The past’s mark on the present as seen through LIDAR

By Erika Lyon

Light Detection and Ranging, also known as LiDAR, is a form of remote sensing used by various professions to examine landscape features in three-dimensions.  Imaging is generally performed by aircraft (though not always) that use lasers, scanners, and GPS to measure reflected light from Earth’s surface.  This light describes changes in distance between the aircraft and surface features (National Ocean Service 2013).  For terrestrial systems, a near-infrared laser is used to collect data (this is known as topographic LiDAR), while aquatic systems make use of green light, which can break through water surfaces (bathymetric LiDAR) (National Ocean Service 2013).  Data on height, latitude, and longitude of geographic features are generated and used to create models of the landscape (National Ocean Service 2013).  LiDAR’s applications have been used in the fields of archeology, geology, and paleontology to study natural and human history, but it is not fully utilized in paleoecological studies.  LiDAR is a powerful remote sensing tool that can provide invaluable information about Earth’s surface and can be especially useful for looking at evidence of past events and land use.

Past events can leave behind footprints on the Earth’s surface, and these footprints may not be easily distinguished from an aerial or satellite imagery alone.  For example, during the summer months of 2012, I inventoried abandoned mine lands in the Midwest, which are notorious for their dangerous highwalls and sinkholes that are often hidden from view by overgrown trees and shrubs.  LiDAR was a very valuable tool in the field because it made many of these hazardous features evident (Fig. 1).  Needless to say, I didn’t go to a mine site without a LiDAR hillshade map.

Fig. 1: Example of an aerial photo (left) and LiDAR hillshade image (right) of an abandoned surface mine.  Maps, like the ones above, are often utilized by state agencies to assess site conditions of abandoned mines.  For more maps of Iowa’s abandoned mines (including 1930s, 1950s, 2008 aerials, and LiDAR hillshade) click here. (Images created by GeoTREE and the Iowa Department of Natural Resources).

Fig. 1: Example of an aerial photo (left) and LiDAR hillshade image (right) of an abandoned surface mine.  Maps, like the ones above, are often utilized by state agencies to assess site conditions of abandoned mines.  For more maps of Iowa’s abandoned mines (including 1930s, 1950s, 2008 aerials, and LiDAR hillshade) click here. (Images created by GeoTREE and the Iowa Department of Natural Resources).

Other landscape impacts caused by humans can also be detected by LiDAR.  A recent study published in the Journal of Archaeological Science utilized LiDAR to discover hidden landscape features in New England, including old building foundations, dams, old roads, and historical farmsteads (Johnson and Ouimet 2014).  So why might this be of importance to a paleoecologist?  As seen in Fig. 2, sites may show evidence of ecological succession after a disturbance caused by past land use.  LiDAR and early aerial photos of the landscape depict land that had been cleared for farming, but after the farm was abandoned, the vegetation in the area changed.  Johnson and Ouimet (2014) suggested that LiDAR in archeology is a powerful, cost-effective tool that can help develop a historical context, and it can also be applied to professions outside of archaeology.

Fig. 2: Modern forest with a) & b) aerial images, c) historical image, and d) LiDAR image (Johnson and Ouimet 2014).  LiDAR imagery displays evidence of past land use not seen in modern aerial images. 

Fig. 2: Modern forest with a) & b) aerial images, c) historical image, and d) LiDAR image (Johnson and Ouimet 2014).  LiDAR imagery displays evidence of past land use not seen in modern aerial images.

In geological analyses, LiDAR can be a valuable asset.  LiDAR was recently implemented in a study done in the Ižica floodplain in Slovenia to increase the resolution of the river’s history.  Through the use of LiDAR, fine details of levees and paleochannels became visible, which depicted a floodplain changing through time (Budja and Mlekuž 2010).  In addition, the study identified fluctuations in hydrology that were linked to “climate anomalies” (Budja and Mlekuž 2010).  In combination with other proxies such as pollen, charcoal, and fossil evidence, these climate anomalies might be better understood.

Fig. 3: Troutbeck Valley geomorphological map overlain on LiDAR and bathymetry data to depict glacial features (Miller et al. 2014).

Fig. 3: Troutbeck Valley geomorphological map overlain on LiDAR and bathymetry data to depict glacial features (Miller et al. 2014).

Integrating geomorphology, sedimentology, and remote sensing tools such as LiDAR can also aid in reconstructing past ice sheets (Miller et al. 2014).  Miller et al. (2014) examined the late-Quaternary history of Windermere Lake in England, with emphasis on the Troutbeck Valley area due to its diverse habitats and past glaciation.  The authors were able to find evidence of regional ice flow events and identify features that indicated a landscape environmental response after retreats of the glaciers in the area.  Ice ages have significantly impacted current distributions of populations and communities (Hewitt 2000), and remote sensing can help detect traces of past glaciers that have shaped the ecosystems we see today.

One of the biggest problems in archaeology, paleontology, and paleoecology is that over time, fossil evidence can deteriorate.  Erosion is a major obstacle in the reconstruction of past environments, and LiDAR may be able to help preserve fossils vulnerable to erosion.  In a study conducted by Bates et al. (2008), LiDAR provided an accurate, high resolution model to preserve and examine fossilized dinosaur tracks.  In their study, LiDAR was used to create three dimensional models of trace fossils and allowed for opportunities of analyses in areas that were too hazardous to reach.  In a sense, now-extinct organisms can almost be brought back to life with LiDAR!

Fig. 4: Scan unit used by Bates et al. 2008 (left) to create LiDAR image from tracks (above).

Fig. 4: Scan unit used by Bates et al. 2008 (left) to create LiDAR image from tracks (above).

The application of LiDAR in many disciplines has demonstrated the value of remote sensing and has potential in the field of paleoecology as well.  LiDAR, in combination with other proxies, can be a great tool for looking at past climate, faunal traces, and previous land use.  Along with pollen, charcoal, and macrofossils, this method of remote sensing can help put sites into context and give past events better resolution.

To download LiDAR and other aerial imaging files found in Maine, click here. 

REFERENCES

Bates, K.T., F. Rarity, P.L. Manning, D. Hodgetts, B. Vila, O. Oms, A. Galobart, and R.L. Gawthorpe. 2008. High-resolution LiDAR and photogrammetric survey of the Fumanya dinosaur tracksites (Catalonia): implications for the conservation and interpretation of geological heritage sites. Journal of the Geological Society 165:115-127.

Budja, M. and D. Mlekuž. 2010. Lake or floodplain? Mid-Holocene settlement patterns and the landscape dynamic of the Izica floodplain (Ljubljana Marshes, Slovenia). The Holocene 20(8):1269-1275.

Hewitt, G. 2000. The genetic legacy of the Quaternary ice ages. Nature 405:907-913.

Johnson, K.M. and W.B. Ouimet. 2014. Rediscovering the lost archaeological landscape of southern New England using airborne light detection and ranging (LiDAR). Journal of Archaeological Science 43:9-20.

Miller, H., C.J. Cotterill, and T. Bradwell. 2014. Glacial and paraglacial history of the Troutbeck Valley, Cumbria, UK: integrating airborne LiDAR, multibeam bathymetry, and geological field mapping. Proceedings of the Geologists’ Association 125:31-40.

National Ocean Service. 2013. LiDAR. http://oceanservice.noaa.gov/facts/lidar.html

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One thought on “The past’s mark on the present as seen through LIDAR

  1. This is so cool! I have never heard of this before, but Figure 2 is absolutely incredible! How do the lasers map out what’s underneath the vegetation?

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