Archaeology is facing a time crunch. Thousands of years of human history risk imminent erasure, from tiny hamlets to entire cities - temples, walls and roads under grave threat of destruction. Urban sprawl and industrial agriculture are but two culprits, smothering ancient settlements beneath car parks and cattle pastures. International conflict and climate change are also damaging vulnerable sites, with warfare and water shortages destroying pockets of history across the world.

The endless excavations of yesteryear are no longer the best solution. Big digs aren’t the big idea they once were: mapping the human archaeological record is now moving upward, into the sky.

Lidar – short for light detection and ranging – has emerged as one of the most widely used technologies for rapid archaeological documentation. Lidar works by sending pulses of light out from a transmitter often mounted to the skid of a helicopter, then recording how long it takes for those pulses to return to a sensor. A virtual 3D map can be generated from a single large-scale survey in less than a day. Archaeological sites that would require years and years of fieldwork to excavate can now be mapped in a single afternoon, their every surface feature captured down to millimeter-scale resolution.

Archaeological sites that would require years and years of fieldwork to excavate can now be mapped in a single afternoon

Thickets and woods, even entire rainforests, are no obstacle. Because individual bursts of light can pass through the tiniest gaps separating branches and leaves in a forest canopy, lidar is also able to map archaeological features beneath heavily overgrown landscapes. The technique’s accuracy, combined with its declining cost as new devices and firms enter the market, means that lidar has found enthusiastic uptake in everything from urban mapping projects and geological hazard management – such as finding previously unknown fault lines – to, of course, archaeology.

Based in a converted helicopter hangar at the Hawthorne airport in Los Angeles, California, the firm GEO1, a subsidiary of NV5 Geospatial, offers lidar services to utility companies and archaeologists alike. Ron Chapple, GEO1’s founder and CEO, came to lidar from a previous career in aerial cinematography. A few years ago, Chapple, 65, was hired to film an electrical transmission line for a municipal client. He and his team did the job so well, they joked, they should have won an Academy Award for best electrical infrastructure film. But as they were packing up their gear, another crew arrived, commissioned to capture imagery of the same transmission line. One of them pulled out a strange new device – not a camera, but a sensor. After trying it out themselves, Chapple and his team invested in their own light sensor equipment.

That decision proved transformative. Chapple now regularly finds himself on call, asked to support overseas archaeological expeditions. For a remote site in Colombia known as Ciudad Perdida, Chapple said, getting to the location on foot would have taken two and a half days of strenuous hiking, and exhaustively mapping the city’s every street and plaza would have taken years, if not decades, of fieldwork. Thanks to lidar, his team was able to capture most of the settlement in a single afternoon.

Processing the results is another story. A single survey can produce several terabytes’ worth of data, requiring powerful software to analyze and present the findings. “The original data only gets better over time as the algorithms improve,” Chapple says. “There was a time when the algorithm was throwing out too much noise – it was actually throwing out valuable points – because the filter hadn’t been adequately tightened. But with one software update, all of a sudden we had more data.” That means data captured five years ago can still reveal new features if Chapple runs it through updated software.

The scope of all that remains to be discovered – whether lost in the algorithm or yet to be scanned – is astonishing

In the time between those two events, however, physical features, overlooked by earlier software, might be destroyed by developers or looted beyond recognition.

The scope of all that remains to be discovered – whether lost in the algorithm or yet to be scanned – is astonishing. Even in the UK, where there are no tropical rainforests hiding lost cities and even the most remote site is only a couple of hours away from the nearest road, undiscovered landscapes lie in wait. David Ratledge spent his career engineering roads, bridges and highways for the English county of Lancashire. For 45 years, pursuing his interests as an amateur archaeologist and local history buff on the side, Ratledge, 77, hiked and wandered the countryside with his friends and colleagues, searching for the lost roads and overgrown highways of Roman Britain. The release of lidar data from the UK Environment Agency transformed his hobby overnight.

Using the data, Ratledge “started finding Roman roads”, he said, “and just got better and better at it.” He and his friends quickly went from poring over digital maps to throwing on their mud boots and trekking out, hoping to locate the roads in person. In one case, a local farmer had no idea that a Roman road passed through his fields – but, Ratledge said, laughing, “he did know where to drive his tractor. He knew if he drove his tractor down this line, he wouldn’t sink into the mud. Sure enough, there was a Roman road underneath it.” Ratledge had found that linear feature in the lidar data.

Ratledge has been maintaining a website which he updates with new discoveries made by his colleagues and himself, publishing approximately two new research papers per year, and uploading the occasional YouTube tour. One section of Ratledge’s website documents possible roads in Cumbria, a category that includes what appear to be straight lines, possibly indicating Roman highways, at one point disappearing into the sands of Morecambe Bay. Other potential roads are hard to verify simply because the data is incomplete. While most of England has now been mapped with lidar, Ratledge said, some parts of the UK remain unscanned and underexamined. There is more to see, he emphasized – much more – and, whether it’s the Colombian rainforest or the British countryside, lidar just might be the best and fastest way to find new stories from the human past before they vanish without a trace.