Wikipedia
ShapeAccelArray (SAA) is a sensor that can be placed in a borehole or embedded within a structure to monitor deformation. It consists of a continuum of segments containing triaxial, micro electro mechanical system ( MEMS) accelerometers Each segment has a known length. By sensing the gravity field at each segment, the bend angles between each segment can be calculated. Using the calculated bend angles and known segment lengths, the shape of an SAA can be determined. SAA can be used to determine 3D shape when installed vertically and 2D shape when installed horizontally. 3D shape can be determined when SAA is installed up to 60 degrees from zenith.
SAA is typically installed in 1” (26 mm ID) PVC conduit which is grouted within a borehole. The flexibility of the SAA joints enables it to bend up to 90° and withstand large deformations. Data can be sent wirelessly to a server for automated processing and to enable remote data analysis in real-time. Data can also be periodically downloaded using a PC for analysis. Millimeter level precision can be achieved using this sensor.