基于MODIS逐日地表反射率数据的青南地区草地生长状况遥感监测研究

大范围草地生长状况遥感监测对研究草地变化动态和草地畜牧业的管理具有重要意义。利用2010-2013年的草地外业调查数据和EOS Terra MODIS每日地表反射率产品MOD09GA,采用空间分析方法分别计算了生长季(5-9月)草地NDVI_max, EVI_max, NDVI_mean和EVI_mean4种植被指数,探讨了这4种植被指数与草地地上生物量之间的遥感反演模型,分析了青南地区草地生长季多年NDVI平均值空间分布特征;根据所选的最优模型反演了青南牧区近10年(2004-2013年)的草地地上生物量,统计分析了地上生物量的空间变化特征。结果表明,青南地区多年NDVI平均值和草地地上生物量总体上均具有由西北向东南逐渐增加的空间分布特点。不同草地类型的生物量差异显著。近10年来山地草甸类的生物量最高,达1280 kg DW/hm²;其次为高寒草甸类、温性草原类、温性荒漠类和沼泽类,生物量介于244.9~902.4 kg DW/hm²;高寒草甸草原类、高寒荒漠类和高寒荒漠草原类生物量较小,在65 kg DW/hm²以下。海拔对生物量具有明显的影响,在3500 m以上地区的草地生物量随海拔的升高而减小。当海拔介于3500~4000 m,最大生物量达1358.8 kg DW/hm²;海拔介于4000~4500 m,生物量小于920 kg DW/hm²;海拔介于4500~5000 m,生物量为574.2 kg DW/hm²;海拔大于5500 m,生物量仅为94.4 kg DW/hm²。统计分析近10年间的NDVI变化趋势发现,三江源地区的黄河、长江和湄公河三大流域及各行政区的草地植被生长状况以轻度改善和改善为主,总体趋于良好。

Monitoring of grassland herbage accumulation by remote sensing using MODIS daily surface reflectance data in the Qingnan Region

Monitoring of grassland herbage accumulation using remote sensing technology has a potentially im-portant role in understanding seasonal changes in grasslands and optimizing animal husbandry and grazing man-agement.In this study above ground biomass (AGB)and its spatial distribution was recorded using in-situ measurements during the growing seasons from 2010 to 2013 in southern Qinghai province,and regression models using in-situ AGB data and the corresponding daily surface reflectance product of Terra MODIS were established.The spatial analysis method was used to calculate four vegetation indices (NDVI max ,EVI max ,ND-VI mean and EVI mean )using MOD09GA data,and the accuracy of the inversion models was then analyzed,and the spatial distribution of the NDVI mean values in the previous 10 years characterized.With the algorithms opti-mized in this way,we estimated the aboveground grassland biomass and its spatial distribution for the previous 10 growing seasons.It was found that the aboveground biomass gradually increases from northwest to south-east,and different grassland types have characteristic biomass differences.The biomass of mountain meadow was highest among the grassland types included in this 10 year study,and reached 1280 kg DW/ha in 2010. The biomass of alpine meadow,warm steppe,warm desert and marsh ranged between 244.9 kg DW/ha and 902.4 kg DW/ha,The biomass values of alpine meadow grassland,alpine desert,and alpine desert grassland were much lower,and were below 65 kg DW/ha.The elevation had a marked effect on biomass,with grass-land biomass decreasing with increasing elevation above 3500 m.At elevations between 3500 and 4000 meters, peak biomass was 1358.8 kg DW/ha;between 4000 and 4500 meters,the biomass was below 920 kg DW/ha, and between 4500 and 5000 meters the biomass averaged approximately 574.2 kg DW/ha.Above 5000 meters elevation,the biomass averaged approximately 94.4 kg DW/ha.The trend of NDVI mean values in last 10 years indicates that most regions in the Three River Headwater region (The Yellow River,The Yangtze River, and The Mekong River),which span different administrative areas,can be categorized as showing ‘mild im-provement’or ‘improvement’.Overall,the trend in grassland vegetation status is positive.