In an article in the New Scientist, it is revealed that NASA has developed a computer program that identifies people by searching for the movement of shadows on the ground and picks up on the walking style. The technique, called gait analysis, could be used to monitor suspected terrorists and known criminals, since it is very difficult for people to disguise their walking style. Minor differences in gait that can help identify individuals include the length of steps, walking speed, the wiggle of hips and the angles of the knee, ankle and hip.
High-altitude spy aircraft and satellites only show the tops of people’s heads, but when the sun shines, it can see the shadow on the ground. The program isolates moving shadows and uses data on the position of the sun and camera angle to ‘correct’ the shadows if they are foreshortened or elongated. The system of course relies on the fact that the suspects walking style is on file.
The technique is still at the earliest stages of development, and it could be many years before it is used by military, police and intelligence services.
Clearly there are also potential flaws. While satellite gait analysis might be useful in countries blessed with warmer climates, trying to identify a suspected terrorist from a shadow in a rainy Manchester is likely to be fraught with difficulties.
