Editing Shadow marks

{{short description|Shadows on the ground that indicate buried archaeological structures.}}
{{Infobox
| title            = Shadow marks
| image            = [[File:Aerial photograph of Maiden Castle from the west, 1937.jpg|250px|alt=Aerial view of Maiden Castle showing shadow marks]]
| caption          = Aerial view showing shadow marks over Maiden Castle hillfort
| label1           = Type
| data1            = Archaeological surface feature
| label2           = Visibility conditions
| data2            = Low sun angle (morning or afternoon), clear skies
| label3           = Detection methods
| data3            = Aerial photography, multispectral imaging, SAR, LiDAR
| label4           = Related techniques
| data4            = Crop marks, soil marks, NDVI, GPR
}}
'''Shadow marks''' are surface patterns formed when low-angle sunlight casts elongated shadows across slight variations in ground elevation, revealing buried or [[eroded]] features otherwise invisible at ground level. <ref name=":0">{{Cite journal |last=Stefano |first=Campana |date=2016 |title=Archaeology, remote sensing |url=https://d1wqtxts1xzle7.cloudfront.net/49462117/Enciclopedia_GeoArchaeoloy_Springer_MENABO_low_res-libre.pdf?1475970604=&response-content-disposition=inline%3B+filename%3DArchaeology_Remote_Sensing_Encyclopedia.pdf&Expires=1746686598&Signature=Wyw0vxrekpWa0xHtrM0iaZZNo0ShI~rVMiqytKzurQfMhO1n1nxD7e1ZbUgMRQsjncwoiGFyTJlzaytCJ9u9ab~MhJGkazldEdaoFQDQy-XsFVwU5J3~YwLEDSK5DwngKbFRmQBZbVUEAnNCAAIoYlgyU-rZkxr3zgtI-VNKnKrQ8VddbcbhpcYDMF8Pnwhee-VyofgsI4hu8oxXVM4eJp-p0KG9k7XoyGLf1cH8tJdrxD0Yg1juN1P0gWM9VN70QyRGqR7qBHVzIjiugXlyX~Nrqu9lRbo2fn5ejqRprO1rQpX21u8V2T4wHx4ArQ9dD7xKt0opYS~Edcer5NEJdQ__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA |journal=Encyclopedia of Geoarchaeology |series=Dordrecht/Heidelberg/New York/London: Springer (2016) |pages=5–6}}</ref> Commonly observed through [[aerial photography]] or [[satellite imagery]], shadow marks assist archaeologists in identifying ancient structures, [[Earthworks (archaeology)|earthworks]], and landscape modifications.<ref name=":5">{{Cite journal |last1=Chen |first1=Fulong |last2=Masini |first2=Nicola |last3=Yang |first3=Ruixia |last4=Milillo |first4=Pietro |last5=Feng |first5=Dexian |last6=Lasaponara |first6=Rosa |date=2014-12-23 |title=A Space View of Radar Archaeological Marks: First Applications of COSMO-SkyMed X-Band Data |journal=Remote Sensing |language=en |volume=7 |issue=1 |pages=27 |doi=10.3390/rs70100024 |doi-access=free |bibcode=2014RemS....7...24C |issn=2072-4292}}</ref> Their visibility depends on lighting angle, [[surface reflectance]] ([[albedo]]), and environmental conditions such as vegetation or cloud cover.<ref name=":6">{{Cite journal |last1=Watteeuw |first1=Lieve |last2=Hameeuw |first2=Hendrik |last3=Vandermeulen |first3=Bruno |last4=Van der Perre |first4=Athena |last5=Boschloos |first5=Vanessa |last6=Delvaux |first6=Luc |last7=Proesmans |first7=Marc |last8=Van Bos |first8=Marina |last9=Van Gool |first9=Luc |date=November 2016 |title=Light, shadows and surface characteristics: the multispectral Portable Light Dome |url=http://link.springer.com/10.1007/s00339-016-0499-4 |journal=Applied Physics A |language=en |volume=122 |issue=11 |page=976 |doi=10.1007/s00339-016-0499-4 |bibcode=2016ApPhA.122..976W |issn=0947-8396}}</ref> Shadow marks differ from crop or soil marks in that they rely on topographic contrast rather than biological or chemical changes.<ref name=":3">{{Cite web |title=Crop Marks and Soil Marks |url=https://www.metaldetectingworld.com/metaldetecting_research_p61.shtml |access-date=2025-05-08 |website=www.metaldetectingworld.com}}</ref><ref name=":2">{{Cite journal |last1=Chen |first1=Fulong |last2=Masini |first2=Nicola |last3=Yang |first3=Ruixia |last4=Milillo |first4=Pietro |last5=Feng |first5=Dexian |last6=Lasaponara |first6=Rosa |date=2014-12-23 |title=A Space View of Radar Archaeological Marks: First Applications of COSMO-SkyMed X-Band Data |journal=Remote Sensing |language=en |volume=7 |issue=1 |pages=30–37 |doi=10.3390/rs70100024 |doi-access=free |bibcode=2014RemS....7...24C |issn=2072-4292}}</ref> Modern [[remote sensing]] techniques—such as [[Lidar|LiDAR]], [[Normalized difference vegetation index|NDVI]], and [[Synthetic-aperture radar|Synthetic Aperture Radar]] (SAR)—are often integrated with shadow mark analysis to improve accuracy and overcome environmental limitations.<ref name=":8">{{Cite journal |last=Stefano |first=Campana |date=2016 |title=Archaeology, remote sensing |url=https://d1wqtxts1xzle7.cloudfront.net/49462117/Enciclopedia_GeoArchaeoloy_Springer_MENABO_low_res-libre.pdf?1475970604=&response-content-disposition=inline%3B+filename%3DArchaeology_Remote_Sensing_Encyclopedia.pdf&Expires=1746686598&Signature=Wyw0vxrekpWa0xHtrM0iaZZNo0ShI~rVMiqytKzurQfMhO1n1nxD7e1ZbUgMRQsjncwoiGFyTJlzaytCJ9u9ab~MhJGkazldEdaoFQDQy-XsFVwU5J3~YwLEDSK5DwngKbFRmQBZbVUEAnNCAAIoYlgyU-rZkxr3zgtI-VNKnKrQ8VddbcbhpcYDMF8Pnwhee-VyofgsI4hu8oxXVM4eJp-p0KG9k7XoyGLf1cH8tJdrxD0Yg1juN1P0gWM9VN70QyRGqR7qBHVzIjiugXlyX~Nrqu9lRbo2fn5ejqRprO1rQpX21u8V2T4wHx4ArQ9dD7xKt0opYS~Edcer5NEJdQ__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA |journal=Encyclopedia of Geoarchaeology |series=Dordrecht/Heidelberg/New York/London: Springer (2016) |pages=6–19}}</ref><ref name=":1">{{Citation |last1=Masini |first1=Nicola |title=Sensing the Past from Space: Approaches to Site Detection |date=2017 |work=Sensing the Past: From artifact to historical site |pages=23–60 |editor-last=Masini |editor-first=Nicola |url=https://link.springer.com/chapter/10.1007/978-3-319-50518-3_2 |access-date=2025-05-08 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-50518-3_2 |isbn=978-3-319-50518-3 |last2=Lasaponara |first2=Rosa |editor2-last=Soldovieri |editor2-first=Francesco}}</ref><ref name=":15">{{Cite journal |last1=Chen |first1=Fulong |last2=Masini |first2=Nicola |last3=Yang |first3=Ruixia |last4=Milillo |first4=Pietro |last5=Feng |first5=Dexian |last6=Lasaponara |first6=Rosa |date=2014-12-23 |title=A Space View of Radar Archaeological Marks: First Applications of COSMO-SkyMed X-Band Data |journal=Remote Sensing |language=en |volume=7 |issue=1 |pages=24–50 |doi=10.3390/rs70100024 |doi-access=free |bibcode=2014RemS....7...24C |issn=2072-4292}}</ref> Recent developments also include AI-assisted image classification and virtual light simulations to enhance detection.<ref name=":13">{{Cite journal |last1=Luo |first1=Lei |last2=Wang |first2=Xinyuan |last3=Guo |first3=Huadong |date=2024-07-01 |title=Transitioning from remote sensing archaeology to space archaeology: Towards a paradigm shift |url=https://www.sciencedirect.com/science/article/abs/pii/S0034425724002189 |journal=Remote Sensing of Environment |volume=308 |pages=4–15 |doi=10.1016/j.rse.2024.114200 |bibcode=2024RSEnv.30814200L |issn=0034-4257}}</ref> Beyond [[archaeology]], shadow marks are applied in [[geomorphology]], [[heritage conservation]], and [[battlefield]] studies, and continue to be a key proxy in multi-sensor approaches to landscape interpretation.<ref name=":0" />

== Description ==
[[File:SIX_88DB623E-A768-403D-BDF0-1250EBC6DFCC.jpg|thumb|The formation mechanism of shadow marks demonstrates that the appearance of shadows on the ground is closely related to the angle of the sun.]]
Shadow marks are surface-visible patterns that emerge due to minor variations in terrain elevation when sunlight strikes at a low angle.<ref name=":0" /> These differences in elevation cast elongated shadows, allowing subtle [[Topography|topographic]] irregularities—such as ancient walls, [[Ditch|ditches]], or mounds—to be visualized from above.<ref name=":5" /> Unlike [[Cropmark|crop marks]], which result from vegetation stress, or [[Soil mark|soil marks]], which emerge from changes in soil texture or color, shadow marks rely primarily on physical relief and light geometry.<ref name=":3" /><ref name=":0" /> As such, they serve as a valuable indicator of buried or eroded archaeological features that are not detectable at ground level.<ref name=":0" />

The visibility of shadow marks is highly sensitive to lighting conditions.<ref name=":0" /> Early morning and late afternoon are ideal times for observation, as the sun is low on the horizon and shadows are longer, enhancing the contrast between elevations.<ref name=":0" /> Even slight undulations in terrain can become apparent under such lighting, particularly in winter months when vegetation is sparse and light angles are optimal.<ref name=":0" /> Archaeologists frequently capture [[Aerial photography|aerial photographs]] during these times to take advantage of the enhanced shadow definition. In flat landscapes, where surface features are often minimal, the interplay between light and surface texture can exaggerate minor topographic variations, making shadow marks particularly effective.<ref name=":1" />

However, the clarity of shadow marks can be influenced by various surface conditions.<ref name=":2" /> [[Vegetation]] cover, ploughed fields, [[soil moisture]], and cloud shadows all affect how light interacts with the ground and, consequently, the visibility of these marks.<ref name=":2" /><ref name=":8" /><ref name=":1" /> For this reason, shadow mark detection often requires repeated aerial surveys under differing environmental and seasonal conditions. In lowland or arid zones, temporary surface features or infrastructure may complicate interpretation, requiring careful visual analysis.<ref name=":2" />

Despite their sensitivity to environmental factors, shadow marks remain a crucial tool for [[archaeological prospection]]. Their topographic basis complements other remote sensing techniques, enabling the detection of features that may not produce biological or chemical contrasts.<ref name=":1" /> When integrated with additional methods, shadow marks help form a composite view of subsurface landscapes and have proven especially useful in revealing long-buried cultural features and terrain modifications.<ref name=":0" />

== Light and shadow ==
The formation of shadow marks relies on the basic principles of physics and optics, especially how light interacts with differences in the earth's [[surface topography]].<ref name=":0" /> When sunlight strikes an uneven surface at a low angle, it casts long shadows that contrast high and low areas more.<ref name=":0" /> This optical effect is integral to observing slight [[Archaeology|archaeological]] features since it permits a visualization of the ground’s irregularities that otherwise would not be apparent under direct, overhead illumination conditions.<ref name=":1" />
[[File:Aerial_photograph_of_Maiden_Castle_from_the_west,_1937.jpg|thumb|This aerial picture shows [[Maiden Castle, Dorset|Maiden Castle]], a prehistoric site located in Dorset, which was taken from the west in 1937. The low angle of the light creates long shadows across the earthworks, and the long shadows highlight the fort's intricate ramparts and ditches. This photo demonstrates shadow marks in aerial archaeology, where slight variations are made visible through the effects of shadow and light on the landscape.]]
The angle of solar illumination is the primary agent for creating shadow marks. In the morning and the evening (late afternoon), the sun is low in the sky, and shadows are longer, meaning even small ground undulations are apparent.<ref name=":0" /> Because of this, archaeologists will conduct aerial surveys during this time to best use shadow marks. However, the effectiveness of shadow marks depends upon the [[latitude]], season, and atmosphere, each of which can affect the scattering of light and shadow clarity.<ref name=":0" />

[[Albedo]], or [[surface reflectance]], is also a key factor in photographs or in other records of shadow marks. Different materials have different albedos with regard to both absorption and reflection of incoming light and thus vary in their ability to create contrast, which may either increase or obscure the shadows.<ref name=":6" /> For example, when a buried stone structure or wall has changed the physical or chemical properties of the surrounding soil—whether that is by compacting it or influencing [[moisture]] retention—the area above is likely to reflect sunlight differently than surrounding, unaltered soils.<ref name=":4">{{Cite journal |last=Verhoeven |first=Geert |date=2017-09-14 |title=Are We There Yet? A Review and Assessment of Archaeological Passive Airborne Optical Imaging Approaches in the Light of Landscape Archaeology |journal=Geosciences |language=en |volume=7 |issue=3 |pages=3–5 |doi=10.3390/geosciences7030086 |doi-access=free |bibcode=2017Geosc...7...86V |issn=2076-3263}}</ref> The variations in surface reflectance, or albedo, sometimes will be observable in aerial photographs as differences in tonal contrast or shadow intensity.<ref name=":4" /> A ploughed field is an example of an exposure that can reveal faint outlines of a buried foundation in the soil due to slight differences in shadow or color even if the foundation remains hidden underground.<ref name=":4" /> Furthermore, the [[moisture content]] may reflect light differently, thus making shadow marks more or less detectable depending on prior weather conditions.<ref name=":1" />

== Remote sensing applications ==
Shadow marks, as elevation-dependent surface indicators, play a central role in archaeological surveys by visually exposing buried or [[eroded]] structures.<ref name=":7">{{Cite journal |last=Neubauer |first=Wolfgang |date=January 2001 |title=Images of the invisible-prospection methods for the documentation of threatened archaeological sites |url=http://link.springer.com/10.1007/s001140000192 |journal=Naturwissenschaften |language=en |volume=88 |issue=1 |pages=13–24 |doi=10.1007/s001140000192 |pmid=11261352 |bibcode=2001NW.....88...13N |issn=0028-1042}}</ref> While their visibility largely depends on lighting—previously discussed—they are especially effective in identifying fortifications and earthworks, particularly in pre-modern agricultural landscapes where terrain alterations are preserved.<ref name=":0" /><ref name=":3" /><ref name=":4" />[[File:Kite aerial photo the site of Ogilface Castle, Woodend, West Lothian in low sunlight.jpg|thumbnail|right|Kite aerial photo of the site of Ogilface Castle, Woodend, West Lothian in low sunlight]][[Aerial photography]] has been the primary method of recording shadow marks, particularly in early 20th-century archaeological explorations.<ref name=":7" /><ref>{{Cite journal |last=Verhoeven |first=Geert |date=2017-09-14 |title=Are We There Yet? A Review and Assessment of Archaeological Passive Airborne Optical Imaging Approaches in the Light of Landscape Archaeology |journal=Geosciences |language=en |volume=7 |issue=3 |page=86 |doi=10.3390/geosciences7030086 |doi-access=free |bibcode=2017Geosc...7...86V |issn=2076-3263}}</ref> Early archaeologists recorded shadow marks via images captured manually in the early morning or evening to highlight the contrast of landscape changes using a traditional camera or aerial photography.<ref name=":7" /> Technology in remote sensing has improved this process by developing high-resolution satellite imagery, surveying with drones, and complimentary surveys using airborne [[Lidar|Light Detection and Ranging]] (LiDAR).<ref name=":8" /> LiDAR has been a significant advancement in the detection of shadow marks, as its main contribution is the ability to generate a [[Digital Terrain Model]] (DTM) that highlights slight variations in the topography that were previously hidden because of dense vegetation.<ref name=":7" />

=== Case studies ===
Real-world case studies demonstrate the practical value of shadow marks in archaeological detection. For instance, aerial surveys over [[Maiden Castle, Dorset|Maiden Castle]] in England revealed complex fortification structures through shadow-enhanced topography.<ref>{{Cite journal |last=Bewley |first=Robert H. |date=2003 |title=Aerial survey for archaeology |url=https://onlinelibrary.wiley.com/doi/10.1046/j.0031-868X.2003.00023.x |journal=The Photogrammetric Record |language=en |volume=18 |issue=104 |pages=273–292 |doi=10.1046/j.0031-868X.2003.00023.x |bibcode=2003PgRec..18..273B |issn=1477-9730}}</ref>  Similarly, in China, [[Synthetic-aperture radar|SAR]] imagery successfully detected shadow patterns of buried city walls beneath agricultural fields.<ref name=":15" />

These examples highlight how shadow marks often provide the first visual cue of subsurface features—especially when crop and soil marks offer limited information.<ref name=":9">{{Cite book |last=Wilson |first=David Raoul |url=https://archive.org/details/airphotointerpre0000wils/mode/2up |title=Air photo interpretation for archaeologists |date=1982 |publisher=New York : St. Martin's Press |others=Internet Archive |isbn=978-0-312-01527-5 |pages=27–69}}</ref><ref name=":1" />  Shadow marks are the most informative when they are used along with other [[remote sensing]] methodologies.<ref name=":9" /><ref name=":10">{{Cite journal |last1=Del Pozo |first1=S. |last2=Rodríguez-Gonzálvez |first2=P. |last3=Sánchez-Aparicio |first3=L. J. |last4=Muñoz-Nieto |first4=A. |last5=Hernández-López |first5=D. |last6=Felipe-García |first6=B. |last7=González-Aguilera |first7=D. |date=2017-08-18 |title=Multispectral Imaging in Cultural Heritage Conservation |url=https://isprs-archives.copernicus.org/articles/XLII-2-W5/155/2017/ |journal=The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences |language=English |volume=XLII-2-W5 |pages=155–162 |doi=10.5194/isprs-archives-XLII-2-W5-155-2017 |doi-access=free |bibcode=2017ISPAr62W5..155D |issn=1682-1750}}</ref> When combined with other forms of remote sensing, shadow marks help triangulate archaeological interpretations through complementary visual, biological, and physical indicators.<ref name=":9" />

Archaeologists today are therefore placing an emphasis on a multiproxy approach. As researchers use shadow mark analysis paired with [[Lidar|LiDAR]] (topography), GPR (subsurface readings), and multispectral band analyses (landscape development); they categorize between anthropogenic and natural features.<ref>{{Cite journal |last=Bitelli |first=Gabriele |date=2012 |editor-last=Lasaponara |editor-first=Rosa |editor2-last=Masini |editor2-first=Nicola |title=Satellite Remote Sensing |url=https://link.springer.com/book/10.1007/978-90-481-8801-7 |journal=Remote Sensing and Digital Image Processing |volume=16 |language=en |pages=113–126 |doi=10.1007/978-90-481-8801-7 |isbn=978-90-481-8800-0 |issn=1567-3200}}</ref> As more data goes into [[Geographic information system|Geographic Information Systems]] (GIS), but shadow marks could also be placed in GIS, the spatial analysis of archaeological sites can improve predictive modeling and our ability to reconstruct cultural landscapes.<ref>{{Cite book |last=Cowley |first=Dave |url=https://www.academia.edu/6730535 |title=Remote Sensing for Archaeological Heritage Management |date=2011-01-01 |isbn=978-963-9911-20-8 |pages=43–58}}</ref> Shadow marks will remain important - even if they are a relatively low technology - in the expanding toolbox of remote sensing archaeology.<ref name=":7" />

=== Limitations and solutions ===
While shadow marks can enhance the visibility of ancient features under ideal lighting conditions, they are also highly susceptible to environmental interference.<ref name=":2" /> Cloud shadows, uneven terrain, vegetation, and surface modifications—such as roads or ploughing—can all distort or obscure shadow patterns, making interpretation less reliable.<ref name=":2" /><ref name=":1" /> These limitations necessitate the use of advanced remote sensing techniques and multi-sensor methodologies.<ref name=":1" /> Passive optical imaging via aerial technology has also improved shadow mark interpretation.<ref name=":8" /> [[Multispectral imaging|Multispectral]] and [[Hyperspectral imaging|hyper-spectral imaging]] makes it possible to filter some atmospheric interferences, such as cloud shadows or remove them and preserve archaeological patterns, as it does compensate for shadow marks on the earth’s surface when recording sunlight and manipulating shadows.<ref>{{Cite journal |last=Verhoeven |first=Geert |date=2017-09-14 |title=Are We There Yet? A Review and Assessment of Archaeological Passive Airborne Optical Imaging Approaches in the Light of Landscape Archaeology |journal=Geosciences |language=en |volume=7 |issue=3 |pages=12–17 |doi=10.3390/geosciences7030086 |doi-access=free |bibcode=2017Geosc...7...86V |issn=2076-3263}}</ref> A multispectral light dome also allows archaeologists to simulate sun angles for interpreting shadow marks in digital reconstructions.<ref name=":6" /> In addition, synthetic lighting simulations can be developed to create shadow conditions artificially, which gives archaeologists the potential capabilities to manipulate digital terrain features that may not be possible in situ.<ref name=":12">{{Cite journal |last1=Hubert |first1=Mara |last2=Krömker |first2=Susanne |date=2017 |title=Visual Computing for Archaeological Artifacts with Integral Invariant Filters in 3D |url=https://diglib.eg.org/server/api/core/bitstreams/25baea81-03f8-4a5a-a8b0-679a5ccc02f2/content |journal=GCH Conference Proceedings |pages=2–7}}</ref>

The environment and seasonal factors can still influence shadow marks, as archaeologists work in areas with frequent cloud cover or shifts in shadow angle of periodical archaeological features.<ref name=":0" /><ref name=":7" /> Likewise, although perfect air and vegetation conditions may be present, modern infrastructure, roads, and contemporary urban development may also distort or compact the shadow marks footprints, making interpretation increasingly difficult.<ref>{{Cite journal |last=Verhoeven |first=Geert |date=2017-09-14 |title=Are We There Yet? A Review and Assessment of Archaeological Passive Airborne Optical Imaging Approaches in the Light of Landscape Archaeology |journal=Geosciences |language=en |volume=7 |issue=3 |pages=9–12 |doi=10.3390/geosciences7030086 |doi-access=free |bibcode=2017Geosc...7...86V |issn=2076-3263}}</ref> To address these, archaeologists now routinely use an integrated methodology, utilizing shadow-marked analysis alongside [[ground-penetrating radar]] (GPR) and [[Geomorphology|geomorphological]] survey applications to verify their past interpretations.<ref name=":7" /> These much-relied-upon interdisciplinary techniques and methodologies provide higher accuracy in the census of archaeological sites and ultimately verify the power of shadow marks in remote sensing applications for archaeology.<ref name=":7" />

In recent applications, spectral indices (such as band ratios and [[Normalized difference vegetation index|NDVI]]) have been used to diminish contrived impacts of cloud shadows, which obscure archaeological features including both crop marks and moist marks.<ref name=":1" /> These indices help counteract not only atmospheric effects, such as cloud interference, but also transient natural shadows that can originate from vegetation growth or passing weather systems.<ref name=":1" /> Using these approaches can improve the visibility of less visible circular marks, including those that result from buried ditches.

In addition, [[Synthetic-aperture radar|synthetic aperture radar]] (SAR) technology—particularly using [[COSMO-SkyMed]] X-band data—has demonstrated the potential to improve the identification of shadow marks under challenging environmental conditions.<ref name=":11">{{Cite journal |last1=Chen |first1=Fulong |last2=Masini |first2=Nicola |last3=Yang |first3=Ruixia |last4=Milillo |first4=Pietro |last5=Feng |first5=Dexian |last6=Lasaponara |first6=Rosa |date=2014-12-23 |title=A Space View of Radar Archaeological Marks: First Applications of COSMO-SkyMed X-Band Data |journal=Remote Sensing |language=en |volume=7 |issue=1 |pages=28–46 |doi=10.3390/rs70100024 |doi-access=free |bibcode=2014RemS....7...24C |issn=2072-4292}}</ref> When SAR data is layered with optical imagery, the combined approach significantly enhances detection reliability—particularly in arid or densely vegetated regions where optical methods alone are insufficient.<ref name=":2" /> Using both multi-temporal averaging and single-date enhancements (including speckle filtering and morphological processing), they sought to improve detection of microrelief marks and structures below the surface.<ref name=":11" /> Two advantages included that:

# Noise can (and was) suppressed while effectively preserving weak signals associated with archeological features or treatments;
# [[Radar]] imaging for sub-surface analysis can complement existing optical methods (and in some situations, exceed optical methods) when visibility is constrained.<ref name=":11" /><ref name=":10" />

Future studies of shadow optics will likely include imaging in real-time adaptive conditions, where agents (e.g., sensors) are tuned by an AI to adjust quickly to the conditions of light.<ref>{{Cite journal |last1=Huang |first1=Xiang |last2=Uffelman |first2=Erich |last3=Cossairt |first3=Oliver |last4=Walton |first4=Marc |last5=Katsaggelos |first5=Aggelos K. |date=September 2016 |title=Computational Imaging for Cultural Heritage: Recent developments in spectral imaging, 3-D surface measurement, image relighting, and X-ray mapping |url=https://ieeexplore.ieee.org/document/7560020 |journal=IEEE Signal Processing Magazine |volume=33 |issue=5 |pages=130–138 |doi=10.1109/MSP.2016.2581847 |bibcode=2016ISPM...33..130H |issn=1558-0792}}</ref> Hyperspectral imaging and improvements in LiDAR will increase the accurate classification of shadows and reduce false positives and errors. Merging physics outcomes and imaging methods will continue to the limits and interpreting shadow marks effectively as a critical framework of remote sensing and archaeologically detecting earth-based sites and features.<ref name=":5" />

== AI applications ==
The collaboration of shadow mark analysis with [[artificial intelligence]] (AI) has paved the way for new opportunities in archaeological remote sensing.<ref name=":13" /> Shadow mark analysis had traditionally relied on the interpretation of aerial photographs to identify archaeological sites. Still, recent technological advances in machine learning and computer vision have led to automated shadow mark analysis with greater efficiency and accuracy. AI-based approaches can allow researchers to analyze countless datasets of aerial and satellite images to identify shadow marks with minimal human involvement.<ref name=":13" />

An evident and prominent development in this area is the deployment of [[Convolutional neural network|convolutional neural networks]] (CNN) in detecting and classifying shadow marks.<ref name=":14">{{Cite journal |last1=Argyrou |first1=Argyro |last2=Agapiou |first2=Athos |date=2022-11-26 |title=A Review of Artificial Intelligence and Remote Sensing for Archaeological Research |journal=Remote Sensing |language=en |volume=14 |issue=23 |pages=3–19 |doi=10.3390/rs14236000 |doi-access=free |bibcode=2022RemS...14.6000A |issn=2072-4292}}</ref> CNNs can distinguish between genuine archaeological shadow features and other artifacts caused by clouds, vegetation, or urban features.<ref name=":14" /> Moreover, researchers have recently demonstrated improved accuracy in the automated detection of shadow marks by training AI models with datasets containing known archaeological sites.<ref name=":13" /> Researchers have recently used unsupervised learning methods such as clustering algorithms to segment aerial imagery and extract shadow features of possible underground features.<ref name=":13" /><ref name=":14" />

Another significant development involves applying 3D photogrammetry and light simulation to improve the visibility of shadow marks. Virtual reconstructions of lighting conditions allow researchers to simulate and recreate both sun angles and the corresponding shadows, allowing them to visualize how an archaeological site would appear under different lighting circumstances. This technique has been beneficial in instances when real-world shadow marks cannot be detected due to seasonal or weather conditions.<ref name=":12" />

AI-driven remote sensing has also begun to employ multi-spectral data processing concurrently with shadow analysis.<ref name=":13" /> By applying spectral indices like the [[Normalized difference vegetation index|Normalized Difference Vegetation Index]] (NDVI), researchers can explore patterns in an object’s shadow mark, establishing a means to differentiate between shadows associated with burial remains from those generated by vegetation differences.<ref name=":13" /> The separation allows researchers to filter out false positive occasions, particularly in dense forest areas where the distinction between tree and archaeological shadows can be problematic.<ref name=":14" />

These AI methodologies for shadow mark detection are still limited by their reliance on high-quality training datasets that are not always available throughout the world.<ref name=":13" /> Another concern is that variable landscapes can also complicate and further diversify the types of shadows produced over time, meaning that AI processes of shadow recognition will require continuous development and improvement.<ref name=":14" /> Regardless, as more datasets become available, it is anticipated that AI methodologies will become a routine part of chronological remote sensing and shadow analysis for archaeological inquiry.<ref name=":13" /><ref name=":14" />

==See also==

* [[Aerial archaeology]]
* [[Archaeological field survey]]
* [[Remote sensing]]
* [[Cropmark]]
* [[Soil mark|Soilmark]]

==References==
<References />

{{DEFAULTSORT:Shadow Marks}}
[[Category:Methods in archaeology]]
[[Category:Archaeological features]]
[[Category:Shadows]]