使用全波形激光雷达从丛林中拉出伪影

Author:Penny Boviatsou

The greatness of Khmer Empire as well as its importance as part of the Cambodian cultural heritage is just beginning to unfold. The most extensive airborne laser scanning campaign ever conducted on an archaeological project revealed a massive complex of ancient cities buried in the Cambodian jungle.

LiDAR is proving to be a catalyst for a better understanding of our history. The innovative technology is transforming archaeology and is fast becoming a powerful tool for archaeologists; the lasers can penetrate overlying vegetation and cover swaths of ground extremely faster than they could be studied on foot.

The Angkor complex is one of the most important archaeological sites in Siem Reap in Southeast Asia and the Angkor Wat one of the world’s most recognisable temples. In the late 12th and early 13th centuries the city was at its peak with historians describing an urban centre extending over nearly 1036 square km. Angkor was the centre of a once massive and powerful nation believed to be the largest in the world at the time, with up to 1 million inhabitants.

Hidden but not forgotten

没有什么能像丢失的大都市的前景那样引起研究人员的想象力。经过多年的研究，柬埔寨的考古学家最近宣布发现了在吴哥附近的热带森林地板和柬埔寨王国的其他考古遗址下发现的多个中世纪城市。巨大的发现挑战了盎格鲁人民最终放弃南部城市的理论，直到最近才相信。由于空降激光扫描技术，考古学家能够发现失去文明的废墟：

• The Khmer Archaeology LiDAR Consortium (KALC) in April 2012 and the
• Cambodia Archaeology LiDAR Initiative (CALI) in April 2015 decided to widen the perspective beyond conventional methods to Khmer history and archaeology.

Both projects were designed by Francisco Gonçalves and Chris Cromarty from PT Map Tiga Internasional (PTMI - formerly PT. McElhanney Indonesia), a Jakarta-based company providing aerial mapping and surveying expertise.

这些项目的前提是，LiDar可以提供隐藏在树冠下的关键信息，以充分评估高棉文明在东南亚，特别是在柬埔寨的程度和影响。为了实现目标，弗朗西斯科·冈卡维斯（Francisco Goncalves），罗兰·弗莱彻（Roland Fletcher）教授和达米安·埃文斯（Damian Evans）博士之间的几个会议工具位置。这些使PTMI了解景观和植被挑战，在收购之前还计划了现场访问。

PTMI购买了Leica Geosystems的LiDAR和数字航空摄影传感器，为研究人员提供高分辨率的空中图像以及高密度地面LIDAR指向考古学家，同时扫描柬埔寨丛林。

The first findings came in 2012 when the company worked closely with Dr. Damian Evans and the Consortium’s associates. By flying a helicopter mounted with a POD carrying, a Leica LiDAR scanner equipped with waveform data capture and a Leica digital aerial camera, PTMI gathered data that confirmed the existence of Mahedraparvata, an ancient temple city whose existence had been known for decades.

The recently analysed data, captured in 2015 duringthe most extensive airborne study ever undertaken by an archaeological project, uncovered the total scale of the Khmer Empire’s urban extent and found the temple complexes to be extremely greater than was previously believed.

“LiDAR generated maps revealed multiple medieval cities hidden on the forest floor and upended what we knew about the lived-in spaces around Angkor and other temple complexes across Cambodia,” said Dr Damian Evans. “The vegetation was obscuring these monumental sites. The LiDAR technology allowed us to see through the vegetation。”

Unveiling the secrets of an empire

In 2015, PTMI covered 1600 square km with the goal to deliver the Cambodia Archaeology LiDAR Initiative, the finest and most complete data coverage of their areas of interest, and provide an opening for future archaeology LiDAR investigation. At the planning stages of the project, PTMI spent approximately a year discussing approaches to the LiDAR and Digital Air Photo (DAP) acquisition.

Francisco Gonçalves and Chris Chromarty walked areas planned for LiDAR and DAP acquisition, and studied the terrain and vegetation under tree cover and the type of archaeological features the LiDAR could detect.

“Archaeology fascinates me,”says Francisco Gonçalves, President Director at PTMI.“隐藏了什么秘密，我们的祖先在其中建造了城市以及为什么放弃了城市。通过Leica Geosystems技术穿透柬埔寨丛林，我们能够获取LiDar Point数据，这些数据不仅揭示了土地景观的结构，还可以揭示结构，道路，运河，结构基础和农业露台。”

PTMI使用Leica Geosystems的LiDAR映射系统来扫描柬埔寨丛林。该公司使用LiDAR技术收集了数据，这些技术渗透到茂密的柬埔寨森林和茂密的植被，收集有关土壤表面和地形高程的信息，使考古学家能够在吴哥附近找到广泛的网络痕迹。数码航空摄影与LIDAR数据同时收集。

罗兰·弗莱彻（Roland Fletcher）教授说：“几个世纪以来，农业领域和其他建筑物一直被种植树木藏起来，但激光雷达技术正在改变我们对世界的看法。”“最近被森林砍伐的土地案件挑战了古森林是'原始生态系统'的理论，人们塑造了森林所在的景观数千年。”

All LiDAR data was acquired using a POD mounted in an AS350 B2 helicopter (HeliStar) based in Cambodia and then adjusted and processed by PTMI using processing workstations equipped with DataPort removable drive carriers, allowing easy movement of the large data files from the aircraft to the processing centre. PTMI planned the data acquisition, adjusted the air imagery and classified the LiDAR into ground and non-ground points. All the results were delivered to CALI where Evans and his team were able to prepare the archaeological analysis.

LiDAR – a new tool for archaeological prospection

LiDAR’s ability to penetrate dense vegetation has meant that the temple complexes and surrounding areas are able to be seen clearly for the first time since the habitation period. With LiDAR-generated maps, subtle topographical changes have traced out road networks, occupation mounds and other urban planning signs that were previously undetectable even from the ground.

The LiDAR-made maps enable the CALI researchers to make more targeted excursions at the site whilst the LiDAR data determine the locations where further research might be useful.

Researchers in the archaeological sphere agree these are the most significant archaeological discoveries in recent years.