Evaluating a UAV-based mobile sensing system designed to quantify
ecosystem-based methane
Abstract
Methane plays an important role in determining the atmosphere’s climate
and chemistry. Fluxes of methane from an ecosystem are often measured
using eddy covariance flux towers; however, there are disadvantages with
this method. Flux towers are expensive to purchase and have high demands
with respect to maintenance and cost of operation, especially in remote
locations, making replication across the landscape a challenge. Using
sensors mounted on a unmanned aerial vehicle (UAV), also known as a
drone, would allow replication of flux measurements across a landscape
as well as enable scientists to measure methane at locations where
towers are not practical (i.e. sites that are ephemeral in nature,
immediately after a disturbance, etc.). In this work, we test the
ability of a UAV equipped with a highly accurate methane sensor to
calculate ecosystem flux using the mass balance method. This method uses
data collected with curtains (transects at various heights) flown both
upwind and downwind of the area of interest. The concentration of
methane within these curtains is then estimated using kriging
techniques. The difference in calculated amounts of methane between the
upwind and downwind curtains is processed to obtain an estimate of flux.
Flights in wetlands that also have eddy covariance towers, providing
corroborating flux values, have been flown in Alaska and California. We
calculated UAV-based flux for the Alaskan flights using a bootstrap
approach from multiple randomly subsampled data points within each full
curtain of data. We compare these calculations to the traditional mass
balance technique. We tested if these different approaches improve the
accuracy of our results, as well as the uncertainty bounds for the small
fluxes emitted from these ecosystems.