Mapping surface currents from HF radar radial velocity measurements using optimal interpolation

Abstract. A coastal observing system for Northern and Arctic Seas (COSYNA) aims at construction of a long-term observatory for the German part of the North Sea, elements of which will be deployed as prototype modules in Arctic coastal waters. At present a coastal prediction system deployed in the area of the German Bight integrates near real-time measurements with numerical models in a pre-operational way and provides continuously state estimates and forecasts of coastal ocean state. The measurement suite contributing to the pre-operational set up includes in situ time series from stationary stations, a High-Frequency (HF) radar system measuring surface currents, a FerryBox system and remote sensing data from satellites. The forecasting suite includes nested 3-D hydrodynamic models running in a data-assimilation mode, which are forced with up-to-date meteorological forecast data. This paper reviews the present status of the system and its recent upgrades focusing on developments in the field of coastal data assimilation. Model supported data analysis and state estimates are illustrated using HF radar and FerryBox observations as examples. A new method combining radial surface current measurements from a single HF radar with a priori information from a hydrodynamic model is presented, which optimally relates tidal ellipses parameters of the 2-D current field and the M2 phase and magnitude of the radials. The method presents a robust and helpful first step towards the implementation of a more sophisticated assimilation system and demonstrates that even using only radials from one station can substantially benefit state estimates for surface currents. Assimilation of FerryBox data based on an optimal interpolation approach using a Kalman filter with a stationary background covariance matrix derived from a preliminary model run which was validated against remote sensing and in situ data demonstrated the capabilities of the pre-operational system. Data assimilation significantly improved the performance of the model with respect to both SST and SSS and demonstrated a good skill not only in the vicinity of the Ferry track, but also over larger model areas. The examples provided in this study are considered as initial steps in establishing new coastal ocean products enhanced by the integrated COSYNA-observations and numerical modelling.

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Quality Assessment of HF Radar–Derived Surface Currents Using Optimal Interpolation

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-14-00109.1 ◽

2015 ◽

Vol 32 (2) ◽

pp. 282-296 ◽

Cited By ~ 6

Author(s):

Ying-Chih Fang ◽

Thomas J. Weingartner ◽

Rachel A. Potter ◽

Peter R. Winsor ◽

Hank Statscewich

Keyword(s):

Chukchi Sea ◽

Positive Definiteness ◽

Hf Radar ◽

Optimal Interpolation ◽

Surface Currents ◽

High Frequency Radar ◽

Least Squares Fit ◽

Ocean Surface Currents ◽

Geometric Dilution Of Precision

AbstractThis study investigates the applicability of the optimal interpolation (OI) method proposed by Kim et al. for estimating ocean surface currents from high-frequency radar (HFR) in the northeastern Chukchi Sea, where HFR siting is dictated by power availability rather than optimal locations. Although the OI technique improves data coverage when compared to the conventional unweighted least squares fit (UWLS) method, biased solutions can emerge. The quality of the HFR velocity estimates derived by OI is controlled by three factors: 1) the number of available incorporating radials (AR), 2) the ratio of the incorporating radials from multiple contributing site locations [ratio of overlapping radial velocities (ROR) or radar geometry], and 3) the positive definiteness [condition number (CN)] of the correlation matrix. Operationally, ROR does not require knowledge of the angle covariance matrix used to compute the geometric dilution of precision (GDOP) in the UWLS method and can be computed before site selection to optimize coverage or after data processing to assess data quality when applying the OI method. The Kim et al. method is extended to examine sensitivities to data gaps in the radial distribution and the effects on OI estimates.

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Coastal observing and forecasting system for the German Bight – estimates of hydrophysical states

Ocean Science Discussions ◽

10.5194/osd-8-829-2011 ◽

2011 ◽

Vol 8 (2) ◽

pp. 829-872 ◽

Cited By ~ 1

Author(s):

E. V. Stanev ◽

J. Schulz-Stellenfleth ◽

J. Staneva ◽

S. Grayek ◽

J. Seemann ◽

...

Keyword(s):

Remote Sensing ◽

Data Assimilation ◽

German Bight ◽

Numerical Models ◽

Coastal Ocean ◽

Hf Radar ◽

Optimal Interpolation ◽

Surface Currents ◽

Arctic Seas

Abstract. A coastal observing system for Northern and Arctic Seas (COSYNA) aims at construction of a long-term observatory for the German part of the North Sea, elements of which will be deployed as prototype modules in Arctic coastal waters. At present a coastal prediction system deployed in the area of the German Bight integrates near real-time measurements with numerical models in a pre-operational way and provides continuously state estimates and forecasts of coastal ocean state. The measurement suite contributing to the pre-operational set up includes in situ time series from stationary stations, a High-Frequency (HF) radar system measuring surface currents, a FerryBox system and remote sensing data from satellites. The forecasting suite includes nested 3-D hydrodynamic models running in a data-assimilation mode, which are forced with up-to-date meteorological forecast data. This paper reviews the present status of the system and its recent upgrades focusing on developments in the field of coastal data assimilation. Model supported data analysis and state estimates are illustrated using HF radar and FerryBox observations as examples. A new method combining radial surface current measurements from a single HF radar with a priori information from a hydrodynamic model is presented, which optimally relates tidal ellipses parameters of the 2-D current field and the M2 phase and magnitude of the radials. The method presents a robust and helpful first step towards the implementation of a more sophisticated assimilation system and demonstrates that even using only radials from one station can substantially benefit state estimates for surface currents. Assimilation of FerryBox data based on an optimal interpolation approach using a Kalman filter with a stationary background covariance matrix derived from a preliminary model run which was validated against remote sensing and in situ data demonstrated the capabilities of the pre-operational system. Data assimilation significantly improved the performance of the model with respect to both SST and SSS and demonstrated a good skill not only in the vicinity of the Ferry track, but also over larger model areas. The examples provided in this study are considered as initial steps in establishing new coastal ocean products enhanced by the integrated COSYNA-observations and numerical modelling.

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Assessment of CODAR SeaSonde and WERA HF Radars in Mapping Surface Currents on the West Florida Shelf*

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-13-00107.1 ◽

2014 ◽

Vol 31 (6) ◽

pp. 1363-1382 ◽

Cited By ~ 54

Author(s):

Yonggang Liu ◽

Robert H. Weisberg ◽

Clifford R. Merz

Keyword(s):

Radial Velocity ◽

Long Range ◽

Hf Radar ◽

Integration Time ◽

Surface Currents ◽

West Florida Shelf ◽

The West ◽

Florida Shelf ◽

Radar Systems ◽

Effective Depth

Abstract Concurrently operated on the West Florida shelf for the purpose of observing surface currents are three long-range (4.9 MHz) Coastal Ocean Dynamics Applications Radar (CODAR) SeaSonde and two median-range (12.7 MHz) Wellen Radar (WERA) high-frequency (HF) radar systems. These HF radars overlook an array of moored acoustic Doppler current profilers (ADCPs), three of which are presently within the radar footprint. Analyzed herein are 3 months of simultaneous observations. Both the SeaSonde and WERA systems generally agree with the ADCPs to within root-mean-square differences (rmsd) for hourly radial velocity components of 5.1–9.2 and 3.8–6.5 cm s−1 for SeaSonde and WERA, respectively, and within rmsd for 36-h low-pass filtered radial velocity components of 2.8–6.0 and 2.2–4.3 cm s−1 for SeaSonde and WERA, respectively. The bearing offset and tidal and subtidal currents of total velocities are also assessed using the ADCP data. Despite differences in a variety of aspects between the direction-finding CODAR SeaSonde (long range, effective depth of 2.4 m, integration time of 4 h, and idealized antenna patterns) and the beam-forming WERA (median range, effective depth of 0.9 m, and integration time of 1 h), both HF radar systems demonstrated good surface current mapping capability. The differences between the velocities measured with the HF radar and the ADCP are sufficiently small in this low-energy shelf that much of these rmsd values may be accounted for by the expected measurement differences due to the horizontal, vertical, and temporal sampling differences of the ocean current observing systems used.

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Backtracking drifting objects using surface currents from high-frequency (HF) radar technology

Ocean Dynamics ◽

10.1007/s10236-012-0546-4 ◽

2012 ◽

Vol 62 (7) ◽

pp. 1073-1089 ◽

Cited By ~ 25

Author(s):

Ana Julia Abascal ◽

Sonia Castanedo ◽

Vicente Fernández ◽

Raúl Medina

Keyword(s):

High Frequency ◽

Hf Radar ◽

Surface Currents

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Remote sensing of surface currents and waves by the HF radar WERA

Seventh International Conference on Electronic Engineering in Oceanography - Technology Transfer from Research to Industry ◽

10.1049/cp:19970686 ◽

1997 ◽

Cited By ~ 11

Author(s):

K.-W. Gurgel

Keyword(s):

Remote Sensing ◽

Hf Radar ◽

Surface Currents

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Assimilation of HF radar surface currents to optimize forcing in the northwestern Mediterranean Sea

Nonlinear Processes in Geophysics ◽

10.5194/npg-21-659-2014 ◽

2014 ◽

Vol 21 (3) ◽

pp. 659-675 ◽

Cited By ~ 30

Author(s):

J. Marmain ◽

A. Molcard ◽

P. Forget ◽

A. Barth ◽

Y. Ourmières

Keyword(s):

Surface Wind ◽

Circulation Model ◽

Radar Data ◽

Hf Radar ◽

Open Boundary ◽

Coastal Current ◽

Surface Currents ◽

Data Set ◽

Radar Measurements ◽

Northwestern Mediterranean

Abstract. HF radar measurements are used to optimize surface wind forcing and baroclinic open boundary condition forcing in order to constrain model coastal surface currents. This method is applied to a northwestern Mediterranean (NWM) regional primitive equation model configuration. A new radar data set, provided by two radars deployed in the Toulon area (France), is used. To our knowledge, this is the first time that radar measurements of the NWM Sea are assimilated into a circulation model. Special attention has been paid to the improvement of the model coastal current in terms of speed and position. The data assimilation method uses an ensemble Kalman smoother to optimize forcing in order to improve the model trajectory. Twin experiments are initially performed to evaluate the method skills. Real measurements are then fed into the circulation model and significant improvements to the modeled surface currents, when compared to observations, are obtained.

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