Monitoring Surface Condition of Upland Swamps Subject To Mining Subsidence with Very High-resolution Imagery

The project investigated the potential of small UAV platforms to capture imagery of the shrub swamp communities to develop monitoring tools for detecting change in condition and composition that may be correlated to the impacts of longwall underground mining.

The project demonstrated the ability to track individual shrubs and tussock grasses over a 15 month period and developed methodology to automatically generate multi-spectral orthophoto mosaics at sub-decimetre resolutions. The photogrammetric method employed in this project is suited to difficult target geometries and is recommended for future monitoring programs where photogrammetric products are required routinely. Photographic coverage of a single shrub swamp community was achieved with low energy fixed wing UAVs in approximately 30min with set up and recovery requiring approximately equal time (total time 1hr). Patchy cloud cover caused significant variability in illumination of the target during a 30min capture window and created artefacts in the orthophoto mosaic. Variability in illumination also required that sensors for all spectral bands required are carried and triggered simultaneously to allow interpretation of spectral indices. Current positional and attitudinal accuracies combined with the difficult photogrammetric targets presented by shrub swamps limited orthophoto geometric accuracies to 15-40cm errors.

Small UAV platforms provide a niche product that provides hyper-temporal and hyper-spatial imagery at community scale. Ground based measures to support image interpretation should be a combination of marked features of concern and cross community transects. Both should be marked to be inherently visible in the imagery collected.