Analyse du processus de croissance de la glace des lacs avec les données du satellite ERS-1 en mode amplitude et interférométrique région de Schefferville
This study presents a detailed analysis of the information content of ERS-1 SAR with respect to the lake ice cover in the Schefferville area. A sequence of 21 radar images was acquired at 3-day intervals from December 25th 1993 to March 28th 1994. From this sequence, 19 interferometric coherence and amplitude images were produced. The study site is located at 54À 53' N, 67 08 ' W. Ice growth and snow fall were modeled to evaluate the ground surface conditions. The model provides good estimates of the ice growth and the snow water equivalent. Coherence data were correlated with ice growth rate, snow water equivalent changes, snow depth, hydrostatic water level and ice thickness for each interval by stepwise multiple regression. Amplitude data were extracted and compared with coherence data to evaluate the different aspects of information content. The results show that in interferometric mode coherence is very sensitive to snow water equivalent change. Vertical movements of the principal reflecting layer (ice/water interface) associated with snow fall and ice growth cause a loss of coherence on lakes, although the coherence on land is well preserved. Ice cracks appear dark on coherence images and occur after each important snow fall. In amplitude mode, the images show mainly ice rugosity effects on the signal. The backscatter amplitude increases at the end of study period. Changes in structural characteristics of the ice cover are observable in all images. Slush formation and ice cracks produce strong backscatter. Snow water equivalent changes do not significantly influence amplitude. However, a very wet snow cover at mid-March produced an amplitude reduction. It also shifted the reflecting surface, causing a loss of coherence.