基于NDVI时序数据的华北地区耕地物候参数时空变化特征

目的]耕地物候作为农业生态系统的重要特征之一,是进行农作物长势监测与估产、田间管理、农作物合理布局等的重要依据。利用遥感方法提取大区域尺度耕地物候参数和种植制度的时空变化特征,有助于从整体上掌握农业资源的空间分布情况,为农业生产决策和区域粮食安全评价提供服务。方法]文章基于1999年和2013年的SPOT/VGT NDVI逐旬时间序列数据,采用TIMESAT软件集成的非对称高斯函数拟合法对数据进行平滑重构,通过比例阈值法提取了华北地区耕地物候参数(生长季开始期和结束期),分析其时空分布特征,并依据年内NDVI变化曲线峰值数目来确定耕地的生长季个数,识别耕地种植制度。结果]华北地区作物生长开始期和结束期都存在明显的空间差异,15年来河北北部、北京、天津等地区,第一季作物返青/出苗期变化不大。而河南南部和中部地区,2013年第二季作物出苗期明显提前,由1999年6月下旬7月上旬,提前至6月上旬。我国华北地区种植制度仍以一年两熟制为主,华北地区北部受热量资源制约,仍旧保持一年一熟制不变。与1999年相比,华北地区2013年两熟制种植面积下降了21.1%,而一熟制种植面积增加了38.7%。结论]华北地区耕地物候的时空变化与种植制度密切相关,同时也受到自然资源和人类活动的共同影响。

SPATIO-TEMPORAL CHARACTERISTICS OF CROPLAND PHENOPHASE IN NORTH CHINA BASED ON NDVI TIME SERIES DATA

The cropland phenophase is an important feature in agro-ecosystems and is the pivotal basis for crop growth monitoring, farm management and regional planning. Studying the spatio-temporal changes of cropland phenology and cropping system at regional scale by using remote sensing could identify the spatial distribution of agricultural resources and provide services for agricultural production and regional food security. Based on the SPOT/VGT NDVI ten days composed time series data in 1999 and 2013, this study investigated the spatio-temporal characteristics of cropland phenology and cropping system in North China. Firstly, smoothing and restructuring the NDVI curves by using Asymmetric Gaussian function reduced the effects of anomalous values caused by atmospheric haze and cloud contamination. Then, it extracted the crop phenological parameters, such as the date of onset-of-growth and end-of-growth, by using a NDVI threshold method. Finally, using the effective peaks identified the cropping system. The results showed that the spatial distribution of the dates of onset-of-growth and end-of-growth were different. During the past 15 years, the starting dates of first crops had no significant changes in Beijing, Tianjin and Northern Hebei province. However, the starting dates of second crops advanced to early June in middle and southern Henan province in 2013. Double cropping system was dominant in North China. Single cropping systems mainly distributed in northern regions of North China because of limitation of thermal conditions. Compared to 1999, the double cropping system area decreased by 21.1% and single cropping system area increased by 38.7% in 2013. In general, spatio-temporal characteristics of cropland phenophase in North China were closely related to the cropping systems, which were influenced by both natural resources and human activities.