Significant wave height estimation from nautical radar data sets

Nautical radars scan the water surface at grazing incidence with HH polarization. Under these conditions the backscatter is mainly due to multipath scattering effects on small scale breaking waves. The pattern of returned electromagnetic power is modulated by the larger oceanic structures, such as swell and wind sea waves. The final pattern shown on the radar screen is commonly known for navigation purposes as sea clutter. Unlike other remote sensing systems, as Synthetic Aperture Radars (SAR) on board satellites or airplanes, navigation radar images cover smaller areas, but this sensor is able to obtain short-term temporal information about sea states using consecutive rotations of the antenna. Hence, the spatial and temporal structure of sea states can be known. Each measurement consists of a temporal sequence of consecutive radar images, where the sampling rates in space and time depend on each marine radar features. The temporal resolution sampling rate is given by the antenna revolution period and the spatial resolution is related to the effective antenna aperture and the radar pulse length. The nautical radar data are directly sampled from the radar video signal by using a Wave Monitoring System (WaMoS II) developed by GKSS research centre. This work deals with an improved method to estimate the significant wave height from sea clutter image time series. This method is based on similar techniques developed for SAR systems. The basic idea is the significant wave height is linearly dependent on the root square of the signal-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. (orig.)Available from TIB Hannover: RA 3251(98/E/28) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Relative proton and γ widths of astrophysically important states in 30^{30}S studied in the β-delayed decay of 31^{31}Ar

Resonances just above the proton threshold in 30S affect the 29P(p, γ )30S reaction under astrophysical conditions. The (p,γ )-reaction rate is currently determined indirectly and depends on the properties of the relevant resonances. We present here a method for finding the ratio between the proton and γ partial widths of resonances in 30S. The widths are determined from the β2p- and βpγ -decay of 31Ar, which is produced at the ISOLDE radioactive ion beam facility at the European research organization CERN. Experimental limits on the ratio between the proton and γ partial widths for astrophysical relevant levels in 30S have been found for the first time. A level at 4689.2(24) keV is identified in the γ spectrum, and an upper limit on the p/ γ ratio of 0.26 (95% C.L.) is found. In the two-proton spectrum two levels at 5227(3) keV and 5847(4) keV are identified. These levels were previously seen to γ decay and upper limits on the γ/ p ratio of 0.5 and 9, respectively, (95% C.L.) are found, where the latter differs from previous calculations