By Shane Zentner, GISP
The Brierley GIS team uses aerial drones equipped with thermographic cameras that aid our ability to detect subsidence features associated with abandoned underground mines throughout southeast Wyoming. Additionally, the combination of aerial and photographic technologies efficiently documents pre-existing conditions with respect to infrastructure, surface features and buildings. Assisting with mine subsidence investigations, Brierley’s DJI M210/M300 UAS (unmanned aerial system) is equipped with an XT2 thermal imaging sensor that includes two cameras – one thermal, and one color which are deployed side-by-side and allows detailed analytics for imagery comparison with baseline conditions.
Thermal imagery collection involves flying at an altitude of 200-400 feet above ground level at a pre-programed flight path with survey ground control. This is an important aspect for repeatable imagery collection to analyze change in conditions overtime. Each mission produces hundreds of images that are stitched together using processing software and built into an orthomosaic dataset which is stored on ESRI’s Site Scan Cloud for ArcGIS viewing and downloading, either by Brierley Technical Staff or our client.
Our pre-construction imagery missions focus on hard surfaces like sidewalks, roadways and exposed ground. These missions require the UAS pilot to fly within 20-30 feet of the target object. The thermal imagery produced from these low altitude missions allows our team to document temperature variations, that might be associated with pre-existing damage, ground deformation or a geohazard. One key aspect of low altitude thermal and color imagery is documenting the absence or presence of features that might be indicative of ground movement or latent damage. Having this information in hand prior to implementing sub-surface void mitigation helps to determine local surface changes or shallow groundwater fluctuations.
Many Wyoming coal mines were operating at the turn of the century, but 21st century technologies are being used as an investigation tool to better understand the potential consequences of historical subsurface mining to deliver successful mitigation strategies. Thermal imagery is one of many tools that help Brierley Associates “fill space underground.”