PALSAR change detection in urban areas of European part of Russia
Alexander Zakharov(1) and Ludmila Zakharova(1)
(1) FIRE RAS, Vvedensky square 1, 141190 Fryazino, Russian Federation
Change detection is most impressive task to be solved with SAR systems as it allows the demonstration of the surface covers instability in various areas. PALSAR strategy of global and repeated mapping provides an opportunity for monitoring the different areas across the world using archival data. In a given report a preference was paid to the areas of karst and landslide areas in European Russia region. These are karst surfaces in proximity of railroad near Dzerzhinsk city, Nizhnii Novgorod region, and Volga riverbank in center of Ylyanovsk city with landslide activity.
Classical DINSAR approach was used for a study, when 2-3 sessions were combined in interferometric set, flat topography was removed and the phase variations on the interferogram were attributed to surface dynamics. Most of the pairs had small spatial baseline, consequently the topography might be neglected. It should be noted that these test sites were intensively studied by now with a use of ERS and ENVISAT data. C-band repeated orbits interferometry data were used for similar studies and discovered to be mostly useless because of temporal decorrelation.
All the PALSAR data obtained during first phase were collected in 2007; consequently, we may conduct probable change observations by now only on relatively short time intervals (one-two repeat periods of PALSAR observations). PALSAR observations of Dzerzhinsk city area in 2007 provided nice datasets allowing clear indication of surfaces subsidence. Interferograms show clear marks of surface sinking in the areas corresponding to pit soils in the beginning of summer, when intensive soils drying led to the surface dynamics in such areas. Similar bright patches generated by surface subsidence are seen on interferograms obtained from different tracks and overlapping in time, what confirms the fact of subsidence. At the same time the presence of karst activity as a reason for of the surface displacements is to be confirmed.
Landslide activity was searched on the interferometric pairs in urban area Ulyanovsk city on the Volga riverbank. No strong dynamics manifestation was detected on a short time intervals, which are peculiar to pairs available, but indication of large-scale displacement of riverbank area with small amplitudes is observed anyways. Looking at C-band SAR data for the same areas we may underline significantly higher coherence on PALSAR interferograms. Another impressive preference of L-band PALSAR data was the fact the coherence exists in the pair of data obtained on winter as well as for autumn-winter period, what is not a case with C–band data, what provides opportunity for the change detection even in unfavorable seasons and meteorological conditions.