Research On The Method Of Extracting Sunspot Umbra Oscillations

With the rapid development of information science and computer science,signal processing technology and digital image processing technology have been applied to various fields.The former mainly uses computer technology or special signal processing equipments to process signals,so as to get useful informations such as the frequency,power,phase and other information in the signal.The latter is a process o f using a computer to deal,which concerts image information into digital information.It mainly uses some technology to extract attributes.They both provide important technical foundation for astronomy.Sunspot is the most significant sign of the active area.It is composed of umbr a and penumbra.There is umbral oscillation in the umbra,its form is similar to the water ripple jitter.Umbral oscillation is a general term of the oscillation in the umbra,it contains a lot of unstable signal components.The accurate analysis and research o n the umbral oscillation signal components are very important for the structure and evolution process of sunspot,which has certain scientific significance.The object of this article is the study of methods which are applied to extract sunspot umbral oscillation.Nowadays,most of methods are through the selection of threshold,so as to identify umbral region.But,threshold value can lead to incomplete identification.Finally,we use the morphological reconstruction technique proposed by Yu et al.to identify the umbral region,which overcomes the disadvantages of traditional methods.Because of the simple calculation,one parameter,the Fourier transform often as the traditional analysis method analyzes the umbral oscillation.However,it can only analyze the signal in the frequency domain,and can not display the local information in the time domain.Moreover,when analyzing phase relationship of two umbra oscillation signal,The traditional Fourier transform analyzes phase relationship by designing a reasonable window function,so as to analyze the phase difference,but this method cannot be applied for high precision,weak signal,and under the conditions of high background noise.Therefore,in the analysis of umbral oscillation,the Fourier transform shows a shortage.Aiming at the disadvantages of traditional method of umbral oscillation analysis,we use wavelet transform to analyze umbral oscillation.It is not only analyze the signal in time domain but also in the time frequency domain.The features that can not be found in the frequency domain can be found clearly in the time domain.The indistinguishable features in th e time domain can be displayed well in the frequency domain.And it is very suitable for the analysis of unstable signals.In order to accurately analyze the mutual influence of two umbral oscillation signals,we use the Cross Wavelet Transform to analyze phase relationship between the two umbral oscillation signals.Wavelet transform overcomes the shortcomings of Fourier transform.In order to extract umbral oscillation,data preprocessing,the umbra region recognition,obtaining the umbral oscillation signal,umbral oscillation signal analysis are the main object of the study in this paper.First,by the mean smoothing filtering technology of the circular region we obtained the de-noising image,Second,according to the method based on morphological reconstruction has been proposed in the literature,we identify the umbra region.Then,to identify the average umbra region in order to get the corresponding umbral oscillation signal.At last,we use continuous wavelet transform to analyze the frequency components and the corresponding time domain information,and then we use cross wavelet transform to analyze the phase relationship between two umbral oscillation.The tool used in the process of experiments is the matlab.We can accurately and effectively get the information that we want by wavelet transform.The experimental results show that compared with the traditional the Fourier transform,the wavelet transform method used in this paper has obviously improved in the measurement accuracy and the detail analysis.To a certain extent,it improves the accuracy and effectiveness of the umbral oscillation analysis.The work in this paper lay a solid foundation for the further study of sunspot umbral oscillation.