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Björn Lund - One of the best experts on this subject based on the ideXlab platform.

  • near surface current mapping by shipboard marine x band Radar a validation
    Journal of Atmospheric and Oceanic Technology, 2018
    Co-Authors: Björn Lund, Hans C. Graber, Jochen Horstmann, Ruben Carrasco, Brian K Haus, Nathan J M Laxague, Guillaume Novelli, Cedric M Guigand, Tamay M Ozgokmen
    Abstract:

    AbstractThe Lagrangian Submesoscale Experiment (LASER) involved the deployment of ~1000 biodegradable GPS-tracked Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CA...

  • Intense deformation field at oceanic front inferred from directional sea surface roughness observations
    Geophysical Research Letters, 2017
    Co-Authors: Nicolas Rascle, Björn Lund, Jeroen Molemaker, Louis Marié, Frederic Nouguier, Bertrand Chapron, Alexis Mouche
    Abstract:

    Fine scale current gradients at the ocean surface can be observed by sea surface roughness. More specifically, directional surface roughness anomalies are related to the different horizontal current gradient components. This paper reports results from a dedicated experiment during the LASER (LAgrangian Submesoscale ExpeRiment) drifter deployment. A very sharp front, 50 m wide, is detected simultaneously in drifter trajectories, sea surface temperature and sea surface roughness. A new observational method is applied, using sun glitter reflections during multiple airplane passes to reconstruct the multi-angle roughness anomaly. This multi-angle anomaly is consistent with wave-current interactions over a front, including both cross-front convergence and along-front shear with cyclonic vorticity. Qualitatively, results agree with drifters and X-Band Radar observations. Quantitatively, the sharpness of roughness anomaly suggests intense current gradients, 0.3 m s−1 over the 50 m wide front. This work opens new perspectives for monitoring intense oceanic fronts using drones or satellite constellations.

  • Multi-directional wave spectra from marine X-Band Radar
    Ocean Dynamics, 2016
    Co-Authors: Björn Lund, Clarence O. Collins, Hitoshi Tamura, Hans C. Graber
    Abstract:

    The signal measured by heave–pitch–roll directional wave buoys yields the first four coefficients of a Fourier series. Data adaptive methods must be employed to estimate a directional wave spectrum. Marine X-Band Radars (MRs) have the advantage over buoys that they can measure “model-free” two-dimensional (2D) wave spectra. This study presents the first comprehensive validation of MR-derived multi-directional wave characteristics. It is based on wave data from the 2010 Impact of Typhoons on the Ocean in the Pacific (ITOP) experiment in the Philippine Sea, namely MR measurements from R/V Roger Revelle , Extreme Air–Sea Interaction (EASI) buoy measurements, as well as WAVEWATCH-III (WW3) modeling results. Buoy measurements of mean direction and spreading as function of frequency, which do not require data adaptive methods, are used to validate the WW3 wave spectra. An advanced MR wave retrieval technique is introduced that addresses various shortcomings of existing methods. Spectral partitioning techniques, applied to MR and WW3 results, reveal that multimodal seas are frequently present. Both data sets are in excellent agreement, tracking the evolution of up to 4 simultaneous wave systems over extended time periods. This study demonstrates MR’s and WW3’s strength at measuring and predicting 2D wave spectra in swell-dominated seas.

  • on shipboard marine x band Radar near surface current calibration
    Journal of Atmospheric and Oceanic Technology, 2015
    Co-Authors: Björn Lund, Hans C. Graber, Katrin Hessner, Neil J Williams
    Abstract:

    AbstractThe ocean wave signatures within conventional noncoherent marine X-Band Radar (MR) image sequences can be used to derive near-surface current information. On ships, an accurate near-real-time record of the near-surface current could improve navigational safety. It could also advance understanding of air–sea interaction processes. The standard shipboard MR near-surface current estimates were found to have large errors (of the same order of magnitude as the signal) that are associated with ship speed and heading. For acoustic Doppler current profilers (ADCPs), ship heading errors are known to induce a spurious cross-track current that is proportional to the ship speed and the sine of the error angle. Conventional mechanical gyrocompasses are very reliable heading sensors, but they are too inaccurate for shipboard ADCPs. Within the ADCP community, it is common practice to correct the gyrocompass measurements with the help of multiantenna carrier-phase differential GPS systems. This study shows how a ...

  • near surface current shear measured by marine x band Radar
    2015 IEEE OES Eleveth Current Waves and Turbulence Measurement (CWTM), 2015
    Co-Authors: Björn Lund, Hans C. Graber, Jeffrey Campana, Eric Terrill
    Abstract:

    This paper presents a new method to measure the near-surface currents' vertical shear by marine X-Band Radar (MR). The data used here were acquired from R/V Roger Revelle during the Impact of Typhoons on the Ocean in the Pacific (ITOP) field campaign in 2010. Existing techniques use MR surface wave signatures to retrieve a single near-surface current vector per analysis period. In essence, this is done by measuring the phase velocity of a wave on a current, which is then compared with the known still-water linear dispersion relationship. The resulting current corresponds to a depth-weighted average over the near-surface ocean layer. We introduce a new method that yields multiple estimates as a function of ocean wavenumber. The “effective” depth of the Radar current measurement increases with the length of the ocean wave it was derived from. Our wavenumber-dependent near-surface currents thus provide information on vertical current shear. This method is analogous to an approach that has already proven successful for multi-frequency high-frequency (HF) Radars. Here, we present first results which are put into the context of shipboard wind, surface wave, and background current measurements.

Hans C. Graber - One of the best experts on this subject based on the ideXlab platform.

  • near surface current mapping by shipboard marine x band Radar a validation
    Journal of Atmospheric and Oceanic Technology, 2018
    Co-Authors: Björn Lund, Hans C. Graber, Jochen Horstmann, Ruben Carrasco, Brian K Haus, Nathan J M Laxague, Guillaume Novelli, Cedric M Guigand, Tamay M Ozgokmen
    Abstract:

    AbstractThe Lagrangian Submesoscale Experiment (LASER) involved the deployment of ~1000 biodegradable GPS-tracked Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CA...

  • Multi-directional wave spectra from marine X-Band Radar
    Ocean Dynamics, 2016
    Co-Authors: Björn Lund, Clarence O. Collins, Hitoshi Tamura, Hans C. Graber
    Abstract:

    The signal measured by heave–pitch–roll directional wave buoys yields the first four coefficients of a Fourier series. Data adaptive methods must be employed to estimate a directional wave spectrum. Marine X-Band Radars (MRs) have the advantage over buoys that they can measure “model-free” two-dimensional (2D) wave spectra. This study presents the first comprehensive validation of MR-derived multi-directional wave characteristics. It is based on wave data from the 2010 Impact of Typhoons on the Ocean in the Pacific (ITOP) experiment in the Philippine Sea, namely MR measurements from R/V Roger Revelle , Extreme Air–Sea Interaction (EASI) buoy measurements, as well as WAVEWATCH-III (WW3) modeling results. Buoy measurements of mean direction and spreading as function of frequency, which do not require data adaptive methods, are used to validate the WW3 wave spectra. An advanced MR wave retrieval technique is introduced that addresses various shortcomings of existing methods. Spectral partitioning techniques, applied to MR and WW3 results, reveal that multimodal seas are frequently present. Both data sets are in excellent agreement, tracking the evolution of up to 4 simultaneous wave systems over extended time periods. This study demonstrates MR’s and WW3’s strength at measuring and predicting 2D wave spectra in swell-dominated seas.

  • on shipboard marine x band Radar near surface current calibration
    Journal of Atmospheric and Oceanic Technology, 2015
    Co-Authors: Björn Lund, Hans C. Graber, Katrin Hessner, Neil J Williams
    Abstract:

    AbstractThe ocean wave signatures within conventional noncoherent marine X-Band Radar (MR) image sequences can be used to derive near-surface current information. On ships, an accurate near-real-time record of the near-surface current could improve navigational safety. It could also advance understanding of air–sea interaction processes. The standard shipboard MR near-surface current estimates were found to have large errors (of the same order of magnitude as the signal) that are associated with ship speed and heading. For acoustic Doppler current profilers (ADCPs), ship heading errors are known to induce a spurious cross-track current that is proportional to the ship speed and the sine of the error angle. Conventional mechanical gyrocompasses are very reliable heading sensors, but they are too inaccurate for shipboard ADCPs. Within the ADCP community, it is common practice to correct the gyrocompass measurements with the help of multiantenna carrier-phase differential GPS systems. This study shows how a ...

  • near surface current shear measured by marine x band Radar
    2015 IEEE OES Eleveth Current Waves and Turbulence Measurement (CWTM), 2015
    Co-Authors: Björn Lund, Hans C. Graber, Jeffrey Campana, Eric Terrill
    Abstract:

    This paper presents a new method to measure the near-surface currents' vertical shear by marine X-Band Radar (MR). The data used here were acquired from R/V Roger Revelle during the Impact of Typhoons on the Ocean in the Pacific (ITOP) field campaign in 2010. Existing techniques use MR surface wave signatures to retrieve a single near-surface current vector per analysis period. In essence, this is done by measuring the phase velocity of a wave on a current, which is then compared with the known still-water linear dispersion relationship. The resulting current corresponds to a depth-weighted average over the near-surface ocean layer. We introduce a new method that yields multiple estimates as a function of ocean wavenumber. The “effective” depth of the Radar current measurement increases with the length of the ocean wave it was derived from. Our wavenumber-dependent near-surface currents thus provide information on vertical current shear. This method is analogous to an approach that has already proven successful for multi-frequency high-frequency (HF) Radars. Here, we present first results which are put into the context of shipboard wind, surface wave, and background current measurements.

  • marine Radar ocean wave retrieval s dependency on range and azimuth
    Ocean Dynamics, 2014
    Co-Authors: Björn Lund, Hans C. Graber, Eric Terrill, Clarence O. Collins, T H C Herbers
    Abstract:

    The strength of the surface wave signal in marine X-Band Radar (MR) images strongly depends on range and azimuth (i.e., the angle between antenna look and peak wave direction). Traditionally, MR wave analysis is carried out in a set of rectangular windows covering the Radar field of view (FOV). The FOV is typically partially obstructed, e.g., due to the coastline or ship superstructures. Especially for ships that are subject to regular course changes, this results in an increased variability or error associated with wave parameters. Using MR measurements from R/P FLIP, acquired off California during the 2010 US Office of Naval Research (ONR) high resolution air–sea interaction (Hi-Res) experiment, this study quantifies the dependency of the Radar-based 2D wave spectrum and parameters on range and azimuth. With the help of reference data from a nearby Datawell Waverider buoy, we propose empirical methods to remove the dependency and we illustrate their efficacy.

Jochen Horstmann - One of the best experts on this subject based on the ideXlab platform.

  • near surface current mapping by shipboard marine x band Radar a validation
    Journal of Atmospheric and Oceanic Technology, 2018
    Co-Authors: Björn Lund, Hans C. Graber, Jochen Horstmann, Ruben Carrasco, Brian K Haus, Nathan J M Laxague, Guillaume Novelli, Cedric M Guigand, Tamay M Ozgokmen
    Abstract:

    AbstractThe Lagrangian Submesoscale Experiment (LASER) involved the deployment of ~1000 biodegradable GPS-tracked Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CA...

  • Significant Wave Height Measured by Coherent X-Band Radar
    IEEE Transactions on Geoscience and Remote Sensing, 2017
    Co-Authors: Ruben Carrasco, Jochen Horstmann, Jorg Seemann
    Abstract:

    Significant wave height is one of the most important parameters for characterizing ocean waves and essential for coastal protection, shipping, as well as off shore industry operations. Within this paper, a robust method is introduced for retrieving significant wave heights from Doppler speed measurements acquired with a coherent-on-receive marine Radar. The Doppler velocity is caused by the surface scattering in the line of site of the Radar. To a huge extent its periodic component is induced by the orbital motions associated with surface waves. The proposed methodology is based on linear wave theory, accounts for projection effects caused by the fixed antenna look direction, and was applied to a coherent-on-receive Radar operating at X-Band with vertical polarization in transmit and receive. To show the overall performance of the method, a data set consisting of approximately 100 days of Radar measurements was analyzed and used to retrieve significant wave heights. Comparisons to wave measurements collected by a wave rider buoy resulted in a root-mean-square (rms) error of 0.21 m and a bias of 0 m without any calibration parameters needed. To further improve the accuracy of significant wave height, a calibration factor needs to be accounted for, which improves the rms error to 0.15 m with a negligible bias of -0.01 m.

  • a simple method for retrieving significant wave height from dopplerized x band Radar
    Ocean Science, 2016
    Co-Authors: Ruben Carrasco, Michael Streser, Jochen Horstmann
    Abstract:

    Abstract. Retrieving spectral wave parameters such as the peak wave direction and wave period from marine Radar backscatter intensity is very well developed. However, the retrieval of significant wave height is difficult because the Radar image spectrum (a backscatter intensity variance spectrum) has to be transferred to a wave spectrum (a surface elevation variance spectrum) using a modulation transfer function (MTF) which requires extensive calibration for each individual Radar setup. In contrast to the backscatter intensity, the Doppler velocity measured by a coherent Radar is induced by the radial velocity (or line-of-sight velocity) of the surface scattering and its periodic component is mainly the contribution of surface waves. Therefore, the variance of the Doppler velocity can be utilized to retrieve the significant wave height. Analyzing approximately 100 days of Doppler velocity measurements of a coherent-on-receive Radar operating at X-Band with vertical polarization in transmit and receive, a simple relation was derived and validated to retrieve significant wave heights. Comparison to wave measurements of a wave rider buoy as well as an acoustic wave and current profiler resulted in a root mean square error of 0.24 m with a bias of 0.08 m. Furthermore, the different sources of error are discussed and investigated.

  • ocean surface wind retrieval from stationary and moving platform marine Radar data
    International Geoscience and Remote Sensing Symposium, 2012
    Co-Authors: Björn Lund, Hans C. Graber, Jochen Horstmann, Eric Terrill
    Abstract:

    In this paper we evaluate different methods to retrieve wind information from marine Radar data. In contrast to traditional in-situ sensors, marine Radar wind data cover a large area and therefore are much less susceptible to air flow distortion by the platform. Unlike previous studies that have been limited to fixed-platform data, this study includes data from a quasi-stationary and moving platform. Images collected with a standard marine HH-polarized X-Band Radar operating at grazing incidence angle exhibit a single intensity peak in the upwind direction. Marine Radar images that are averaged over about 1 min may also show wind streaks, which are usually well-aligned with the mean surface wind direction. Here, we use both phenomena to retrieve wind directional information and compare results to determine the best approach under the given conditions. To retrieve wind speeds, an empirical model function which relates average backscatter intensity to wind speed is developed.

  • a marine Radar wind sensor
    International Geoscience and Remote Sensing Symposium, 2006
    Co-Authors: H Dankert, Jochen Horstmann
    Abstract:

    A method, called WiRAR, is developed to measure the wind vector using a marine X-Band Radar as sensor. WiRAR extracts local wind directions from wind induced streaks, which are visible in Radar images at scales above 50 m. It is shown that the streaks are very well aligned with the mean surface wind directions. Wind speeds are derived with WiRAR from the normalized Radar cross section (NRCS), by parametrization of its dependency on the wind vector, which was performed by training of a Neural Network. The dependency of the NRCS on sea state and atmospheric parameters, such as air-sea temperatures and humidity, were studied with respect to further improvement of WiRAR. Therefore, sea state parameters are extracted from Radar-image sequences by derivation of the Signal-to-Noise Ratio (SNR) and wave phase speed at the spectral peak cp. The SNR is directly related to the significant wave height Hs- Recently, the research platform FINO-I has been set-up in the German Bight. This platform provides various environmental data, such as wind measurements at different heights of up to 100 m for studying the atmospheric boundary layer, as well as air-sea temperatures, humidity, and other meteorological and oceanographical parameters. WiRAR is applied to Radar-image sequences acquired by a marine X-Band Radar aboard FINO-I. The derived wind vectors are compared to wind measurements at the platform. The comparison of wind directions resulted in a correlation coefficient of 0.99 with a standard deviation of 12.8deg and for wind speeds with a correlation coefficient of 0.99 with a standard deviation of 0.41 ms-1, respectively. In contrast to traditional offshore wind sensors, the retrieval of the wind vector from the backscatter of the ocean surface makes the system independent of the sensors motion and installation height and reduces the effects due to platform induced blockage and turbulence effects.

Francesco Soldovieri - One of the best experts on this subject based on the ideXlab platform.

  • Normalized Scalar Product Approach for Nearshore Bathymetric Estimation From X-Band Radar Images: An Assessment Based on Simulated and Measured Data
    IEEE Journal of Oceanic Engineering, 2018
    Co-Authors: Giovanni Ludeno, Matteo Postacchini, Claudio Lugni, Maurizio Brocchini, Antonio Di Natale, Francesco Soldovieri, Francesco Serafino
    Abstract:

    This paper investigates the capability of X-Band Radar systems to estimate nearshore bathymetry fields by considering both simulated and measured Radar data. For the first time, a sensitivity analysis is performed to evaluate how sea-state conditions affect bathymetric estimates. For this purpose, sea wave fields generated by means of a numerical model, based on a nonlinear shallow-water equation solver, are used. Starting from the synthetic Radar data, which represent the input of the bathymetric estimation algorithm, the bathymetric reconstruction is performed through the normalized scalar product (NSP) estimation strategy, exploiting a spatial partitioning of the Radar data. In this way, it is possible to improve the accuracy of the estimates in nearshore areas, where the space-varying behavior of the sea depth and the presence of coastlines or coastal structures typically leads to a spatial inhomogeneity of the wave motion. In this regard, it is shown how the choice of the partitioning settings affects the bathymetric estimates obtained from high-resolution X-Band Radar images by using the NSP strategy. In addition, an adaptive partitioning strategy that takes into account the wave evolution in nearshore shallow waters is devised. Based on both simulated and measured Radar data, the accuracy of the bathymetric estimates achievable through the proposed adaptive partitioning process and that obtained by exploiting the approach using uniform spatial partitioning are compared. The results obtained confirm the robustness of the NSP technique with respect to sea conditions and, moreover, demonstrate that the proposed adaptive partitioning strategy provides more accurate bathymetric estimates than those obtained with the space-invariant partitioning procedure.

  • coupling of wave data and underwater acoustic measurements in a maritime high traffic coastal area a case study in the strait of sicily
    Journal of Atmospheric and Oceanic Technology, 2017
    Co-Authors: F Raffa, Giovanni Ludeno, Giuseppa Buscaino, Rosario Grammauta, Domenico Spoto, Salvatore Mazzola, Francesco Soldovieri, Gianmaria Sannino, A. Carillo, Francesco Serafino
    Abstract:

    AbstractUnderwater acoustic monitoring combined with real-time sea surface observations and numerical model forecasts could improve the efficiency of natural and anthropogenic sound source discrimination. In this work, acoustic sound pressure levels at different frequencies were compared with significant wave heights, measured using an X-Band Radar system, and then matched against independent data derived from a Simulating Waves Nearshore (SWAN) model in order to confirm their reliability. The acoustic data were recorded from a fixed buoy located in the Sicilian Channel at 4.9 km from the coast and 33 km from the X-Band Radar system installed at Cape San Marco (in the southwest region of Sicily). All data were acquired during two different periods: 28 February–16 March 2015 and 23 April–27 May 2015. The level of noise at the 16-Hz octave band showed the best linear correlation , with in situ Radar observations of significant wave height. Radar measurements of wave height coupled with in situ acoustic meas...

  • a novel approach based on marine Radar data analysis for high resolution bathymetry map generation
    IEEE Geoscience and Remote Sensing Letters, 2014
    Co-Authors: Giovanni Ludeno, Claudio Lugni, Francesco Soldovieri, S Flampouris, F Serafino
    Abstract:

    This letter deals with the analysis of a novel data processing approach to estimate the local depth in a shallow coastal area starting from data collected by an in situ X-Band Radar system. The reconstruction approach is based on the maximization of the normalized scalar product (NSP) between the measured and the theoretical wave dispersion relation, which embeds the dependence on the searched for parameter (local depth). The use of NSP approach allows obtaining a high-resolution spatial map of the investigated area, and a thorough statistical analysis is carried out by comparing the local depth estimation results with the ground-truth data made available by a multi-beam echo-sounder survey. In addition, the improved accuracy of the NSP approach is demonstrated with respect to other methods previously used for the analysis of the same area.

  • remocean a flexible x band Radar system for sea state monitoring and surface current estimation
    IEEE Geoscience and Remote Sensing Letters, 2012
    Co-Authors: Francesco Serafino, Claudio Lugni, Giovanni Ludeno, Daniele Arturi, Marco Uttieri, B Buonocore, Enrico Zambianchi, Giorgio Budillon, Francesco Soldovieri
    Abstract:

    This letter deals with the use of the wave-Radar REMOCEAN system for sea-state monitoring starting from images collected in the X-Band at two different test sites. In particular, the measurement surveys were carried out at two coastal sites in the Gulf of Naples by means of the installation of the Radar on a fixed and on a movable platform, respectively. The effectiveness of the system was also tested by means of a comparison between the REMOCEAN results and the high-frequency coastal Radar observations, with emphasis to the sea surface current estimation.

  • a simple strategy to mitigate the aliasing effect in x band marine Radar data numerical results for a 2d case
    Sensors, 2011
    Co-Authors: Francesco Serafino, Claudio Lugni, Jose Carlos Nieto Borge, Francesco Soldovieri
    Abstract:

    For moderate and high speed values of the sea surface current, an aliasing phenomenon, due to an under-sampling in the time-domain, can strongly affect the reconstruction of the sea surface elevation derived from X-Band Radar images. Here, we propose a de-aliasing strategy that exploits the physical information provided by the dispersion law for gravity waves. In particular, we utilize simplifying hypotheses and numerical tests with synthetic data are presented to demonstrate the effectiveness of the presented method.

Youngsun Jung - One of the best experts on this subject based on the ideXlab platform.

  • simulations of polarimetric x band Radar signatures in supercells part ii zdr columns and rings and kdp columns
    Journal of Applied Meteorology and Climatology, 2017
    Co-Authors: Jeffrey C. Snyder, Howard B. Bluestein, Daniel T Dawson, Youngsun Jung
    Abstract:

    AbstractA high-resolution numerical model and polarimetric forward operator allow one to examine simulated convective storms from the perspective of observable polarimetric Radar quantities, enabling a better comparison of modeled and observed deep moist convection. Part I of this two-part study described the model and forward operator used for all simulations and examined the structure and evolution of rings of reduced copolar cross-correlation coefficient (i.e., ρhv rings). The microphysical structure of upward extensions of enhanced differential reflectivity (ZDR columns and ZDR rings) and enhanced specific differential phase (KDP columns) near and within the updrafts of convective storms serve as the focus of this paper. In general, simulated ZDR columns are located immediately west of the midlevel updraft maximum and are associated with rainwater lofted above the 0°C level and wet hail/graupel, whereas ZDR rings are associated with wet hail located near and immediately east of the midlevel updraft ma...

  • simulations of polarimetric x band Radar signatures in supercells part i description of experiment and simulated ρhv rings
    Journal of Applied Meteorology and Climatology, 2017
    Co-Authors: Jeffrey C. Snyder, Howard B. Bluestein, Daniel T Dawson, Youngsun Jung
    Abstract:

    AbstractWith the development of multimoment bulk microphysical schemes and polarimetric Radar forward operators, one can better examine convective storms simulated in high-resolution numerical models from a simulated polarimetric Radar perspective. Subsequently, relationships between observable and unobservable quantities can be examined that may provide useful information about storm intensity and organization that otherwise would be difficult to obtain. This paper, Part I of a two-part sequence, describes the bulk microphysics scheme, polarimetric Radar forward operator, and numerical model configuration used to simulate supercells in eight idealized, horizontally homogenous environments with different wind profiles. The microphysical structure and evolution of copolar cross-correlation coefficient (ρhv) rings associated with simulated supercells are examined in Part I, whereas Part II examines ZDR columns, ZDR rings, and KDP columns. In both papers, some systematic differences between the signature see...