There is a lack of published experimental forward-scattering radar sea clutter data at very low (almost zero) grazing angle over the sea. This data is necessary to provide a fundamental understanding of the operating environment for the development of forward-scatter radar systems for maritime applications. Experimental data has therefore been recorded at frequencies of 7.5 GHz, 9.3 GHz, 24 GHz, and 37.5GHz using Forward Scatter Radar with static, medium gain antennas for low sea states 1-3. Results of clutter power spectral density measurements are presented and conclusions drawn from the results.

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Abstract. The results of laboratory experiments on rock sample destruction and the observation data obtained from several series of the hydro-acoustic observations in which the researchers succeeded to register the signals in the critical stage of the earthquake (EQ) preparation were compared. According to theoretical research (Alekseev et al., 2001) two distinct dilatant zones occur in the EQ preparation stage. The first one is located around the source and the second one represents the near-surface dilatant zone. Only high-frequency seismic-acoustic signals (SAS) radiated from the near-surface dilatant zone do not attenuate completely on the passage through a solid medium. Parameters of the SAS such as the source depth under the ocean floor, frequency maximum and the signal power level were estimated. It was shown that the critical stage of the EQ preparation continues several tens hours and this process has a hierarchical nature. At first the micro-ruptures are formed over a large area. Then the high frequency radiation begins to decrease, the SAS emission area begins to shrink and the micro-earthquakes occur in the area surrounding the epicenter. The obtained results are in close agreement with the theoretical conception about the evolution of the SAS in the surface dilatant zone and with the results of laboratory experiments.

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