D7 Ornithological Radar

Topic

Radar is a remote sensing instrument that enables the study of birds in flight without the need to capture or tag them; it can operate at night, in fog, and at ranges of up to two hundred kilometers—conditions under which no other observation method works. Furthermore, it is the only method capable of simultaneously providing the position, speed, and density of entire flocks of birds, rather than being limited to describing a single individual.

In this simulator, the radar operates in two distinct modes. The first is surveillance radar, which measures the position and Doppler velocity of echoes reflected by either an individual bird or a group of birds flying together; based on this position and Doppler velocity, the surveillance radar calculates the migratory flux in the observed area and the altitude at which the detected birds are flying.

The second mode is micro-Doppler analysis of wingbeats: the temporal signature of the signal received back by the radar varies with the wingbeat frequency and the speed of the wingtip of the bird reflecting the signal, as each flap modulates the reflected signal in a characteristic way. By analyzing this micro-Doppler temporal signature, the radar can identify the bird species and its flight mode, even at distances where direct visual observation is no longer possible.

These two operating modes make radar the primary diagnostic tool for addressing two questions that no other instrument can answer on the same scale. The first concerns the altitudinal distribution of a flock under extreme conditions: by simultaneously measuring the altitude and Doppler velocity of all birds in a flock traversing a region of low air density or intense turbulence, surveillance radar allows for the reconstruction of how the flock redistributes itself vertically as air conditions become more severe. The second question concerns the detection of large-scale disruptions to formations: since the radar simultaneously measures the position, speed, and density of an entire flock, it can detect and quantify the moment a collective flight formation breaks apart due to an external disturbance, and—through successive observations—track how that disruption propagates through the flock and how long it takes for the flock to regain its previous order.

Whether or not a radar can detect a specific species—and at what range—depends on the radar range equation, which links the instrument's own parameters (such as transmitted power, receiver sensitivity, and operating frequency) to the size and reflectivity of the target bird. This radar range equation enables the design of a surveillance or micro-Doppler analysis radar configuration tailored to each species and research question—whether regarding altitudinal distribution under extreme conditions or the disruption of a collective flight formation—that will effectively detect the birds at the required distance.

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