Arrayed laser image contrast evaluation (Alice) for human body detection

Human body detection is an important research area with potential for numerous applications, including search and rescue missions, safe driving, surveillance, and security. Here, we propose and experimentally validate a novel concept named ‘arrayed laser image contrast evaluation’ (Alice) to detect the human body, based on the unique optical properties of human skin. In the Alice system, an NIR dot array laser is used for illumination, and the irradiated area is detected using a near infrared (NIR) camera. Human skin has the characteristic optical properties of relatively low light absorption and high light scattering in the NIR region. When human skin is illuminated with focused laser dots, the NIR light penetrates deeply. Light is scattered multiple times inside the skin before it is re-emitted. The light intensity distribution of the reflected light tends to be diffuse. Human skin can be easily identified using arrayed laser image contrasts, calculated from the reflected light intensity distribution. With the Alice system, an almost entirely hidden person can be successfully detected using information from even a tiny patch of skin. The Alice human body detection system thus has potential for use in a wide range of applications.