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Hazard Mitigation
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Drought and Vegetataion Monitoring in the Arid and Semi-Arid Regions of the Mongolia using Remote Sensing and Ground Data
are steeper and shorter, whereas the wet (1994) years lines are gentler and longer. The mean values of the NDVIdifferenced and LSTdifferenced of drought years' are always located in the lower-right part of the NDVI-LST space-system, i.e., they have a positive NDVIdifferenced and the negative LSTdifferenced value in the drought year. In the opposite, wet year's mean values are positioned in the upper-left part in throughout the arid and the semi-arid zones.
Figure 3. Warm seasonal time trajectories (upper part) of the NDVIdirrerenced vs. LSTdirrerenced (subtracted from1993) for drought years (1992 and 1995) and the wet year (1994) on the sample plots correspond to arid area (A) and semi-arid (B) zones. The lines (bottom part) connected between the maximum LSTdifferenced with minimum NDVIdifferenced and minimum LSTdifferenced with maximum NDVIdifferenced values correspond to upper parts.
5. Summary and Conclusions
Several previous investigations have shown that the multi-temporal NOAA-AVHRR based NDVI and LST are suitable study for land cover classification in Africa, climate variability in southern Sahel, deforestation of Central African evergreen forest, and for quantify droughts in sparse vegetated area of the Negev Desert. All of those area located in relatively low latitude when there were drastic negative relations between those two parameters. We get such kind of relations in the middle latitude area, such as in the Gobi Desert arid area. But in the semi-arid area in the middle latitude we could discover positive relations between those two parameters. Based on differenced method we found a drought indicator - well suitable in the arid and semi-arid area of Mongolia. Due to moisture stress on the vegetation, NDVI (LST) value recorded in the dry years should be lower (higher) than those values recorded in a "normal" year; therefore in drought occurred areas, drought indicator - NDVIdifferenced (LSTdifferenced) values will be high (low) than normal and wet years. It is concluded that the AVHRR based NDVI and LST can provide valuable information for drought detecting and monitoring by operationally.
Acknowledgements
The authors would like to thank to Dr. Arnon Karnieli of the Remote Sensing Laboratory of the J. Blaustein Institute for Desert Research (BIDR) for his discussions, comments and assistance for able to present this paper on the ACRS-2000. We would also like to thank Ph.D. Q. Zhihao, Spatial Modelling Center of the Sweden for his suggestion and assistance for calculating the LST on study area.
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