Currently there is no common altitude reference for manned and unmanned aviation, or between different drone manufacturers. Traditional methods to determine altitude, and ensure vertical separation, are based on pressure altitude.

Partners in the ICARUS project are developing a universal flight altitude reference system based on a geodetic approach as opposed to the traditional barometric based system used in manned aviation.

Altitude information is critical for traditional aviation since it is needed to avoid collisions with ground obstacles and maintain vertical separation between aircraft. That’s why pilots measure and transmit their altitude continuously.

Currently, drones use both barometric and satellite systems to measure their altitude. However, barometric altitude measurements are affected by local environmental conditions, for example temperature gradients in built areas. Also, drones can take off and land almost everywhere, not only from designated airfields, ruling out the local barometric altitude system as a common reference.

This is where satellite systems come in. The geodetic altitude computed using global navigation satellite systems (GNSS) using multi constellation configurations introduce significant improvements as the basis for common altitude reference for drones, especially in very low-level airspace. The accuracy of the altitude estimation is enhanced, i.e. altitude measured in centimetres rather than in tens of feet, while augmentation techniques (such as the European EGNOS system) ensure a high precision and error detection.

The ICARUS project will develop a solution and validate in real-life environment using a new U-space service that will provide, at the strategic (flight planning) and tactical (flight execution), phases:

• Real-time information of vertical distance to the ground, to ensure collision avoidance, and
• Conversion of different altitude reference systems, to ensure vertical separation of traffic

Ultimately, the project aims to develop the safest possible system for a common altitude reference system to address the needs of manned and unmanned traffic.

This project has received funding from the SESAR Joint Undertaking within the framework of the European Union's Horizon 2020 research and innovation programme under grant agreement No 894593.