Aerial Photographs

Aerial photographs are photos taken by either low flying air craft, balloons and in some cases kites. There are two kinds of aerial photographs these are vertical photos which are taken directly above the ground these are not the preferred type of photo as they do not show all archaeological evidence that oblique photos do. However they are very available as there are lots of records them which can be found at The National Monument of Records and satellite photos can now be found on Google maps and other websites. Archaeologists prefer to use oblique photos as evidence even though these are much more difficult to obtain than the vertical photographs.

Crop marks

These are marks that show features that may be beneath the crops. Positive crop marks are darker marks which show that there could be a ditch below the surface of the ground, as ditches contain lots of moisture which marks the crops grow to a larger size, therefore making a darker mark on an aerial photograph. Whereas negative marks show lighter marks when see on an aerial photograph, this is because there is a wall underneath the crops. The wall makes it difficult to for crops to grow therefore they are smaller and the soil is lighter so a light crop mark would be shown on an aerial photograph. Although crop marks can be very useful to archaeologists as they reveal things that archaeologist would not be able to see from the ground there are several negatives in using crop marks. One of the negatives is that the marks can only be seen on  a few days a year, this means that an aircraft would have to continuously fly over the area just to record the crop marks, this is very time consuming and very costly. Crop marks are often only visible when there is a drought this means that it is difficult to take aerial photographs which show the crop marks. This figure shows an aerial photograph of the Damerham area in Hampshire. This photograph shows negative crop marks this tells us that there is possible evidence of circular walls being buried beneath these crops.

Shadow site

Shadow sites are sites which have survived as low earth works, this are buildings that are made of earth e.g. Banks or ditches. The shadows can be recorded by using earth craft to take oblique photographs of  an area. Shadow sites can not be seen using vertical photographs, which means archaeologist may have to carry out there own aerial photographs as they may not be able to use the photos that have been recorded making the process very expensive. The best time of year to take these is during the winter when the sun is low either in the early morning or late afternoon. This is the best time as the low lighting helps to accentuate the shadows, winter is also a good time to take the photos as snow fall and flooding make it easier to see the shadows.