The short revisit time in the ERS Tandem experiment shows the data quality reachable when the temporal coherence is high. Sentinel 1 will have a revisit time of 12 days. Using the 3 days repeat data from the ice phase of ERS1, we evaluated the improvements for distributed scatterers interferometry. Slow ground motion, visible in many successive images, allows the estimation of the subsidence rate from the interferogram stacks and not only from Persistent Scatterers. Interferograms at multiple spans can be optimally combined. The dispersion of the subsidence rate estimate obtained in one year using interferogram stacks compares favourably to a PS, if the number of pixels used is greater than say 100. We compare the Cramér Rao bound for the subsidence estimates for a Markov model of the temporal decorrelation to an approximated optimal linear estimate found from the covariances of the interferograms at different spans. The unbiased subsidence rate estimates are consistent