The data of marine-controlled source electromagnetic exploration collected in shallow waters are considerably influenced by airwaves.Thus,finding ways to eliminate this influence is important.Decomposing the electroma...The data of marine-controlled source electromagnetic exploration collected in shallow waters are considerably influenced by airwaves.Thus,finding ways to eliminate this influence is important.Decomposing the electromagnetic field into the upgoing and downgoing fields is an effective method to resolve this problem.By utilizing the Stratton-Chu integral transform,this study proposes a novel method that can separate a 3D electromagnetic field into upgoing and downgoing electromagnetic fields through rigorous mathematical deduction.We examine the spectral characteristics to determine the effectiveness of the method.The results show that a practical digital filter can be achieved by selecting a reasonable window size and spatial step,as demonstrated through spectral comparisons with an analytical filter.展开更多
The airwave effect greatly influences the observational data from controlledsource electromagnetic exploration in shallow seas, which obscures the abnormal effects generated by exploration targets and, hence, affects ...The airwave effect greatly influences the observational data from controlledsource electromagnetic exploration in shallow seas, which obscures the abnormal effects generated by exploration targets and, hence, affects the accuracy of the late exploration data interpretation. In this study, we propose a method to separate the main part from the anomalous field of marine controlled-source electromagnetic method （MCSEM） data based on Stratton-Chu integral transforms to eliminate the airwave effect, which dominates observed electromagnetic （EM） response in shallow seawater. This method of separating the main part from the anomalous field is a type of finite impulse response filter based on a discrete data set. Theoretical analysis proved that the method is stable and able to effectively depress noise. A numerical test indicated that the method could successfully eliminate the airwave effect from the observed EM signals generated by an air water interface and a seawater layer. This technique is applicable for seawater models with either flat or rough seabeds.展开更多
In planning and executing marine controlled-source electromagnetic methods, seafloor electromagnetic receivers must overcome the problems of noise, clock drift, and power consumption. To design a receiver that perform...In planning and executing marine controlled-source electromagnetic methods, seafloor electromagnetic receivers must overcome the problems of noise, clock drift, and power consumption. To design a receiver that performs well and overcomes the abovementioned problems, we performed forward modeling of the E-field abnormal response and established the receiver＇s characteristics. We describe the design optimization and the properties of each component, that is, low-noise induction coil sensor, low-noise Ag/AgCI electrode, low-noise chopper amplifier, digital temperature-compensated crystal oscillator module, acoustic telemetry modem, and burn wire system. Finally, we discuss the results of onshore and offshore field tests to show the effectiveness of the developed seafloor electromagnetic receiver and its performance： typical E-field noise of 0.12 nV/m/rt（Hz） at 0.5 Hz, dynamic range higher than 120 dB, clock drift lower than 1 ms/day, and continuous operation of at least 21 days.展开更多
基金supported by the National Natural Science Foundation of China(42074085).
文摘The data of marine-controlled source electromagnetic exploration collected in shallow waters are considerably influenced by airwaves.Thus,finding ways to eliminate this influence is important.Decomposing the electromagnetic field into the upgoing and downgoing fields is an effective method to resolve this problem.By utilizing the Stratton-Chu integral transform,this study proposes a novel method that can separate a 3D electromagnetic field into upgoing and downgoing electromagnetic fields through rigorous mathematical deduction.We examine the spectral characteristics to determine the effectiveness of the method.The results show that a practical digital filter can be achieved by selecting a reasonable window size and spatial step,as demonstrated through spectral comparisons with an analytical filter.
基金supported by the National Natural Science Foundation of China(No.41574067)863 Program(No.2012AA09A404)
文摘The airwave effect greatly influences the observational data from controlledsource electromagnetic exploration in shallow seas, which obscures the abnormal effects generated by exploration targets and, hence, affects the accuracy of the late exploration data interpretation. In this study, we propose a method to separate the main part from the anomalous field of marine controlled-source electromagnetic method （MCSEM） data based on Stratton-Chu integral transforms to eliminate the airwave effect, which dominates observed electromagnetic （EM） response in shallow seawater. This method of separating the main part from the anomalous field is a type of finite impulse response filter based on a discrete data set. Theoretical analysis proved that the method is stable and able to effectively depress noise. A numerical test indicated that the method could successfully eliminate the airwave effect from the observed EM signals generated by an air water interface and a seawater layer. This technique is applicable for seawater models with either flat or rough seabeds.
基金sponsored by the 863 Program(No.2009AA09A2012012AA09A201)+1 种基金China Geological Survey Project(No.201100307)the Fundamental Research Funds of the Ministry of Education for the Central Universities(No.2652011249)
文摘In planning and executing marine controlled-source electromagnetic methods, seafloor electromagnetic receivers must overcome the problems of noise, clock drift, and power consumption. To design a receiver that performs well and overcomes the abovementioned problems, we performed forward modeling of the E-field abnormal response and established the receiver＇s characteristics. We describe the design optimization and the properties of each component, that is, low-noise induction coil sensor, low-noise Ag/AgCI electrode, low-noise chopper amplifier, digital temperature-compensated crystal oscillator module, acoustic telemetry modem, and burn wire system. Finally, we discuss the results of onshore and offshore field tests to show the effectiveness of the developed seafloor electromagnetic receiver and its performance： typical E-field noise of 0.12 nV/m/rt（Hz） at 0.5 Hz, dynamic range higher than 120 dB, clock drift lower than 1 ms/day, and continuous operation of at least 21 days.
