InSAR has the ability to analyze archived SAR data to provide measurements of historical ground movement. This historical data can be used to assess the impact of past operations on the surface movement.
RADARSAT-1 and -2, TerraSAR-X, ENVISAT, ERS-1 and -2 all have archives stretching back to the early 1990s that can be used for historical analysis.
Historical data is also useful for establishing the baseline stack which is required for atmospheric noise removal. As the number of images in a stack increases, the measurement accuracy increases because the removal of atmospheric noise in improved. By using a pre-existing historical data as the starting point, high accuracy measurements can be achieved from the very beginning of a monitoring period.