Time series analysis of satellite remote sensing data for monitoring vegetation and landscape dynamics of the dried sea bottom adjacent to the lower amu darya delta

Abstract

The Aral Sea region is a rapidly transforming landscape due to the continuous desiccation process. This study describes the vegetation and landscape dynamics in the lower Amu Darya Delta and adjacent parts of the dried sea bottom using MODIS (Moderate Resolution Imaging Spectroradiometer) surface reflectance data and EVI time series for the years 2001-2011. The potential of MODIS time series for monitoring landscape and vegetation dynamics of the dried sea bottom adjacent to the lower Amu Darya Delta was evaluated concerning data availability and spatial and temporal resolution. Two time series with different quality considerations were generated to subsequently characterize the yearly changes in the dried part of the sea bed, a simple layerstack (LS) of observations and quality-filtered and smoothed time series using a double logistic function (DL). The EVI (Enhanced Vegetation Index) values show a small dynamic inter- and intra-annual range. The majority of the EVI values fluctuate between-0.2 and +0.1, which indicates generally low vegetation dynamics in the desiccated areas. Looking at the inter-annual behavior of the LS/DL time series plots, the noise of the data and data fluctuations seem to become less for areas which have been dry for a longer period. A regional differentiation of the landscape dynamics between the Eastern and the Western basin of the southern Aral Sea could be observed. The observation points for the Western basin show a more stable behavior of the EVI values in comparison to the samples on the Eastern basin as seasonal or inter-annual flooding is less frequent. A typical pattern as a result of clear vegetation dynamics could not be observed in the EVI, LS and DL time series plots.