【摘要】 基于2015年大气校正后的时间序列Landsat8影像,研究了归一化植被指数NDVI与增强型植被指数EVI随植被覆盖度增加的变化规律,定量分析了二者监测低、中、高植被覆盖的差异,比较分析了NDVI和EVI分布频率曲线差异及时间序列曲线差异。结果表明:地表刚出现植被时,NDVI和EVI的增加速度最快,随着地表植被覆盖度的增加,NDVI与EVI的增加速度减缓。低植被覆盖下NDVI的增加速度大于EVI,中等植被覆盖下NDVI和EVI的增加速度接近,高植被覆盖下NDVI的增加速度小于EVI,不同植被覆盖下的NDVI值始终大于EVI值。NDVI和EVI分布频率曲线能描述不同植被覆盖度像元数量和随时间的变化。NDVI和EVI时间序列曲线能清晰反映一种作物的长势变化规律及不同作物在同一时期的长势差异。在作物生长初期或低植被覆盖下,NDVI、EVI都偏高估计植被覆盖度,NDVI估计值略高于EVI的估计值。在作物生育中期或中等植被覆盖下,二者对植被描述能力相似。在作物生育高峰期或高植被覆盖下,监测作物长势变化EVI比NDVI更敏感。综上所述,监测作物时可根据作物生育期植被覆盖度变化特点合理选取NDVI和EVI植被指数,也可同时选用NDVI和EVI两种植被指数互为补充。更多还原

【Abstract】 Based on time series Landsat8 images of atmospheric collected in 2015,the change rules of normalized vegetation index( NDVI) and enhanced vegetation index( EVI) with the increase of vegetation coverage were studied. Their monitoring vegetation cover differences were analyzed quantitatively. The differences of NDVI and EVI distribution frequency curves and the differences of NDVI and EVI time series curves were analyzed. The results showed that NDVI and EVI were increased most rapidly when vegetation appeared on the surface,and with the increase of surface vegetation coverage,the increase rate of NDVI and EVI slowed a descending trend. NDVI with low vegetation coverage was increased faster than EVI,NDVI with medium vegetation coverage was close to EVI,and NDVI with high vegetation coverage was increased lower than EVI. Under different vegetation coverages,NDVI value was always greater than EVI value. NDVI and EVI distribution frequency curves can describe the number of pixels of different vegetation coverage and the change with time. NDVI and EVI time series curves can clearly reflect the growth change rule of a crop and the growth difference of different crops in the same period. The following conclusions were drawn: in the early stage of crops growth or under low vegetation coverage,NDVI and EVI overestimated vegetation coverage,and estimated value of NDVI was slightly higher than that of EVI’s. Their ability to describe vegetation was similar in the middle growth stage or in the middle vegetation coverage. EVI was more sensitive than NDVI to monitor crops growth during crops growth peak or under high vegetation coverage. To sum up,NDVI and EVI may be reasonably selected according to the change characteristics of vegetation coverage during crops growth period,and NDVI and EVI may also be used to supplement each other.更多还原