The Design Of Vibroseis Pseudo-random Signal Generator Based On DSP

Vibroseis is the source of the seismic signal, which is an important component of the seismic exploration technique. Vibroseis is a kind of large equipment of oil seismic prospecting. In seismic exploration, in order to overcome the environmental noise and other resistance factors, Vibroseis must need certain energy. From the point of energy, the output of large energy signal in short time could be approximated by the output of short energy signal inlong time, which benefits from approximation technology. Therefore, vibroseis seismic prospecting recording quality is greatly affected by vibroseis sweep signal autocorrelation function.In vibroseis seismic prospecting, scanning signal after power amplification was sent to the underground.What’s more, the signal is placed on seismograph records after the reflection of underground medium,the seismic record is a collection of scanning signal autocorrelation which is dressed by reflection coefficient and transmission characteristics.So the correlation functions of sweepping signal are corresponding to the wavelet of the traditional seismic records or correlation wavelet. Traditional seismic exploration resolution depends on the seismic wavelet resolution, with echoes of is, vibroseis seismic exploration resolution depends on the "correlation wavelet" resolution. In vibroseis data processing, correlation wavelets come from crosscorrelation of scanning signal with echo signal (that is the reflected signal detected by detector). The echo signal is deconvolution of scanning signal and earth factor, so the correlation wavelet is deconvolution of scanning signal autocorrelation function and the earth filtering factor. Wavelet morphology and phase have an important impact on wavelet resolutiom,if we want to have higher resolution,we might let the wavelet main lobe outstand,let side lobe and main lobe side lobe attenuation ratio small, conversely low.Zero phase wavelet resolution is higher than the wavelets of the minimum phase and mixed phase.That’s to see,the shape of seismic exploration resolution is deeply affected by he shape of seismic exploration resolution,it is very significant to discuss vibroseis scanning technique for improving the resolution of vibroseis exploration.The main factors on affecting the resolution and Signal to Noise Ratio of vibroseis is the shape of scanning signals autocorrelation, that’s to say, improving the performance of it is the best way to enhance the effect of seismic expIoration.Pseudo random signal with good autocorrelation function which is close to white noise, similarly, the autocorrelation function is similar to white noise characteristics, concreting on the autocorrelation function of the double value,it also have certain periodic and is random in each period, what’s more,whose characteristics is the same as the pulse’s, there is a narrow or wide peak power spectral density. And pseudo random sequence also has a predetermined certainty and anti-interference ability, which makes it easy to interference from other signals or noises. Therefore, we research the vibroseis pseudo-random scan mode by suppressing the sidelobes for highlighting the main lobe for amending the autocorrelation function of the characteristics, so as to improve the seismic prospecting vibrator resolution and SNR in the seismic exploration. It has good development prospect.This article first elaborated the topic of background on the subject, purpose and significance, then introduced kinds of suitable scanning signal for the seismic exploration technology, thus,comparatived analysis of the advantages and disadvantages of these signals, after that discussed pseudo-random scan signal which is in nonlinear signal in detail.Secondly, combined with the principle of seismic exploration, according to the characteristics of vibroseis and the effected seismic exploration, how to generate the ternary pseudo-random code was researched, based on the obtained pseudo-random code, ternary pseudo-random sweeping signals were given, and carried on the simulation analysis with the three pseudo random signal in the Matlab platform. And results gotten from analyzing the scanning signals reveal the relationships between the ternary pseudo-random scanning signals of primitive polynomial and carrier frequency and autocorrelation, and the effect of the two parameters on the autocorrelation.Finally, introducing the TMS320C5416series of DSP signal generator, and show some peripheral equipments such as timers, clock generator, and interrupt, the AD sample, the DA output in detail, as well as the working principle of the peripheral equipments and these peripherals how to coordinate deal with each others, gave the design scheme、 principle and software programming ideas and flow chart of the program,then output thepseudo-random scan signal which has been generated by DA, observe the waveform on the oscilloscope,analyzed the reason for the deviation and the hardware implementation of the diagram. At the end of this paper, analyzing some problems in this design, and pointing out the key point and the difficulty in the experiment, as well as what we should do in the future.