The analysis and digital signal processing of NOAA's surface current mapping system

Leise, James A.

doi:10.1109/joe.1984.1145604

Cited by 33 publications

(11 citation statements)

References 11 publications

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“…The minimum in HK kk for u , corresponding to the maximum expected observation error, is adjacent to the coast where the angle of intersection of the radial beams from the CODAR transmitters are almost parallel. This is consistent with the expected limitations of the CODAR system in resolving both components of velocity [ Lipa and Barrick , 1983; Leise , 1984].…”

Section: Assimilation Of Hf Radar Datasupporting

confidence: 88%

Assimilation of surface velocity data into a primitive equation coastal ocean model

et al. 2002

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[1] A data assimilation system (DAS) of the wind-driven, mesoscale shelf circulation off the Oregon coast is developed. The DAS assimilates low-pass filtered surface velocity measurements, obtained from land-based high-frequency coastal radar arrays, into a primitive equation coastal ocean model using a sequential optimal interpolation scheme. Inhomogeneous and anisotropic estimates of the forecast error covariances required for the assimilation are assumed to be proportional to typical cross-correlations between modeled variables. These correlations are estimated from an ensemble of model simulations for 18 different summers. Similarly, the observation error covariances are assumed to be proportional to the actual covariances of the observations. A timedistributed averaging procedure (TDAP) that effectively low-pass filters the model forecast for comparison with the observations and introduces the corrections to the model state gradually over time is used in order to overcome problems of data compatibility and initialization. The correlations between direct subsurface current measurements and subsurface currents obtained from model-only and assimilation experiments for the summer of 1998 are 0.42 and 0.78, respectively, demonstrating the effectiveness of the DAS. Our estimates of the error covariances are shown to be appropriate through a series of objective statistical tests. Analysis of the term balances of the model equations show that the dominant modeled dynamical balances are preserved by the DAS and that uncertainties in the spatial variability of the wind forcing are likely to be one source of model error. By varying the relative magnitudes of the estimated forecast and observation error covariances the DAS is shown to be most effective when approximately 80% of the analysis is made up of the model solution.

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Section: Assimilation Of Hf Radar Datasupporting

confidence: 88%

Assimilation of surface velocity data into a primitive equation coastal ocean model

et al. 2002

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“…The asymmetry is thus a feature of individual Doppler spectra, rather than a result of modulation induced power variations from one spectrum to the next and must be accounted for when velocities are estimated from the Doppler spectra. The usual practice at HF has been to estimate Doppler spectrum peak positions from the centroid of a restricted portion of the Doppler spectrum [Leise, 1984].…”

Section: Resultsmentioning

confidence: 99%

Ocean surface currents obtained from microwave sea‐echo Doppler spectra

McGregor¹,

Poulter²,

Smith³

1997

J. Geophys. Res.

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Abstract. Ocean currents may be determined from the positions of Bragg peaks in Doppler spectra of radar echoes from the sea surface. In this paper the applicability of this technique at microwave frequencies is investigated. Advantages of high range resolution and sensitivity to currents within centimeters of the ocean surface ensue from the short Bragg wavelength at microwave frequencies. A disadvantage is that the technique is restricted to low wind speed, fetch-limited sea conditions for which individual Bragg peaks are resolvable in the Doppler spectra. Experiments at low grazing angles with an $ band (3 GHz) Frequency-modulated interrupted continuous wave radar show that in these conditions surface drift currents can be measured to better than 4-2 cm s -1 accuracy over a large range of azimuth angles with respect to the wind direction. In conditions under which the Bragg peaks are not resolvable, currents may be measured by using local wind direction measurements to correct the mean Doppler velocity for the relative contributions of the advancing and receding Bragg peaks. Experiments revealed that the accuracy of current measurements obtained in this manner was better than ß 5 cm s -1. The technique was applied to the mapping of tidal currents in an inlet, demonstrating the significant potential of the radar measurements for nearshore and coastal dynamics studies.

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“…Power spectra were computed for each time series, and each frequency estimate (near the main Bragg peaks) provided a single radial surface current estimate. The angular position within the appropriate annulus was estimated from the phase difference measured across the receive antenna using the Liese (1984) algorithm. This is the weakest part of the radar system.…”

Section: Field Programmentioning

confidence: 99%

The effects of short space and time scale current variability on the predictability of passive ichthyoplankton distributions: an analysis based on HF radar observations

Helbig

Pepin²

2002

Fisheries Oceanography

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The importance of small scale variations in currents on the predictability of spatial distributions of fish eggs is investigated using dense observations of surface currents. The currents were measured with HF radar and used to drive an advection–diffusion model of ichthyoplankton concentration. We first demonstrate that the model produces acceptable agreement with observed egg fields. We then use the predicted egg fields as a basis for comparison with model runs made with currents subsampled in space and filtered in time. Significant error was found for spatial sampling intervals as small as 3 km, even though most of the variance in the currents occurred at much longer length scales. This was primarily due to the loss of the rich small scale variability in horizontal divergence. Nevertheless, most of the error is due to the misfit in the egg fields at larger length scales; that is, small scale forcing is necessary in this system for the larger scale features to be reproduced. This study thus suggests that considerable caution should be exercised before assuming that circulation models, even very sophisticated and detailed ones, capture enough of the variability of marine systems to make accurate forecasts of plankton distributions.

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The analysis and digital signal processing of NOAA's surface current mapping system

Abstract: Abstract

Cited by 33 publications

References 11 publications

Assimilation of surface velocity data into a primitive equation coastal ocean model

Assimilation of surface velocity data into a primitive equation coastal ocean model

Ocean surface currents obtained from microwave sea‐echo Doppler spectra

The effects of short space and time scale current variability on the predictability of passive ichthyoplankton distributions: an analysis based on HF radar observations

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