Robust Source Localization Based On Difference Frequency In Mid- And High- Frequency Situation

Conventional matched field processing is an important method for underwater source lo-calization.As a model-based method,the performance of conventional matched field process-ing largely depends on the accuracy of model parameters.In a complex oceanic waveguide environment,environmental parameters and system parameters vary temporally and spatially.The mismatch between model parameters and actual parameters degrades the performance of conventional matched field processing.The phase fluctuation of the mid- and high-frequency signal varies greatly with waveguide parameters.Therefore,it is difficult to accurately locate the mid- and high-frequency source using conventional matched field processing in an uncertain environment.Worthmann et al.proposed the frequency difference matched field processing,which can downshift the processing frequency and therefore perform source localization in the low frequency domain.The frequency difference matched field processing realizes source lo-calization by matching the frequency difference signal and the low frequency replicas.Due to the effect of seabed attenuation and signal multipath,the frequency difference signal is in-trinsically different from the low frequency signal.Source frequency and the receiving array aperture can influence this difference and therefore influence the performance of frequency dif-ference matched field processing.In this thesis,a tolerant source localization method for mid-and high-frequency source is proposed.Based on the frequency difference matched field processing,we first discuss the influence of the source frequency and the receiving array aperture on the source localization performance.The modal amplitudes of the frequency difference signal and low frequency signal are inves-tigated.The results show that the increase of the source frequency and the decrease of the re-ceiving array aperture can increase the difference between the two signals,which degrades the performance of source localization.In view of the intrinsic difference between the two signals,we joint the matched beam processing with the frequency difference processing,and propose the frequency difference matched beam processing.The difference frequency matched beam processing transforms the frequency difference signal and the low frequency replicas into beam domain before matching the difference frequency signal and the low frequency replicas.With the help of matched beam processing,spatial filtering is realized to restrict the reflected beam from the seabed and reduce the influence of the frequency selective attenuation of the seabed.Next,we compare the source localization performance of conventional matched field pro-cessing and frequency difference matched beam processing in uncertain environment.We show that the frequency difference matched beam processing is much more tolerant to mismatch than conventional matched field processing.The mismatch types include environmental mismatch and the sensor position mismatch.In the environmental mismatch analysis,the impact of mis-match on frequency difference signals and high frequency signals are compared from the per-spective of modal amplitude.In the sensor position mismatch analysis,we establish a three-dimensional sensor position error model.The influence of the sensor position mismatch is analyzed from the perspective of ray propagation time error.Finally,experimental data from the sea experiment are processed to validate the frequency difference matched beam processing.The localization result is compared with the conventional matched field processing result.It proves that the source localization errors of the difference frequency matched beam processing is smaller than that of the conventional matched field pro-cessing when the experimental parameters are uncertain.