Quantifying the effects of near surface density variation on quantum technology gravity and gravity gradient instruments
Quantifying the effects of near surface density variation on quantum technology gravity and gravity gradient instruments
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DOI：
10.1016/j.jappgeo.2019.03.012
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发表时间：
2019-05-01
影响因子：
2
通讯作者：
Tuckwell, George
中科院分区：
文献类型：
--
作者：
Boddice, Daniel;Metje, Nicole;Tuckwell, George
近地表土壤（即顶部5米）的自然密度变化导致用重力仪器进行的地球物理调查所记录的数值发生变化。虽然这种“土壤噪音”太小，无法用当前的仪器（例如Scintrex CG-5和CG-6）察觉，但未来使用更精确的仪器，如量子技术重力传感器，特别是在梯度仪配置中使用时，会使这种噪声源更加重要，需要进行表征和量化。本文利用英国地质调查局（BGS）国家岩土特性数据库的数据回顾了近地表密度变化的幅度和分布，然后用计算机模拟来量化密度变化对实际重力测量的影响。桌面研究发现，近地表密度变化尺度一般在600-900 kg/m(3)之间，与下伏地质、浅层沉积、地表以下深度无明显关系。密度分布从正态分布到正态分布和均匀分布或双峰分布之间。正演模拟计算机模拟表明，如果新的仪器能够达到更高的精度水平，特别是重力梯度仪器，将对重力测量产生重大影响。通过对重力梯度仪器设计抑制该噪声源的可能方法的分析表明，虽然增加仪器离地高度在降低土壤噪声尺度方面的效果几乎是其两倍，但增加传感器垂直间距可能是首选方案。这是由于对新传感器的灵敏度要求放宽，并且在比感兴趣的目标更短的信号波长带中保留噪声，这不仅减少了错误的感兴趣特征的情况，而且还提供了空间滤波的可能性，以便用于增强感兴趣目标的信号。(C) 2019 Elsevier B.V.版权所有
Natural density variations in the near surface soil (i.e. the top 5 m) cause variations in the values recorded by geophysical surveys undertaken with gravity instruments. Whilst this 'soil noise' is too small to be noticeable with current instruments (e.g. Scintrex CG-5 and CG-6), the future use of more accurate instruments such as quantum technology gravity sensors, especially if used in a gradiometer configuration makes this noise source more significant and in need of characterisation and quantification. This paper reviews the magnitude and distribution of density variations in the near surface using data from the British Geological Survey (BGS) national geotechnical properties database which is then used to quantify the effect on practical gravity measurements in computer simulations.The desk study identified that the scale of density variation in the near surface was typically within a range of 600-900 kg/m(3), and showed no obvious relationship with underlying geology, superficial deposits or depth below the surface. The distribution of density varied, from normally distributed to between normal and uniform or bimodal distributions. The forward modelled computer simulations showed a significant impact on the measurements of gravity if new instruments can reach greater levels of accuracy, especially for gravity gradient instruments. Analysing possible methods of suppressing this noise source through the design of gravity gradient instruments showed that, although increasing the height of the instrument above the ground is almost twice as effective at decreasing the scale of the soil noise, increasing the sensor vertical spacing may be the preferred option. This is due to relaxed sensitivity requirements on the new sensors and the preservation of the noise in shorter signal wavelength bands than the targets of interest, which not only reduces the cases of mistaken features of interest but also provides the possibility of spatial filtering to be used in order to enhance the signals from targets of interest. (C) 2019 Elsevier B.V. All rights reserved.