Remote sensing's armamentarium of and digital instruments can optical now detect prehistoric footpaths beneath the canopy Costa Rican of a rainforest. Indicators on the color infrared photograph of the Tilaran region of Costa Rica , top, point to footpaths used by prehistoric peoples more than 1,000 years ago. Because infrared film is sensitive to vegetation, pastures appear in lighter red and forests in darker red. Below, two workers excavate a prehistoric footpath previously detectedby aerial infrared photography. November/December 1988 29