| Urban shallow surface exploration is an innovative geophysical method which mainly studies the urban geophysical field and its dynamic changes.Nowadays,China is still a developing country.The acceleration of urban underground space development has become an important symbol of the world's rapid urbanization.Urban construction of underground rail transit network and underground shopping malls need mature urban shallow surface exploration technology.Therefore,urban shallow surface exploration has important research significance.The exploration depth of micro-motion exploration is generally less than 100 meters,which meets the requirements of urban underground space exploration depth,and the microtremor exploration USES passive source exploration.It does not destroy the existing underground pipeline system and underground traffic network system of the city,and it is not necessary to break ground by using the part originally considered as urban noise to extract effective information.The arrangement of micro-motion exploration also does not need large sites and complex forms,and its operation is very convenient,which makes the microtremor exploration have the advantages of energy saving,green,fast and high efficiency,in line with China's sustainable development strategy.But urban shallow surface micro exploration still faces significant challenges.The first is the urban noise has strong influence on micro measurement results.The second is be affected by man-made interference due to the detection depth of dozens of meters.The third is the analysis of the influence factors of micro detection results is also not clear,the noise of the four is the current seismic instrument circuit often swamped the motion of weak signal,exploration of micro demand.Therefore,this paper analyzes the influencing factors of the detection results of the two typical micro-motion exploration methods,proposes the appropriate micro-motion method and array arrangement for the unique urban environment,and optimizes the existing seismic instrument circuit with low noise,so that it can meet the requirements of micro-motion exploration.The main research work of this paper consists of three parts.First,for the twodimensional array,the signal influencing factors of spatial autocorrelation method(SPAC)are analyzed,mainly from the four perspectives of different array types,signal incidence range,incoherent noise and urban low-rise and low-rise terrain.Second,for single-point exploration,the signal influencing factors of empirical spectral ratio method(H/V)are analyzed,mainly from two perspectives of different signal azimuths and acquisition signal seasons.Third,the optimization of the existing seismic instrument circuit,first analyzed the influence of different instruments of the micro signal,detection instrument noise is also micro signal is one of the important factors of the second low noise of the circuit module for the optimization design,finally to make the micro exploration work more convenient,the existing real-time monitoring system,the optimization design of the circuit.In this paper,influence factors of micro-motion exploration signal based on SPAC method are discussed.Taking SPAC coefficient deviation as the parameter,it can be seen that the more vertices in array layout,the smaller SPAC coefficient deviation,and the denser array arrangement,the smaller SPAC coefficient deviation,and the better signal quality.When the incident signal is concentrated in the range is 0 to 60 °,SPAC coefficient of minimum deviation of 0.1.Adding incoherent white noise can reduce the threshold value of low frequency band with SPAC coefficient deviation and obtain better micro signal quality.The influence of high and low relief on the SPAC coefficient deviation mainly comes from the change of the radius of the circumferential circle,and the inclination Angle has little influence on the SPAC coefficient deviation.Based on the H/V micro exploration signal influence factors of different incidence azimuth signal in 70-80°or 160-180°,minimal impact on microtremor signal.For the collection time and season of microtremor signal on the impact is small.The low-noise circuit of the seismic instrument USES three 2Hz moving coil detectors combined with the advanced acquisition system.The highprecision AD chip and noise matching technology are selected to control the node noise.The gain of the three channels of the noise level is-2dB,which meets the expected requirements of the acquisition accuracy.In this paper,the influence factor analysis of urban shallow surface micro movement signal is applied to two-dimensional array and single point exploration,the optimization of seismic instrument circuit provides a strong basis for improving the shortcomings of existing instruments,and provides constructive guidance for urban shallow surface micro movement exploration... |
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