de 1997): 242–47. http://dx.doi.org/10.1017/s0373463300023845.
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The principles of radar beacons (racons) are described and their significance for navigation discussed. Developments in radars which may affect the operation of racons are considered and ways of meeting the requirement to locate and identify aids to navigation on a radar display are considered. The developments in non-radar band transponders are reviewed to determine whether they might present an alternative to racons in the future.
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Gorbunov, Igor G., Vladimir I. Veremyev, Vadim D. Shestak, Gleb V. Komarov, Stanislav A. Myslenkov y Ksenia P. Silvestrova. "Verifying Measurements of Surface Current Velocities by X-Band Coherent Radar Using Drifter Data". Journal of the Russian Universities. Radioelectronics 26, n.º 3 (6 de julio de 2023): 99–110. http://dx.doi.org/10.32603/1993-8985-2023-26-3-99-110.
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Introduction. Conventional contact measurements of hydrographic parameters frequently fail to provide the necessary accuracy of data in the field of water area monitoring. This problem can be solved using coherent radars enabling direct measurements of surface current velocities.Aim. To establish the accuracy of surface current velocities measured by a Doppler radar using drifter data.Materials and methods. In June 2022, coastal operational oceanography studies were conducted at the hydrophysical test site of the Institute of Oceanology of the Russian Academy of Sciences in the Black Sea near Gelendzhik. Measurements were carried out using a coherent X-band radar installed on the Ashamba research vessel simultaneously with drifter experiments using Lagrangian drifters of the near-surface layer with an underwater 0.5 m sail. Coordinates were transmitted via mobile communication. The drifter data on the current velocity and direction were used to verify radar measurements. Measurements were taken onboard of the research vessel at a low speed and different distances from the shore, near the drifters. The tracks of the vessel and drifters were recorded simultaneously. Processing of the radar data involved obtaining Doppler spectra of signals to estimate the dynamic processes on the sea surface, including the current velocity.Results. Radial components of the near-surface current velocity were calculated. Then, the current velocity values obtained based on the drifter and radar data were compared.Conclusion. The present work makes a contribution to the advancement of methods for measuring surface currents from the board of a moving ship by Doppler radars. The obtained results confirm the suitability of the radar hardware and software and signal processing algorithms for measuring currents. The radar measurement data were found agree well with drifter data in the velocity range from 15 cm/s.
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Kirincich, Anthony. "Toward Real-Time, Remote Observations of the Coastal Wind Resource Using High-Frequency Radar". Marine Technology Society Journal 47, n.º 4 (1 de julio de 2013): 206–17. http://dx.doi.org/10.4031/mtsj.47.4.22.
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AbstractThere is now a large installed base of high-frequency (HF) coastal ocean radars in the United States able to measure surface currents on an operational basis. However, these instruments also have the potential to provide estimates of the spatially variable surface wind field over distances ranging from 10 to 200 km offshore. This study investigates the ability of direction-finding HF radars to recover spatial maps of wind speed and direction from the dominant first-order region radar returns using empirical models. Observations of radar backscatter from the Martha’s Vineyard Coastal Observatory HF radar system were compared to wind observations from an offshore tower, finding significant correlations between wind speed and the backscatter power for a range of angles between the wind and radar loop directions. Models for the directional spreading of wind waves were analyzed in comparison to data-based results, finding potentially significant differences between the model and data-based spreading relationships. Using empirical fits, radar-based estimates of wind speed and direction at the location of the in situ wind sensor had error rates of 2 m/s and 60°, which decreased with hourly averaging. Attempts to extrapolate the results to the larger domain illustrated that spatially dependent transfer functions for wind speed and direction appear possible for large coastal ocean domains based on a small number of temporary, or potentially mobile, in situ wind sensors.
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Zhang, Wei, Naoto Ebuchi, Yasushi Fukamachi, Feng Cheng, Kay I. Ohshima, Brian M. Emery, Takenobu Toyota, Hiroto Abe y Kunio Shirasawa. "Sea Ice Observation With Oceanographic HF Radar". IEEE Transactions on Geoscience and Remote Sensing 58, n.º 1 (enero de 2020): 378–90. http://dx.doi.org/10.1109/tgrs.2019.2936576.
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Statscewich, Hank, Hugh Roarty, Michael Smith, Ed Page, Scott Glenn y Tom Weingartner. "Enhancing Arctic Maritime Domain Awareness Through an Off-Grid Multi-sensor Instrument Platform". Marine Technology Society Journal 48, n.º 5 (1 de septiembre de 2014): 97–109. http://dx.doi.org/10.4031/mtsj.48.5.1.
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AbstractSurface current mapping high-frequency radars were installed along the northwest corner of Alaska during the open water periods of 2011‐2013. A combination of wind and solar renewable energy inputs supplied electricity to a single radar site operating at Point Barrow, Alaska, via an off-grid remote power module (RPM). The radar at Point Barrow was able to simultaneously collect measurements of ocean surface currents, measure the position and velocity of passing vessels, and provide meteorological data in real time. This paper provides a summary of the performance of the power module from 2011 to 2013 and vessel detection results from 2013 with corresponding Automated Identification System (AIS) data. The RPM provided infrastructure to meteorological stations, high-frequency radars, and AIS in a resilient and robust manner and serves as an example of how the multi-use capability of integrated sensor modules can provide enhanced maritime domain awareness and persistent surveillance capabilities in remote Arctic environments.
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Briggs, John N. "Detection of Marine Radar Targets". Journal of Navigation 49, n.º 3 (septiembre de 1996): 394–409. http://dx.doi.org/10.1017/s0373463300013618.
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A radar must detect targets before it can display them. Yet manufacturers' data sheets rarely tell us what the products will detect at what range. Many of the bigger radars are Type Approved so we consult the relevant IMO performance standard A 477 (XII). Paraphrasing Section 3.1 of the draft forthcoming revision (NAV 41/6): under normal propagation conditions with the scanner at height of 15 m, in the absence of clutter, the radar is required to give clear indication of an object such as a navigational buoy having a radar cross section area (RCS) of 10 m2 at 2 n.m. and, as examples, coastlines whose ground rises to 60/6 m at ranges of 20/7 n.m., a ship of 5000 tons at any aspect at 7 n.m. and a small vessel 10 m long at 3 n.m.This helps, but suppose we must pick up a 5 m2 buoy at g km? What happens in clutter? Should we prefer S- or X-band? To answer such questions we use equations which define the performance of surveillance radars, but the textbooks and specialist papers containing them often generalize with aeronautical and defence topics, making life difficult for the nonspecialist.This paper attempts a concise and self-contained engineering account of all main factors affecting detection of passive and active targets on civil marine and vessel traffic service (VTS) radars. We develop a set of equations for X- and S-band (3 and 10 cm, centred on 9400 and 3000 MHz respectively), suited for spreadsheet calculation.Sufficient theory is sketched in to indicate where results should be valid. Some simplifications of conventional treatments have been identified.
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Murata, Yasuhiro, Toshiro Nagakura y Takahiro Kokai. "TSUNAMI EARLY DETECTION:ENHANCED RESOLUTION OF HF OCEANOGRAPHIC RADAR". Coastal Engineering Proceedings 1, n.º 32 (23 de enero de 2011): 4. http://dx.doi.org/10.9753/icce.v32.currents.4.
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HF Oceanographic radar is an equipment, for instantaneously sensing velocity distribution of sea surface current. It has a
wide field of view, which extends approximately ±45° in direction and beyond 50km in distance. There are high
expectations that the radar observation of Tsunami will become a new road path for preventing disasters. In this paper, we
describe a method to enhance the resolutions of radar in both time and current. At first, resolutions required for tsunami
observation are estimated by simulating a Tokachi-oki earthquake tsunami (2003). Here it is pointed out that traditional
data processing indicates inadequate resolutions for tsunami early detection. Secondly, two techniques are proposed to
achieve the necessary resolutions. Short-time Fourier transform (STFT), in place of normal FFT, enhances the time
resolution of Doppler analysis. Further, zero-padding technique improves the current resolution, by interpolation of data
within the frequency domain. Finally, by means of simulation, it is verified that these proposed techniques give improved
resolutions in both time and current.
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Zhu, Langfeng, Tianyi Lu, Fan Yang, Bin Liu, Lunyu Wu y Jun Wei. "Comparisons of Tidal Currents in the Pearl River Estuary between High-Frequency Radar Data and Model Simulations". Applied Sciences 12, n.º 13 (27 de junio de 2022): 6509. http://dx.doi.org/10.3390/app12136509.
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High-frequency (HF) radar data, derived from a pair of newly developed radar stations in the Pearl River Estuary (PRE) of China, were validated through comparison with in situ surface buoys, ADCP measurements, and model simulations in this study. Since no in situ observations are available in the radar observing domain, a regional high-resolution ocean model covering the entire PRE and its adjacent seas was first established and validated with in situ measurements, and then the HF radar data quality was examined against the model simulations. The results show that mean flows and tidal ellipses derived from the in situ buoys and ADCP were in very good agreement with the model. The model–radar data comparison indicated that the radar obtained the best data quality within the central overlapping area between the two radar stations, with the errors increasing toward the coast and the open ocean. Near the coast, the radar data quality was affected by coastlines and islands that prevent HF radar from delivering high-quality information for determining surface currents. This is one of the major drawbacks of the HF radar technique. Toward the open ocean, where the wind is the only dominant forcing on the tidal currents, we found that the poor data quality was most likely contaminated by data inversion algorithms from the Shangchuan radar station. A hybrid machine-learning-based inversion algorithm including traditional electromagnetic analysis and physical oceanography factors is needed to develop and improve radar data quality. A new radar observing network with about 10 radar stations is developing in the PRE and its adjacent shelf, this work assesses the data quality of the existing radars and identifies the error sources, serving as the first step toward the full deployment of the entire radar network.
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Luther, Mark E., Sherryl A. Gilbert y Mario Tamburri. "Status of Sensors for Physical Oceanographic Measurements". Marine Technology Society Journal 42, n.º 1 (1 de marzo de 2008): 84–92. http://dx.doi.org/10.4031/002533208786861227.
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This paper draws from recent workshops held by the Alliance for Coastal Technologies to summarize the present status of sensors and sensor platforms for making physical oceanographic observations. Technologies reviewed include those for current measurements, HF Radar, wave sensors, drifting buoys, profiling floats, surface meteorological observations, and automated vessel-based systems, as well as related issues of data telemetry and biofouling.
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Shrira, Victor I. y Philippe Forget. "On the Nature of Near-Inertial Oscillations in the Uppermost Part of the Ocean and a Possible Route toward HF Radar Probing of Stratification". Journal of Physical Oceanography 45, n.º 10 (octubre de 2015): 2660–78. http://dx.doi.org/10.1175/jpo-d-14-0247.1.
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AbstractInertial band response of the upper ocean to changing wind is studied both theoretically and by analysis of observations in the northwestern Mediterranean. On the nontraditional f plane, because of the horizontal component of the earth’s rotation for waves of inertial band with frequencies slightly below the local inertial frequency f, there is a waveguide in the mixed layer confined from below by the pycnocline. It is argued that when the stratification is shallow these waves are most easily and strongly excited by varying winds as near-inertial oscillations (NIOs). These motions have been overlooked in previous studies because they are absent under the traditional approximation. The observations that employed buoys with thermistors, ADCPs, and two 16.3-MHz Wellen Radar (WERA) HF radars were carried out in the Gulf of Lion in April–June 2006. The observations support the theoretical picture: a pronounced inertial band response occurs only in the presence of shallow stratification and is confined to the mixed layer, and the NIO penetration below the stratified layer is weak. NIO surface magnitude and vertical localization are strongly affected by the presence of even weak density stratification in the upper 10 m. The NIO surface signatures are easily captured by HF radars. Continuous 1.8-yr HF observations near the Porquerolles Island confirm that shallow stratification is indeed the precondition for a strong NIO response. The response sensitivity to stratification provides a foundation for developing HF radar probing of stratification and, indirectly, vertical mixing, including spotting dramatic mixing events and spikes of vertical heat, mass, and momentum exchange.
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Hansford, R. F. "The Development of Shipborne Navigational Radar". Journal of Navigation 50, n.º 3 (septiembre de 1997): 390–99. http://dx.doi.org/10.1017/s0373463300019019.
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This paper was first published in the Journal in 1947 (Vol. 1, p. 118). Sections 1 and 2 are summarized in order to save space. Sections 3, 4 and 5 are reprinted with only a little abridgment. The paper is followed by comment from the original author.The original paper gave a comprehensive account of the development of navigational radar in the United Kingdom from the beginning of World War II up to the time of writing.The use that was made of the very early radars was mentioned and the improvements brought about by the introduction of the PPI (Plan Position Indicator) and centimetric radar were described. An account was given of how radar assisted the Normandy landings, and of the techniques employed including the use of radar predictions of the Normandy coastline (produced in great secrecy) which were optically superimposed on the PPI. Also shown on the predictions were the planned approach tracks to the shore. An example of one of these predictions compared with the post-invasion radar photograph is shown in Fig. 1. This superimposition of geographical information on the PPI was to become of great significance in later years.
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Harlan, Jack, Eric Terrill, Lisa Hazard, Carolyn Keen, Donald Barrick, Chad Whelan, Stephan Howden y Josh Kohut. "The Integrated Ocean Observing System High-Frequency Radar Network: Status and Local, Regional, and National Applications". Marine Technology Society Journal 44, n.º 6 (1 de noviembre de 2010): 122–32. http://dx.doi.org/10.4031/mtsj.44.6.6.
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AbstractA national high-frequency radar network has been created over the past 20 years or so that provides hourly 2-D ocean surface current velocity fields in near real time from a few kilometers offshore out to approximately 200 km. This preoperational network is made up of more than 100 radars from 30 different institutions. The Integrated Ocean Observing System efforts have supported the standards-based ingest and delivery of these velocity fields to a number of applications such as coastal search and rescue, oil spill response, water quality monitoring, and safe and efficient marine navigation. Thus, regardless of the operating institution or location of the radar systems, emergency response managers, and other users, can rely on a common source and means of obtaining and using the data. Details of the history, the physics, and the application of high-frequency radar are discussed with successes of the integrated network highlighted.
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Guerrero, José Miguel, Andreas Muñoz, Matilde Santos y Gonzalo Pajares. "A new Concentric Circles Detection method for Object Detection applied to Radar Images". Journal of Navigation 72, n.º 04 (27 de febrero de 2019): 1070–88. http://dx.doi.org/10.1017/s0373463318001169.
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In this work, a new concentric circles detection method for object detection is proposed. It has been applied to the images of a commercial radar, captured with a Charge-Coupled Device (CCD) camera. The processing includes the detection of centres and concentric circles in the images and the identification of the radar scale. Several methods found in the literature have been applied and compared with our novel proposal for multiple concentric circles detection, called “Propagation Method based on Circular Regression”. This methodology has been validated with real radar images, proving its efficiency in obtaining the distance of any object to a marine vessel, with high accuracy and low computational cost, in real time. This system can not only be applied to most existing radars in the market by adjusting the parameters of each model but our proposal for concentric circle detection can be also applied to other sensing applications.
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Chen, L., G. H. Wang, Y. He y I. Progri. "Analysis of Mobile 3-D Radar Error Registration when Radar Sways with Platform". Journal of Navigation 67, n.º 3 (16 de diciembre de 2013): 451–72. http://dx.doi.org/10.1017/s0373463313000799.
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For mobile radars installed on a gyro-stabilised platform (GSP) that can steadily follow an East-North-Up (ENU) frame, attitude biases (ABs) of the platform and offset biases (OBs) of the radar are linear dependent variables. Therefore ABs and OBs are unobservable in the linearized registration equations; however, when combining them as new variables, the system becomes observable, and this model has been called the unified registration model (URM). Unlike GSP mobile radars, un-stabilised GSP (or UGSP) mobile radars are installed on the platform directly and rotate with the platform simultaneously. For UGSP, it is testified that both types of biases are independent and observable because the time-varying attitude angles (AAs)1 of the platform are included in the registration equations, which destroy the dependencies of both kinds of biases and lead us to propose a completely different linearized registration model– the All Augmented Model (AAM). AAM employs all OBs and ABs in the state vector and a Kalman filter (KF) to produce their estimates. Numerical simulation results show that the estimated performance of AAM is close to the Cramér-Rao lower bound (CRLB) and that the Root Mean Square Errors (RMSEs) of the rectified measurements by using AAM are more than 500 m smaller than by URM in all directions.
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Curtis, Robert G., Elisabeth M. Goodwin y Mark Konyn. "The Automatic Detection of Real-Life Ship Encounters". Journal of Navigation 40, n.º 3 (septiembre de 1987): 355–65. http://dx.doi.org/10.1017/s0373463300000618.
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There are now radar installations which track ships automatically, and these radars can provide the researcher with statistics on collision-avoidance manoeuvres. The extraction, by hand, is laborious and time consuming. This paper describes a mathematical model which automatically detects collision-avoidance manoeuvres. The model operates on an adaption of the Range to Domain Over Range Rate (RDRR) principle, which enables ships to be identified for analysis shortly before they are expected to initiate a collision-avoidance manoeuvre. The model has been computerized and results presented.
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Hwang, Ji-Hwan, Duk-jin Kim y Ki-Mook Kang. "Multifunctional Scatterometer System for Measuring Physical Oceanographic Parameters Using Range-Doppler FMCW Radar". Sensors 22, n.º 8 (9 de abril de 2022): 2890. http://dx.doi.org/10.3390/s22082890.
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A multifunctional scatterometer system and optimized radar signal processing for simultaneous observation of various physical oceanographic parameters are described in this paper. Existing observation methods with microwave remote sensing techniques generally use several separate systems such as scatterometer, altimeter, and Doppler radar for sea surface monitoring, which are inefficient in system operation and cross-analysis of each observation data. To improve this point, we integrated separate measurement functions into a single observation system by adding a measurement function of Doppler frequency to the existing system. So it enables to simultaneously measure the range and polarimetric responses of backscattering as well as movements of the sea surface. Here, the simultaneous measurement function of Doppler frequency was implemented by sampling an FMCW (frequency modulated continuous wave) radar signal as 2D raw data consisting of fast- and slow-time samples, i.e., the range and backscattering of radar target signals are analyzed from the fast-time samples while the Doppler frequency by the radar target’s movement extracts from the slow-time samples. Through the Fourier transformed-based range-Doppler signal process, distance (R), backscattering (σ°), and Doppler frequency (fD) are sequentially extracted from the 2D raw data, and a correlation to the physical oceanographic parameters is analyzed. Operability of the proposed system was examed through total 3 times of field campaigns from June 2017 to August 2020 and the observation data retrieved by the radar measurement data (R, σ°, fD) was also cross-analyzed with in-situ data: e.g., tide, significant wave height, and wind speed and direction. Differences in the comparative results as an observational accuracy are as follows. Tidal level (Root Mean Square Error 0.169 m (R)), significant wave height (RMSE 0.127 m (R), 0.362 m (σ°)), wind speed (RMSE 1.880 m/s (fD), 2.094 m/s (σ°)) and direction (18.84° (fD)).
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Ogata, Kohei, Shuji Seto, Ryotaro Fuji, Tomoyuki Takahashi y Hirofumi Hinata. "Real-Time Tsunami Detection with Oceanographic Radar Based on Virtual Tsunami Observation Experiments". Remote Sensing 10, n.º 7 (17 de julio de 2018): 1126. http://dx.doi.org/10.3390/rs10071126.
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The tsunami generated by the 2011 Tohoku-Oki earthquake was the first time that the velocity fields of a tsunami were measured by using high-frequency oceanographic radar (HF radar) and since then, the development of HF radar systems for tsunami detection has progressed. Here, a real-time tsunami detection method was developed, based on virtual tsunami observation experiments proposed by Fuji et al. In the experiments, we used actual signals received in February 2014 by the Nagano Japan Radio Co., Ltd. radar system installed on the Mihama coast and simulated tsunami velocities induced by the Nankai Trough earthquake. The tsunami was detected based on the temporal change in the cross-correlation of radial velocities between two observation points. Performance of the method was statistically evaluated referring to Fuji and Hinata. Statistical analysis of the detection probability was performed using 590 scenarios. The maximum detection probability was 15% at 4 min after tsunami occurrence and increased to 80% at 7 min, which corresponds to 9 min before tsunami arrival at the coast. The 80% detection probability line located 3 km behind the tsunami wavefront proceeded to the coast as the tsunami propagated to the coast. To obtain a comprehensive understanding of the tsunami detection probability of the radar system, virtual tsunami observation experiments are required for other seasons in 2014, when the sea surface state was different from that in February, and for other earthquakes.
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Tokashiki, Yudai y Satoshi Fujii. "Cause of Double-Peak Spectrum in Hyuga-Nada by the HF Radar". Journal of Marine Science and Engineering 11, n.º 3 (25 de febrero de 2023): 503. http://dx.doi.org/10.3390/jmse11030503.
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High-frequency (HF) radar is a land-based instrument that can observe the radial distribution of oceanographic information, such as surface currents, wave heights, and wind directions. The first-order echo peak of the Doppler spectrum is often splits in this observation, and the levels of the split peaks are of approximately the same magnitude. We call this the double-peak spectrum. Because such a spectral shape may affect the derivation of oceanographic information, we examined the factors that cause double-peak spectra. The Kuroshio Current flows near the observation area of this study’s radar, which may have caused the double-peak spectrum. By mapping the spatial distribution of the double-peak spectra, we found areas in which the double-peak spectra occur relatively often at each radar station. The area of high vorticity ahead of the northeastward Kuroshio Current coincided with the area in which the double-peak spectra occurred, indicating the complexity of the currents occurring there; furthermore, more than two current velocity patterns can be mapped. These results show that the distance and directional continuity of the double-peak spectra can be used to calculate the flow-changing region with better spatial resolution.
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Popstefanija, I., D. S. McQueen y R. E. McIntosh. "A stepped-frequency delta-K microwave radar for oceanographic studies". IEEE Transactions on Geoscience and Remote Sensing 31, n.º 3 (mayo de 1993): 681–91. http://dx.doi.org/10.1109/36.225534.
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Stawell, W. B. "A Note on the use of the Global Positioning System (GPS) for the Identification of Marine Radar Contacts". Journal of Navigation 46, n.º 3 (septiembre de 1993): 437–41. http://dx.doi.org/10.1017/s0373463300011887.
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The Global Positioning System (GPS) is a cheap, accurate (±100 m), satellite-based position fixing system. These qualities suggest that it might be used in the identification of marine radar targets. The first application of such a system on any scale will probably be as part of a Vessel Traffic Service (VTS) and here GPS would seem to be ideally suited. Vessels entering the VTS control zone would need to be fitted with GPS interfaced with either a dedicated VHF receiver or a ‘guard’ channel on their normal receiver A VTS radar operator needing to identify an echo would work out the echo's position from the radar range and bearing and transmit that position as the interrogating signal. Only the vessel in the control zone with that position (derived from its GPS interface) would respond with its identity. There would thus be no possibility of interference between responses or garbling that can be a problem in interrogation systems based on secondary radar. Even if the VTS had several radars, these could easily be synchronized to prevent simultaneous interrogations. However, outside VTS zones there is a clear need for a universal identification system that would allow any ship to identify any other. It would be unfortunate and wasteful if a system developed for VTS was found to be unsuitable for this general application. This note will therefore discuss the adequacy of GPS as the basis of a universal marine identification system.
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Višnjević, Vjeran, Reinhard Drews, Clemens Schannwell, Inka Koch, Steven Franke, Daniela Jansen y Olaf Eisen. "Predicting the steady-state isochronal stratigraphy of ice shelves using observations and modeling". Cryosphere 16, n.º 11 (23 de noviembre de 2022): 4763–77. http://dx.doi.org/10.5194/tc-16-4763-2022.
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Abstract. Ice shelves surrounding the Antarctic perimeter moderate ice discharge towards the ocean through buttressing. Ice-shelf evolution and integrity depend on the local surface accumulation, basal melting and on the spatially variable ice-shelf viscosity. These components of ice-shelf mass balance are often poorly constrained by observations and introduce uncertainties in ice-sheet projections. Isochronal radar stratigraphy is an observational archive for the atmospheric, oceanographic and ice-flow history of ice shelves. Here, we predict the stratigraphy of locally accumulated ice on ice shelves with a kinematic forward model for a given atmospheric and oceanographic scenario. This delineates the boundary between local meteoric ice (LMI) and continental meteoric ice (CMI). A large LMI to CMI ratio hereby marks ice shelves whose buttressing strength is more sensitive to changes in atmospheric precipitation patterns. A mismatch between the steady-state predictions of the kinematic forward model and observations from radar can highlight inconsistencies in the atmospheric and oceanographic input data or be an indicator for a transient ice-shelf history not accounted for in the model. We discuss pitfalls in numerical diffusion when calculating the age field and validate the kinematic model with the full Stokes ice-flow model Elmer/Ice. The Roi Baudouin Ice Shelf (East Antarctica) serves as a test case for this approach. There, we find a significant east–west gradient in the LMI / CMI ratio. The steady-state predictions concur with observations on larger spatial scales (>10 km), but deviations on smaller scales are significant, e.g., because local surface accumulation patterns near the grounding zone are underestimated in Antarctic-wide estimates. Future studies can use these mismatches to optimize the input data or to pinpoint transient signatures in the ice-shelf history using the ever growing archive of radar observations of internal ice stratigraphy.