Formation Wing-Beat Modulation (FWM): A Tool for Quantifying Bird Flocks Using Radar Micro-Doppler Signals

TL;DR

This paper introduces the formation wing-beat modulation (FWM) effect in radar signals from bird flocks, enabling quantification of bird numbers and wingbeat rates, which advances radar ornithology and aero-ecology research.

Contribution

It identifies and characterizes the FWM effect in radar micro-Doppler signals, providing a novel method to quantify bird flock parameters.

Findings

FWM signals are present in radar echoes of bird flocks.

FWM correlates with bird number and wing-beat frequency.

FWM can be used to estimate bird migration and flight behavior.

Abstract

Radar echoes from bird flocks contain modulation signals, which we find are produced by the flapping gaits of birds in the flock, resulting in a group of spectral peaks with similar amplitudes spaced at a specific interval. We call this the formation wing-beat modulation (FWM) effect. FWM signals are micro-Doppler modulated by flapping wings and are related to the bird number, wing-beat frequency, and flight phasing strategy. Our X-band radar data show that FWM signals exist in radar signals of a seagull flock, providing tools for quantifying the bird number and estimating the mean wingbeat rate of birds. This new finding could aid in research on the quantification of bird migration numbers and estimation of bird flight behavior in radar ornithology and aero-ecology.