Floating Weak Target Detection In Low Signal-to-Clutter Ratio Case

The detection of floating targets in the sea surface has always been a problem highly concerned by related experts,and this problem is significant in both military and civilian areas.The radar transmitting signals can be reflected by the sea surface to produce the sea clutter,with the characteristics of non-Gaussian,non-uniform,and non-stationary.In low signal-to-clutter ratio(SCR)cases,the useful target echo signals are always submerged in irregular sea clutter environments,which are difficult to be detected successfully.The detection probabilities of traditional detection methods that are based on signals' amplitude distribution deteriorate rapidly in low SCR cases.Therefore,it is urgently needed to develop detection methods,improving detection probabilities of weak targets in low SCR cases.In this thesis,firstly we analyze the amplitude distribution characteristics,fractal properties and time-frequency characteristics of the sea clutter in high-resolution radar.And then,based on the IPIX radar database,we test the detection performance of the commonly used CFAR detectors and ANMF detectors for the floating weak target in the case of low SCR.The test results show that,when the false alarm rate(FAR)is fixed on 0.1%and the SCR of the radar echo is lower than 5dB,the detection probabilities of commonly-used detectors are lower than 50%,which cannot meet the needs of practical application.Secondly,the existing weak target detecting techniques usually process the radar echo s entire Doppler spectrum.But in fact,the sea clutter often distributes throughout the whole normalized spectrum while the target returns spectrum mainly converges in a limited range.Therefore,we present a scheme to filter the radar echo by a specific band-pass filter to retain the useful target return signals and suppress the sea clutter,improving the SCR of radar echo,and thus increasing the detection probability of CFAR.Mathematical analysis proves that the hidden target return signals are more likely to be detected after filtering than that in the original radar echo under certain FAR settings.Finally,based on the analysis mentioned above,this thesis propose a sub-band CFAR detector structure to decompose the radar echo in frequency domain,keeping the target-containing spectrum regions and suppressing the clutter-only regions to further improve the detection probabilities.In particular,we design a band-pass filter bank,the passbands of which can fully cover the whole normalized frequency domain,to decompose the received signal into several sub-bands.Each sub-signal sequence is detected by a CFAR detector separately.At last,the CFAR detection results in all sub-bands are fed into a multi-channel joint decision module,and the overall decision result is obtained,that is,whether there are target return signals in the radar echo.We use the realistic IPIX radar database to test the detection performance of the proposed sub-band CFAR detector.Experimental results show that,compared with general CFAR and ANMF detectors,the proposed sub-band CFAR detector has better detection probabilities in lower FAR and low SCR cases.In conclusion,we analyze the problem of target signal detection in sea clutter environments,and a sub-band CFAR detector structure is proposed to improve detection probabilities of the floating weak target in low SCR cases.