A method to estimate sea surface elevation maps from marine radar image sequences is presented. This method is the extension of an existing inverse modeling technique to derive wave spectra from marine radar images, which assumes linear wave theory with temporal stationarity and spatial homogeneity of the observed sea surface elevation. The proposed technique to estimate wave elevation maps takes into account a modulation transfer function (MTF), which describes the radar imaging mechanisms at grazing incidence and horizontal polarization. This MTF is investigated and empirically determined by wave measurements and numerical simulations. The numerical simulations show that shadowing is the dominant effect in the radar imaging mechanism at grazing incidence and horizontal polarization. Further comparisons of wave spectra, as well as comparisons of the wave height probability distributions obtained by the wave elevation maps and the corresponding buoy measurements with the theoretical Rayleigh distribution, confirm the applicability of the proposed method.

This work analyses the structure of the different contributions to the image spectrum derived by the three-dimensional Fourier decomposition of sea clutter time series measured by ordinary X-band marine radars. The goal of this investigation is to derive a method to estimate the significant wave height of the ocean wave fields imaged by the radar. The proposed method is an extension of a technique developed for the analysis of ocean wave fields by using synthetic aperture radar systems. The basic idea behind this method is that the significant wave height is linearly dependent on the square root of the signal-to-noise ratio, where the signal is assumed as the radar analysis estimation of the wave spectral energy and the noise is computed as the energy due to the sea surface roughness, which is closely related to the speckle of the radar image. The proposed method to estimate wave heights is validated using data sets of sea clutter images measured by a marine radar and significant wave heights derived from measurements taken by a buoy used as reference sensor.

The objective of the EuroROSE (European Radar Ocean Sensing) project was to combine area covering ground-based remote-sensed wave and current data with high-resolution numerical forecast models to provide nowcasts and forecasts for coastal marine operators. Two experiments to test and to demonstrate the system took place: one on the coast of Norway, north of Bergen in March 2000 and the second on the north coast of Spain at Gijon in October -November 2000. Qualitative and quantitative intercomparisons of the wave measurements and wave model products from these experiments are presented. These include measurements using the Wellen Radar (WERA) high-frequency (HF) radar, the WaMoS (Wave Monitoring System) Xband radar, a directional Waverider and output from the WAM wave model. Comparisons are made of the full directional spectra and of various derived parameters. This is the first-ever intercomparison between HF and X-band radar wave measurements and between either of these and WAM. It has provided a data set covering a much wider range of storm and swell conditions than had been available previously for radar wave-measurement validation purposes and has clarified a number of limitations of the radars as well as providing a lot of very useful radar wave data for future model-validation applications. The intercomparison has led to improvements in the data quality control procedures of both WaMoS and WERA. The two radar sytems measured significant wave height with mean biases of 3% and 6%, respectively, and mean direction differences of less than 2j in both cases. Limitations in the WAM model implementation are also discussed. D

New analytical, circular eddy solutions of the nonlinear, reduced-gravity, shallow-water equations in a rotating system are presented. While previous analytical solutions were limited to the description of pulsons, which are oscillating, frontal, warm-core eddies with paraboloidic shape and linear velocity components, the new solutions describe more general radial structures of eddy shape and azimuthal velocity. In particular, the new solutions, which contain as a subset the circular pulson solution, also allow for the description of circular, frontal, warmcore eddies with small azimuthal velocities at their periphery and/or with motionless cores, which are frequently observed characteristics of warm-core eddies in the World Ocean.

The Wave Monitoring System WaMoS II was developed for real time measurements of directional ocean waves spectra to monitor the sea state from fixed platforms in deep water or coastal areas as well as from moving vessels. The system is based on a standard marine X-Band radar used for navigation and ship traffic control. WaMoS II digitises the analogous radar signal and analyses the sea clutter information to obtain directional wave spectra from the sea surface in real time even under harsh weather conditions and during night. Spectral sea state parameters such as significant wave height, peak wave period and peak wave direction both for wind sea and swell are derived. Within the EU funded project ‘MaxWave’ and the German project ‘SinSee’ new algorithms were developed to determine sea surface elevation maps from radar images which are used to investigate the spatial and temporal evolution of single waves simultaneously. In this paper a short overview describes the calculation of surface elevation maps and the detection of individual waves. Considering two case studies, the results of spatial single wave detection and corresponding temporal single wave properties are compared and discussed. Individual wave parameters derived from radar images are compared to individual waves measured by a buoy. An application of the method to characterise extreme sea states is discussed.