An unusual use of radar has enabled surveyors to check the damage to a famous monument, previously hidden underneath its stone cladding.
Fenced off since 2005 due to falling debris, the Wellington monument on the Blackdown Hills in Somerset has been abseiled by surveyors using a ground penetrating radar machine to look for damage.
Work on the 174ft (53m) high tower, originally built in 1817 as a tribute to the Duke of Wellington's military achievements at the Battle of Waterloo, was considered “crucial” by Ken Evans, building surveyor from The National Trust.
The trust believes the monument has been struck by lightning twice in its history and renovating the landmark every 10 to 15 years has been "expensive and unsustainable".
Mr Evans said the radar study was one of several being carried out to "understand this unique and somewhat complex monument".
"We have been using wind and movement sensors which have already surprised us by showing that it doesn't flex in the wind quite as much as we expected," he said.
"The ground-penetrating radar seeks to identify voids and gaps in the stonework under the surface but should also tell us more about the materials which were used to build the obelisk."
Data from the detailed survey will also be used to build a computer model of the obelisk and help with a "more effective repair approach".