Tuesday, 10 April 2018

Mayans and the LiDAR

Recently, using the LIDAR technique, researchers have found the picture of a Mayan city, which have been covered by the dense jungle of Guatemala's Peten region. This city is as much bigger a Mumbai or Chennai, with lakhs of people's presence.



Image credits : National Museum of Anthropology in Mexico City. Maya mask. Stucco frieze from Placeres, Campeche. Early Classic period (c. 250 - 600 AD. Joyce Kelly 2001 An Archaeological Guide to Central and Southern Mexico, p.105. ISBN 0-8061-3349-X.

If we are considering ourselves a well-settled civilization, we should give a second thought for that. There are images of houses, pyramids, temples, agricultural fields, irrigation canals and other infrastructures. Also, there were fences made as boundaries, water flow systems, huge sewage systems. 


Image credits : Wild Blue media /national Geographic



Image credits : Wild Blue media /national Geographic


It was a group of Researchers from Europe, Guatemala and America behind this discovery. They have mapped more than 50000 structures inside the forest. The forest and trees just grew over the abandoned city, which preserved the entire city but made it impossible to see the city forever. Among the structures, there were even some big structures which looked like fort

“Can’t be called anything other than a Maya fortress.” said, Thomas Garrison, Assistant Professor of Anthropology at Ithaca College in New York ,who was a part of the team.


Know more about The Mayans from Wiki


Well, the news got to an end, but have you thought why wasn't this possible earlier?
It just because of the unavailablity of the Lidar technique.

LiDAR: Light detection and ranging / Laser detection and ranging.

Lidar is simply a technical method used to detect the distance of a source. Distance is measured by illuminating that particular source with a Pulsed Laser of suitable need. 
What is Pulsed laser? 
Usually, Laser glows continuously when it is switched on. A Pulsed laser only switches the laser on, for a particular duration. after that, it switches off. Simply, a pulsed laser is a time controlled laser.

Then we study the variation in its wavelength and time period for each pulse to come back after hitting the source, we determine the distance. (there are some other spectroscopic techniques along with this, which can be exploited along, as per the need)

Later, the laser will perform the duty of a scanner; it will be continuosly pointed to some region and collect the data. There are programms which helps us to image the contour of the region, with which we can see the toplogy of entire region.

Remember, Lidar works not only in visible region, but also in Ultraviolet and Infrared region, which means, they would be invisible for our eyes, but sensible for the detectors.

well, where else they are being used?
Its mainly being used in aeroplanes, to make the image of the ground for landing and other purposes, even if the sky is couldy. Usually, on a cloudy time, the pilot is not able to see the bottom, neither the cameras. This will enable them to create a visual even if it is dark.
This is also being used in most of the rough imaging areas including meteorological surveys to find out the amount and area of minerals inside earth, to find the irregularities inside a solid object and so on. Imaging of earth's topology is lso being used, or the real time 3D maps of Earth's surface is obtainable.

One of the main use for Lidar in future will be in the area of Artificial Intelligence. We have seen robots scanning objects and taking actions based on it. Its nothing, but the Lidar technology. Right now there are automated robots in the area of agriculture and many industrial purpose, where detection and further actions are being programmed onto a machine with the data from Lidar's in them.


Lidars in space!

Lunar Laser Ranging experiment is one of the famous program, in which the lasers are pointed towards the mirror planted in moon, during Appollo missions. By studying the time taken by laser to return, is catalogued and precise distance to moon is calculated.
Distance to moon = (speed of light in vaccuum × time taken for laser light to reflect back) / 2 is a simple equation you all can understand.
This also paved the way to verify a part of Einstein's Equivalence principle, regarding tides.

Almost all the imaging techniques in the space, detection of elements on moon are being done using Lidar technique.


Here are some links that might help you :

Mars Orbiter Altimeter
General Relativity 
Lunar Laser Ranging 
Digital Elevation 
Hydrography 
Introversion Software 
Structure from motion

Credits : 
https://en.wikipedia.org/wiki/Lidar
http://www.miradorbasin.com/about.php
https://news.nationalgeographic.com/2018/02/maya-laser-lidar-guatemala-pacunam/

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