Tests of remote skywave measurement of ocean surface conditions

Ahearn, J. L.; Curley, S. R.; Headrick, J. M.; Trizna, D.B.

doi:10.1109/proc.1974.9508

Cited by 37 publications

(9 citation statements)

References 2 publications

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“…Various investigators (Long and Trizna 1973;Tyler et al 1974;Stewart and Barnum 1975) suggested methods for inferring dominant wind/wave directions from first-order sea echo by postulating models for ocean-wave directionality about the mean wind direction. Algorithms for extracting wind speed were also postulated; Stewart and Barnum (1975) related the wind speed to the breadth of the dominant first-order line at a level 10 dB below the maximum, while Ahearn et al (1974) suggested the ratio of the first-order peaks to the continuum at zero Doppler shift as a wind speed parameter.…”

Section: Introductionmentioning

confidence: 99%

Scattering of HF Radio Waves from the Sea: A Review of the Theory Based upon a Simplified Model

McGann¹,

Robson²

1991

Aust. J. Phys.

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A simplified, physically intuitive model of diffuse scattering of radio waves from a rough surface is used to present a self-contained derivation of first- and second-order cross sections, essentially in agreement with the standard expressions. Incoherent addition of the second-order contributions (electromagnetic and hydrodynamic) leads to a cross section which is slightly different from the more rigorously derived cross sections of Barrick (1972b) and Johnstone (1975). A surface current v has been incorporated in this model, with the main change to the cross section being a frequency shift of the entire spectrum by an amount Llw = -2ko . v.

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Section: Introductionmentioning

confidence: 99%

Scattering of HF Radio Waves from the Sea: A Review of the Theory Based upon a Simplified Model

McGann¹,

Robson²

1991

Aust. J. Phys.

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“…Since these ocean wave components respond rapidly to local wind excitation (characteristic response times of from minutes to a few hours) and also decay rapidly when the wind been essentially empirical, involving best fit relationships between various second-order parameters of the Doppler spectrum and winds measured in the scattering area, the assumption being that the particular spectral parameters chosen best represent, in some gross way, the 'state of development' of the sea, and hence the magnitude of the exciting wind. Parameters employed include (1) the decibel ratio of first-order to second-order spectral peaks [Barrick et al, 1974], (2) the decibel ratio of first-order peak to second-order continuum at zero Doppler frequency [Ahearn et al, 1974], and (3) breadth B of the principal first-order peak at a level 10 dB below the maximum [Stewart and Barnum, 1975]. Features of these various approaches are discussed in more detail by Sandham [1980] and Dexter [1981].…”

Section: Introductionmentioning

confidence: 99%

Surface wind speed extraction from HF sky wave radar Doppler spectra

Dexter¹,

Theodoridis²

1982

Radio Science

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The ability to obtain sea surface wind speeds from HF sky wave radar backscatter spectra is important if such a radar is to make a meaningful contribution to a meteorological or oceanographic observation network. Since the radar measures wave parameters only, wind vectors must be inferred from the wave measurements in the light of what knowledge we have concerning the processes of wave generation. Previous attempts to extract wind speeds have proved unsatisfactory for a variety of reasons. We present here a new technique to enable such a derivation, which uses sea state parameters obtained with an appropriate inversion technique, together with relevant empirical/theoretical relationships on the growth of a wind-generated sea. The procedure is illustrated with a Doppler spectrum obtained during the JASIN experiment, and some comparisons made with other JASIN surface data.Paper number IS 1924. 0048-6604/82/0506-1924508.00 ceases, this has both advantages and disadvantages for wind vector derivation: (1) It is advantageous for determining wind direction, since this direction will be virtually coincident with the mean wave propagation direction, which may be deduced (in principle) directly from first-order features of the backscatter spectrum.(2) It is disadvantageous for deriving wind speeds, since these wave components will saturate rapidly and thus offer no information on the magnitude of the excitation. Recourse must then be made to second-order Doppler spectral features [Barrick, 1972; Johnstone, 1975], with a variety of attendant difficulties. Some of these difficulties are discussed below, in conjunction with the presentation of a technique for inferring wind speeds, which forms the basis of this paper. Various techniques are currently available for extracting mean wave (and wind) direction from the first-order Doppler spectrum [e.g., Long and Trizna, 1973; Stewart and Barnum, 1975; Sandham, 1980]. All require essentially the ratio of the two first-order Bragg lines, combined with an assumed functional form for the directional distribution of the resonant ocean wave components about the mean. Although details of the techniques differ, the principle is now well established. The chief uncertainty lies in the dependence of most assumed wave directional distributions on wind speed, implying a dependence of measured mean wind direction on some prior knowledge of wind speed. Other extraction techniques for wind speeds have 643 644 DEXTERAND THEODORIDIS WIND SPEED EXTRACTION FROM RADAR SPECTRA 645

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“…While it seems likely (Crombie 1971;Barrick 1972b) that ionospheric Doppler shifts will normally be manifested as displacements of the first-order peak from its theoretical position, these must inevitably lead to the broadening of the Bragg peak and to uncertainties in the position and magnitude of the secondary spectral peaks as longer periods of data are included in deriving each spectrum. Attempts by Long and Trizna (1973) and Ahearn et al (1974) to overcome this problem have involved the use only of the two (positive and negative Doppler frequencies) first-order Bragg peaks and the neglect of higher-order details. This approach relies on empirical relationships which are themselves subject to considerable uncertainty, particularly for complex sea surface conditions.…”

Section: Theory and Interpretationmentioning

confidence: 99%

A Long-range Ocean Radar for Ocean Surface Studies using Backscatter Via the Ionosphere

Ward¹,

Dexter²

1976

Aust. J. Phys.

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An HF Doppler radar, designed for use at long range via an ionospheric propagation mode, has been developed primarily for the determination of wave states over large ocean areas. The operating frequency is 21 �840. MHz, and the array is physically rotatable through a full 3600 of azimuth, thus allowing for great flexibility in the choice of target area. The experimental technique utilizes a well-known resonance interaction mechanism for electromagnetic waves backscattered from a moving sea wave surface to derive sea state parameters in the scattering region for input to oceanographic and meteorological synoptic data networks. An ultimate angular resolution of less than 10 of azimuth, coupled with high operational flexibility, suggest possible utilization of the aerial array for tracking and interrogating free-floating ocean buoys, tracking radio noise associated with tropical cyclones and investigating aspects of ionospheric dynamics.

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Tests of remote skywave measurement of ocean surface conditions

Cited by 37 publications

References 2 publications

Scattering of HF Radio Waves from the Sea: A Review of the Theory Based upon a Simplified Model

Scattering of HF Radio Waves from the Sea: A Review of the Theory Based upon a Simplified Model

Surface wind speed extraction from HF sky wave radar Doppler spectra

A Long-range Ocean Radar for Ocean Surface Studies using Backscatter Via the Ionosphere

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