MMAV—a miniature unmanned aerial vehicle (Mini-UAV) for meteorological purposes

At the Institute for Aerospace Systems, Technical University of Braunschweig, Germany, the "Carolo" family of miniature unmanned aerial vehicles was developed. The hand-launched aircraft operate completely autonomously from start to landing. They have wingspans from 0.40 m to 1.40 m and take-off weights from 0.4 kg up to 2 kg. The largest version has an endurance longer than 30 minutes and allows for payloads up to 0.3 kg (tradeoff with endurance). These features, combined with easy handling and complete reusability, make it a useful carrier for meteorological probes in the atmospheric boundary layer.

The flight trajectory is defined by means of a special ground control software running on a common PC or notebook. The user simply sets waypoints on a digital map. The waypoint list is checked for violations of flight-mechanical or regulatory limits and transferred to the aircraft. After the start, the mission is conducted completely autonomously, but can be supervised via telemetry link. This also allows for adjustments to the mission at any time.

Basic meteorological applications are the measurement of the air temperature, humidity, pressure and the wind vector. The latter will be achieved using three dimensional GPS and inertial measurements for attitude alignment, and a miniature five-hole probe. The aircraft is already equipped with a static pressure sensor, needed for the autopilot system, and a digital camera. The implementation of sensors for humidity and temperature is in progress. For humidity, a HumiCap with a comparably low time response will be used. The temperature will be measured by two sensors, one sealed Pt100 element for long-term stability and accuracy and one open element with fast response time and high relative accuracy. The nominal sampling frequency will be approximately 30 Hz, which leads to a spatial resolution of 0.5 m at a nominal flight speed of 15 m/s. Chemical thin-film sensors for the measurement of air pollution and trace gases are scheduled.

With the basic set of meteorological sensors, the aircraft forms a reusable auto-homing radio probe for the lower atmosphere (up to 2 km). This system permits very short measurement cycles as an economic supplement during meteorological campaigns. Besides this classical measurement tasks, the aircraft enables completely new applications. For example, the altitude controller of the aircraft can be adjusted not to follow the barometric pressure, but to follow the potential temperature in thermally stable layers. Due to its high agility, the aircraft can follow even small spatial structures. Combined with the data logging of the exact position, this enables the mapping of equi-isentropic planes, thus visualizing the potential temperature's spatial distribution.

The first measurement flights will take place this year, the implementation of the miniaturized five-hole probe, which now passes through wind tunnel tests, is scheduled for 2005.