Logistical and technical considerations for the use of unmanned aircraft systems in coastal habitat monitoring: A case study in high-resolution subaquatic vegetation assessment

In recent years, the technology and regulation surrounding the use of unmanned aircraft systems (UASs) has rapidly advanced. This has resulted in the availability of such technology for more common applications. Here we compare manned versus UAS platforms for acquiring high-resolution imagery of subaquatic habitat for the purpose of boat propeller scar delineation in seagrass meadows in Redfish Bay, Texas. We acquired aerial seagrass imagery in three 20-hectare plots using two UASs and one manned aircraft platform. The three plots represented a priori designations of low, moderate, and high seagrass scarring intensity. Overall, we observed that a smaller amount of scarring was detected in the manned aircraft imagery compared to that collected by the two UAS platforms, and that this disparity was much greater for the high scarring intensity plot. The observed differences in scar feature delineations were at least partially related to logistical difference between these two platforms — specifically, the lower altitude flown by the UASs results in a higher spatial resolution of the imagery that is less dependent on the camera specifications. From a logistical standpoint, the potential gain in spatial resolution via lower altitude flight could result in a reduced pricetag for high-resolution mapped products. Further, the rapid deployment and local operation typically resulting from the accessibility of UAS training greatly simplify the logistics of planning imagery acquisition at the appropriate scale. However, we realize that the current trade-off with regard to higher altitude is the ability to cover large areas with fewer transects and shorter flight time. Coverage limitations for UASs is currently rooted in both technological and legal issues. However, as technology and regulations evolve, the technical and logistical comparison of imagery products from UAS and manned platforms will become increasingly important to natural resource managers and researchers looking to make this transition to UAS.