A red highlighted region of the echo signal shown above is animated to the left. The animation shows how the echo changes over 9 seconds as a flap-coasting migrant moves along the stationary beam away from the radar. Notice how the bird's echo signal peak varies considerably in strength as the bird flaps, then becomes relatively steady as the bird coasts. The bird target dissappears as it moves out of the beam. By comparison, ground clutter appears as a non-moving peak of relatively constant echo strength throughout the duration of this sample. The wing beat rate of this bird can be estimated by stepping through the animation and noting the difference in time between 2 succeeding high peaks during a period of flapping flight. For example, adjacent wing beats occur at 4.88 and 4.97 seconds, a difference of 0.09 seconds. We then calculate wing beat rate as 1/period = 1/0.09 = 11 wing beats per second - definitely not an insect.

A red highlighted region of the echo signal shown above is animated to the left. The animation shows how the echo changes over 8 seconds as an insect moves along the stationary beam away from the radar. Unlike the bird depicted above, the insects's echo signal decreases relatively monotonically in strength during flight as it slowly moves out of the beam (left to right). Ground clutter appears as a non-moving peak of relatively constant echo strength throughout the duration of this sample.