基于MODIS TVDI和模糊数学方法的藏北地区旱情等级遥感监测

为了实现对藏北区域范围内春夏旱情的动态连续监测,基于温度植被干旱指数(TVDI)和模糊数学方法建立了遥感干旱的划分标准,研究时段为1980-2017年。首先利用MODIS产品数据计算TVDI,然后根据气象干旱等级监测结果,采用模糊数学法建立基于MODIS TVDI的干旱等级划分标准,并对监测结果进行精度验证,最后分析了近年来藏北地区旱情的时空变化特征。得到的主要结论:①基于归一化植被指数(NDVI)和增强植被指数(EVI)计算得到的温度植被干旱指数TVDIN和TVDIE,均与20 cm实测土壤水分含量在0.05的水平达到显著相关,TVDIE的决定系数更高;②基于TVDIE将旱情划分为无旱、轻旱、中旱、重旱、特旱5个等级,其中,据此标准获得的藏北地区旱情等级与气象干旱等级监测结果大体一致;③近年来藏北地区旱情整体不太严重,且总体趋缓,其中,2009年最严重,发生中旱及以上旱情的区域面积达24%,年内旱情在6月最严重。就旱情的空间分布特征而言,研究区西南部和中部干旱比较严重,北部和东南部相对较轻。研究成果可为藏北地区干旱监测提供数据支撑,遥感干旱等级的划分方法可为其他地区的干旱研究提供参考。

Remote Sensing Monitoring of Drought Level in North Tibet Based on MODIS TVDI and Fuzzy Mathematics

A dynamic and continuous monitoring of spring and summer drought in north Tibet during the period of 1980-2017 was carried out. The temperature vegetation drought index (TVDI),fuzzy mathematics and monitored results of meteorological drought level were used to develop the classification standard of remote sensing drought,and the accuracy of monitored results was verified. The spatiotemporal variation of drought in north Tibet in recent years was analyzed. The main conclusions are as follows: ① TVDIN and TVDIE calculated based on the normalized vegetation index (NDVI) and enhanced vegetation index (EVI) were significantly correlated with the soil moisture content at 20 cm in depth at 0. 05 significance level. The determination coefficient of TVDIE was higher;②Based on TVDIE,drought could be divided into four levels including without drought,slight drought,moderate drought,heavy drought and severe drought. On which it was obtained that the drought level in north Tibet was consistent with the monitored results of meteorological drought level;③ Drought in the study area was not very serious in recent years,and the holistical drought situation was somewhat alleviative. The drought was the most serious in2009,and the area proportion of moderate and above drought was as high as 24%. Monthly,the drought was the most serious in June. In terms of the spatial distribution,the drought in the southwest and the central part of the study area was relatively serious,and it was relatively slight in the north and southeast. The research results could be referred in monitoring drought in north Tibet.