基于时序植被指数的华北地区作物物候期/种植制度的时空格局特征

随着气候变化对农业系统的影响不断加剧,为保障粮食安全,须掌握变化中的自然与人文因素,而农业生态系统中变化最为明显直观的是农作物物候特征,如何提取大区域尺度上农作物物候期以及种植制度的时空格局特征,是评价区域粮食安全的重要因素.基于多时相遥感信息可以有效反映年内/年际农作物物候特征变化的原理,首先利用近10a来的SPOT/VGT-NDVI时间序列数据,在进行数据序列平滑重构处理基础上,提取了华北地区农作物典型物候期的数量分布与空间格局特征;然后,基于上述物候期的分异特性建立了一年一熟和一年二熟等种植制度类型的遥感识别标志;最后,重点分析了上述种植制度的空间格局及其时间波动特征,并利用农业统计资料对提取结果进行了简单验证.分析结果表明,作物物候期特征的数量分布和空间分布在不同生长季均具有显著差异,直接体现了与外界环境条件(诸如区域温度、降水和光照等)的匹配程度以及作物类型自身的生长特征;从主要种植制度空间分布来看,华北地区南部地区农作物类型以夏收作物和二熟秋收作物为主,与之对应的农田种植制度以一年两熟为主;华北地区北部主要为一熟制区域,作物类型以一年一熟秋收作物为主,作物种植制度空间分布随着纬度递减呈现出简单到复杂的总体趋势;从近10a的种植情况来看,一年一熟作物种植面积最大,年际变化幅度亦较大,一年二熟的夏收作物种植比例次之,而年际变幅最小,二熟秋收作物比例最低,其年际变幅居中.研究中亦提出,在进一步加强多时相遥感技术监测大区域农业生态系统动态变化的同时,亦需深入探讨作物物候特征及种植制度变化的驱动因素及其对国家粮食安全的影响.

Research on spatiotemporal pattern of crop phenological characteristics and cropping system in North China based on NDVI time series data

As the increasingly impacts of climate changes, more researches are starting to focus on the responses of agroecosystem, including changes in crop phenology and crop yield, which have important implications for predicting the potential impacts on grain security in the future. In this study, we investigate spatiotemporal patterns of crop phenological characteristics and classification in North China Plain, by using the SPOT/VGT NDVI ten day composed time-series data collected from April 1998 to March 2008. Firstly, to minimize the effects of anomalous values caused by atmospheric haze and cloud contamination, the software TIMESAT was used to generate smooth time series of NDVI based on an asymmetric Gaussian function; secondly, The characteristics of crop phenology in North China, such as the timing of onset and end of the growing season, length of the growing season, and date of the maximum NDVI, were then defined based on the smoothed NVDI time-series dataset; Thirdly, from the variability of frequency distribution, we try to build classification rules to identify the main grain crops, including summer harvesting crop, autumn harvesting crop with single cropping and autumn harvesting crop with double cropping. Finally, the temporal trends of changes and spatial patterns of the main crops were analyzed and the relationship between the remotely sensed results and agricultural statistical data was evaluated by using Pearson correlation analyses. From the analysis it can be inferred that the crop phenology in North China is mainly characterized by a distinct spatial difference and the compositions of the main grain crops become complex as moving from the North to the South. Correspondingly, spatial patterns of crop phenology and compositions are highly related to its climate conditions and geo-physical environment. In details, the autumn harvesting crop in single-cropping system was the dominant class in this area with the maximum inter-annual variation. The proportion of summer harvesting crop was moderate with least temporal variation, and the distribution of autumn harvesting crop in double-cropping system was almost same to summer harvesting crop, but it had a lower degree of inter-annual variation. In fact, Crop phenology and composition are fluctuating year by year due to the changing natural and social conditions. How to extract the spatiotemporal variation of crop phenological characteristics and identify the driving factors on a regional scale is important for strengthening our current knowledge concerning food security assessment and agricultural development．