San José, Costa Rica, since 1956

Pre-Columbian Road Hunt Goes High-Tech

THREE U.S. National Aeronauticsand Space Administration (NASA) jetsoutfitted with infrared cameras and radarhave detected a subterranean network ofancient rock-paved roads that lace CostaRica from the Central Valley throughoutthe Caribbean slope.Sometime between 8,000 B.C. and theSpanish conquest in the 16th century, still undeterminednumbers of people laid thestones that now poke through the topsoil inplaces – on farms, in highway cuts, or anywherethe sites have been disturbed orhave avoided soil deposits over time.Since the late 1970s, Costa Ricanarchaeologists tracked the roads by wordof mouth and a steel rod. They would followrumors of ancient roads on mountainousjungle estates until they found therocky evidence of a stone-paved road.Then they’d walk along it, sinking a metalbar into the earth every few steps – if itstruck stone, they were on track.Maureen Sánchez, an archaeology professorat the University of Costa Rica(UCR), called it road finding through the“oral tradition.” Highway cuts, she said,were a boon when they intersected with anancient path. They yielded the currency ofthe archaeological trade: pot shards, theremains of campfires and other clues to thecultures of the thousands of people wholived here before the conquest.NOW, training the power of space-agetechnology on the remnants of those civilizations,the UCR archeology and physicsdepartments have teamed up to applyinfrared sensors and radar to a science thatwas floundering in the dark ages.NASA teams combed most of CostaRica’s national territory in three jets startingin 2003, with the last series of flightsending in April (TT, April 8). Outfittedwith radar, as well as infrared and conventionalcameras, the jets recorded thousandsof images and hundreds of hours of digitalvideo, most of which has not yet returnedfrom being processed at NASA.“It’s much faster – archaeologists stillhave to go to the field to confirm the findings,but the photos tell us where to directour attention,” Sánchez said.The information gleaned from the firstseries of flights in March 2003 has broadenedarcheologists’ understanding of thepeople who lived here before the Spanisharrived.“THE technology allowed us to see thatsome drawings we had made were incomplete,”Sánchez said. “The photos let us seethat some structures had different shapes andthey helped us find other structures.”Perhaps more importantly, the collaborationprovided an addictive first taste ofthe power of a multidisciplinary focus onarchaeology.“The project is just beginning,”Sánchez said. “Later we could see thesisstudents in archaeology, physics, chemistry,even engineering studying (these civilizations).We want to encourage that – it’sa broad new field of research.”In March 2003, a WB-57 high-altituderesearch aircraft flew over 70% of thecountry, equipped with an RC10 colorinfrared camera and a MASTER multi-spectralsensor that can take up to 50 photossimultaneously, overlapping the imagesto see minute detail.THE cameras film visible light andnear, mid-range and far, or thermal,infrared waves. Thermal infrared is theheat any object radiates; the warmer theobject, the more thermal infrared waves itemits, although even cold objects, such asice, emit infrared light. Since objects in theground conduct heat at different rates, theyemit different amounts and types ofinfrared waves, a tendency that shows upin pictures. A partially buried stonewall,for example, looks different to an infraredsensor than the sand surrounding it.Javier Bonatti, a UCR physics professor,translates the images as they returnfrom NASA, helping the archaeologistsunderstand what they are seeing.“Simple sight is useless… with thistechnology, (the details) are startling. Butit is subtle. You have to do a more precisejob later,” Bonatti said, referring to thearchaeological fieldwork that follows.IN March 2004, a DC-8 made a seriesof flights over the country equipped withthe Airborne Synthetic Aperture Radar(AirSAR), which can penetrate the forestcanopy and record images of structures asmany as 10 meters underground (TT,March 4, 2004).A WB-57 made the latest series offlights this year, this time equipped with aHyMap hyperspectral sensor, a geologicalmapping device used in such fields ascommercial mineral exploration. A conglomerationof government institutionsincluding the Environment Ministry andthe National Water and Sewer Institute(AyA) contracted the equipment to gatherinformation for land-use studies, and thearchaeology department hitched on tobroaden its research.The last flights patched the holes leftby the flights in 2003, when cloudsobscured the Guápiles region, on theCaribbean slope, and others, Bonatti said.He is anxious to see the photos and theradar images from the last two series offlights, he said, but does not expect themfor several more months.Each of the series of flights cost about$2 million, Bonatti said, but NASA helpedfoot the bill through an agreement withCosta Rica’s National Center for HighTechnology (CENAT).GUAYABO, near Turrialba in the easternmountains, is the site of the largestCosta Rican civilization before the arrivalof the Spaniards. Hunter and gatherer societieswere living in the Turrialba Valley asfar back as 10,000 years ago, at the end ofthe last ice age, Sánchez said.There, the first pre-Columbian road,called a calzada in Spanish, was discoveredin 1979. It was named calzadaCaragra, “just to give it a name,” Sánchezsaid, and runs southeast from Guayabo. In1982 and 1983, another road runningnorthwest was discovered. Both roads supportbranched networks of secondaryroads.The Spanish explorers, who were notfamiliar with the rain forest, must haveused the roads, Sánchez said. They laterwidened them to support their pack animals– beasts that, with the exception ofthe Peruvian llama, had not set foot in theAmericas since their extinction there 8,500years before.Sánchez and other researchers trackedroads to riversides, then detoured to crossthe river at a safe point. When they arrivedat the point directly across from where theroad had left off, the road picked up again.“It made me think that they perfectlywell could have made bridges,” she said.“Photos from 100 years ago show hammockbridges made of plant fibers” thatindigenous cultures maintained.

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