Study On Marine Controlled-source Electromagnetic Data De-noising Based On Adaptive Filtering Method

Marine Controlled Source Electromagnetic method is a frequency domain electromagnetic method based on the resistivity difference between the submarine reservoir and the surrounding rock.Its advantage is that it is sensitive to marine high resistivity reservoir.At the same time,it is also an important method for reservoir evaluation.At present,in working drag mode,the transmitter is towed over the seabed and moved along the line,and the receiver is fixed to the seabed for signal reception.Due to the complexity of the seabed environment,the receiver receives different levels of noise in the signal,which seriously affects the accuracy and credibility of the data interpretation,so it is necessary to carry out signal noise attenuation in MCSEM data processing.In this paper,we deduced the electromagnetic response of marine controllable source galvanic sources in different geoelectric models in detail,and made an analysis and discussion on electromagnetic response to different geoelectric models,Simultaneously deduced the one-dimensional theoretical formula of marine electromagnetic field,the algorithm was used to analyze marine electromagnetic signal response.Based on the theoretical model,the MVO response of the marine controllable source electromagnetic field is calculated and analyzed the geological information contained on the MVO curve.The theoretical calculation model of F1 DM is established,and the response curve of marine electromagnetic model with different parameters is calculated by using the derived forward theory formula,and then analyzes its characteristics.By changing the model parameters,the influence of the posture and emission frequency of the marine electromagnetic transmitter on the response of the marine electromagnetic signal is studied in detail,moreover,we researched the influence of hydrothermal and seawater depth on the electromagnetic signal of marine controllable source.The purpose of noise attenuation is to restore the original data characteristics as much as possible,which through various methods to filter out noise signals and preserve the original information of the signal,providing reliable data for further explanation of the data.The existing noise attenuation algorithms are based on the traditional method of technology.The noise attenuation effect of the data largely depend on the parameter of inputs,greatly limits the noise attenuation effect of the MCSEM data.In this paper,the source and type of the electromagnetic noise of the ocean are analyzed,and the de-noising is studied for the random noise in the signal.The ocean is a low-pass filter,and all highfrequency man-made noise will not cause interference to the ocean electromagnetic signal,and the influence of air waves is mainly affected by shallow sea electromagnetic exploration.And the interference for deep-sea air waves is mainly in the far-off range,so by selecting the appropriate transceiver distance to effectively reduce the interference of air waves.Adaptive filtering technology,which is largely used in the communication engineering,is introduced into marine electromagnetic signal noise processing for the first time.This article deduces the theoretical formula of adaptive filtering technology in detail,and study minutely LMS adaptive algorithm.In the LMS adaptive filtering algorithm,the step factor greatly affects the convergence speed and misalignment of LMS algorithm.Large step size factor can accelerate the convergence rate of the system,but too large step size factor will make the system chaos and imbalance phenomenon.While the small step size factor,although to ensure stable convergence of the system,but will affect the system’s convergence speed,greatly increasing the load of system.And the order of the filter will also affect the filtering effect of the system,larger filter order can improve the quality of noise attenuation,but at the same time increase the overhead of the system.In this paper,after analyzing the advantages and disadvantages of the LMS adaptive filtering algorithm,a new variable step size DLMS algorithm based on distance factor adjustment is proposed by combining the characteristics of MCSEM data with offset.The algorithm can better balance the convergence rate and steady-state error of the system,and improve the convergence rate and the offset problem of the existing algorithm.Using the DLMS algorithm to process the theoretical model and the measured data,through a large number of simulation examples of the noise attenuation study shows that the algorithm to suppress the random signal system is very effective.On the basis of this research,the algorithm is applied to the noise attenuation process of marine electromagnetic signals.Through the theoretical model and the noise attenuation of measured data,the results show that the algorithm improves the convergence speed of the iteration,and maintains the smoothness of the system,which can effectively restore the characteristics and details of the MVO curve and the apparent resistivity curve.It is proved that this method can be used in the actual noise attenuation of marine electromagnetic signals,which provides a new research idea for the study of noise attenuation of marine electromagnetic data;and extends the new method of noise suppression of marine electromagnetic;provides an effective means of data processing for subsequent ocean electromagnetic data processing and data interpretation.On the basis of the above research,the data noise processing module of the marine electromagnetic based on the.Net framework is carried out.The module has the function of basic management of data,preprocessing,noise suppression and one-dimensional modeling and inversion.And the module can be in the visual interface to establish forward modeling data,which greatly improves the facility of the program module.