- The borderline between Israel and Sinai is characterized by a sharp contrast that is caused by the low spectral re ectance on the Israeli side (Negev desert) and the high spectral re ectance on the bare Egyptian side (Sinai desert). This contrast across the political border has been discussed in many publications over the last two decades. In this study, satellite images acquired by NOAA Advanced Very High Resolution Radiometer (AVHRR) over a time period of 3 years (June 1995 to June 1998) were analysed. In addition, extensive eld studies were carried out on the Israel side of the border. The current research shows that the re ectance values in Sinai seem to be quite stable over the entire year, however re ectance values in the Negev show a signi cant diVerence between the dry and the rainy seasons. Comparison between the AVHRR-derived Normalized DiVerence Vegetation Index (NDVI) values and rainfall data from the Negev shows that the highest AVHRR-derived NDVI values occur a few weeks after the main rainfall. Field observations, based on spectrometer measurements of diVerent surface components (bare sands, biological soil crusts, annuals, and perennials) and estimation of vegetation cover on the Israeli side of the border, show that the peak NDVI of the perennials occurs at the same time as the satellite observed peak. The spectral diVerence between both sides of the border during the dry season is caused by the dense cover of the higher vegetation and the biological soil crusts and by the photosynthetic activity of perennials during the dry season. The highest diVerence between both sides during the rainy season is caused by the photosynthetic activity and vegetation cover of the annuals and perennials.