摘要
海洋电磁理论是建立在水平发射偶极的基础上.然而,由于海底洋流作用海洋可控源发射偶极可能产生水平摆动、倾斜和水平旋转,造成测量数据与理想状态的水平电偶极子的电磁响应有较大的偏差.为了研究发射源姿态变化对场的影响,本文提出利用欧拉旋转将发射偶极由源坐标系转换到地球坐标系,进而分析发射源姿态变化造成海洋电磁观测数据的误差分布特征.研究发现,对于发射源水平摆动和倾斜造成的海洋电磁观测数据的畸变,其分布规律取决于接收机所在区域.以发射频率1Hz为例,对于由发射源水平摆动或倾斜导致的地球坐标系中的两个等效电偶极子分量产生的水平电场Ex,在旁线区域,二者的相位差约为360°,接收机接收到的电场信号约为两个偶极子场之和;而在同线区域,二者的相位差接近于180°,接收机接收到的信号为两者之差.在两个区域的交界处,发射源姿态对电磁信号影响最大.相比之下,发射源水平摆动只改变发射源的位置,不会改变源的性质,其影响主要发生在收发距较小的区域.本文的研究成果有助于海洋电磁系统设计时确定发射源姿态变化的参数指标,同时也为未来实际海洋电磁观测时分析和校正发射源姿态变化造成的观测数据误差提供理论基础.
The marine controlled source electromagnetic（MCSEM） theory is based on the assumption of a horizontal electrical dipole（HED）.In actual practice,the transmitter exhibits roll,pitch,and yaw rotation due to the turbulence at the ocean bottom.This makes the survey data quite different from those of an ideal HED.In order to study the transmitter attitude effect on the observed data,we use the Euler rotation to transform the transmitter coordinate system back to the earth coordinate system to obtain the equivalent components from the dipole transmitter.Theoretical investigation shows that the errors resulted from transmitter pitch and yaw rotation depend on receiver＇s position.Taking 1Hz of transmitting frequency as example,the two horizontal electric fields Ex from two equivalent electric dipole components in the earth coordinate system,transformed from a unit dipole in the transmitter coordinate system,have a phase difference of almost 360 degrees in the broadside zone,so the observed field is the sum of the fields from two equivalent dipoles.However,in the inline zone,the phase difference of fields from the two equivalent dipoles is roughly 180 degrees,leading to the observed signal being the difference of the two dipole fields.At the junction area of two regions,the transmitter attitude has the largest effect on observed data.Compared with pitch and yaw rotation,the roll rotation only affects the signal of small transmitter-receiver offsets because it only changes the transmitter location but not the characteristics of transmitter.Our research can help determine the parameters for MCSEM transmitting system design and provide theoretical basis for the analysis and correction of MCSEM data.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2012年第8期2757-2768,共12页
Chinese Journal of Geophysics
基金
国家自然科学基金(40874050)
国家863重大项目(2012AA09A20103)资助
