Another technique being utilized for monitoring in Western Norway (the Aknes/Tafjord Project) is short range laser monitoring.  This technique, taken from the off shore oil rigs in the North Sea, shoots a laser on one side of a crack to a heated plate on the other side.  This allows for year round monitoring and can track millimeter level deformations of point sources.  This system requires a power source for the laser and heated plate but has shown very good results over one year at the Aknes site in Norway.