Posted by: signalhillarchaeology | July 18, 2010

A Different Perspective…

Here is yet another student post, this time about how a different view of a site can give you a totally different perspective.  Here’s Steven’s thoughts on why archaeologists look at aerial photos of a site.

–Amanda (Instructor)

Hi! My name is Steven England and I’m a student on the Memorial University Archaeology Field School at Signal Hill.  Today, I’d like to talk to you about aerial photography, and its great value to archaeologists. Aerial photos are most often used as a means of examining large swathes of land in a fairly short time period. That makes sense; from that high up one can see a great deal of landscape. What may look like hills and natural depressions at ground level may take on a whole new appearance from the air. Evidence for human occupation sites may be seen, such as the remains of a wall fortification or an irrigation canal, for example. Vegetation growth is a great indicator of these sites; for example, plants will grow taller and thicker in a buried canal due to the depth of the soil changing moisture and nutrient availability. However their growth will be stunted if they exist over a buried stone work for the opposite reason; a lot less soil may be present. Having a bird’s eye view can really make vegetation growth differences stand out.

There are two main types of aerial photography; oblique and vertical. Oblique photos are taken at an angle and allow the observer to see changes in elevation in the land, as well as being able to provide a three dimensional view of the site if multiple photos are taken and overlapped. The other type of aerial photography is vertical. This is taken from a top-down perspective, and is often done by other organizations such as mineral survey and forestry groups. Archaeologists can gain access to these photos though, and can use them to look for features in the landscape that point to a site.

There is technically a third type of aerial photography, taken from high altitudes. Can you guess what it is? If you said satellite imagery, you get a sticker! [Amanda notes: sticker offer is only hypothetical; requests will not be honoured].  Satellite imagery can be a useful tool to archaeologists; it can be used to show networks such as roads, as well as the extent of an agricultural area used by an old society. There are drawbacks to using these techniques however; the most pressing issue being the high cost; it’s not cheap getting photos from a satellite or fueling a plane to fly over a portion of land to take photos. However the data is becoming more accessible, innovations such as Google Earth make archaeological site hunting an activity that any average person could do, if they were so inclined.

A practical application of aerial photography can be seen in the picture below.  This is an example of a vertical photograph:

An aerial view of Signal Hill, with our site and its surroundings indicated by the white rectangle.

As the name suggests and as this picture shows, vertical photographs are taken at a 90 degree angle to the ground, usually from high altitudes in planes. In this particular picture, the general area of our site is highlighted in the white box. This picture is from the Survey & Mapping Division of Newfoundland.

This next picture was taken from Google Earth, showing a satellite view of the area around our site:

Another view of our site, with the surrounding area in white, and the immediate area of the site in orange.

The lookout is highlighted in white again, and the rough area of our dig site is within the orange square. As you can see, this satellite image does not show detail as clearly as an aerial photo.  [Amanda notes: clearly, it’s time to take up a collection to launch our own Field School Satellite…]

Last but not least, is an oblique aerial photograph, showing the same general area of our site, but in much greater detail:

A fantastic view of our site... you can see the terrace that we're working on just at the top centre of the image; below that, on the terrace below, are the stabilized archaeological remains of the nineteenth century canteen. Several of the prominent ridges that you see are actually large man-made stone walls that surround the terraces. Signal Hill may look abandoned today, but in its heyday as a British mililtary site, it was a highly engineered, built-up hillside. Click on the image to view a larger version.

I obtained this photo from a local photographer named Andrew Collins, who was nice enough to let me use it for this entry. [Amanda notes: Andrew, my thanks as well for giving permission to post this amazing photo!!!].  As you can see oblique photographs show relief and shadows on the terrain, and can help pick out significant features in the landscape. By looking at the above photo, one can see that there was a rockslide nearby where we are working. As of last week, we’re focusing on finding the exact location and dimensions of the British barracks that was built here. Due to this rockslide, it could be possible that a portion of the building’s north foundations may have slipped down the hill too; making our job a lot more difficult if my hunch is correct. Further excavation will solve the mystery, hopefully.

There you have it folks, a quick introduction to aerial photography. Not only are these photos very useful, but they’re fun to look at to try and find your house too!

–Steven England, Student.


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