Monitoring phenological cycles of desert ecosystems using NDVI and LST data derived from NOAA-AVHRR imagery
The potential of the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) for monitoring phenological cycles in semi-arid lands has been demonstrated in this study. Attention was focused on two areas located only a few kilometres apart but across the political border between the Negev (Israel) and Sinai (Egypt). Although the areas are identical from the pedological, geomorphological, and climatic points of view, due to different land management, the Negev is under a continuous rehabilitation process while Sinai is under a desertification process. Four years of digital data were used to compute the Normalized Difference Vegetation Index (NDVI) and Land Surface Temperatures (LST) over two sampling polygons. The NDVI was used to monitor the vegetation reaction to rainfall, while LST proved to be a good indicator of seasonal climatic fluctuations. Using these biological and physical variables, the potential for following the vegetation dynamics throughout the year was demonstrated. Through cluster analysis, it was shown that the movements of the Sinai desertified side in the LST-NDVI space are only due to seasonal climatic fluctuations. On the Israeli recovered side, on the other hand, three different parts of the annual ecological cycle of the indigenous vegetation are evident: the dry season in which plants reduce their activity, the rainy season, and a growing season characterised by relatively intense biological activity. Within the LST-NDVI space it was also shown that Sinai is positioned similarly to the Sahara biome and the Negev similarly to the Sahel biome. Finally, LST-NDVI data were used to estimate phenological parameters that can be exploited for defining protection policies or, on the long term, for climate change studies.