Science and Technology

Sneak a peek

M Ramesh | Updated on: Jun 12, 2022
Mapping a tropical forest without setting foot in it

Mapping a tropical forest without setting foot in it | Photo Credit: RICARDO STUCKERT

How lidar helped ‘unearth’ lost cities in an Amazonian forest

They could never have been spotted otherwise. They lay for centuries under dense vegetation and remained inaccessible due to the treacherous forest terrain — outcrop, root networks, foliage and all.

For long, the fabled “lost cities of the Amazonian forests” exerted an irresistible pull upon explorers, fortune seekers and archaeologists, many of whom disappeared into the forests to never return — so if one of them had, in fact, found the legendary city of gold, El Dorado, we’d never know about it.

And now, scientists from Germany and the UK decided to jointly take a renewed stab at it, this time with a top-down approach. They hired a helicopter and whirred in the air about 650 ft above the Bolivian Amazon forests, with an equipment that beamed down infrared rays — thousands per second. It was a time-tested equipment that they used — Lidar, or light detection and ranging.

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Lidars are used in many areas. Wind energy companies use it to gauge wind speeds at different heights. Lidars could be used in driverless cars for navigation.

So, here was a familiar technique being tried for an entirely new application. Like sound waves in sonar, these infrared beams are reflected back by the objects they hit. The reflected beams are caught and analysed by a computer, giving a good picture of what lies beneath. Then the software also erases all the trees, in a sort of digital deforestation, and you get an image of the land minus the forest cover. This way, they overcame the difficulties of mapping sites in tropical forested settings.

The results, published in the latest issue of Nature, were amazing. They found “two remarkably large sites (147 ha and 315 ha) of dense four-tiered settlement system” of the Casarabe culture (500-1400 AD), in the Llanos de Mojos savannah.

The historical information that the study threw up is another story, but the interesting fact is how lidars were used to sneak a peek into an otherwise impregnable territory.

Published on June 12, 2022
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