Specialist Services: A closer look at UAV remote sensing

Today we continue to take a closer look at our specialist services by focusing on UAV remote sensing.

Unmanned Aerial Vehicles (UAVs), commonly known as drones, have revolutionised the field of archaeology. Building on traditional methods used in aerial archaeology over the last hundred years, this approach offers a greater depth of non-invasive investigation from the air – and provides projects and clients with a range of benefits that can reduce time, money, and resources on site.

Here are some of the ways in which UAVs are advantageous:

• Aerial Imaging: UAVs equipped with high-resolution cameras can capture detailed aerial imagery of archaeological sites and historic structures. This imagery provides a bird’s-eye view of the site, enabling archaeologists and consultants to identify features, patterns, and structures that may be invisible from ground level. It also facilitates the rapid creation of accurate topographic maps.

• Rapid Data Collection: Drones can swiftly collect large amounts of data in a short time, significantly reducing the time and effort required for surveying and mapping. This efficiency can result in cost savings for clients and expedited project timelines, as well as opening up new and exciting possibilities.

• Site Documentation: UAVs can efficiently document archaeological sites, assisting researchers and clients in maintaining a comprehensive and up-to-date record of the area. This documentation is vital for monitoring site conditions over time and for future reference.

• Non-Invasive Exploration: UAVs are non-invasive and do not disrupt the archaeological site, preserving its integrity. Traditional excavation methods can be destructive, whereas drones enable the collection of valuable information without physically disturbing the site.

• Advanced Capabilities: Furthermore, drones can be equipped with various advanced technologies, such as multi-spectral imaging, 3D modelling, photogrammetry, and LiDAR, all of which enhance their versatility and data-gathering capabilities.

• Cost-Effective: While there is an initial investment in purchasing and maintaining UAV equipment, the long-term cost-effectiveness becomes evident through reduced fieldwork expenses, quicker data collection, and more efficient project management.

As mentioned above, two key capabilities of remote mapping via UAV are high-resolution LiDAR and multispectral imagery. These are innovative and powerful techniques which are increasingly deployed as part of archaeological investigations. Capturing detailed imagery across large landscapes, the data is then analysed to identify archaeological remains, providing additional information on the extent of archaeological features beyond what is visible on the ground as macro-earthworks. We’ll be taking a more in-depth look at these techniques in a future piece, but for now you can see more of them in action below!

Example 1: compare the two images left and centre (above). On the left we have a simple local relief model derived from the UAV’s LiDAR. In the centre, the digital terrain model (DTM) which has been further processed to really make the features pop, producing differing visualisations to highlight subtle earthworks that would otherwise be difficult to observe. In this example, the UAV LiDAR survey identified and recorded the remains of a monastic and agricultural landscape that spans the medieval and post-medieval periods. You can see what the features are in the third map.

Example 2: in the first image, LiDAR highlights rake scars, hollow ways and trackways associated with extensive mineral extraction. These are easily identified in the northern aspect of this DSM. The second image offers an illustrated interpretation of the features.

Example 3: from the same site as above, we have a UAV thermal image (left) and GRVI (right, see below for explanation). Aside from archaeological features, these multispectral visualisations can also reveal the impact of the underlying geology on crop growth (particularly noticeable in the thermal output).

Most multispectral visualisations effectively are a measure of the “greenness” of vegetation. Measures of greenness are helpful in visualising crop stress – and thus possible cropmarks relating to archaeological remains which may not be visible to the naked eye or in aerial photography.

Green Atmospherically Resistant Vegetation Index (GRVI) is an index of plant “greenness” or photosynthetic activity. It is a chlorophyll index and is used at later stages of development, as it saturates later than NDVI.

Normalised Difference Vegetation Index (NDVI) quantifies vegetation by measuring the difference between near-infrared (which vegetation strongly reflects) and red light (which vegetation absorbs).

Thermal Sensitivity relies on infrared radiation emitted by objects and their environs.

 

As you can see, by leveraging UAV technology, archaeologists and their clients can achieve more comprehensive, efficient, and cost-effective archaeological investigations, ultimately contributing to a deeper understanding of our historical and cultural heritage. 

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