The Lençóis Maranhenses National Park (LMNP) constitutes the largest coastal dune field in South America. It is a remarkable reservoir of biodiversity facing important preservation challenges due to the rapid development of anthropogenic activities, including tourism. The objective of this study is to introduce preliminary results on the understanding of seasonal sand dune dynamics. For this purpose, we used Sentinel 2 time series from 29/07/17 to 17/09/18 in order to monitor the intra-annual migration of interdunal ponds. The method relied on three steps: 1) automatic Spectral Mixture Analysis to estimate the proportion of vegetation, mineral and water in each pixel, 2) rule-based classification and 3) extraction of interdunal areas to assess their dynamics. The average offset distance was 21.6 meters and the angle was 72.6°, corresponding to the main west-southwest wind direction. Additional studies to assess the long term expansion of the dune field are necessary.