The Multi-Purpose Airborne Sensor Carrier (MASC) is a small unmanned aerial vehicle (UAV) developed for atmospheric boundary layer research. It is designed and operated by the Environmental Physics group at the Eberhard Karls Universität Tübingen, Germany.
The typical payload for this UAV is a meteorological measurement system, designed to calculate turbulent fluxes. Compared to terrestrial systems or aircrafts, the MASC UAV is a cost-effective and valuable tool for researches such as wind energy plant site evaluation in complex terrain.
“IN-FLIGHT” WIND SPEED COMPUTATION
In-flight wind computation might be tricky because airspeed and incident angles, measured by the embedded
airflow probe, need to be compensated by the actual UAV behavior. By subtracting the UAV ground speed and attitude from the airflow vector, wind speed and direction can be calculated. Thus, a precise inertial measurement unit is crucial to perform the UAV flight analysis.
IG-500N, CHOSEN FOR UAV FLIGHT ANALYSIS
Turbulence plays an important role in the transport and exchange of energy in the lower atmosphere. A high data rate is required to record these very fast fluctuations in the wind speed.
“We were looking for a precise inertial measurement unit. Required specifications were an accuracy in attitude angles of <1°, and a high data output rate (100Hz)” declares Uwe Putze,
Dr.-Ing. at the Eberhard Karls Universität Tübingen. As the unit had to be mounted in a small unmanned aerial vehicle, small size and low weight were also important for the project. “The IG- 500N was selected because it fulfills all the requirements and provides a unique balance of accuracy, size and weight,” adds the Project Engineer. Small-size and light-weight, the IG-500N offersmore than attitude and heading measurement. It fuses inertial data with GPS and pressure sensor information to provide a robust position and an enhanced altitude accuracy. The report showing the sensor dynamic calibration over the full temperature range made the team even more confident that the system would meet the announced
IG-500N, MORE ACCURATE THAN EXPECTED
The IG-500N has been easily integrated into the on-board measurement computer through a serial interface.
While the airflow probe measures airspeed and incident angles, the IG-500N records the UAV position, ground speed, and attitude angles. Raw data is stored in the computer, and can also be displayed in real-time on the ground station, thanks to a telemetry link.
By using this sensor, the system can measure wind speed with an accuracy of +/- 0.5 metres per second in all threes axes, and record speed variation at up to 20Hz. The output rate of 100Hz made any data interpolation unnecessary.
As a conclusion, Dr-Ing. Putze adds “We were surprised by the high quality of the output data. We use the IG-500N in our wind measurement probe. To estimate the accuracy of the resulting wind measurement, we did an error calculation based on the accuracy written in the IG-500N data sheet. The analysis of the actual measurement data showed a better accuracy than what was announced.”
The measurement system has been tested in several field campaigns. Based on several results and experience, the Environmental Physics Group works on improving the system and data analysis tools to further increase accuracy.
As the IG-500N performed so well during tests, the group is already integrating the sensor in several other
Dr.-Ing. Uwe Putze, Eberhard Karls
& Hélène Leplomb, SBG Systems