The strongest assistance of dense archeology -laser radar

Humans are small and stubborn on the earth. On this vast earth, how does our ancestors live? They plant food, build houses, form tribes, and build cities, leaving traces of existence.

Through the exploration of monuments, we can infer the level of lifestyle, social culture, and technological development of the ancients. However, after thousands of years, it is not easy to find the ruins left by the ancients.

Because of the vicissitudes of the sea, the original building may have been buried under the ground. Whether it is vast vegetation or dense forest, they can easily stop our exploration of the underground world. However, the emergence of lidar technology can help us unveil the "veil" on the land, and let us see the most primitive "appearance" of the earth.

Lidar, the weapon of exploration relics

At the beginning of the 20th century, British explorer Percy Fawceet went deep into the Amazon region many times to find the ancient civilization that once existed on that land, but in the operation of the ruins, he was always lost in Amazon's dense forests. Essence As a result, the historical relics in Amazon disappeared from people's vision with the expedition.

However, recently published a paper in the "Nature" magazine. Scientists used laser radar and finally got the appearance of ancient urban relics in the Amazon River Basin. Let's take a look at what the ruins look like:

(Source: References 1)

The buildings shown in the figure were built between the Casarabe community from 500-1400 AD and were traces of artificial things such as the previous houses, terraces, and fences. This picture was explorated by the helicopter with laser radar over the forest and was processed by later images.

But maybe you will find that this picture seems to be a little different from time to time. In fact, the biggest difference is that the woods are gone.

Left: Forest pictures obtained by aerial camera: Pictures obtained by Lidar detection at the same place (source: reference: reference 1)

Without the obstruction of the woods, the traces under the relics of ancient buildings became unobstructed. Archaeological work has become much more smooth. Think about the laser radar, in order to explorate the relics in the forest, you must first learn to survive in the wild. To.

Now with laser radar, archeologists can avoid the interference of trees and clearly observe the ancient building sites. So, how is the topographic diagram of trees disturb?

Active imaging, illuminate the dark corner

The dense forests, the leaves cover most of the sun, and rarely the sun can expose to the ground under the woods. When observing from the sky, the ordinary camera has almost no way to get the image of the ground. The shadow.

Camera is a passive imaging equipment. The camera can form photos after receiving or reflected the light from the outside world. Lidar is an active detector, which itself will emit laser to detect the appearance of the outside world.

For the complex appearance of forests, there are still many laser light that can reach the ground under the woods. The point cloud data obtained by lidar detection will be sent to the computer. What data points are identified by the computer. Filtering the point cloud data of the forest, the rest is the appearance data of the ground.

The original point cloud data obtained by Lidar (source: Answers.usgs.gov)

Computers classify the point cloud (the data of the black dot is the data point of the vegetation, the data point of the color point is the data point) (Figure source: reference 2)

Filtering the topographic surface of the topographic surface after filtering the vegetation point cloud, also known as the digital high -primary model (DEM) (the source: Answers.usgs.gov)

The "superpowers" of laser radar in terrain drawing make archaeologists all over the world like it. In 2016, Pacaunam plans to conduct a large -scale lidar survey on the Mayan Biosphere Reserve in Guatemala. The investigation found more than 60,000 ancient buildings and more than 100 kilometers of embankment. The Mayan civilization composed of millions of people.

The survey and inspection of the Liangzhu Ancient City also used this technology. Lidar radar scanned the Liangzhu ancient city site. After filtering the vegetation on the ground, the water conservancy facilities of the ancient city, the structure of the outside Guo, and other structures were all appeared.

Not only can the past be found, but also a warning of the future

In addition to the use of lidar detection relics, the clear presentation of laser radar on terrain and landforms also allows it to play a role in preventing landslides.

Landscapes are one of the common geological disasters. Every year, people lose their lives due to landslides and even lose their lives. Understanding the production mechanism of landslides, observing the precursor of the occurrence of landslides, and establishing a corresponding landslide forecasting system is an important means to alleviate the hazards of the landslide.

The high -precision digital high -primary model (HRDEM) obtained by using laser radar surveying is to help geologists analyze the landslide mechanism of the landscape and establish an early warning model.

Studying a landslide, a large amount of landslide data requires a large amount of landslide data. Scientists used observation methods such as remote sensing satellites, lidar, and aviation cameras to establish a landslide map map.

The map indicates the landslides of each region, the appearance of the landslide, and also contains information such as rainfall, soil type, and earthquake vibration in the area. Using the landslide list map, people can calculate the possibility of landslides in each district. Based on the landslide list map obtained by laser radar surveying, areas of different colors represent different types of landslides in different types of landslides. The red color blocks in the small map in the lower right corner of the lower corner of the lower corner represent deep landslides, and the blue color block represents shallow landslides. (Picture source: reference 3)

Before the landslide occurs, the bottom of the landslide will form a certain height bulge, and the slope will cause cracks. Because of the coverage of vegetation, there is no way to observe these signs with the naked eye or camera, but with the help of laser radar, this problem can be solved well.

Deploy drones with laser radar with high landslides in the mountains, and continuously scan the surface of the surface of the slope surface. Observation data will effectively improve our ability and accuracy of landslide.

It is not a simple matter to explore the ruins of the past land that happened in the past. Over time, the traces left by human activities or the changes in crust will gradually be drowned by nature. However, lidar gave us the opportunity to re -understand the "past", let us find the inspiration to the future from the "past" relics.

Produced: Popular Science China

Production: salted fish in the sea

Producer: China Science Popularization Expo

Edit: Wang Tingting

references:

[1] Erickson C L. An Artificial Landscape-SCALE FISHERY in the Bolivian Amazon. [J]. Nature, 2000, 408 (6809): 190-3.

[2] Vanvalkenburgh P , Cushman K C . Lasers Without Lost Cities: Using Drone Lidar to Capture Architectural Complexity at Kuelap, Amazonas, Peru[J]. Journal of Field Archaeology, 2020, 45(supplement 1).

[3] Gorum, Tolga. Landslide Recognition and MAPPING in a Mixed Forest Environment from Airborne Lidar Data.

[4] M, J, Lato, Et Al. Reducing Landslide Risk USIRBORNE LIDAR Scanning Data [J]. Journal of Geotechnical and Geoenvroniconmental Engineering, 2019, 145 (9).

[5] https://www.usgs.gov/faqs/what-difference-dapen-data-digital-digel-model-dem

[6] http://m.app.cctv.com/video/detail/aa9c36ee6d92B0A7A7A7A7A7A7A7A7A7A7A7A7A7A7A7A7A7A7A98d2F86EB447C/index.shtml

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