Free-flying birds flight paths are traced with a high power tracking radar. The radar locks to the target, and the amplitude of the radar echo varies as the area of the target changes. This happens e.g. every wing beat. Hence, it is (at least theoretically) possible to estimate the wing-beat frequency of a tracked bird from the variation of the radar echo amplitude.
The Pico Technology ADC200 is a high speed PC-based measuring
instrument. Using the versatile and easy to use driver libraries
supplied with the unit, we have developed a software that samples
the radar echo signal.
Another external signal, derived from the tracking circuitry of
the radar, is fed to the trigger input of the ADC200. The trigger
frequency is locked to 84 Hz. Triggering occurs slightly before
the maximum amplitude of the echo signal.
Upon each trigger input, the ADC200 takes 15 samples with 20 ns
interval and transfers data to the PC. Later, the software
extracts peak values of every sampling sequence. The peak values
are then displayed as in figure 1, and frequency content is
calculated with FFT analysis.
Figure 1. Raw data (wave) of about 4 seconds sampling - randomly chosen:
Figure 2. The fft chart of the data above. The wing beat frequency of this particular Swift (Apus apus) is on average 7.82 Hz:
Links:
Pico Technology
Ltd (U.K.) Manufacturer of the
ADC200 virtual instrument
L.A.N.Z.O.
Sweden AB
The Swedish distributor of Pico Technology products.
This page was created by Johan Backman , last update 1999-08-20 Kl. 02:39
The Migratory Bird Group - Department of Animal Ecology, Ecology building, University of Lund, Sweden.