UAV-based approaches for gaseous emissions assessment in cattle farming

The use of unmanned aerial vehicles (UAVs) as in-flight sensing platforms for atmospheric chemical research is rapidly growing, with an increasing number of field studies published in the past 5 years and with the appearance on the market of gas sensors specifically designed for UAVs. Nevertheless, the main applications are connected to air quality and emission monitoring in urban or industrial contexts. Aiming to provide a comprehensive view on the perspectives of application in dairy farming, we investigated and tested UAV-based approaches for gaseous emissions assessment focusing on equipment (drones, sensors), technical solutions and methods for fluxes estimation. While rotorcrafts represent the primary option, due to their manoeuvrability and autonomous GPS-based hovering, drone size choice largely varies depending on the utilized gas sensing equipment. Non-Dispersive Infrared Sensors (NDIR) are considered suitable for measuring CO2, with small-sized and low-cost options available and providing sufficient accuracy. Measuring CH4 in farming contexts requires sensors with appropriate limit of detection and accuracy. Finding miniaturized and low-cost options on the market with such performances is currently challenging since most available sensors, both electrochemical and NDIR, have limits of detection of 100 ppm. Methane sensing over livestock facilities, thus, requires high accuracy sensors that can be used in-flight. Ground-based analysers (e.g. CRDS analysers) are also used to measure methane and N2O concentrations using UAVs as mobile platforms for air sampling. When coming to fluxes estimation using UAVs, current methods rely on mass balance or on the use of plume inversion techniques. Both approaches require the simultaneous collection of accurate gas measurements and atmospheric data as temperature, relative humidity, atmospheric pressure and wind measurements. Together with literature information, the outcomes of an experimental application of a prototype multi-sensor platform for UAV and ground gaseous measurements in cattle dairy farms is presented and discussed.