基于位场分离方法的极地冰盖重力异常剥离:以模型试验为例

Using the Potential Field Separation Method to Extract the Gravity Anomalies Caused by the Ice Sheet in the Polar Region:Taking Model Test as An Example

为了提高极地重力数据处理的质量,降低巨厚冰层对重力数据解释的影响,将极地大陆冰盖引起的重力异常从叠加异常中剥离出来成为极地重力数据处理的重要步骤之一。针对该问题,本文建立两个极地大陆冰层构造模型,对不同模型进行正演获得对应布格重力异常,再尝试利用三种位场分离方法,包括趋势分析法、向上延拓法和优化滤波法,对冰层引起的重力异常进行剥离试验,基于模型试验结果对比分析不同位场分离方法对极地冰层重力效应剥离的应用效果。模型试验结果显示,趋势分析法在冰层界面起伏较平缓情况下效果较好,但当冰层界面起伏复杂时难以用数学表达式精确拟合区域场,因此易在结果中引入虚假异常;向上延拓法在局部场源较浅的异常分离中效果较好,但由于极地模型冰盖深度较深及延拓高度选取不合理,在试验中出现了分离不足的情况;优化滤波法在相对复杂模型中分离效果相对好,但由于频段选取的主观性,使得该方法也易出现分离不足或过度情况。综合上述模型试验表明,在剥离极地冰盖引起的重力异常时,由于极地冰盖厚度起伏等地质情况复杂多变,应结合实际地质情况及其他可获得的地球物理资料进行综合分析,选择适用于具体情况的分离方法。

To improve the gravity data processing quality and reduce the impact of super-thick ice sheet on gravity data interpretation,it is important to separate the gravity anomalies caused by ice sheet from the superimposed anomalies.To address this problem,we establish two continental polar ice structural models and simulate the Bouguer gravity anomalies of these models.Subsequently,three separation methods(i.e.,polynomial fitting,upward continuation,and preferential filtering)are used to extract the ice sheet-related gravity anomalies.Based on the results,the application effects of different separation methods are compared and analyzed.Our results demonstrate that the polynomial fitting method is effective when the density interface fluctuation is relatively gentle,but artificial anomalies are easily introduced when the interface fluctuates greatly.The upward continuation method works well in discriminating anomalies caused by shallower sources.However,due to the greater depth of the polar model and unreasonable continuation height selection,insufficient separation occurs in the test.The preferential filtering method yields better separation result for the complex model,but its performance depends greatly on the frequency band selection.Therefore,when stripping the gravity anomalies caused by polar ice sheet,due to the complex geological conditions(e.g.,thickness and fluctuation of polar ice sheets),available geological and geophysical materials should be adopted to determine the appropriate separation method for specific conditions.