Perry Canyon, Nevada. Acid Mine Drainage and UAS remote sensing

Weathering and transport of potentially acid generating material (PAGM) at abandoned
mines can degrade downstream environments and contaminate water resources. Monitoring the
thousands of abandoned mine lands (AMLs) for exposed PAGM using field surveys is time intensive.
Here, we explore the use of Remotely Piloted Aerial Systems (RPASs) as a complementary remote
sensing platform to map the spatial and temporal changes of PAGM across a mine waste rock pile on
an AML. We focus on testing the ability of established supervised and unsupervised classification
algorithms to map PAGM on imagery with very high spatial resolution, but low spectral sampling.
At the Perry Canyon, NV, USA AML, we carried out six flights over a 29-month period, using
a RPAS equipped with a 5-band multispectral sensor measuring in the visible to near infrared
(400–1000 nm). We built six different 3 cm resolution orthorectified reflectance maps, and our tests
using supervised and unsupervised classifications revealed benefits to each approach. Supervised
classification schemes allowed accurate mapping of classes that lacked published spectral libraries,
such as acid mine drainage (AMD) and efflorescent mineral salts (EMS). The unsupervised method
produced similar maps of PAGM, as compared to supervised schemes, but with little user input.
Our classified multi-temporal maps, validated with multiple field and lab-based methods, revealed
persistent and slowly growing ‘hotspots’ of jarosite on the mine waste rock pile, whereas EMS
exhibit more rapid fluctuations in extent. The mapping methods we detail for a RPAS carrying a
broadband multispectral sensor can be applied extensively to AMLs. Our methods show promise to
increase the spatial and temporal coverage of accurate maps critical for environmental monitoring
and reclamation efforts over AMLs.