The UA/NSSL Remotely Piloted Vehicle

Small aircraft have been explored for in situ meteorological measurements since, at least 1970 when Konrad et al. used a small radio-controlled airplane to make temperature and humidity soundings from the surface up to a height of 800 m. Holland et al.(1992) and McGeer and Holland (1993) developed a small RPV for atmospheric measurements (Aerosonde). Their RPV is fully autonomous, costs over US$20,000 and is capable of ranging over 7,000 km in flights lasting up to 4 days.

We developed a very economical (costing less than US$2,500, including the costs of the radiosonde sensors) reusable RPV for in situ measurements from the surface up to the middle troposphere. Our goal was to build a sturdy model airplane (weighing less than 5 kg) carrying radiosonde sensors to make high quality measurements of pressure, temperature, and humidity in the lower troposphere. In order for the pilot at the ground to be able to fly the radio-controlled RPV out-of-visual range, it is equipped with a simple autopilot, a GPS radio receiver, and a telemetry system to send the data in real time to the ground station.

In particular, our RPV consists of a model airplane containing a simple autopilot, a Vaisala RS-80 radiosonde, circuitry for decoding the radiosonde signal, a GPS radio receiver, a terminal node controller (TNC) for digitizing the radiosonde and GPS signals, and a 2 m radio transmitter for sending the signals to a ground receiver. The ground station consists of a 2 m radio receiver, a TNC, a laptop computer, an automatic positioning system (APRS) software, and software for decoding the radiosonde signal. The autopilot is used keep the RPV stable when it flies out-of-visual range or through a convective vortex. The wind speed can be estimated using the RPV's on-board GPS sensor which is used to monitor the RPV's horizontal position and ground velocity.

Our RPV is flown either autonomously or by a pilot at the ground, while its location and ground velocity are telemetered to the ground station every two seconds. The RPV's location and the velocity vector are plotted in a map displayed in a laptop computer. The RPV is portable and can be easily disassembled for transport. The small size and low weight of the RPV makes it sufficiently durable that even severe atmospheric turbulence does not cause structural damage. Thus, our RPV is sufficiently inexpensive to allow for occasional losses. Therefore, it shows considerable promise for measurements in cumulus clouds and perhaps even in thunderstorms. Our RPV has been used to make soundings from the surface to about 4 km altitude.