Seafloor massive sulphide exploration using deep-towed controlled source electromagnetics: Navigational uncertainties
Seafloor massive sulphide exploration using deep-towed controlled source electromagnetics: Navigational uncertainties
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DOI：
10.1093/gji/ggz513
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发表时间：
2019-11
影响因子：
2.8
通讯作者：
R. Gehrmann;A. Haroon;M. Morton;A. Djanni;T. Minshull
中科院分区：
文献类型：
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作者：
R. Gehrmann;A. Haroon;M. Morton;A. Djanni;T. Minshull
深拖地球物理勘测需要精确了解仪器位置和方向等导航参数，因为导航不确定性反映在数据中，从而反映在推断的海底地球物理特性中。我们针对从受控源电磁数据推断出电导率的情况来解决这个问题。我们表明，由于深拖期间的不规则运动，以及电导率的横向变化（包括地形引起的变化），数据误差会横向变化。为了解决这种变异性并在反演之前量化数据误差，我们提出了二维扰动研究。我们的工作流程可为多分量和多频率反演提供稳定且地质可靠的结果。提出了一种误差估计工作流程，其中包括导航不确定性的评估、导航参数的扰动以及均匀海底电导率模型和异质海底电导率模型的电场幅度正演建模。一些导航不确定性是根据直接测量的变化来估计的。反演所需的其他导航参数是从测量量导出的，并且通过误差传播来计算它们的误差。一些导航参数显示与测量的电场直接相关。例如，天线倾角与垂直电场相关，而深度与水平电场相关。对于扰动研究，每个标准偏差都添加到导航参数中。针对每个扰动运行正向模型。幅度偏差与叠加误差正交求和，得到横向变化的总数据误差。由于电导率范围较大（几个数量级），对异质海底模型重复进行误差估计，这会影响正演模型。该方法使我们能够利用反演中多个组件（多个电场、频率和接收器）的数据来约束最终模型并减少模糊性。最终模型在地质上是合理的，在这种情况下能够识别海底导电金属硫化物矿床。
Deep-towed geophysical surveys require precise knowledge of navigational parameters such as instrument position and orientation because navigational uncertainties reflect in the data and therefore in the inferred geophysical properties of the sub-seafloor. We address this issue for the case of electrical conductivity inferred from controlled source electromagnetic data. We show that the data error is laterally variable due to irregular motion during deep towing, but also due to lateral variations in conductivity, including those resulting from topography. To address this variability and quantify the data error prior to inversion, we propose a two-dimensional perturbation study. Our workflow enables stable and geologically reliable results for multi-component and multi-frequency inversions. An error estimation workflow is presented, which comprises the assessment of navigational uncertainties, perturbation of navigational parameters, and forward modelling of electric field amplitudes for a homogeneous and then a heterogeneous sub-seafloor conductivity model. Some navigational uncertainties are estimated from variations of direct measurements. Other navigational parameters required for inversion are derived from the measured quantities and their error is calculated by means of error propagation. Some navigational parameters show direct correlation with the measured electric fields. For example, the antenna dip correlates with the vertical electric field and the depth correlates with the horizontal electric field. For the perturbation study each standard deviation is added to the navigational parameters. Forward models are run for each perturbation. Amplitude deviations are summed in quadrature with the stacking error for a total, laterally varying, data error. The error estimation is repeated for a heterogeneous sub-seafloor model due to the large conductivity range (several orders of magnitude), which affects the forward model. The approach enables us to utilize data from several components (multiple electric fields, frequencies and receivers) in the inversion to constrain the final model and reduce ambiguity. The final model is geologically reasonable, in this case enabling the identification of conductive metal sulphide deposits on the seafloor.