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摘要:
重力场向下延拓能够突出局部和浅部的异常信息，分离叠加的异常特征.但是向下延拓通常具有过程不稳定、下延深度小、结果不准确等问题.针对向下延拓所存在的不足，本文利用重力场及其垂向一阶导数，基于辛普森（Simpson）求积公式，推导出重力场向下延拓米尔尼（Milne）公式.将本文向下延拓方法应用于模型数据，向下延拓模型结果及误差曲线表明，相对于向下延拓快速傅里叶变换（FFT）法和积分迭代法，向下延拓Milne法的深度更大，相对误差更小；相对模型值，向下延拓Milne法能够获得稳定且准确的结果.对加拿大乃查科（Nechako）盆地地区实测航空重力数据进行本文方法向下延拓验证，处理结果表明，相对于实测异常，本文方法向下延拓结果能够很好还原实测数据，并且在进一步向下延拓中反映原始异常的趋势，增强局部和细小异常信息.
Abstract:Downward continuation of gravity field can highlight the anomaly of the local and shallow part of the earth, and can separate the anomaly feature from the overlying field. But downward continuation is usually unstable, with shallow downward continuation depth and inaccurate result. To this end, this paper presents a Milne formula method for downward continuation of gravity field by using gravity field and its first-order vertical derivatives, and based on Simpson quadrature formula. The method is applied to the synthetic model. The synthetic result and the error curve show that compared with the fast Fourier transform downward continuation method and the integral iteration downward continuation method, the new method's depth of downward continuation is larger, the relative error is smaller, and the result is stable and accurate to the model. The method is applied to the downward continuation of the measured airborne gravity data of Nechako basin in Canada. The downward continuation result of this method can restore the original data accurately. And the result can reflect the tendency of the original anomaly and enhance the local and tiny anomaly.
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Key words:
- Milne formula /
- Gravity downward continuation /
- Vertical derivative /
- Different heights
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图 2
向下延拓2倍点距(2 m)结果(图中色标单位为mGal)
Figure 2.
The synthetic result of downward continuation with 2 m
图 3
向下延拓10倍点距(10 m)结果(图中色标单位为mGal)
Figure 3.
The synthetic result of downward continuation with 10 m
图 5
加拿大Nechako盆地重力数据向下延拓比较结果
Figure 5.
The comparison result of downward continuation over Nechako in Canada
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