Geospatial Accuracy of Small Unmanned Airborne System Data in the Coastal Environment

May 1, 2019

Army Engineer Research and Development Center, Alexandria, Virginia

The purpose of this study was to assess the ability of commonly available COTS software to produce geometrically accurate orthometric mosaics and terrain models from low-altitude UAS imagery.

Sample flight plan over the FRF site generated by the SenseFly eMotion flight planning software. In this example flight plan, both east/west and north/south flight lines are shown.

The coastal zone is a dynamic environment that requires temporal monitoring from flexible remote sensing tools. Changing weather, winds, and tides introduce difficulties when attempting to use sensors that are constrained by schedule to include satellite overflight or aircraft with hard collection dates and times. However, these collection requirements are well suited for small unmanned airborne system (UAS) platforms that can be deployed and made operational with minimal notice. Additionally, the low collection altitude, combined with short focal length imagers (often integrated into these small UAS platforms) are capable of producing very high spatial resolution horizontal and vertical data. These data have direct application for addressing many of the questions associated with coastal environments including beach and dune erosion, wetland conditions, impervious surface mapping, and species composition/health.

Along with the growth of small UAS aircraft has been the related development of many processing software packages to exploit these new data sources. Current commercial-off-the-shelf (COTS) and government-off-the-shelf software are capable of harnessing the multi-core, multi-graphical processing unit architectures. The four software packages selected for this study represent a cross section of use within the community and the USACE. The software packages chosen were: 1) Agisoft Photoscan, 2) SimActive Correlator3D, 3) Bentley Context Capture, and 4) École Polytechnique Fédérale de Lausanne (EPFL) Pix4D.

These packages are very efficient at addressing problems that require solving many independent calculations, which is exactly the case with photogrammetric processing. This capability has migrated photogrammetric processing (traditionally executed on high-end, expensive workstations) to low-cost commodity notebook personal computers (PCs). The UAS data processed by these software packages was collected from a Sensefly eBee UAS over the USACE Field Research Facility (FRF) in October 2015 and September 2016. Ground control had been placed and modified periodically over that time period (unrelated to the eBee flights) and was utilized to perform image mosaic georegistration and evaluate positional accuracy.

While most of the COTS tools have the same basic functionality, there are substantial differences with detailed capabilities, cost, ease of use, integration to platforms, and adaption to existing workflows. These parameters will differ by data requirements and final usage. Even within the U.S. Army Corps of Engineers (USACE), different laboratories and sections may desire/require different end products. However, some processes and products are relatively standard across users and applications, specifically the generation of the digital surface/elevation models as well as orthometric mosaics. These were the products generated and analyzed as part of this effort.

This work was done by Robert L Fischer, Jeffrey G. Ruby, Aaron J. Armstrong, and Jarrod D. Edwards, Nicholas J. Spore and Katherine L. Brodie for Army Engineer Research and Development Center. ERDC-0005