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Vasileios Savvakis
,
Martin Schön
,
Matteo Bramati
,
Jens Bange
, and
Andreas Platis

Abstract

The negative effects of relative humidity to measurements of particulate matter (PM) due to hygroscopic growth are often not inherently handled by low-cost optical particle counters (OPCs). This study presents a new approach in constructing a miniaturized diffusion dryer, for use with an OPC mounted on an uncrewed aircraft system (UAS), namely, the DJI S900 (weight of 7.5 kg and flight endurance of 20 min) for short-term measurements under humid conditions. In this work, an OPC of type N3 (Alphasense) was employed alongside the dryer, with experiments both in the laboratory and outdoors. Evaluation of the dryer’s performance in a fog tank showed effective drying from almost saturated air to 41% relative humidity for 35 min, which is longer than the endurance of the UAS, and therefore sufficient. Changes in the flow rate through the OPC-N3 with the dryer showed a 17% reduction compared to an absent dryer, but the measured PM values remained unaffected. Airborne measurements were taken from four hovering flights near a governmental air pollution station (Mannheim-Nord, Germany) under humid conditions (88%–93%) where the system gave agreeable concentrations when the dryer was in place, but significantly overestimated all PM types without it. At a rural area near the Boundary Layer Field Site Falkenberg (Lindenberg, Germany), operated by the German Meteorological Service (DWD), vertical profiles inside a low-altitude cloud showed sharp increase in concentrations when the UAS entered the cloud layer, demonstrating its capability to accurately detect the layer base.

Open access
Martin Schön
,
Vasileios Savvakis
,
Maria Kezoudi
,
Andreas Platis
, and
Jens Bange

Abstract

Atmospheric aerosols affect human health and influence atmospheric and biological processes. Dust can be transported long distances in the atmosphere, and the mechanisms that influence dust transport are not fully understood. To improve the database for numerical models that simulate dust transport, measurements are needed that cover both the vertical distribution of the dust and its size distribution. In addition to measurements with crewed aircraft, uncrewed aircraft systems (UASs) provide a particularly suitable platform for this purpose. In this paper, we present a payload for the small fixed-wing UAS of the type Multiple-Purpose Airborne Sensor Carrier 3 (MASC-3) for aerosol particle measurements that is based on the optical particle counter (OPC) OPC-N3 (Alphasense, United Kingdom), modified by the addition of a dryer and a passive aspiration system (OPC-Pod). Based on field tests with a reference instrument in Mannheim, Germany, wind tunnel tests, and a comparison measurement with the UAS-mounted aerosol particle measurement Universal Cloud and Aerosol Sounding System (UCASS) during a dust event over Cyprus, we show that the OPC-Pod can measure particle number concentrations in the range of 0.66–31 μm as well as particle size distributions. The agreement of the OPC-Pod with UCASS is good. Both instruments resolve a vertical profile of the Saharan dust event, with a prominent dust layer between 1500 and 2800 m MSL, with particle number concentrations up to 35 cm−3 for particles between 0.66 and 31 μm.

Open access
Aline van den Kroonenberg
,
Tim Martin
,
Marco Buschmann
,
Jens Bange
, and
Peter Vörsmann

Abstract

The meteorological mini unmanned aerial vehicle (M2AV) was used for measuring the meteorological wind. The wind is the vector difference between the aircraft speed relative to the earth (inertial velocity) and relative to the airflow (true airspeed). The latter was computed from five-hole-probe pressure measurements in combination with calibration–coefficient polynomials obtained during wind tunnel calibration. The aircraft inertial velocity, position, and attitude were calculated using a Kalman filter that combined data from a global positioning system (GPS) and an inertial navigation system (INS). The temporal (and spatial) resolution of the M2AV wind measurement is remarkably fine. An inertial subrange of locally isotropic turbulence can be measured up to 40 Hz (or 0.55 m at 22 m s−1 airspeed).

The first M2AV wind estimation showed some systematic deviations compared to the expected values (like a constant mean wind in every flight direction). Therefore, an in-flight wind calibration technique was developed that corrects for the inaccuracy of the true heading, the constant offset of the pitch angle, and the underestimation of the true airspeed. The final adjusted wind measurements were verified during a field experiment at the measurement field of the German Meteorological Service, southeast of Berlin. The mean horizontal and vertical wind measured by the M2AV agreed well with simultaneous sodar and tower measurements.

Full access
Martin Schön
,
Keri Anne Nicoll
,
Yann Georg Büchau
,
Stefan Chindea
,
Andreas Platis
, and
Jens Bange

Abstract

Atmospheric electricity measurements made from small unmanned aircraft systems (UAS) are rare but are of increasing interest to the atmospheric science community due to the information that they can provide about aerosol and turbulence characteristics of the atmospheric boundary layer (ABL). Here we present the first analysis of a new dataset of space charge and meteorology measurements made from the small, electric, fixed-wing UAS model MASC-3. Two distinct experiments are discussed: 1) Flights past a 99 m metal tower to test the response of the charge sensor to a fixed distortion of the electric field caused by the geometry of the tower. Excellent agreement is found between the charge sensor response from the MASC-3 and modeled electric field around the tower. 2) Vertical profiles up to an altitude of 2500 m to study the evolution of the ABL with the time of day. These flights demonstrated close agreement between the space charge profiles and temperature, relative humidity, and turbulence parameters, as would be expected on a fair-weather day with summertime convection. Maximum values of space charge measured were of order 70 pC m−3, comparable with other measurements in the literature from balloon platforms. These measurements demonstrate the suitability of small UAS for atmospheric electrical measurements, provided that care is taken over the choice of aircraft platform, sensor placement, minimization of electrical interference, and careful choice of the flight path. Such aircraft are typically more cost-effective than manned aircraft and are being increasingly used for atmospheric science purposes.

Free access
Matteo Bramati
,
Martin Schön
,
Daniel Schulz
,
Vasileios Savvakis
,
Yongtan Wang
,
Jens Bange
, and
Andreas Platis

Abstract

The use of small uncrewed aircraft systems (UAS) can effectively capture the wind profile in the lower atmospheric boundary layer. This study presents a calibration process to estimate the horizontal wind vector using a rotary-wing UAS in hovering conditions. This procedure does not require wind tunnels or meteorological masts, only the data from the flight control unit and a specific set of calibration flights. A model based on the UAS drag coefficient was proposed and compared to a traditional approach. Validation flights at the German Weather Service MOL-RAO observatory showed that the system can accurately predict wind speed and direction. A modified DJI S900 hexacopter with a Styrofoam sphere casing was used for the study and calibrated for wind speeds between 1 and 14 m s−1. Power spectral density analysis showed the system’s ability to resolve atmospheric eddies up to 0.1 Hz. The overall root-mean-square error was less than 0.7 m s−1 for wind speed and less than 8° for wind direction.

Open access
Jakob Boventer
,
Matteo Bramati
,
Vasileios Savvakis
,
Frank Beyrich
,
Markus Kayser
,
Andreas Platis
, and
Jens Bange

Abstract

One of the most widely used systems for wind speed and direction observations at meteorological sites is based on Doppler Wind LiDAR (DWL) technology. The wind vector derivation strategies of these instruments rely on the assumption of stationary and homogeneous horizontal wind, which is often not the case over heterogeneous terrain. This study focuses on the validation of two DWL systems, operated by the German Weather Service (DWD) and installed at the boundary layer field site Falkenberg (Lindenberg, Germany), with respect to measurements from a small, fixed-wing uncrewed aircraft system (UAS) of type MASC-3. A wind vector intercomparison at an altitude range from 100 to 500 m between DWL and UAS was performed, after a quality control of the aircraft’s data accuracy against a cup anemometer and wind vane mounted on a meteorological mast also operating at the location. Both DWL systems exhibit an overall root mean square difference in wind vector retrieval of less than 22% for wind speed and lower than 18° for wind direction. The enhancement or deterioration of these statistics is analyzed with respect to scanning height and atmospheric stability. The limitations of this type of validation approach are highlighted and accounted for in the analysis.

Open access
Cathy Hohenegger
,
Felix Ament
,
Frank Beyrich
,
Ulrich Löhnert
,
Henning Rust
,
Jens Bange
,
Tobias Böck
,
Christopher Böttcher
,
Jakob Boventer
,
Finn Burgemeister
,
Marco Clemens
,
Carola Detring
,
Igor Detring
,
Noviana Dewani
,
Ivan Bastak Duran
,
Stephanie Fiedler
,
Martin Göber
,
Chiel van Heerwaarden
,
Bert Heusinkveld
,
Bastian Kirsch
,
Daniel Klocke
,
Christine Knist
,
Ingo Lange
,
Felix Lauermann
,
Volker Lehmann
,
Jonas Lehmke
,
Ronny Leinweber
,
Kristina Lundgren
,
Matthieu Masbou
,
Matthias Mauder
,
Wouter Mol
,
Hannes Nevermann
,
Tatiana Nomokonova
,
Eileen Päschke
,
Andreas Platis
,
Jens Reichardt
,
Luc Rochette
,
Mirjana Sakradzija
,
Linda Schlemmer
,
Jürg Schmidli
,
Nima Shokri
,
Vincent Sobottke
,
Johannes Speidel
,
Julian Steinheuer
,
David D. Turner
,
Hannes Vogelmann
,
Christian Wedemeyer
,
Eduardo Weide-Luiz
,
Sarah Wiesner
,
Norman Wildmann
,
Kevin Wolz
, and
Tamino Wetz

Abstract

Numerical weather prediction models operate on grid spacings of a few kilometers, where deep convection begins to become resolvable. Around this scale, the emergence of coherent structures in the planetary boundary layer, often hypothesized to be caused by cold pools, forces the transition from shallow to deep convection. Yet, the kilometer-scale range is typically not resolved by standard surface operational measurement networks. The measurement campaign Field Experiment on Submesoscale Spatio-Temporal Variability in Lindenberg (FESSTVaL) aimed at addressing this gap by observing atmospheric variability at the hectometer-to-kilometer scale, with a particular emphasis on cold pools, wind gusts, and coherent patterns in the planetary boundary layer during summer. A unique feature was the distribution of 150 self-developed and low-cost instruments. More specifically, FESSTVaL included dense networks of 80 autonomous cold pool loggers, 19 weather stations, and 83 soil sensor systems, all installed in a rural region of 15-km radius in eastern Germany, as well as self-developed weather stations handed out to citizens. Boundary layer and upper-air observations were provided by eight Doppler lidars and four microwave radiometers distributed at three supersites; water vapor and temperature were also measured by advanced lidar systems and an infrared spectrometer; and rain was observed by a X-band radar. An uncrewed aircraft, multicopters, and a small radiometer network carried out additional measurements during a 4-week period. In this paper, we present FESSTVaL’s measurement strategy and show first observational results including unprecedented highly resolved spatiotemporal cold-pool structures, both in the horizontal as well as in the vertical dimension, associated with overpassing convective systems.

Open access