Aerial Photography
Aerial photos are one of the most useful tools that an archaeologist has for finding archaeological sites. They show what archaeology might be underneath a piece of land. They are photographs taken from a plane and they come in 2 types these are called oblique photos and vertical photos. Aerial photographs are usually called "APs".
- Oblique just means that the photo is taken from a slight angle over to one side of the site;
Bishopton, motte and bailey (an oblique photo)
© Tees Archaeology - Vertical means that they are taken from directly above the site;
Ringlemere Cup findspot - can you see the dark ring show up?
(A vertical photo) © Kent County Council
How do they work?
Aerial photographs work by showing up the differences between land that has been disturbed and land that hasn't. For example, if a ditch has been dug, even if it has been filled in over time, it will show up as a dark line on an aerial photograph. Something that sticks out of the ground like a burial mound will show up in the opposite way as a light-coloured circle. It is all to do with how shadows are created by the contours of the ground.
These things like ditches and mounds under the ground surface are called 'features' by archaeologists. Other "features" that show up on aerial photographs include walls, foundations of buildings, field boundaries and pits.
What affects the aerial photos?
- The time of day and the time of year affect an aerial photograph and how good it is, in other words, what it shows up on the photo.
- Oblique photos work best if there are some shadows but not when the shadows are too long, so early morning and early evening are good times to take these.
- For vertical photos, good strong sunlight is best and shadows don't really matter too much so they are usually taken at mid day.
- If a crop is being grown by a farmer on the site, it is best to take the aerial photograph when the crop is fully grown. The reason for this is that when there is a strong growth on top of the land, it can highlight the features that lie beneath the soil. The crop will grow best where it can put its roots down nice and deeply, as it will get more nutrients and a better water supply. Where the crop can't put down strong roots, it will grow less well. So, if a crop is growing over a ditch, it will put its roots down a long way and grow thick and strong. This will make the ditch show up even more as a dark line on an aerial photograph. Can you think of an example where the opposite is true and a crop doesn't grow well, so it doesn't look nice and dark on an aerial photograph?
