基于多时相Landsat影像的庆元县植被覆盖变化研究

Image analysis of vegetation coverage and changes(1994-2007) in Qingyuan County using multi-temporal Landsat remote sensing

利用多时相陆地资源卫星Landsat TM和增强型专题绘图仪ETM影像数据,使用像元二分模型对浙江省庆元县1994-2007年植被覆盖度及其动态变化进行研究。结果表明:13 a来,庆元县植被覆盖度持续增长,至2007年高植被覆盖度区域占全县总面积的90.77%,植被覆盖度等级间的转移方向以中高覆盖区(50%～75%)向高覆盖区(>75%)转变为主,其中1994年至1999年间的变化最为显著。13 a间植被覆盖度随坡度的增大而增加,坡度越小植被覆盖度增长幅度越大,特别是地形平缓区域(<15°)的植被覆盖度增长幅度达15%以上。全县植被覆盖度时空变化分级统计结果显示,1994-1999年,庆元县东部地区的植被恢复较为明显,1999-2007年,百山祖自然保护区等地的植被恢复较好。13 a间各类植被覆盖区的景观破碎度不断降低,平均斑块面积不断增大,特别是高覆盖区在总体面积大幅提高的同时,平均斑块面积由9.66 hm2增长到182.82 hm2,增加了18倍。

It is very important to obtain vegetation information for evaluating ecology environment.In this study,the dimidiate pixel model was used to determine vegetation coverage of Qingyuan County from 1994 to 2007 based on multi-temporal Landsat Thematic Mapper（TM） and Enhanced Thematic Mapper Plus（ETM＋） image data.Then temporal-spatial changes of the vegetation coverage during this period were analyzed using a change classification method and six landscape fragmentation indexes with four types of vegetation coverage：high（75% coverage）,medium high（50%-75%）,medium low（25%-50%）,and low（25%）.Results showed that in 2007,90.8% of the total area was considered a high vegetation coverage area with 657.4 km2 of the medium high vegetation coverage area during these 13 years being converted into high vegetation coverage,especially from 1994 to 1999.During the research period,the steeper sloping area had higher vegetation coverage.However,the less the slope,the faster the vegetation coverage increased with gently sloping areas（15°） increasing to over 15% coverage.Results of vegetation coverage change showed that in the eastern part of Qingyuan County,vegetation restoration was favorable from 1994 to 1999 as it was in the Baishanzu Nature Reserve from 1999 to 2007.Also,during the 13 year research period,the landscape fragmentation index continuously decreased,whereas the mean patch size increased,especially for the high vegetation coverage area that saw an increase from 9.66 to 182.82 hm2.Thus,from 1994 to 2007,vegetation coverage in Qingyuan County increased favorably.Our study confirms that this is a feasible approach in the estimation of vegetation coverage over large area from remote sensing data.[Ch,2 fig.6 tab.15 ref.]