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Theoretical Calculation Of Marine Transient Electromagnetic Response And Research Of Shallow Sea-floor Detection Technology

Posted on:2008-02-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:H LiFull Text:PDF
GTID:1100360212997625Subject:Earth Exploration and Information Technology
Abstract/Summary:PDF Full Text Request
70% of the earth surface is the ocean, in our country, the total area of ocean is equal to the first-third of the land area, the coast line is long and the most area is shallow, significant mineral resources such as oil field, multi-metals sulphuret and sand mineral etc, had been discovered in Bohai Gulf of our country. But explore degree in beach and shallow sea area is very low, the quick and efficient new method technique is also needed in ocean engineering explore in inshore ocean. The method and technique introduced in this paper is applicable to beach and shallow sea.The sea-floor is the biggest resources mine in the world, a great deal of petroleum, natural gas and various minerals are in it; the land area and the resource is reduced gradually with the expansion of mankind, developing the new resources environment is extremely urgent. People have already concentrated the attention to the ocean, beginning to build the sea-floor oil pipeline and correspondence cable, developing sea-floor habitation and recreation rooms would be possible with the growing ability of exploring and constructing in the sea-floor. Therefore, some methods, which are of light ruin, wide extension of adaptive depth and simple operating in exploring resource and surveying engineering in sea-floor, are necessary. Besides the earthquake method, Sea Electromagnetic method is a main sea physical geography method.This thesis is completed under the assistance of significant item-Ocean Resources Development Technique belonged to The National High Technology Research and Development Program of China (863 Plan). So as to achieve the transient electromagnetic detection of beach and near shallow undersea (3 to 30 meters), it has build two strong electric half space models-the sea model and the sea-floor model, the sea transient electromagnetic response is computed under these models. Aiming at the concrete problems of sea detection, it has studied the antenna equip adapted to sea-floor detection and the instrument system. Concrete research achievements are as following:1. It is based on Maxwell equation and set out from frequency-domain, deducing the transient electric field and the vertical magnetism field of vertical magnetism dipole equips under the seawater and the sea-floor two strong half-space models, and concluding the inductive voltage expressions of the vertical magnetism dipole equip and the center loop-line equip. The influence of the seawater on the induction voltage is studied by the emulate research and comparison to that of the land, and the laws of dipole moment on step signal response is analyzed while the vertical magnetism dipole equips are different. It provides the theory foundation for the selection of antenna equip used in sea-floor transient electromagnetic detection, judging the curve form of sea-floor transient response, designing of system and data explanation.2. The sea-floor detection is not the same to that in the land. The antenna equip must be designed and sealed well before starting the experiments on the sea. The antenna equip is confirmed to be used in sea-floor probing by follow aspects: dynamic scope of the receiver; the best coupling between transmission loop-line and receive loop line; exceptional curve is as simple as possible; the state of coil is towed simply, etc. Lots of gutter experiments indoor and outside are tested so as to ensure the validity of combination mode of coil selected.3. Miniaturizing of transmission and receive antenna (coil) is studied. Transmission coil should be wrapped many turns when small coil is used, in this way the scope value of induction voltage would be higher correspondingly. To the limit, time-constant of lead of transmission coil selected is short, choose the thin lead which can output the maximum current and ensure that transmission wave turning off time is shorter correspondingly and the detection data is more accurate in shallow area.4. The distilling technology of the transition course and the all-time transient electromagnetism signals response of receive coil is analyzed so as to judge the sea-floor transient response curve correctly. Based on the circuit theory, it has studied the theory modeling and step response characteristic of receive coil, analyzed the first induction voltage and the second induction voltage and their affection of transition course while transmitting current is ramp step pulse, acquired the response curves of the first induction voltage, transition course of the first induction voltage, the second induction voltage and transition course of the second induction voltage in the case of tilted turning off current, analyzed the effect of transition course on all-time transient induction voltage and studied on the removing of the first induction voltage and distilling technology of all-time transient induction voltage.5. Made study on long distance supervision correspondence mode, designed long distance supervision software and dynamic channel data processing software, the three-point index nonlinear smooth filtering technology is adopted in order to suppress noise and remove singular points; it is confirmed that sea-floor transmitter should send continuous bipolar rectangle wave and the receiver should work on timing sampling continuous operation mode by land towed testing; the dynamic scope of receiver is ascertained by emulate compute and experiments, etc. The Sea-floor Transient Electromagnetic Detection System is developed based on above research.6. It confirms the implementing scheme of the sea-floor transient electromagnetism exploring system on the sea. The tugboat tows the instruments airproof cabin sink in the bottom, the coil is sink as deeply as possibly and behind the cabin, don't keep too near so as to avoid to be influenced by electromagnetic instruments. It has designed sea-floor instrument, air-proof for antenna equips, anti-pressing in sea-floor and matched weight for sinking and chosen the nonmagnetic materials for air-proof. The cabin had been test in gutter and lake for many times to ensure the feasibility of work mode and excellent ability of air-proof and anti- press.7. In order to prove the validity and accuracy of theory explanation method and antenna selection and the reliability of instruments, a number of field experiments were done,including land,lake and marine experiments. Search for the exact position of transport-oil pipe and seabed model creation were accomplished by applying the technical approach adopt in this paper.Main creations in the paper:1. It has build the sea-floor and seawater two electric half space models, calculated the transient electromagnetism response of vertical magnetic dipole-dipole equip and center loop-line equip and analyzed the effect of seawater. It has achieved firstly the shallow sea-floor transient electromagnetism detection used by vertical magnetic dipole-dipole equip and center loop-line equip at home. The achievement could be applied to shallow sea resource exploring and engineering environment investigation.2. It has brought forth sea-floor towed measurement achieved by small antenna equips and studied on the response characteristic and the facture of small coil. That the Transmission coil should be wrapped with many turns when small coil is used is confirmed, in this way the scope value of induction voltage would be higher correspondingly. Choose the thin lead which can output the maximum current, ensure that transmission wave turning off time is shorter correspondingly. This antenna equip is flexible, convenient, sensitive to high conductance sea-floor and simply to achieve towed measurement.3. The Dynamic Channel Idea of Sea-floor Transient Electromagnetic Method is brought forth. The three-point index nonlinear smooth filtering and the real-time section curve disposing of equal logarithm interval channel were achieved by the communication between the instrument system and the master during transient electromagnetic system towed measurement. That the abnormal sea-floor detection could be discovered in time made up the fault which normal transient electromagnetic method is dealt with afterwards and achieve the sea-floor towed continuous measure.The paper modeled two half-space and studied the sea transient electromagnetic response characteristic, it has discussed the implementing schemes of main technology in shallow sea-floor electromagnetic detection from coil equips to instrument system and data processing, and focused on the achievement of the whole system. But thanks to the complexity of detecting goal in the sea-floor and inclemency while working on sea, it is necessary to take further study on Shallow Sea-floor Transient Electromagnetic Detection technology Research based on above achievements. There are as following:1. Make study on transient electromagnetic response modeling and emulate calculation of sea-floor three-dimension objects, such as sphere, electric sheet, etc, consider the influence of the depth of seawater upon the results and analyzed accurately the ability of detection while the depth of seawater is limit.2. Make research on Array Towed Measure Method and Technology so as to improve the accuracy of observation and suppress seawater noise.3. Achieve the accurate position of coil in sea-floor and the posture measurement of coil by the sensor fixed on the coil, it is convenient to revising the observation data while processing data and get more reliable explanation results.
Keywords/Search Tags:Marine transient electromagnetic method, Vertical magnetic dipole-dipole system, Central loop system, Sea-floor conductivity, electromagnetic field, Transient response, Transient process
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