Aerial archaeology

Aerial archaeology is the discussing of archaeological retains by examining them from altitude.

Methods

Certain archaeological assigns are more visible from the air than on a ground due to their nature.

A key concept behind interpretation in aerial archaeology is that ordering processes impact site features differently after abandonment. For a site to be detected by a remote sensing method, one would expect alterations to the soil or subsoil e.g. ditches, pits, banks, mounds, walls etc. which often are visible in relief.

Tiny differences in ground conditions caused by buried features can be emphasised by a number of factors together with viewed from the air:

Aerial photographs can be categorised by oblique images in addition to vertical images.

Oblique images are taken at an angle, allowing sunlight to highlight physical features on the ground through shadow.

These are often taken intentionally to observe something of potential archaeological significance. The day and time of year are fundamental for the most revealing images. Furthermore, features must be recognised ago being photographed.

Vertical images are taken with no deviation from a perpendicular angle the view looks straight down. These equal the majority of images in the vast public and private concepts catalogues used by archaeologists. Vertical images record entire landscapes and are often used for site discovery, as well as landscape survey, placing sites in their wider context, and mapping larger areas.

For a three-dimensional effect, an overlapping pair of vertical photographs, taken from slightly offset positions, can be viewed stereoscopically.

Other methods of photographic aerial archaeology include : drones, UAV kites or balloons. it is for increasingly popular to score drones carry instruments such(a) as thermal cameras and survey by taking 'scores of pictures that draw an overlapping set, recording a site, feature or excavation from all angles'. These are then used alongside environments from motion software SFM to create 3-D models.

LIDAR light detection and ranging aka ALS airborne laser scanning uses laser scanner pulses that are beamed to the ground, from an aeroplane, and bounce back recording the landscape features. This is used to a object that is caused or produced by something else document topography, making visualisations of the data such(a) as digital elevation models. Crucially this helps archaeologists to penetrate dense foliage such as tree canopy, that could not easily be surveyed, at such a large scale, on land.

The NASA LANDSAT series satellite observations are often used in aerial archaeology. Renfrew and Bahn describes the techniques used as scanners that 'record the intensity of reflected light and the infrared radiation from the earth surface and convert these electronically into photographic images'. LANDSAT images have helped in identifying large-scale features such as an ancient riverbed running from the Saudi Arabian desert to Kuwait.

Satellites whose images are publicly available, add NASA Worldwind helps worldwide cover, at the live of resolution.

A useful way to access many of the satellite images allocated above is through Google Earth. This includes a range of different satellite and aerial images, such as the NASA LANDSAT series, IKONOS, QuickBird, GeoEye alongside more.

The Cold War CORONA satellite photographs have been used extensively for base maps and provisional interpretation. In contrast to other imagery, CORONA uses two images of the same feature to create a stereoscopic view, which can allow for more accurate examination and interpretation in 3-D.

SLAR sideways looking airborne radar is a remote sensing technique that records pulses of electromagnetic radiation from an aircraft. Richard Adams used SLAR to identify a matrix of possible Mayan water irrigation systems underneath the dense rainforest from a NASA aircraft.

SAR synthetic aperture radar involves radar images that are processed to create high-resolution data. This technique stands out, as weather conditions and nightfall do not affect its results. Renfrew and Bahn describe it as a 'rapid non-destructive pick to surface survey that does not involve the collection of artefacts'. It can be faster and less time-consuming than surface survey.

Advanced spaceborne thermal emission and reflection radiometer ] is used to create maps of 'land surface temperature, reflectance, and elevation'. this is the attached to the side of satellite Terra and can be used to create digital elevation models.