Comparison of radar signatures based on flight morphology for large birds and small birds

The identification of bird size from radar echoes is a mission in radar ornithology. Yet, neither radar cross-section nor wingbeat frequency measured from radar signals of birds is good recognition discriminant. In this study, the authors propose that large birds habitually carry their feet stretched out behind them during flight, leaving their feet apart from the body and being recognisable to both human observation and radar detection, while small birds tend to carry their feet drawn up in front, clinging to the body, thus hiding their feet from detection. The 23 most common bird species groups involved in bird strike hazards are consistent with this classification criterion. The visibility of a bird's feet will register radar signatures on bird echoes, and these signatures contribute to the classification of radar echoes from different sized birds in relatively short data sampling time. Their Ku-band avian radar data indicated that those radar signatures, including distribution of scattering centres and the modulation in radar echoes from small birds and large birds, do differ in radar echoes from large birds and small birds.