Abstract. During test operation of a geological latent heat storage system as a potential option in the context of heat supply for heating and cooling demands a part of a shallow quaternary glacial aquifer at the “TestUM” test site is frozen. To evaluate the current thermal state in the subsurface the dimension of the frozen volume has to be known. With the target being too deep for high resolution imaging from the surface, the use of borehole Ground-Penetrating-Radar (GPR) is assessed. For imaging and monitoring of a vertical freeze-thaw boundary, crosshole zero-offset and reflection measurements are applied. The freezing can be imaged in ZOP, but determination of ice body size is ambiguous, because of lacking velocity information in the frozen sediment. Reflection measurements are able to image the position of the freezing boundary with an accuracy determined through repeated measurements of ±0.1 m, relying on the velocity information from ZOP. We found, that the complementary use of ZOP and reflection measurements make for a fast and simple method, to image freezing in geological latent heat storage systems. Problematic is the presence of superimposed reflections from other observation wells and low signal-to-noise ratio. The use in multiple observation wells allows for an estimation of ice body size. A velocity model derived from zero-offset profiles (ZOP) enabled to extrapolate geological information from direct-push based logging and sediment cores to a 3D-subsurface model.

中文翻译：

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结合跨孔和反射钻孔探地雷达进行浅层含水层控制冻结成像

摘要。在地质潜热储存系统作为供暖和制冷供热需求的潜在选择的测试运行过程中，“TestUM”测试地点的浅层第四纪冰川含水层的一部分被冻结。为了评估地下当前的热状态，必须知道冻结体积的尺寸。由于目标太深，无法从地表进行高分辨率成像，因此对钻孔探地雷达 (GPR) 的使用进行了评估。为了对垂直冻融边界进行成像和监测，采用了跨孔零偏移和反射测量。冻结可以在 ZOP 中成像，但由于冻结沉积物中缺乏速度信息，冰体尺寸的确定不明确。反射测量能够根据ZOP 的速度信息对冻结边界的位置进行成像，精度通过重复测量确定为 ±0.1 m 。我们发现，ZOP 和反射测量的互补使用可以提供一种快速而简单的方法，以在地质潜热存储系统中进行图像冻结。问题是存在来自其他观测井的叠加反射和低信噪比。在多个观测井中的使用可以估计冰体的大小。从零偏移距剖面 (ZOP) 导出的速度模型能够将地质信息从基于直推的测井和沉积物岩心推断到 3D 地下模型。