Airborne implements two technologies, namely ARVA and RECCO. The ARVA and RECCO technologies are different and often simultaneously used in real scenarios.
The ARVA system is composed by two elements which are a transmitter, worn by the missing people, and a receiver, held by the rescuer. The transmitter is active and emits a pulsating (electro-)magnetic field, which looks like a classic magnetic dipole (see Figure), which is sensed by the rescuer’s device (and in perspective installed on the drone).
The available data, at the receiver side, are the angle d between the longitudinal receiver direction and the magnetic field, and the distance d inversely proportional to the modulus of the magnetic field (see Figure). These two outputs assume different values based on the three operative search phases introduced in the previous section:
- Primary search: When the victim is outside the sensor range the two sensor outputs (d, d) are meaningless and both conventionally fixed to “-1”;
- Secondary search: as soon as the receiver get sufficiently close to the transmitter, a valid ARVA is captured and the sensors provides the angle d and the distance d to the victim (see Figure).
- Tertiary search (pinpointing): as soon as the intensity of the magnetic field exceeds a certain threshold, which happen when the sensor gets really close to the victim, the receiver only outputs the distance d to the victim. The final search, then, is only conducted with an intensity measure.
Also the RECCO technology is based on two devices which are a transceiver and a reflector. In particular the transceiver is held by the rescuer and is composed by a transmitter and a receiver. The transmitter emits an electro-magnetic field which, echoed by the reflector worn by the missing people, is elaborated by the receiver to provide a acoustic feedback to the rescuer. The signal intensity varies based on the relative distance between the transceiver and the reflector and their relative orientation. For this reason the rescuer is called to rotate the transceiver for finding, for each relative position, the best relative attitude maximizing the sound intensity. Furthermore, the rescuer can regulate the transceiver output power during the search operation in order to pass from a course search to the final accurate pinpointing. In particular the search procedure is the following:
- Rescuer start with the transceiver set at the maximum power. In these operative condition the geometric range in which the reflector can be detected is wide and so not accurate;
- Once the first signal is detected, the rescuer gradually decreases the emitted power which approaching to the reflector. In this way, since the geometric range in which the reflector is detectable decrease, the search is gradually more accurate;
- Once the transceiver is set to the minimum power, the fine pinpointing search is performed, similarly to the ARVA case.