卫星动态观测数据揭示中国地表色调分布及时序变化特征

本文对2001年—2010年的MODIS光谱反射率数据进行时空聚类,得到2001年—2010年8天合成的色调信息,并初步分析了中国地表色调的时空分布格局及变化趋势,得出以下主要结论:(1)中国地表主色调主要由代表植被的绿色、裸土的褐色、裸土与植被混合的黄色、水体的蓝色以及冰雪的白色这5种颜色组成。分布在西北地区的褐色在一年中4个季节都为主色调。NDVI值较低的绿色光谱簇在春秋冬3个季节都为主色调,分布在南方的热带、亚热带针叶林以及灌木区。NDVI值较高的绿色光谱簇只在夏季一个季节为主色调,分布在长江中下游、华南、西南以及东北部分地区。永久白色主要分布在西藏、青海、四川等多年积雪地区。(2)黄淮海平原农业区色调在一年中呈现褐色—绿色—褐色—绿色—褐色的变化,与第一轮生长—间歇—第二轮生长物候历一致。长江中下游以及华南水稻播种和插秧时节有独特的光谱簇,呈现出植被与水体混合的特征。从华南地区、长江中下游地区到河北、陕西、甘肃、宁夏再到黑龙江,从南到北呈现出作物播种时间推迟、收割时间提早、生长期变短的现象。(3)甘肃北部、四川北部、山西北部、河北北部是年际主色调在绿色和黄色之间变化最为频繁的区域。这些年际主色调变化频繁区域也是中国绿度变化最显著的区域,也是在LUCC分类中易产生错误的地区。

The spatiotemporal changes of surface cover color in China revealed by satellite observations

The spectral reflectance data of Moderate-Resolution Imaging Spectroradiometer (MODIS) from 2001 to 2010 was clustered in spatial and temporal dimension and we analyzed the spatial distribution and temporal changes of land-surface cover color of China. The conclusions are: (1) Land surface colors are composed of green of vegetation, brown of bare soil, yellow of mixture of soil and vegetation, blue of water and white of snow and ice. Brown color distributed in north-west China is the dominant color in all seasons; Green color of low Normalized DifferenceVegetation Index(NDVI) is the dominant color in spring, autumn and winter; Green color of high NDVI is the dominant color of summer, distributed in the middle and lower reaches of Yangtze River, South China, south-west and north-east China. (2) Color in the agricultural regions of Huang-Huai-Hai plain appeared in a brown-green-brown-green-brown pattern during the year, that are in agreement with the pattern of crop cultivation in a phenological calendar of first growth-fallow-the second growth-harvest. The unique spectral cluster characteristics of the paddy fields in the middle and lower reaches of Yangtze River and South China imply a mixture of vegetation and water in the sow and growth period. From south to north, crops are sown later and reaped earlier, presenting a trend of decreasing growth period. (3) The dominant color often transforms from green to yellow in the southern part of Gansu, southern part of Shanxi, northern part of Sichuan, northern part of Shanxi and the northern part of Hebei. Those regions with the most frequent color changes are also the regions with significant greenness change and uncertainty in land use and land cover.