Development of a small unmanned aircraft system to derive CO ₂ emissions of anthropogenic point sources

A reduction of the anthropogenic emissions of inline-formulaCO₂ (carbon dioxide) is necessary to stop or slow down man-made climate change. To verify mitigation strategies, a global monitoring system such as the envisaged European Copernicus anthropogenic inline-formulaCO₂ monitoring mission (CO2M) is required. Those satellite data are going to be complemented and validated with airborne measurements. Unmanned aerial vehicle (UAV)-based measurements can provide a cost-effective way to contribute to these activities. Here, we present the development of an sUAS (small unmanned aircraft system) to quantify the inline-formulaCO₂ emissions of a nearby point source from its downwind mass flux without the need for any ancillary data. Specifically, inline-formulaCO₂ is measured by an NDIR (non-dispersive infrared) detector, and the wind speed and direction are measured with a 2-D ultrasonic acoustic resonance anemometer. By means of laboratory measurements and an in-flight validation at the ICOS (Integrated Carbon Observation System) atmospheric station Steinkimmen (STE) near Bremen, Germany, we estimate that the individual inline-formulaCO₂ measurements have a precision of 3 inline-formulappm and that inline-formulaCO₂ enhancements can be determined with an accuracy of 1.3 inline-formula% or 0.9 inline-formulappm, whichever is larger. We introduce an anemometer calibration method to minimize the effect of rotor downwash on the wind measurements. This method derives the fit parameters of a linear calibration model accounting for scaling, rotation, and a potential constant bias. For this purpose, it analyzes wind measurements taken while following a suitable flight pattern and assuming stationary wind conditions. From the calibration and validation experiments, we estimate the single measurement precision of the horizontal wind speed to be 0.40 inline-formulam s⁻¹ and the accuracy to be 0.33 inline-formulam s⁻¹. By means of two flights downwind of the ExxonMobil natural gas processing facility in Großenkneten about 40 inline-formulakm west of Bremen, Germany, we demonstrate how the measurements of elevated inline-formulaCO₂ concentrations can be used to infer mass fluxes of atmospheric inline-formulaCO₂ related to the emissions of the facility.