IMOS - ACORN - Direction finding ocean radar system (Seasonde)

沿海海面雷达是一种陆基技术，它利用粗糙海面的散射来获得因海洋动力学而产生多普勒频移的回波。 已经表明（Crombie，1955），散射主要是无线电波和海洋表面重力波之间的布拉格相互作用，其在相同方向上传播，并且具有无线电波的一半波长。 这种布拉格相互作用在回波频谱中给出了两条强的一阶线;一条来自径向远离站移动的共振重力波，另一条来自朝向站移动的共振重力波。<br /> <br /> 测向系统通过比较交叉环形接收天线上的幅度和相位信号来确定源点的方位角方向。测向计算是在指定距离的多普勒频移谱上进行的，该距离包括来自所有方位角的返回回波。 这意味着频谱被扩展，并且来自一个方向的二阶回波被来自其他方向的一阶回波淹没。 因此，使用二阶回波的参数提取在常规基础上是不可能的。 通过分析一阶回波幅度的全方位扩展，产生每个雷达站所在位置的方向波谱，并通过取正布拉格回波和负布拉格回波的比率，得出网格点上的风向。<br /> <br /> SeaSonde高频海洋雷达站用于西澳大利亚州的Turquoise海岸（Seabird和塞万提斯）和南澳州的Bonney海岸（诺拉Creina和Blackfellows Cave）。

Coastal ocean surface radar is a land-based technique which uses scattering from the rough sea surface to obtain echoes which are Doppler shifted by the dynamics of the sea. It has been shown (Crombie, 1955) that the scatter is predominantly a Bragg interaction between the radio wave and the sea surface gravity wave that is propagating in the same direction and with half the wavelength of the radio wave. This Bragg interaction gives two strong first-order lines in the echo spectrum; one from the resonant gravity wave moving radially away from the station, and one from the resonant gravity wave moving towards the station.<br /> <br /> Direction-finding systems determine the azimuthal direction of a source point by comparing amplitude and phase signals on crossed loop receive antennas. The direction finding calculation is done on Doppler shift spectra for a specified range which includes return echoes from all azimuths. This means that the spectra are spread and second-order echoes from one direction are swamped by the first-order echoes from other directions. Consequently, parameter extraction using second-order echoes is not possible on a routine basis. Directional wave spectra at the location of each radar station are produced by analysing the full azimuthal spread of first-order echo amplitudes, and wind directions are derived across the grid points by taking the ratio of the positive and negative Bragg echoes.<br /> <br /> SeaSonde HF ocean radar stations are used on the Turquoise Coast (Seabird and Cervantes), Western Australia, and on the Bonney Coast (Nora Creina and Blackfellows Cave), South Australia.