Border Security, One Footprint at a Time

摘要

To patrol the remote 262-mile stretch of the U.S.-Mexico border south of Tucson, agents monitor surveillance cameras, sensors, and infrared scopes in the desert. They stalk through mountainous wilderness on foot and horseback. They also search for footprints. The agents try to identify if the shoes that formed the prints are sneakers, work boots, or other footwear; the objective is to match them with shoes worn by people caught crossing the border illegally. (The agents regularly sweep the desert floor clean so they can spot fresh tracks.)