Exploring the potential of the RPA system SUMO for multipurpose boundary-layer missions during the BLLAST campaign

Abstract

Abstract. In June and July 2011 the RPAS (Remotely Piloted Aircraft System) SUMO (Small Unmanned Meteorological Observer) performed a total number of 299 scientific flights during the BLLAST (Boundary Layer Late Afternoon and Sunset Turbulence) campaign in southern France. Three different types of missions were performed: vertical profiling of the mean meteorological parameters (temperature, humidity and wind), horizontal surveys of the surface temperature and horizontal transects for the estimation of turbulence. The manuscript provides an introduction to the corresponding SUMO operations, including regulatory issues and the coordination of manned and unmanned airborne operations for boundary-layer research that have been pioneered during the BLLAST campaign.The main purpose of the SUMO flight strategy was atmospheric profiling at high temporal resolution. A total of 168 profile flights were performed during the campaign with typically more than 10 flights per Intensive Observational Period (IOP) day. The collected data allow for a detailed study of boundary-layer structure and dynamics and will be used for further analysis, e.g. the determination of profiles of sensible and latent heat fluxes. First, tests of a corresponding method have shown very promising results and have provided surface-flux values in close agreement with those from ground-based eddy-covariance measurements. In addition, 74 horizontal surveys of the IR emission of the surface were performed at altitudes of around 65 m. Each of those surveys covers a typical area of around 1 km 2 and allows for an estimation of the surface-temperature variability, important information for the assessment of the heterogeneity of the surface forcing as a function of soil and vegetation properties. The comparison with other surface-temperature measurements shows that the raw data of the airborne and ground observations can differ considerably, but that even a very simple multiple regression method can reduce those differences to a large degree. Finally, 49 flight missions for the measurement of velocity variance have been realized during the BLLAST campaign. For that, SUMO has been equipped with a 5-hole probe (5HP) sensor for the determination of the flow vector at 100 Hz. In particular, for this application there is still need for further improvement, both with respect to the aircraft and sensor hard-and software, and the algorithms and methods for data analysis and interpretation. Nevertheless, the SUMO operations during the BLLAST campaign have shown the vast potential of small and lightweight RPA systems with low infrastructural demand for atmospheric boundary-layer research.

Proof of concept for turbulence measurements with the RPAS SUMO during the BLLAST campaign

“…Three peaks are visible (at ∼ 1 Hz for u and v and at ∼ 2 Hz for w), which we relate to aircraft control mechanisms in the horizontal and the vertical directions (Reuder et al, 2016). This will be investigated in more detail in the future, so that we can most appropriately remove this contribution from the SUMO data.…”

“…The two basic assumptions that have to be fulfilled are Taylor's hypothesis and horizontal homogeneity. As described by Lothon et al (2014) the area of interest was characterized by different kinds of surfaces, partially causing significant differences in the surface temperature (Reuder et al, 2016), and consequently in the surface forcing expressed by sensible and latent heat fluxes. These surface heterogeneities are likely to influence the two measurement systems in different ways.…”

“…For more information on the missions the reader is referred to Lothon et al (2014) and Reuder et al (2016). All turbulence flights took place in the vicinity of the two main instrumented locations in the campaign area, Site 1 and Site 2 (Lothon et al, 2014).…”

“…5) in fairly constant values over one flight leg, but in a slight decrease over the whole flight due to the charging level of the battery, which is at the moment only compensated for in a simple linear way. A more detailed description of the SUMO airframe and the sensors used during the BLLAST campaign is given in Reuder et al (2016).…”

Estimation of the advection effects induced by surface heterogeneities in the surface energy budget

“…The air temperature was measured by a Sensirion SHT 25 sensor, mounted inside a radiation protection tube on the wing, while the surface temperature was estimated with a MLX90614 IR sensor, which had an angle of view of approximately 90 • , with an effective resolution at the ground close to 100 m. The typical ground speed was around 20 m s −1 . The SUMO operations during the BLLAST campaign and the data processing of the surface temperature data are described in detail in Reuder et al (2016). Meso-NH: the simulation outputs of this non-hydrostatic model (Lafore et al, 1998) are used.…”