Abstract
We have made observations of X-band radar sea clutter from the sea surface and sea-surface state in the Uraga Suido Traffic Route, which is used by ships entering and leaving Tokyo Bay, and the nearby Daini Kaiho Sea Fortress. We estimated the distributions of reflected amplitudes due to sea clutter using models that assume Weibull, Log-Weibull, Log-normal, and K-distributions. We then compared the results of estimating these distributions with sea-surface state data to investigate the effects of changes in the sea-surface state on the statistical characteristics of sea clutter. As a result, we showed that observed sub-ranges not containing a target conformed better to the Weibull distribution regardless of Significant Wave Height (SWH). Further, sub-ranges conforming to the Log-Weibull or Log-normal distribution in areas contained a target when the SWH was large, and as SWH decreases, sub-ranges conforming to a Log-normal. We also showed that for observed sub-ranges not containing a target, the shape parameter, c, of both Weibull and Log-Weibull distribution correlated with SWH. The correlation between wave period and shape parameters of Weibull and Log-Weibull distribution showed a weak correlation.
Highlights
As electronics technology has advanced, equipment supporting marine navigation has become computerized, and highly automated vessels have begun to appear
This tendency is striking when the Significant Wave Height (SWH) is low. This shows that, regardless of whether the sea clutter reflected amplitude distribution is a Weibull distribution or not, the presence of the target prevents adequate estimation of the distribution. This result shows that threshold-detection Constant False Alarm Rate (CFAR) cannot be done accurately, because it sets an amplitude threshold based on the results of estimating the distribution and attempts to detects targets while maintaining a constant false-alarm rate [2,3]
In order to investigate how changes in the state of the sea surface affect the statistical characteristics of sea clutter, we analyzed the correlation between the SWH and wave period and the parameters calculated from the distribution estimation, for the 65 observation data sets under (a) study and the range with no reflective objects other than waves
Summary
As electronics technology has advanced, equipment supporting marine navigation has become computerized, and highly automated vessels have begun to appear. Sea charts are essential for safe navigation, and Electronic Chart Display and Information Systems (ECDIS) [1] have been realized, able to display radar data overlaid on the charts. This has contributed to radar becoming essential for safe navigation of sea vessels. The signal received by radar contains reflections from various objects besides the intended targets, such as land, clouds, rain, and the sea surface. All such undesired reflections from non-targets are referred to as clutter.
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