1999年锡林郭勒草地AVHRR-NDVI时空变化研究

Exploring the Temporal-Spatial Dynamics of Grasslands in Xilingol, Inner Mongolia Using AVHRR-NDVI: 1999 Growing Season

采用地面样地和遥感数据,分析了锡林郭勒草原4种草地1999年AVHRR-NDVI的时空变化。NDVI时间序列显示,草甸草地和典型草地NDVI在5月份开始返青,但荒漠草地和沙地草地NDVI在5月份为全年最低。6月份草地生长最快,以4月平均NDVI作为各草地的基准,草甸草地全年NDVI最大时的增加值为0.42,其中4～6月份的NDVI增加值为0.34,占81%;典型草地全年NDVI最大时的增加值为0.30,其中4～6月增加值为0.22,占73%;沙地草地全年NDVI最大时的增加值为0.27,其中4～6月增加值为0.10,占37%。NDVI空间分布呈现明显的东西过渡特点。从5月开始,NDVI自东向西增长,其推进特点是南北两侧快,中部缓慢。8月草地植被达到全盛时,NDVI=0.1的等值线呈现由西向东的"楔型"。5～8月之间,NDVI=0.1等值线由东向西移动3个经度。由于植被指数对低覆盖植被比较敏感,该等值线的形态和位置可能是气候变化的一个指标。

This paper explores the temporal-spatial dynamics of four grasslands (temperate meadow-steppe, temperate steppe, desert-steppe, and sand-steppe) in Xilingol, Inner Mongolia using 1999 monthly AVHRR-NDVI. The averaged monthly NDVIs show that there is only minor variation for desert-steppe in whole year. Temperate meadow-steppe and temperate steppe start to grow in May, but NDVI of the other two steppes reach their nadir during the same month. June is an important period for NDVI gain of meadow-steppe and steppe. Taking April as NDVI baseline, the net gain of NDVI in whole year is 0.42 for meadow, yet by the end of June, 81% of it has completed. Similarly, the NDVI net gain for temperate steppe is 0.30, and 73% of it completed before July. The spatial dynamics are characterized by an east-west profile. The iso-line of NDVI=0.1 is between 116°-117°E in May, and pushes forward to 113°-114°E in August when all grasslands reach their potentials. Since NDVI is very sensitive to the change of vegetation density in low covered area, the shape and position of NDVI=0.1 iso-line maybe a good indicator for long term climate changes.