Base control points of the aquifer contours enhanced with airborne electromagnetic (AEM) surveys of the principal aquifer for portions of the North Platte, South Platte, and Twin Platte Natural Resources Districts, western Nebraska

The U.S. Geological Survey and its partners have collaborated to complete airborne geophysical surveys for areas of the North and South Platte River valleys and Lodgepole Creek in western Nebraska. The objective of the surveys was to map the aquifers and bedrock topography of selected areas to help improve the understanding of groundwater-surface-water relationships to be used in water management decisions. Frequency-domain (2008 and 2009) and time-domain (2010) helicopter electromagnetic surveys were completed, using a unique survey flight line design, to collect resistivity data that can be related to lithologic information for refinement of groundwater model inputs. To make the geophysical data useful to multidimensional groundwater models, numerical inversion is necessary to convert the measured data into a depth-dependent subsurface resistivity model. This inversion model, in conjunction with sensitivity analysis, geological ground truth (boreholes), and geological interpretation, is used to characterize hydrogeologic features. The two- and three- dimensional interpretation provides the groundwater modeler with a high-resolution hydrogeologic framework and a quantitative estimate of framework uncertainty. This method of creating hydrogeologic frameworks improved the understanding of the actual flow path orientation by redefining the location of the paleochannels and associated bedrock highs. The improved models represent the hydrogeology at a level of accuracy not achievable using previous data sets.

美国地质调查局（U.S. Geological Survey）及其合作伙伴已合作完成内布拉斯加州西部北普拉特河谷、南普拉特河谷与洛奇波尔溪区域的航空地球物理勘测项目。本次勘测的核心目标是绘制选定区域的含水层与基岩地形分布图，以深化对地下水-地表水相互作用关系的认知，为水资源管理决策提供科学支撑。本次勘测采用独特的测线布局方案，完成了2008、2009年度的频域及2010年度的时域直升机电磁勘测，采集可与岩性信息关联的电阻率数据，用于优化地下水数值模型的输入参数。为使地球物理数据可适配多维地下水模型，需通过数值反演将实测数据转换为深度依赖型地下电阻率模型。该反演模型结合敏感性分析、地质实地验证数据（钻孔资料）与地质解译结果，可用于表征区域水文地质特征。二维与三维解译可为地下水建模人员提供高分辨率水文地质框架，以及该框架不确定性的定量估算结果。本研究方法通过重新确定古河道及相关基岩高地的空间位置，深化了对实际径流路径走向的认知。优化后的模型以过往数据集无法企及的精度表征了区域水文地质条件。