Visible Light Imaging
Visible light imaging is a well-established remote sensing technique in archaeological research. Within the AMZ cycle, it is particularly useful during the exploratory and mapping phases of a field survey. Under suitable conditions, this method can effectively reveal archaeological features in terrestrial contexts, providing valuable insights for further investigation.
What?
How does it work?
Visible light imaging refers to the process of capturing visible light to create images, commonly known as photography.
There are two main types of visible light imaging: analogue photography and digital photography, which differ in how images are captured and stored. Analogue photography uses a chemical process to record images on a physical medium, typically a film negative. Light passing through a lens is focused onto the film, which reacts to the light and creates a latent image. Digital photography, on the other hand, uses an electronic sensor to capture images in digital form. Here, light passing through a lens is focused onto the sensor, recording the image as a series of digital pixels.
In archaeology, photography serves as a remote sensing tool for gathering information about archaeological sites and landscapes. This often involves taking photographs from an elevated perspective, such as an aerial platform. From above, patterns and features—such as crop marks, soil marks, and shadow marks—become visible that may not be apparent from ground level, potentially indicating buried archaeological features (figure 1).

In-depth explanation X
Visible light covers only a small portion of the entire electromagnetic spectrum, roughly between 0.4 and 0.7 μm, but includes all the colors perceptible to the human eye (figure 2).

Vertical aerial photos are taken perpendicular, while oblique aerial photos are captured at an angle. Multiple images can be combined using photogrammetry to create 3D models of archaeological sites or artifacts (figure 3). This process involves using a series of overlapping photos to generate a detailed, accurate 3D model of an object or area. Common points are identified in each image and used to create a 3D point cloud, which is then used to produce elevation models and 3D meshes.

What do you need?
To capture visible light images (photos), digital cameras with large sensors and high image resolution are commonly used. These cameras are sometimes offered as part of an integrated UAS system (drone), where a live feed can be displayed on a screen, but there are also other solutions with less integration with the drone’s hardware and software.. Individual photos can be used, but for archaeological purposes, it is more useful to capture series of images. Using photogrammetric techniques, highly accurate 3D models of entire landscapes can be created (figure 4).

Handheld cameras can be used to capture objects photographically or photogrammetrically at shorter distances.
Optical satellites provide a valuable tool for studying large-scale landscapes from space. They allow for the regular acquisition of images from the same locations, making them useful for monitoring landscape changes over time. In the Netherlands, optical satellite data is provided by the Netherlands Space Office through the satellite data portal.
Want to know more?In-depth explanation X
Even with relatively simple cameras, high-quality photos can be captured. However, there are key technical specifications to consider for achieving accurate results. Important factors include a fixed lens of adequate quality to ensure a high depth of field. In the case of drone photogrammetry, a global shutter is essential to avoid distortions.
Can be used with..
Using a handheld camera or a camera mounted on a drone allows for capturing very high-resolution images at close range. Thanks to the rise of UAS technology, optical photography for archaeological prospection, like multispectral imaging, has made significant advances, enabling the collection of high-resolution images at precisely chosen (and potentially optimal) times of the year. However, there are limitations in geographic reach due to legislation and limited battery life.
Want to know more?Archaeological Applications
Place in the Dutch archaeological heritage management process
Visible light imaging can, like most other archaeological remote sensing methods, be applied during the exploratory and mapping phases of archaeological surveys. Satellite imagery is also commonly used during desk-based research to identify potential sites or features that warrant further investigation. The collected and analyzed images produce a set of spectral anomalies, along with descriptions and interpretations. These can be used to better understand both the underground and surface archaeological features, and potentially inform new prospecting or excavation research. Since visible light imaging, when combined with photogrammetric data processing, can also produce high-quality 3D models, the technology can be applied in excavation research as well.
Want to know more?In-depth explanation X
In combination with drone platforms: due to current legal (maximum distance from the pilot, limited visibility after sunset) and technical (e.g., battery life) constraints, the use of drones equipped with optical cameras over large areas is often difficult to implement. For this reason, this type of research is often carried out in areas where there is at least a strong suspicion of the presence of archaeological remains.
What types of archaeological materials/landscapes
Optical photography as a prospecting method is applicable in any situation where color or shape differences between archaeological features and the natural landscape can be observed. Whether these differences can be detected depends heavily on local conditions. Typical scenarios include fields with crops in late summer, where differences in crop health are often most pronounced, making them highly visible as crop marks. Additionally, visible light imaging can be used as a 3D documentation method, for example, during an excavation.
Furthermore, optical cameras are particularly effective during low sunlight conditions, such as at sunrise or sunset, for capturing shadow marks. When the sun is low, small variations in the landscape cast longer shadows, making subtle contours of underlying archaeological structures visible. These shadows can provide clues about features like old ditches, mounds, or foundations, which remain impossible or very difficult to detect under normal lighting conditions.
Want to know more?In-depth explanation X
It is important to realize that the ability to observe archaeology in the form of crop marks depends heavily on the state of the vegetation, as well as the season and the specific growth cycle of the crop. Weather conditions also play a significant role. In years with, for example, drought, crop marks will be more quickly and clearly visible.
Limitations/uncertainties
The process of capturing optical imagery on which potential crop marks, soil marks, and shadow marks can be identified is highly dependent on specific lighting and weather conditions. Additionally, the photogrammetric post-processing is a complex process that can be influenced by various variables, which ultimately affect the final output. When the goal is to produce a high-quality 3D model, several factors become particularly important, including camera and lens settings, lighting conditions, and the strategy used for capturing images.
Want to know more?In-depth explanation X
Due to the wide variety of landscapes and climates worldwide, as well as in the Netherlands, the relative effectiveness of optical imaging is a subject of ongoing research. An important aspect of this research is the recording of situational parameters during drone surveys, as well as the use of complementary and potentially validating prospecting techniques. The potential of visible light imaging to detect archaeological features also depends on vegetation types and growth cycles. This makes it essential to compare workflows and outputs with data obtained from other sources.
Casestudies
Curious about how visible light imaging has already been successfully used in archaeological fieldwork? Click on the tiles below to explore the case studies where this sensor technique has been applied!
References/further reading
Van Doesburg, J., van der Heiden, M., Waagen, J., van Os, B., & van der Meer, W. (2022). Op zoek naar lijnen: De waarde van elektromagnetische inductie en optische en thermische infraroodbeelden in Siegerswoude (Friesland). Rapportage Archeologische Monumentenzorg 273.
Netherlands Space Office. Satellietdataportaal
Rensink, E., Theunissen, L., Feiken, R., Bourgeois, J., Deforce, K., van Doesburg, J., Emaus, R., van der Heiden, M., de Jong-Lambregts, N., Karagiannis, N., de Kort, J. W., Liagre, E., van Londen, H., Meylemans, E., Orbons, J., Stichelbaut, B., Terlouw, B., Timmermans, G., Waagen, J., & van Zijverden, W. (2022). Vanuit de lucht zie je meer. Remote sensing in de Nederlandse archeologie. Nederlandse Archeologische Rapporten (NAR) 80.
Waagen, J. (2023). In search of a castle: Multisensor UAS research at the Medieval site of ‘t Huijs ten Bosch, Weesp. 4D Research Lab report series, 4. https://doi.org/10.21942/uva.23375486.v2