aerial survey

Magnitude Surveys provides aerial photography, videography, photogrammetry and multispectral imaging services.

Data collection is measured in minutes, and can be carried out from a safe location without the need for working at height.

The aerial mapping information that UAV surveys can provide makes it an ideal complement to terrestrial surveying methods.

photogrammetric mapping

DSM over LiDAR data <————————> Orthomosaic over Satellite

The UAV is flown over an area in swaths and takes a series of overlapping photographs. By combining GPS coordinates from the UAV with known ground control points, an accurately geo-referenced 3D reconstruction can be produced.

The processed data can be viewed as a point cloud, 3D model, orthomosaic image or as a digital surface model (DSM), all with a resolution of a few centimetres or less.

The surface model data is useful for rapid, detailed earthwork surveys, especially where open LiDAR data may be unavailable, out of date, or not of a high enough resolution. The orthomosaic can be used for site mapping and reconnaissance.

multispectral imaging

RGB Index <——————-> MS Index

A technique borrowed from precision agriculture, this method uses a cluster of light sensors to detect changes in plant health which aren’t visible to the human eye. This method can be effective during more phases of crop growth than visible-light photography.

Variations in these datasets can be used like cropmarks to identify sub-surface archaeological features such as ditches, pits, and structural remains.

This example shows a round barrow under excavation, captured with a multispectral camera over weeds and volunteer crop.

photogrammetric modelling

For complex heritage assets, such as standing buildings and structures, a mixture of flight patterns produce a detailed 3D reconstruction, which can be viewed as a point cloud or a textured model.

As well as recording features, this technique is also useful for conducting condition monitoring surveys and inspections. Defects can be easily identified and reviewed within the original photographs.

Aerial Reconnaissance

Incorporating aerial methods during ‘walkover’ surveys extends the visual range of the surveyor, allowing more information to be captured from angles that simply aren’t possible in a terrestrial survey. Areas that aren’t accessible on foot can also be surveyed over safely from the air.

This means surveys are not only more efficient, but the outputs are of a higher quality, including geotagged photos and video flyovers. The results can lead to more informed decision-making in subsequent programme design, further saving time and costs by reducing the need for redeployments. 

Example Datasets

Aerial multispectral data (NDVI, left), and terrestrial magnetic data (right)
A 3D model (mesh) of a former bell pit, rendered with colour values from the photographs (left) and with false colours derived from elevation (right)