Using Radar Signatures to Classify Bird Flight Modes Between Flapping and Gliding

In this work, we find that radar signatures registered by wingbeats can work as a chronophotograph in radar version to record bird flight modes. When a bird flies, its wings and body compose a corner reflector, and the incident radiation upon either face of this wingbeat corner reflector impinges onto the other face and is reflected toward the illuminator, which enhances the bird signal intensity by 0-10 dB. When a bird flaps its wings, the corner works at a right angle, and the wingbeat corner reflector strongly modulates the radar signal; therefore, the contribution is strong and stably approaches 10 dB. During gliding, the wingbeat corner reflector fades away, the modulation effect significantly decreases, and the contribution approaches 0 dB. This difference can assist in classifying bird flight modes between flapping and gliding over a long sampling period. Both the Ku-band data from a duck in an anechoic chamber and the Ku-band radar data from a pigeon in an outside environment support the ability of this signature to classify gliding and flapping modes. We present flight mode transitions between flapping and gliding extracted from the radar echoes of small and large oncoming and outgoing birds.