Use of Micro-UAS for Estimation of Turbulent Surface Fluxes of Heat and Moisture

Unmanned aircraft systems (UAS) are beginning to see widespread use in observing the Earth system.  The range of scales in aircraft employed is large, ranging from 10s of centimeters to the NASA Global Hawk, with a wingspan of over 35 meters.  One of the most attractive classes of unmanned aircraft for reseach is the “micro” UAS class, consisting of vehicles in categories 1 or 2 of the latest Federal Aviation Administration guidelines, and including vehicles under five pounds of total weight.  One such platform is the University of Colorado DataHawk aircraft, with a wingspan of just over one meter, and a total weight under one kilogram.  This aircraft has been deployed around the world to make scientifically relevant measurements of the lower troposphere.  Its low cost (<$1000), ease of deployment and small operational footprint make it a flexible observational platform.

One of the most desirable measurements obtainable from such a vehicle is information on turbulent fluxes of heat and moisture at the Earth’s surface.  These measurements of the surface sensible and latent heat fluxes come with a variety of challenges related to instrument response times, accuracy and ability to fly in the correct location.  The DataHawk provides measurements of temperature (fast and slow), atmospheric humidity, pressure, winds, and surface temperature necessary to estimate the transfer of heat between the atmosphere and the underlying surface.  Additionally, this platform allows access to regions where it is difficult to deploy traditional flux measurement systems often deployed on towers, ships, or manned aircraft, with flights completed at altitudes as low as 2 m above the Earth's surface.

In this presentation, we will provide an overview of the measurement techniques applied to this platform and provide examples of flux measurements made.  This includes work spent characterizing and calibrating instrumentation, direct comparisons with traditional flux sensor packages, and examples of fluxes measured from a variety of locations.  This includes information on turbulent fluxes over a variety of Arctic surface types including thawed and frozen tundra, ponds, the Arctic Ocean and over sea ice, obtained during multiple deployments to the Oliktok Point facility on the North Slope of Alaska.  We will provide insight into the biggest challenges for flux estimation with these platforms, as well as a glimpse into new directions being pursued to improve measurement accuracy.