View sheds, Mobile phones and Archaeology

I have a fascination for archaeology and the way we lived our lives in the past. I am also wedded to my mobile phone (Windows Omnia 7) and feel cast adrift if I am out of signal range.

We are all familiar with the network coverage diagrams on the websites of the mobile phone companies, which tell us with reasonable accuracy where we might expect our mobiles to work. These diagrams are produced by calculating the theoretical viewshed of each mobile phone transmission mast and plotting this on a map.

What do we mean by this?

Mobile phone signals travel in straight lines (there is some bending or refraction of signals by the atmosphere). Generally speaking, the signal will not penetrate through hills, but will pass through trees, vegetation and most buildings (although some attenuation or reduction does take place). To all intents and purposes, if you were to stand  at the top of a mobile phone mast, the terrain you could see from your perch would define the area where you might expect your mobile phone to work. This is the viewshed for this mast.There will be some valleys, or land hidden by hills that you would not be able to see, and in these hidden locations your mobile phone would not be able to communicate with the the mast and you would be out of signal range. Of course, the strength of the signal diminishes with distance from the mast and this also has an effect on reception.

There are several freely available software solutions for plotting the viewshed of a given mobile telephone mast. The one I use is web based at:

http://www.heywhatsthat.com/

This will plot a viewshed on Google Maps or you can export a kmx file to view the viewshed in Google Earth. The link below shows the viewshed for a mobile telephone mast at Pigeons Lane, to the west of Ipswich , Suffolk. You will need to have Google Earth installed on your computer to view this.

http://sdrv.ms/RXysFB

The use of viewshed calculations can be used for planning the area that a radio station might be able to cover from a given location. This would be particularly important when planning communication networks for an emergency relief operation or a military command post.

However, apart from carrying out analyses and planning for future requirements, viewshed software plays an important role in trying to understand the past. Archaeologists use such techniques to establish, for example, whether inter-visibility between monuments might have been important. The analysis of the viewshed can help us learn about why monuments and buildings might have been built in a given location.

The link below gives you the viewshed plot on Google Earth for Sutton Hoo, in Suffolk.

http://sdrv.ms/RXDNN1

Looking at the viewshed allows us to consider whether the visibility of the cemetery site was influential in it being selected for the burial of a Saxon king. For more information about Sutton Hoo, follow the links below:

The Sutton Hoo Society:
 http://www.suttonhoo.org/index.asp

The National Trust:
http://www.nationaltrust.org.uk/sutton-hoo/


The British Museum:

http://www.britishmuseum.org/explore/young_explorers/childrens_online_tours/sutton_hoo/sutton_hoo.aspx



More about viewsheds next time.


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