Science Heresy - January 2012
Strategy to Avoid Mass Strandings
Every year we experience the tragedy and
occasional triumph of whale strandings and rescue attempts, with the hard work
of many volunteers and official organisations involved.
A corner reflector
(designed to reflect radar rather than sound)
The most obvious apparatus for reflecting whale navigation signals is a corner reflector. A corner reflector consists of three intersecting mutually perpendicular plane surfaces and has the property of reflecting radiation back along the path by which it arrived so giving a large return signal. Such devices are commonly used for reflecting light and radar waves. The "cats eyes" along the centre of the road are corner reflectors. Light weight corner reflectors made from aluminium foil are hung below meteorological balloons to allow them to be tracked by "wind-follow" radar. Wave theory tells us that a reflector needs to be at least one half wavelength in size in order to be effective.
Most baleen whales make sounds at about 15–20 hertz (Wikipedia). The velocity of sound in sea water is 1560 m/s. Hence the wavelength of a whale sound is around 100 m. A corner reflector needs to be larger than half a wavelength so its minimum dimension is 50 m. Perhaps such a gadget could be constructed from stainless steel mesh and either allowed to lie on the bottom outside the breaker zone or suspended in mid-water by a suitable flotation device.