Airborne geophysical survey: Menominee, Michigan

Aeromagnetic data were collected along flight lines by instruments in an
aircraft that recorded magnetic-field values and locations. In the earlier
days of surveying, the only way to represent this data was to generate an
analog map with contour lines. This dataset is a representation of the
digitized contour lines either by following the lines or by choosing the
intersection of the contour and flight-line to create a value of the magnetic
field. The values presented are latitude, longitude, and map magnetic-field
values.

航空磁力数据（aeromagnetic data）由航空器搭载的测量仪器沿飞行航线（flight lines）采集，同步记录磁场强度数值与测点位置信息。在航空磁测发展初期，此类数据的唯一可视化表达手段为绘制带有等值线（contour lines）的模拟地图（analog map）。本数据集为数字化等值线成果：通过沿等值线追踪采样，或提取等值线与飞行航线的交点以生成对应磁场数值。数据集包含的字段为纬度、经度与图载磁场数值。