与激光雷达一起去黄金

Airborne LiDAR is a fast and relatively inexpensive means of gathering topographic information critical to the success and safety of mining operations. McElhanney Consulting Services Ltd. of Vancouver, B.C., Canada, has introduced two new bare-earth mapping services developed specifically for the exploration and exploitation phases of the mining industry. In the first application, McElhanney used LiDAR to find surface structures and lineaments that have been missed by aerial photography and satellite imaging because of dense vegetative cover. McElhanney, an engineering, mapping, and surveying company, verified the use of LiDAR bare-earth digital elevation models (DEMs) for lineament and fault identification in a gold mining district of British Columbia.

Surface lineaments are linear ground features associated with complex subsurface geological structures, including faults, fractures, and other features such as contacts between different rock types. Sometimes just a half meter wide, lineaments may extend for hundreds of meters in length. Due to their large scale, these features can be difficult to spot from ground level, and they can be even harder to see in most remotely sensed imagery if obscured by vegetation or loose sediment.

“轮廓提供地下地质的线索nd are a valuable aid to geological mapping – a crucial part of any gold exploration or mine engineering project,” says Azadeh Koohzare, Ph.D., P.Eng. “Geologists can interpret the pattern and direction of these surface features and, as many gold deposits are associated with geological structures, use this information when selecting and prioritizing exploration targets.”

点密度高要求
揭示隐藏表面地质的关键是一种强大的多元气载激光扫描仪或激光雷达，解释了Koohzare。McElhanney拥有三个Leica Geosystems LiDAR扫描仪和两个Leica Geosystems ADS数码相机，使用Leica ALS60启动了座位映射项目，并正在升级到更强大的500 kHz ALS70-HP系统。

这些LiDAR系统提供的至少两个平方米的点（每2.4平方码2点）生成具有准确性和分辨率足以揭示狭窄线性表面特征的裸露DEM所需的密度。在不列颠哥伦比亚省的试点项目中，麦克尔汉尼（McElhanney）以2500 - 3,000 m（8,200 - 9,800 ft）的海拔高于平均海平面以收集数据集的高度运营LIDAR。标准处理删除了与植被相关的收益，以产生一个裸露的DEM，其垂直（4英寸）和30至50 cm（12至20英寸）的水平精度。

“The Leica Geosystems ALS LiDAR operates with a high pulse rate to ensure the vegetation is penetrated with a point density that is sufficient to find surface lineaments measuring just 50 cm (20 in) in width,” says Koohzare. “And the high power of the unit means the dense point data can be captured at high aircraft speed, which saves time and money.”

地面沉降
McElhanney devised its idea for ground subsidence monitoring in Saskatchewan where potash deposits are mined and used for fertilizer. Potash extraction poses a higher risk of ground subsidence than many other types of mining because the evaporate deposits are found in soft rock formations that are structurally less than ideal for tunneling. As a result, potash mines must be continually monitored for subsidence or sinking of ground above and around the excavation site.

Koohzare说：“矿山上方的沉降提前警告说，内部人员可能有洞穴或倒塌的危险。”他补充说，沉降和抬高可能会导致从矿山朝任何方向朝任何方向造成5公里（3英里）的问题地点。除了矿山内部的危险外，地面运动还可以切断管道，损坏道路和在受影响地区的裂缝建筑基础。

通常使用昂贵且耗时的传统地面调查技术来监测钾盐矿以及其他矿产提取项目周围的沉降。麦克埃尔汉尼（McElhanney）根据数百个项目的激光运营，其中许多涉及能源和采矿客户，说空中雷达是监测地面沉降的最快，最具成本效益的方式。

The 10 cm (4 in) vertical accuracy of bare-earth DEMs routinely generated from the firm’s Leica ALS60 and ALS70 laser scanners can identify significant shifts in the ground surface – either up or down – that may signal dangerous conditions in the mine. McElhanney recommends collecting an initial baseline data set above each mine site and then continuing to collect new data every year. Once subsidence is revealed, monitoring flights should be repeated while steps are taken inside the mine to minimize the danger.

与谱系映射一样，LiDar传感器的高孔速率对于在矿场周围穿透营养冠层至关重要，以获得地面或裸露地面的非常准确的高程测量。

The Leica ALS70 is one of the few airborne laser scanners with the power and multi-pulse capability able to provide the quality of bare-earth DEM required for these mining applications.

Written by Kevin P. Corbley