Statistical characteristics of sea clutter and its identification with the CINRAD

Radar echo from sea clutter is an unpredictable event which often contaminates the precipitation measurement and other radar products in coastal areas. According to the sea clutter observed by SA Doppler radars in Fuzhou, and Wenzhou, it is divided into two kinds by the time when it appears. The first kind of sea clutter with strong strength mainly appears before and after a precipitation process during the period without typhoon. The second kind of sea clutter whose strength is generally weak and uniform only appears close to sea areas near the radar position during a typhoon. The reflectivity, radial velocity, spectrum width of velocity, and their spatial variations for sea clutter which are different from the corresponding precipitation in terms of echo are examined to determine the membership functions based on the sea clutter detection algorithm (SCDA). For the first kind of sea clutter, considering its rare overlap with precipitation echo, the algorithm is based on the fuzzy logic and the echo piece-divizing using SCIT. Firstly, the pre-processing criteria can be used to determine when sea clutter is likely to take place so that sea clutter detection algorithm can be applied. Secondly, echoes are combined into pieces using SCIT, and if the area of an echo piece is more than 100 km2 the echo piece would be given an attribute value. The echoes would be calculated with an algorithm based on the fuzzy logical if the attribute value of the echo piece meets suitable conditions and the area of the echo piece is less than 100 km2. Inspired by Liu's two-step ground clutter detection algorithm, the author improved Liu's approach to identify the dynamic threshold. For the second kind of sea clutter, the algorithm is based on the fuzzy logic and the improved two-step approach. The analyses results show that most of sea clutters are detected effectively by the two kinds of identification method. The method of echo piece-divizing using SCIT and the improved two-step approach have obviously reduced the possibility of misidentifying precipitation echoes as sea clutters.