Optical Machine Vision Navigation System Found in Flies
In December 2012, a study entitled “Flying Drosophila Orient to Sky Polarization” was published in Current Biology. In it, the authors, one Michael Dickinson, a University of Washington biology professor and doctoral student Peter Weir of the California Institute of Technology discuss the means by which flies and other insects are able to use natural sunlight to navigate unerringly where they wish to go.
As the title implies, they do this with nothing but their vision systems, using the polarization pattern of natural skylight.
The researchers noted that insects such as monarch butterflies and locusts maintain a constant heading while migrating thousands of miles across continents, while bees and ants hunting for food successfully find their way hundreds of feet back to the nest without a problem. That has led scientists to believe that the animals must possess a compass of sorts.
To assess how insects orient themselves, Weir and Dickinson examined the behaviour of Drosophila melanogaster, a species commonly referred to as a fruit fly, in outdoor lighting conditions in a specially designed “arena” atop a building tall enough to be higher than treetops and other visual landmarks.
The researchers used a light-cured glue to attach the insects to a metal pin, which was then placed within a magnetic field that allowed the flies to move and rotate naturally but held them in place. Digital cameras tracked flight headings.
During the hour before and the hour after sunset, the headings of flies relative to the position of the arena were recorded for 12 minutes. The arena was rotated 90 degrees every three minutes, and when natural light was not altered by optical filters some of the flies compensated for the rotations and maintained a consistent heading.
When the arena was covered with a circularly polarizing filter, eliminating natural linear polarization light patterns, the flies did not shift their heading significantly in response to arena rotations.
The results indicate Drosophila has the ability to coordinate eye and brain functions for rudimentary navigation using light polarization patterns, the researchers concluded. The flies are able to hold a straighter course under normal polarization patterns than they can when those patterns are shifted.
Now, the pair of researchers are only looking to explain insect navigation abilities, rather than develop a new method of navigation for automated systems. But, in effect they have done both.
Our flying robots and UAVs typically include a host of sensors to calculate their precise position and heading. A compass is an easy item to include on even the smallest such construction. Larger vehicles can afford the space and power for GPS. Maybe even WAAS or EGNOS systems to augment GPS as well.
But, compasses can be swayed by proximity to magnetic fields, and GPS can be spotty in urban environments such as where a bird-sized flying robot is going to be operating. Worse, a dragonfly-sized flying robot doesn't have the space or weight requirements for such complex systems with sufficient power and still be able to actually fly.
So, a navigation system that is essentially based off of the polarisation of the light that is hitting the optic sensors is definitely a viable alternative.
Yes, as the study readily points out, it is easily disrupted by artificial lighting powerful enough to compete with natural light at least in local proximity. However, as a way to augment the other sensing apparatus – such as the compass and gyroscope – it is definitely a worthy contender. Especially as cameras and the machine-vision software to be able to recognise obstructions those cameras see, is already a mandatory part of the navigation systems of such low-level eyes in the sky. We already have everything we need, on-board such systems to be able to implement route navigation by natural light polarisation.
Increased reliability of on-board navigation systems by the addition of an extra sense, without increasing weight or cost.
Flying Drosophila Orient to Sky Polarization (Current Biology, Volume 22, Issue 1, 21-27, 15 December 2011)