| Life detection radar transmits electromagnetic waves to penetrate walls and other obstacles,and realizes the life signal detection and human range estimation by receiving and analyzing target echoes behind obstacles.Compared with the life detectors utilizing optical imaging,infrared ray,audio and acoustic waves,the life detection radar shows the great advantages of immunity to temperature,noise and visibility in severe weather conditions.So it is widely used in judicial investigation,post-disaster emergency rescue,and defence against terrorism.In practical application,the accurate extraction of life signal is particularly difficult in the low signal to noise and clutter ratio(SNCR)environment.This is because radar echoes contain not only life signal,but also static clutter,linear trend,noise,non-static clutter,and external electromagnetic interference,which put forward higher requirements for radar probe signal and life detection algorithm.Random signal radar uses the random code signal including chaotic signal or noise signal as the detection signal,obtains the range information through correlation ranging(CR)technology,and extracts the breathing frequency of human target by range accumulation in slow time,which can realize the high range resolution in centimeters and strong anti-electromagnetic interference(anti-EMI)measurement.In addition,the variational mode decomposition(VMD)can decompose the original complex signals into intrinsic modal functions reflecting their local characteristics at different time scales,which has solid mathematical theory support.Therefore,Boolean-chaos signal and wideband noise signal are used as the detection signal in this thesis.Based on the correlation ranging,the improved VMD is used to remove the static clutter,linear trend and noise,and the constant false alarm rate(CFAR)is utilized to eliminate the non-static clutter.The life detection method of wideband random signal radar in the low SNCR environment is proposed and experimentally verified.The main research work is summarized as follows:(1)The research background and significance of life detection radar were introduced.The advantages and disadvantages of different types of life detection radar were summarized.The research status of existing life detection algorithm were analyzed,and the application of random signal and VMD method to life detection in the low SNCR environment was proposed.(2)The basic theory of life detection by the random signal radar was introduced.The formation reason of low SNCR environment was analyzed,and the existing noise and clutter suppression algorithms were introduced in detail.And then the mathematical theory and realization process of VMD method were emphasized.(3)A life detection method of wideband chaotic radar in the low SNCR environment was proposed and experimentally verified.The Boolean-chaos signal was used as the probe signal,and life detection in the low SNCR environment was realized based on CR-VMD-CFAR life detection algorithm.Experimental results show that the proposed method can simultaneously estimate the breathing frequencies and ranges of multiple human targets in the low SNCR environment,which contains penetrating four obstacles,human target with different positing positions,and five human targets behind the wall.In addition,benefiting from the broadband characteristic of Boolean-chaos signal,the range resolution can reach 15 cm.(4)The applicability of life detection algorithm based on CR-VMD-CFAR for wideband noise radar in the low SNCR environment was experimentally studied.Compared with chaotic radar,the noise radar has the larger bandwidth and is more conducive to accurately distinguish multiple human targets with small spacing.The experimental results demonstrate that the noise radar can realize life detection in the low SNCR environment,and compared with the existing noise and clutter suppression algorithms,the life detection algorithm is more robust in the low SNCR environment. |
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