MODERN technology is being used to unlock age old secrets of mediaeval Christchurch Castle.

Using ground penetrating radar, sound waves and electrical impulses, a team of local enthusiasts backed up by experts is probing the earthen mound and surrounding courtyard of the ruined stone keep of the Norman castle.

The painstaking process, which could take months, is aimed at building up a picture of the castle foundations and extent of the defensive bailey ditch without excavating the sensitive site.

Roger Hills, of the Christ-church Antiquarians group which is carrying out the self-funded project, said: "We are making slow but good progress, but the real work begins when we start interpreting the data."

As well as the geophysical survey which will be extended to the adjoining bowling green when the season ends in October, the Antiquarians will also be carrying out documentary research of the castle's early history.

Now a scheduled monument administered by English Heritage, the castle was already disused and partially dismantled when it was slighted by Parliamentarian troops during the English Civil War.

It is thought the castle was built in the 12th century by Lord of the Manor Baldwin de Redvers to replace an earlier wooden stockade built on the same site in the wake of the Norman conquest.

De Redvers also had castles at Carisbrooke on the Isle of Wight, Tiverton in Devon and Plimpton in Somerset.

These will also be studied for clues to the design and history of the Christchurch site.