Detection Of Weak Signals And Restore Of Events In Prospecting Seismology Basing On Chaos Theory

Recently, the theory of chaos has been applied gradually into many fields such as medicine,ecology, electronic countermeasures. It is calling attention of scientists to apply the chaostheory to detection of weak signals. It is one of the main characteristics of the chaos systemthat the system is sensitive greatly to the initial parameters of the function. The new detectionmethod based on the chaos theory is completely different from other kinds of detectionmethods. Basing on the great sensitivity of the chaotic system to the initial parameters of thefunction, the detected signal is put into the chaotic detection system, which could lead tochange the chaotic system's dynamic behavior greatly. as the change of the system's dynamicbehavior is aroused by the detected signal completely, the weak signal covered by the noisecould be detected out by the change of the phase plane trajectory of the chaotic system.Currently, the information detection technology based on chaos theory could be divided intothree forms below:(1) the background signals are known, reconstruct the phase space of the backgroundsignals by the received signals, then the forecast model can be gotten, the detected signalsubmerged in the chaotic background signals will be detected out by reducing the forecastedsignals from the received signals.(2) the detection of high accuracy is realized by using the chaos detection systemconstructed by chaos theory. Chaos detection is a method to pick up and deal with informationwith the system in the unstable, unbalanced and different states. It shows the changingcondition of the signal really, which has a high sensitivity and resolution.(3) let the dynamic behavior in some state, then let the detected signal be the complement ofthe special parameters of the chaos system, the detection of the weak signal disturbing bystrong noise will be realized basing on the phase change of the chaos system using the chaossystem's sensitivity to the change of parameters.Some achievements have been gotten in the aspect of detecting the amplitudes of harmonicand square waves under the background of strong noise using chaos detection system, the gateof SNR reached about -60dB, but the work is limited to detected the existence and theamplitude of the known signals. Actually there exist many harmonic waves with unknownfrequency, up to now there has been only one method called array of the oscillators based onthe frequency-locking theory to detect the frequency of signals;the steps of the method arecomplex. Aiming at a great lot of signals with unknown frequency in practice, we put up themethod using nonlinear chaotic dynamic system, namely to compute the frequency bycirculation detection technology, the relative error and absolute error of the computationresults are analyzed, the quantitative relation between parameters of the restoring force itemand nonlinear of the Duffing oscillator and the SNR detecting weak signals, which establishbasement for building a chaos system of good detection results. As for the problem ofdetecting the frequency and amplitude at the same time, namely ω ,A detection, a methodis put up, the theoretical analysis and simulation experiments are given.The accuracy and reliability of the seismic detection is affected directly by theSNR of the seismic data. It is one of the important items of resource explorationand seismic detection to enhance the SNR of seismic data. The characteristic of thechaotic system, namely immunity to noise, is used to develop the function of thechaos oscillator to detect periodic signal and get the condition in which the methodcould be applied in the seismic detection. The condition classify and descriptionmethod of pseudo period of seismic prospecting signals are analyzed;try to dealwith the channel group chosen from the seismic data corresponding to the relevantstratum;use the chaos theory of the nonlinear subject to develop the chaososcillator pick-up technology of the seismic prospecting signal. Provide technicalbasement for the high resolution seismic prospecting and the reconstruction of theinner structure of the earth. In the seismic prospecting, the application conditionsof the chaotic oscillator contain how to build the chaotic system and the signal tobe dealt with should be of some periodicity. Firstly, the reflected signals of thesame reflected plane are of some similarity without considering the noise. Basingon the similarity the steps to move the seismic waves to the same time axis can bedone, then the system chosen could be used to detect the seismic signal. Incondition, the strong noise should be considered;apparently the average power ofthe noise is limit, the gate value of the SNR below which the chaotic system canbe used could be gotten by formal experiments;at the time of application, the gatevalue will descend greatly. At the beginning the basic theory of applying the chaostheory to detecting weak signals is studied, three kinds of methods by which theseismic record of common resource is detected are built, the chaotic systemdetection is done to detect the aberrant Ricker wavelets as an example. At last, thedetection ability of the chaotic system detecting the detected signals in the seismicdata is discussed. The phase state of the chaos oscillator system used to detectsignals will be affected by many aspects, such as the construction of the quasiperiodic signals, the strength of the noise;for the same kind of phase events, themore the aberration is, the lower the SNR of the chaos oscillator system is, for thesame aberration, the closer the scanning velocity get to the right velocity, thehigher the SNR of the detection is;the scanning velocity will show asymmetricalwhich make the chaos oscillator system go into large scale periodic phase state;inthe condition that the system is in the large scale periodic phase state, the ratio ofthe coefficients of the phase events has a large range of variation.