Isegoria

I’ve mentioned dazzle camouflage before — in which impossible-to-hide ships aren’t painted to blend into the ever-changing background but to stand out jarringly and unnaturally — and now a PLoS ONE paper shows that such patterns do in fact affect speed perception as intended:

The experimental textures used were chosen to represent the typical range of components used in previously used dazzle camouflage: stripes, zigzags and checks. When moving quickly, two of the high contrast patterns tested caused a significant reduction in perceived speed of around 7%. These patterns – zigzags and checks – were two-dimensional, in contrast to the other, one-dimensional, patterns tested. Patterns which were less visible (low contrast) or slow moving had no effect on perceived speed; the former finding indicates that the effect is not simply due to texture per se, and implies that straightforward background-matching camouflage (which is generally lower contrast) would not produce a speed distortion: high contrast texture, as used for dazzle camouflage, is necessary.

The fast condition used (20 deg/s) translates into about 13 km/h (8 mph) at a distance of 10 m, and scales linearly upwards. So at the sort of ranges typical of naval warfare, we have no evidence that dazzle camouflage disguised the speed of ships in the two World Wars. Its efficacy in distorting other properties, such as size, shape, range and heading remains untested but, as outlined above, there are good reasons to suppose that these distortions occurred. A straightforward contrast effect on perceived speed [15] does not account for the data reported here: only two-dimensional patterns resulted in distorted speed perception, and only at high contrasts.

Thus dazzle patterns can distort perceived speed, if that speed is sufficiently high. As such, dazzle camouflage should be effective in situations where visual contact is still important: in nature and in low-tech battlefields. In the former case, dazzle may be one reason for high-contrast two-dimensional coloration (e.g. zebras). In the latter case, note that our experimental targets correspond approximately to a Land Rover at 70 m moving at 90 km/h. This is a typical distance between a rocket propelled grenade launcher and its target [22]. So if the target speed were sufficiently high, dazzle patterning should offer some protection from such devices. The effect size observed for check and zigzag patterns at this speed is an error of c.7% (fig.3d). An approximate calculation, based on the best available knowledge of the flight characteristics of a typical weapon, shows that the grenade takes around 0.5 s to reach a target at 70 m [22]; in 0.5 s a 90 kmh vehicle moves 12.5 m, and so a 7% error is about 90 cm. In other words, the missile would hit around 1 m behind where it was aimed, a difference which may be sufficient to prevent loss of life. Furthermore, the inherent variability of the effect with pattern, speed and contrast implies that using different patterns across vehicles will result in unpredictability: a good way to avoid easy compensation for the effect of the camouflage.

(Hat tip to Nyrath.)

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