Toolik Field Station : Vegetation Mapping
The Bureau of Land Management’s (BLM) Assessment, Inventory, and Monitoring (AIM) Strategy is a national initiative tasked with the design of a reliable mechanism for reporting the status of renewable resources on public lands. The Alaska State BLM Office selected the National Petroleum Reserve Alaska (NPR-A) as an AIM site in line with its mandate of supplying national energy needs, while protecting surface resources. The AIM strategy is four-fold: 1) to develop a consistent set of ecosystem indicators and methods to measure them, 2) develop and implement a statistically valid sampling method, 3) apply remote sensing technologies, and implement data acquisition and management plans. To meet their third objective, BLM tapped the University of Alaska Fairbanks’ (UAF) experience with unmanned aircraft systems (UAS) to conduct a pilot study to determine the feasibility of applying remote sensing technologies to monitor vegetation. Toolik Field Station, 370 miles north of Fairbanks in Arctic Alaska, was chosen as a proxy for NPR-A for this proof-of-concept pilot study, since it is accessible by road and the actual NPR-A is not.
The research team consisted of BLM, Alaska Natural Heritage Program, Alaska Center for UAS Integration (ACUASI), and University of Alaska Fairbanks Scenarios Network for Alaska Arctic Planning. The team assembled at the Toolik Field Station operations site which is operated and managed by the Institute of Arctic Biology at the University of Alaska Fairbanks with support from the National Science Foundation. The site provides a location for environmental monitoring and preservation of long-term research studies, core laboratories and scientific services, and data management. Over 106 academic institutions have participated in research at Toolik since 2008.
The NPR-A ranges from the Coastal Plain of the Arctic Ocean to the northern Foothills of the Brooks Range, and the most common vegetation community is tussock tundra. The landscape stratification developed by the Alaska Natural Heritage Program, however, describes 14 vegetation communities, or strata. The scope of the pilot study was to collect imagery from strata that are in common between NPR-A and the Toolik Lake region. This included the foothills, alpine and floodplain broad strata and excluded the coastal plain and coastal zones.
Mid-August was selected as the optimal time for the mission to occur as it was near the end of the growing season when plant phenology varies from north to south and spectral signatures differ more than during the height of the growing season.
The survey team flew a helicopter to a central location to collect as many samples as possible with UAS flying 77 flights in a 4.5 day window of marginal weather. A clustered random stratified sample strategy was used to randomly identify 10-km cells. BLM AIM protocol uses the line-point-intercept method for sampling vegetation with a plot size of 30 meters radius. The team flew complete coverage of plots with very precise renderings without having to put down ground control points. Some technical challenges were initially encountered, such as the quality of the GPS accuracy, but these challenges were overcome and the pilot study campaign was successful.
Data gathered allowed the production of surface elevation models with the goal of quantifying vegetation height and structure. The combination of imagery and surface model structure provided information useful for identifying broad strata or vegetation communities, and ultimately species within functional types of vascular plants. This data will enable BLM to monitor impacts to habitat while responsibly developing Alaska’s natural resources.