Expert: Ralph Salier - 1/25/2011

Question
In an aerial photograph, how does one destinguish between the works of Human hands, vs. that of nature? Or,in an aerial photograph, what qualites for a given feature, would indicate that it is of Human origin?

Answer
Hi Viktor,

Before you can get a read on prehistoric sites from aerial pics, you need to become comfortable with what modern features look like and their regularity.  Drainage ditches, irrigation ditches, channalized streams and rivers, earth works such as levies and burms.  Even t he lay out of cities and towns have a particular order to them.  Then look at extant archaeological sites like Teotehuacan in Mexico, Chichen Itza, Cuzco, Machu Pichu, Ankor Wat and other cities that are ancient but very visable and compare modern to  these to get a feel for what you are seeing. Then look at Chahokia across t he Mississippi River from St. Louis MO.  Chahokia is a city of earth works build some 1500 years ago and has been partly restored by archaeologists.  

Sites in open fields are sometimes easy to see because of changes in vegetation but these could also be impacted by relatively modern activities too.

Take a look at Stone Henge in the UK and this will give you an idea of what these markings look like.  You can also follow Roman roads for miles even  though they have been long buried.  

This progression will give you a g ood start.  There are new technologies like side scan radar, differential foliage temperature, and infrared photography that can also identify sub soil changes.  

There are web sites that talk to some of these technologies and if you look in some of the more recent National Geographic magazines, they illustrate some of these as well.

I hope this helps, ask more questions if you need more clarification.