对陆上生态体系而言,植物生理季节性变化是衡量其对气候转变反响的关键度量尺度,尤其对全球气温上升现象极为敏感的高纬度与高海拔地带的植物生理季节性。本研究借助MOD13A1卫星遥感资料,叠加温度与降水数据,剖析2000~2021年间蒙古国西...对陆上生态体系而言,植物生理季节性变化是衡量其对气候转变反响的关键度量尺度,尤其对全球气温上升现象极为敏感的高纬度与高海拔地带的植物生理季节性。本研究借助MOD13A1卫星遥感资料,叠加温度与降水数据,剖析2000~2021年间蒙古国西部地区植被生长季始期(Start of growing season,SOS)、生长季长度(Length of growing season,LOS)以及生长季末期(End of growing season,EOS)的时空变化特征和海拔依赖性变化机制。结果如下:(1)蒙古国西部地区的SOS主要集中在第90~125 d,近22 a来SOS呈微弱的提前趋势,提前幅度为0.23 d/a。(2)植被物候与气象要素的关系表明,2月的气温和降水与SOS显著负相关(P<0.05),1月的气温和降水与SOS显著正相关(P<0.05),而EOS主要受8月气温和降水的影响。(3)草甸草原和典型草原SOS主要受降水影响,高山草原、荒漠草原以及针叶林的SOS主要受气温影响,所有植被类型的EOS对温度的响应更大。总的来说,研究区植被物候与气候因子表现出季节性的差异,响应规律复杂。展开更多
利用黑龙江省2012年16 d 250 m的MODIS NDVI数据,使用Savitsky-Golay滤波法、Logistic调合函数模型和非对称Gaussian模型3种方法对曲线拟合重构,引入均方根误差比较3种方法的优劣;在曲线平滑的基础上提取物候参数,分别对森林和农用地用...利用黑龙江省2012年16 d 250 m的MODIS NDVI数据,使用Savitsky-Golay滤波法、Logistic调合函数模型和非对称Gaussian模型3种方法对曲线拟合重构,引入均方根误差比较3种方法的优劣;在曲线平滑的基础上提取物候参数,分别对森林和农用地用固定阈值和动态阈值提取其物候参数,目的在于比较两种阈值设定方法的优劣,并获取阈值使物候参数结果与作物农事历信息吻合。结果表明,Savitsky-Golay滤波法在与原始曲线近似度方面优于另外两种拟合方法。展开更多
Drought Monitoring by remotely sensed moisture vegetation indexes is being an active research subject as the vegetation spectral responses are showed to be highly correlated to water content. The MODIS (MODerate resol...Drought Monitoring by remotely sensed moisture vegetation indexes is being an active research subject as the vegetation spectral responses are showed to be highly correlated to water content. The MODIS (MODerate resolution Imaging Spectro-radiometer) sensor of the Terra satellite provides MOD09A1 product of BRDF (Bidirectional Reflectance Distribution Function) used in computing moisture vegetation indexes (MVI). The exploration of an MVI time-series in the Kroumirie forest in Northern Tunisia showed important noise due to both clouds contamination and sensor defaults that had to be removed. Amongst methods for removing these imperfections, TIMESAT tool was designed for correcting time-series of satellite data and also to retrieve seasonal parameters from smoothed vegetation indexes. The methodology of smoothing functions to fit the time series data is based on two stages. First, a least square fit to the upper envelope of the vegetation indices series is applied. The second stage is achieved by local and adaptive fitting functions. The corrections have been made by spikes removal due to abrupt change of MVI variations and by fitting the MVI time-series to the upper envelop to correct the negative biases of remote sensing vegetation indexes. The adaptive Savitsky-Golay function filter compared to local filtering process produces variations that conserve local variations for all the tested MVI. Seasonal vegetation parameters were extracted for each year of the time-series analysis and compared to the Standardized Precipitation Index (SPI) calculated at meteorological station level and for different time scales. Positive relations were found between SPI and the seasonal parameters expressed by the length and the amplitude of the season, indicating MODIS derived MVI sensitivity to water deficit or surplus conditions. The 6-month SPI showed the best performance when related to water sensitive indexes suggesting that MODIS derived indexes are more correlated to the precipitation variations over seasons.展开更多
植物生长季的变化反映了全球气候变化对生态环境的影响。本研究以2000-2006年间MODIS-NDVI影像数据集,使用TIMESAT软件从归一化植被指数（NDVI）时间序列中,分别提取福建省不同森林植被的生长季开始日期（Start of Season,SOS）、生长...植物生长季的变化反映了全球气候变化对生态环境的影响。本研究以2000-2006年间MODIS-NDVI影像数据集,使用TIMESAT软件从归一化植被指数（NDVI）时间序列中,分别提取福建省不同森林植被的生长季开始日期（Start of Season,SOS）、生长季结束日期（End of Season,EOS）和生长季长度（Length of season,LOS）等物候参数,并与全省尺度的气温与降水量进行相关分析。结果表明：不同森林类型NDVI与当月月均气温之间具有较显著的相关性（R2为0.72-0.79,p〈0.01）,同期温度变化对植被生长的影响相对于降水量更重要;而植被生长对降水量的响应存在大约2个月的时滞效应（R2为0.54-0.75,p〈0.01）,说明前期的降水累积对于后续植被生长有较显著影响。福建省森林植被生长季持续时间约213-223 d,开始于每年4月初到4月中旬（第98-103 d）,结束于11月中旬前后（第316-321 d）。其中,南亚热带森林生长季长于中亚热带森林,相同气候条件下的阔叶林生长季时间略长于针叶林。另外,春季（2-4月）气温变化是导致福建省内2个气候带森林生长季开始时间、生长季结束时间及生长季长度变化的关键因素,而伴随春季温度升高,植被生长季开始时间提前（R^2为0.83,p〈0.01）,同时生长季长度延长（R2为0.80,p〈0.01）。7 a间,生长季持续时间呈现微弱延长趋势,总体延长幅度为2.4-3.1 d。展开更多
文摘对陆上生态体系而言,植物生理季节性变化是衡量其对气候转变反响的关键度量尺度,尤其对全球气温上升现象极为敏感的高纬度与高海拔地带的植物生理季节性。本研究借助MOD13A1卫星遥感资料,叠加温度与降水数据,剖析2000~2021年间蒙古国西部地区植被生长季始期(Start of growing season,SOS)、生长季长度(Length of growing season,LOS)以及生长季末期(End of growing season,EOS)的时空变化特征和海拔依赖性变化机制。结果如下:(1)蒙古国西部地区的SOS主要集中在第90~125 d,近22 a来SOS呈微弱的提前趋势,提前幅度为0.23 d/a。(2)植被物候与气象要素的关系表明,2月的气温和降水与SOS显著负相关(P<0.05),1月的气温和降水与SOS显著正相关(P<0.05),而EOS主要受8月气温和降水的影响。(3)草甸草原和典型草原SOS主要受降水影响,高山草原、荒漠草原以及针叶林的SOS主要受气温影响,所有植被类型的EOS对温度的响应更大。总的来说,研究区植被物候与气候因子表现出季节性的差异,响应规律复杂。
文摘利用黑龙江省2012年16 d 250 m的MODIS NDVI数据,使用Savitsky-Golay滤波法、Logistic调合函数模型和非对称Gaussian模型3种方法对曲线拟合重构,引入均方根误差比较3种方法的优劣;在曲线平滑的基础上提取物候参数,分别对森林和农用地用固定阈值和动态阈值提取其物候参数,目的在于比较两种阈值设定方法的优劣,并获取阈值使物候参数结果与作物农事历信息吻合。结果表明,Savitsky-Golay滤波法在与原始曲线近似度方面优于另外两种拟合方法。
文摘Drought Monitoring by remotely sensed moisture vegetation indexes is being an active research subject as the vegetation spectral responses are showed to be highly correlated to water content. The MODIS (MODerate resolution Imaging Spectro-radiometer) sensor of the Terra satellite provides MOD09A1 product of BRDF (Bidirectional Reflectance Distribution Function) used in computing moisture vegetation indexes (MVI). The exploration of an MVI time-series in the Kroumirie forest in Northern Tunisia showed important noise due to both clouds contamination and sensor defaults that had to be removed. Amongst methods for removing these imperfections, TIMESAT tool was designed for correcting time-series of satellite data and also to retrieve seasonal parameters from smoothed vegetation indexes. The methodology of smoothing functions to fit the time series data is based on two stages. First, a least square fit to the upper envelope of the vegetation indices series is applied. The second stage is achieved by local and adaptive fitting functions. The corrections have been made by spikes removal due to abrupt change of MVI variations and by fitting the MVI time-series to the upper envelop to correct the negative biases of remote sensing vegetation indexes. The adaptive Savitsky-Golay function filter compared to local filtering process produces variations that conserve local variations for all the tested MVI. Seasonal vegetation parameters were extracted for each year of the time-series analysis and compared to the Standardized Precipitation Index (SPI) calculated at meteorological station level and for different time scales. Positive relations were found between SPI and the seasonal parameters expressed by the length and the amplitude of the season, indicating MODIS derived MVI sensitivity to water deficit or surplus conditions. The 6-month SPI showed the best performance when related to water sensitive indexes suggesting that MODIS derived indexes are more correlated to the precipitation variations over seasons.
文摘植物生长季的变化反映了全球气候变化对生态环境的影响。本研究以2000-2006年间MODIS-NDVI影像数据集,使用TIMESAT软件从归一化植被指数（NDVI）时间序列中,分别提取福建省不同森林植被的生长季开始日期（Start of Season,SOS）、生长季结束日期（End of Season,EOS）和生长季长度（Length of season,LOS）等物候参数,并与全省尺度的气温与降水量进行相关分析。结果表明：不同森林类型NDVI与当月月均气温之间具有较显著的相关性（R2为0.72-0.79,p〈0.01）,同期温度变化对植被生长的影响相对于降水量更重要;而植被生长对降水量的响应存在大约2个月的时滞效应（R2为0.54-0.75,p〈0.01）,说明前期的降水累积对于后续植被生长有较显著影响。福建省森林植被生长季持续时间约213-223 d,开始于每年4月初到4月中旬（第98-103 d）,结束于11月中旬前后（第316-321 d）。其中,南亚热带森林生长季长于中亚热带森林,相同气候条件下的阔叶林生长季时间略长于针叶林。另外,春季（2-4月）气温变化是导致福建省内2个气候带森林生长季开始时间、生长季结束时间及生长季长度变化的关键因素,而伴随春季温度升高,植被生长季开始时间提前（R^2为0.83,p〈0.01）,同时生长季长度延长（R2为0.80,p〈0.01）。7 a间,生长季持续时间呈现微弱延长趋势,总体延长幅度为2.4-3.1 d。
