Key Technologies And Hardware Research Of Marine Electric Field Low-Noise Detection

The use of marine electromagnetic method to detect and develop the subsea oil,gas hydrates and solid mineral resources has far-reaching strategic significance on relieving the pressure on the dwindling land resources in our country.The weak signal detection technology of marine electric field can improve the ability to detect deep sea of marine electromagnetic method.Currently,only a few countries abroad master the technology and implement technology blockade to our country.Therefore,marine electric field low-noise detection technology becomes one of the key technologies of marine electromagnetic detection in our country.Marine electric field sensor system with excellent performance is the hardware foundation and prerequisite of executing marine electric field detection.With an increasing number of marine electromagnetic surveys in the deep ocean,carefully designed electric field sensors and amplifiers with low-noise levels have important significance on improving the detection accuracy of the deep field signal of marine electromagnetic survey in our countryFor the weak signal detection technology of marine electric field,we analyzed the characteristics of the electric field signal in marine environment,put forward the technical requirements of low noise testing of the marine electric field.We simulated the attenuation response of the natural electromagnetic field signal under the condition of different water depth and different underwater medium by use of a seawater-earth layered medium model,and then calculated the approximate amplitude of the underwater electric field signal.By establishing a uniform layered medium model containing high resistance layer,we forward simulated the marine controlled source electric field response of different transmission frequency.A new low-noise marine electric field sensor system was developed,including the new marine electric field sensor and high sensitivity chopper amplifier.The new electric field sensor was fabricated using electrolytic preparation process.A dense and uniform AgCl was generated on the surface of Ag by use of electrolysis principle,thereby generating Ag|AgCl substance the body material of the electric field sensor.The study of the key parameters in the electrolysis process improves the stability and reduced the noise floor of the electric field sensor.Through the establishment of the equivalent noise circuit model,we analyzed the noise matching characteristics of the chopper amplifier circuit and developed the high sensitivity chopper amplifier.The noise matching between electric field sensor and chopper amplifier was achieved using the transformer impedance transform.The nested chopper technology reduces the residual offset caused by the signal demodulation process.The low-noise design of AC amplifier circuit further reduces the noise floor of chopper amplifier,thereby improving the overall noise performance of the electric field sensor system.Indoor test results show that the main indicators of new low-noise marine electric field sensor and high sensitivity chopper amplifier meet the design requirements.The noise floor indicator has reached the leading domestic level.Ocean test verifies the overall performance of new marine electric field sensor system.The new type low-noise marine electric field sensor system reduces the noise of China's marine electric field collection system,improves the overall technology performance of the instrument,and offers high-tech support for controlled source electromagnetic exploration of natural gas in the South China Sea.