Work at Saqqara is usually done in September and October each year. Most of the team are employed by universities, and this ties in with the academic year.
It is also a time of the year when the temperatures are beginning to cool to around 80–90 degrees Fahrenheit after the fierce heat of summer.
This also gives the team the winter months to write up the season's work and process the raw geophysical data in publishing form.
Seeing Beneath the Sand – The Geophysics
The project uses the techniques of modern science to explore the remains of ancient Egypt hidden beneath the sand. The methods used are either active (touching or probing the ground), or passive (not touching the ground).
An active method where the probes are pushed into the ground. An electric current is passed through them and measured.
Some materials allow electricity to pass easily but others are very resistant. Looking at how these measurements vary over an area makes it possible to locate objects buried beneath the sand.
This method is excellent for finding walls and large stone structures up to 10 to 15 metres below the surface.
A passive method of measuring the electrical properties of underground materials.
A four metre long plastic pole has a transmitter at one end and a receiver at the other. The difference in the electrical properties of the material below the pole can then be measured.
The survey is made at walking speed, so large areas can be covered quickly and depths of up to four metres can be penetrated. This gives a good general picture of the area.
Ground Penetration Radar
An active method where a transmitter and receiver are pulled along the surface.
Radio waves are sent through the ground. They continue to travel until they meet an object, which reflects them. The radio waves bounce back to the surface and the time taken to travel the distance can be measured.
The results produce a picture of what is under the ground to a depth of three to four metres.
This method is very useful for locating individual graves and tombs.
A passive method that measures the magnetic field of the earth and compares this with the magnetic fields produced by the materials beneath the instrument. When plotted, this builds up a very good picture of what lies three to five metres below the ground.
This method is excellent for picking up mud-brick structures. The computer picture looks just like an aerial photograph of surface ruins, when they are actually buried deep beneath the sand.