Geodetic measuring is undertaken in order to monitor and map the deformation of Vasa's hull. We have chosen this particular geodetic measuring system as it is extremely accurate, showing deformation of less than 1 mm.
Measurements have been made twice a year in the spring and autumn since the year 2000, and takes two people about two weeks to carry out. We measure 350 points on the outside of the hull and 50 on the inside. The system was constructed in collaboration with the Royal Institute of Technology.
Every measurement begins with positioning the measuring instrument, a total station, in our coordinate system measured in to a number of prisms which are mounted on the walls of the museum. We have to assume that the building is stable. Each target point on the hull is then measured from at least two different sets of points and then twice more from every succeeding point. This increases the accuracy of the measurement and minimizes the risk of faulty readings.
After each measuring session, the data is analysed and compared with previous results. We are then able to see how the positions of the 400 points change over time. We can say with certainty that Vasa is settling downwards ca 1 mm per year, although there are some more localized deformations. Vasa's preservation unit is working to develop a new support system as well as improving Vasa's current structural stability.
Geodesy (from Latin geo = earth and desi = part): meaning fixing a point's position in a coordinate system.