The determination of the natural remanent magnetization (NRM) of archaeological features can be used for magnetic modelling, joining of shards, archaeomagnetic dating or the investigation of the firing–cooling–collapsing order of ancient buildings. The measurement of NRM is normally conducted on cylindrical or cubic samples in the laboratory. Nevertheless, archaeological finds should preferably not be destroyed, and laboratory instruments are high in costs. Therefore, we propose a lightweight and portable measurement set-up including already available field magnetometers (preferably caesium magnetometers) in which the archaeological sample of arbitrary shape, in our case a piece of daub, is mounted inside a gimbal to be rotated in all directions. The magnetic field of the sample is measured at a large number of rotational positions with the magnetometer kept at fixed position. In these measurements, the unknown direction of the NRM vector of the sample is rotated, whereas the average magnetic susceptibility of the sample and the ambient magnetic field are constant and known. Hence, the vector of NRM can be determined through least-squares inversion. For the inversion computation, the sample volume is discretized either as voxel model or approximated as an equivalent sphere. Under certain conditions depending on sample–sensor distance, dipole moment and radius of the sample, the approximation by a sphere is valid without effect on the accuracy of results. Empirically determined functions quantifying these conditions for different sensor sensitivities and noise levels are provided. Validation with laboratory measurements on palaeomagnetic subsamples from the destroyed daub samples indicate that the NRM can be determined by our proposed method with a maximum error in inclination of 2°, in declination of 20° and in magnetization of ±0.6 A/m. This is accurate enough, for example, to determine from daub pieces of burnt house remains whether the building was burnt and cooled before or after it collapsed.

中文翻译：

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使用场磁力计现场无损测定考古发现的剩磁

考古特征自然剩磁（NRM）的测定可用于磁建模、碎片连接、考古磁测年或古建筑烧-冷-倒序的调查。NRM 的测量通常在实验室中对圆柱形或立方体样品进行。尽管如此，考古发现最好不要被破坏，而且实验室仪器的成本很高。因此，我们提出了一种轻巧便携的测量装置，包括已经可用的场磁力计（最好是铯磁力计），其中任意形状的考古样品，在我们的例子中是一块涂抹物，安装在万向节内，可以向各个方向旋转. 在磁力计保持在固定位置的情况下，在大量旋转位置测量样品的磁场。在这些测量中，样品的 NRM 矢量的未知方向是旋转的，而样品的平均磁化率和环境磁场是恒定且已知的。因此，NRM 的向量可以通过最小二乘反演来确定。对于反演计算，样本体积被离散化为体素模型或近似为等效球体。在取决于样品-传感器距离、偶极矩和样品半径的特定条件下，球体近似是有效的，不会影响结果的准确性。提供了针对不同传感器灵敏度和噪声水平量化这些条件的经验确定函数。对来自被破坏的涂抹样品的古地磁子样品进行实验室测量的验证表明，NRM 可以通过我们提出的方法确定，最大误差为 2°、20° 的倾角和 ±0.6 A/m 的磁化强度。例如，这足以准确地确定建筑物在倒塌之前或之后是否被烧毁和冷却。