Analysis Of Low-drifting Seismic Data Acquisition With Modulating System

Modern seismic survey system is based on the observation network of digital technology. Signals in the seismic stations are digitized, transmitted by networks, collected by computer systems for process and storage. Digital seismic data acquisition is an important part in earthquake observation, the key function is converting analog signals into digital signals, and analog-digital converter technology standards largely determine the quality of the data observation. Seismic signals mostly distribute in the low-frequencies ( 10^-3 Hz- 10³Hz), and data acquisition will produce 1/f noise characteristics to the observation accuracy in the low frequency range. The paper has done some preliminary discussions on this issue based on an algorithm theory.First, the paper describes the types of seismic signals, the composition of seismic observation network and principles of digital-analog conversion. Then the paper analyzes the short circuit 1/f noise characteristics in data acquisitions, and some features of the auto-zero technique for weakening the 1/f noise. Based on this technology, the improved algorithm is proposed.The results show that two methods essentially modulate base band signals to high frequency range and weaken the impact of 1/f noise on measurement accuracy. The paper finally combines two technologies and proposes the modulation algorithm. A set of input signals were tested to show that 1/f noise can effectively be weakened through the modulation model. The paper also uses the actual data to analyze the result whether data through the modulation model to observe low-frequency noise is effectively eliminated. The result is optimistic.The paper also use pseudo-random sequence as the signal modulation and demodulation algorithm based on the proposed square-wave. Pseudo-random sequences have the characteristics of confidentiality and interference; pseudo-random sequence can also be used as a modulated signal to eliminate 1 / f noise, with a similar square wave output from the simulation. Confidentiality can be good for the occasion. The paper, based on the modem, also proposed an algorithm to improve the output signal to noise ratio. The modulated system is linear system, so the spectrum in the moving process to avoid the 1 / f noise band, but did not change the noise floor. The paper also analyze the energy loss of square wave and sine wave modulation and demodulation sequence as a weighted average for proposing the algorithm and prove the correctness of the weighted average algorithm in theory. Experimental data also show that the signal to noise ratio has improved to some extent, and are in good Consistent with the calculated value.