The Chinese Carbon Dioxide Observation Satellite Mission(TanSat)is the third satellite for global CO2 monitoring and is capable of detecting weak solar-induced chlorophyll fluorescence(SIF)signals with its advanced te...The Chinese Carbon Dioxide Observation Satellite Mission(TanSat)is the third satellite for global CO2 monitoring and is capable of detecting weak solar-induced chlorophyll fluorescence(SIF)signals with its advanced technical characteristics.Based on the Institute of Atmospheric Physics Carbon Dioxide Retrieval Algorithm for Satellite Remote Sensing(IAPCAS)platform,we successfully retrieved the TanSat global SIF product spanning the period of March 2017 to February 2018 with a physically based algorithm.This paper introduces the new TanSat SIF dataset and shows the global seasonal SIF maps.A brief comparison between the IAPCAS TanSat SIF product and the data-driven SVD(singular value decomposition)SIF product is also performed for follow-up algorithm optimization.The comparative results show that there are regional biases between the two SIF datasets and the linear correlations between them are above 0.73 for all seasons.The future SIF data product applications and requirements for SIF space observation are discussed.展开更多
Vegetation phenology is an indicator of vegetation response to natural environmental changes and is of great significance for the study of global climate change and its impact on terrestrial ecosystems.The normalized ...Vegetation phenology is an indicator of vegetation response to natural environmental changes and is of great significance for the study of global climate change and its impact on terrestrial ecosystems.The normalized difference vegetation index(NDVI)and enhanced vegetation index(EVI),extracted from the Moderate Resolution Imaging Spectrometer(MODIS),are widely used to monitor phenology by calculating land surface reflectance.However,the applicability of the vegetation index based on‘greenness'to monitor photosynthetic activity is hindered by poor observation conditions(e.g.,ground shadows,snow,and clouds).Recently,satellite measurements of solar-induced chlorophyll fluorescence(SIF)from OCO-2 sensors have shown great potential for studying vegetation phenology.Here,we tested the feasibility of SIF in extracting phenological metrics in permafrost regions of the northeastern China,exploring the characteristics of SIF in the study of vegetation phenology and the differences between NDVI and EVI.The results show that NDVI has obvious SOS advance and EOS lag,and EVI is closer to SIF.The growing season length based on SIF is often the shortest,while it can represent the true phenology of vegetation because it is closely related to photosynthesis.SIF is more sensitive than the traditional remote sensing indices in monitoring seasonal changes in vegetation phenology and can compensate for the shortcomings of traditional vegetation indices.We also used the time series data of MODIS NDVI and EVI to extract phenological metrics in different permafrost regions.The results show that the length of growing season of vegetation in predominantly continuous permafrost(zone I)is longer than in permafrost with isolated taliks(zone II).Our results have certain significance for understanding the response of ecosystems in cold regions to global climate change.展开更多
The first Chinese Carbon Dioxide Observation Satellite Mission(TanSat), which was launched on December 21, 2016, is intended to measure atmospheric CO_2 concentration.The high spectral resolution(0.044 nm) and high SN...The first Chinese Carbon Dioxide Observation Satellite Mission(TanSat), which was launched on December 21, 2016, is intended to measure atmospheric CO_2 concentration.The high spectral resolution(0.044 nm) and high SNR(360 at 15.2 mW m^(-1) sr^(-1) nm^(-1)) measurements in the region of the O_2-A band of the Atmospheric Carbon dioxide Grating Spectroradiometer(AGCS) module onboard TanSat make it possible to retrieve solar-induced chlorophyll fluorescence(SIF) from TanSat observations at the global scale.This paper aims to explore the potential of the TanSat data for global SIF retrieval.A singular vector decomposition(SVD) statistical method was employed to retrieve SIF using radiance over a micro spectral window(～2 nm) around the Fe Fraunhofer lines(centered at 758.8 nm).The global SIF at 758.8 nm was successfully retrieved with a low residual error of 0.03 mW m^(-1) sr^(-1) nm^(-1).The results show that the spatial and temporal patterns of the retrieved SIF agree well with the global terrestrial vegetation pattern.The monthly SIF products retrieved from the TanSat data were compared with other remote sensing datasets, including OCO-2 SIF, MODIS NDVI, EVI and GPP.The overall consistency between TanSat and OCO-2 SIF products(R^2= 0.86) and the consistency of the spatial patterns and temporal variations between the TanSat SIF and MODIS vegetation indices and GPP enhance our confidence in the potential and feasibility of TanSat data for SIF retrieval.TanSat, therefore, provides a new opportunity for global sampling of SIF at fine spatial resolution(2 km × 2 km), thus improving photosynthesis observations from space.展开更多
植被物候是监测陆地生态系统和全球气候变化的重要生物指标。基于经典遥感植被指数的陆表物候监测在不同植被类型的精确分析方面存在较大挑战,日光诱导叶绿素荧光(SIF)可以直接反映植被实际光合作用的动态变化,能够更精确地刻画出植被...植被物候是监测陆地生态系统和全球气候变化的重要生物指标。基于经典遥感植被指数的陆表物候监测在不同植被类型的精确分析方面存在较大挑战,日光诱导叶绿素荧光(SIF)可以直接反映植被实际光合作用的动态变化,能够更精确地刻画出植被的年际变异。本研究基于2001~2020年GOSIF数据集,通过D-L拟合函数和动态阈值法提取东北地区植被物候参数,结合一元线性回归分析、稳定性和持续性分析,在多时空尺度下分析2001~2020年东北地区植被物候的时空演变特征,并探讨植被物候对气候变化的响应机制。结果表明:(1)植被生长季开始(Start of Season,SOS)、结束(EndofSeason,EOS)、生长季长度(LengthofSeason,LOS)和生长峰值(Position of Peak,POP)整体上分别呈现出提前、推迟、延长和提前趋势;(2)草丛SOS提前、EOS推迟趋势较为显著,针叶林EOS提前趋势显著;SOS提前、EOS推迟导致LOS延长,除针叶林外,所有植被类型LOS均呈现出延长趋势;除草丛和草原外,其余植被类型POP均呈提前趋势;(3)20年来植被SOS、EOS、LOS和POP变化较为稳定,变异系数均小于0.1;(4)大部分区域植被SOS、EOS、LOS和POP的H值介于0.35~0.5之间,说明其变化趋势与过去相反,将呈现微弱延迟、提前、缩短和延长的趋势;(5)整体上气温和降水对植被物候的影响机制相反,即气温升高(降水增加)导致SOS和POP提前(推迟)、EOS推迟(提前)以及LOS延长(缩短);相对湿度与植被物候参数均呈负相关关系。本研究结果有助于理解植被进行光合作用的时空格局变化及对气候变化的响应机制,也为东北地区生态环境的评估和管理提供参考。展开更多
基金This study was supported by the National Key R&D Program of China(No.2016YFA0600203)the Key Research Program of the Chinese Academy of Sciences(ZDRW-ZS-2019-1&ZDRW-ZS-2019-2)the Youth Program of the National Natural Science Foundation of China(41905029).The TanSat L1B data service was provided by the International Reanalysis Cooperation on Carbon Satellite Data(IRCSD)(131211KYSB20180002)and the Cooperation on the Analysis of Carbon Satellite Data(CASA).The authors thank the OCO-2 team for providing the Level-2 SIF data products.
文摘The Chinese Carbon Dioxide Observation Satellite Mission(TanSat)is the third satellite for global CO2 monitoring and is capable of detecting weak solar-induced chlorophyll fluorescence(SIF)signals with its advanced technical characteristics.Based on the Institute of Atmospheric Physics Carbon Dioxide Retrieval Algorithm for Satellite Remote Sensing(IAPCAS)platform,we successfully retrieved the TanSat global SIF product spanning the period of March 2017 to February 2018 with a physically based algorithm.This paper introduces the new TanSat SIF dataset and shows the global seasonal SIF maps.A brief comparison between the IAPCAS TanSat SIF product and the data-driven SVD(singular value decomposition)SIF product is also performed for follow-up algorithm optimization.The comparative results show that there are regional biases between the two SIF datasets and the linear correlations between them are above 0.73 for all seasons.The future SIF data product applications and requirements for SIF space observation are discussed.
基金Under the auspices of National Key Research and Development Projects(No.2018YFE0207800)National Natural Science Foundation of China(No.41871103)。
文摘Vegetation phenology is an indicator of vegetation response to natural environmental changes and is of great significance for the study of global climate change and its impact on terrestrial ecosystems.The normalized difference vegetation index(NDVI)and enhanced vegetation index(EVI),extracted from the Moderate Resolution Imaging Spectrometer(MODIS),are widely used to monitor phenology by calculating land surface reflectance.However,the applicability of the vegetation index based on‘greenness'to monitor photosynthetic activity is hindered by poor observation conditions(e.g.,ground shadows,snow,and clouds).Recently,satellite measurements of solar-induced chlorophyll fluorescence(SIF)from OCO-2 sensors have shown great potential for studying vegetation phenology.Here,we tested the feasibility of SIF in extracting phenological metrics in permafrost regions of the northeastern China,exploring the characteristics of SIF in the study of vegetation phenology and the differences between NDVI and EVI.The results show that NDVI has obvious SOS advance and EOS lag,and EVI is closer to SIF.The growing season length based on SIF is often the shortest,while it can represent the true phenology of vegetation because it is closely related to photosynthesis.SIF is more sensitive than the traditional remote sensing indices in monitoring seasonal changes in vegetation phenology and can compensate for the shortcomings of traditional vegetation indices.We also used the time series data of MODIS NDVI and EVI to extract phenological metrics in different permafrost regions.The results show that the length of growing season of vegetation in predominantly continuous permafrost(zone I)is longer than in permafrost with isolated taliks(zone II).Our results have certain significance for understanding the response of ecosystems in cold regions to global climate change.
基金supported by the National Key Research and Development Program of China (2017YFA0603001)Scientific Research Satellite Engineering of Civil Space Infrastructure Projectthe National Natural Science Foundation of China (41671349, 41701396)
文摘The first Chinese Carbon Dioxide Observation Satellite Mission(TanSat), which was launched on December 21, 2016, is intended to measure atmospheric CO_2 concentration.The high spectral resolution(0.044 nm) and high SNR(360 at 15.2 mW m^(-1) sr^(-1) nm^(-1)) measurements in the region of the O_2-A band of the Atmospheric Carbon dioxide Grating Spectroradiometer(AGCS) module onboard TanSat make it possible to retrieve solar-induced chlorophyll fluorescence(SIF) from TanSat observations at the global scale.This paper aims to explore the potential of the TanSat data for global SIF retrieval.A singular vector decomposition(SVD) statistical method was employed to retrieve SIF using radiance over a micro spectral window(～2 nm) around the Fe Fraunhofer lines(centered at 758.8 nm).The global SIF at 758.8 nm was successfully retrieved with a low residual error of 0.03 mW m^(-1) sr^(-1) nm^(-1).The results show that the spatial and temporal patterns of the retrieved SIF agree well with the global terrestrial vegetation pattern.The monthly SIF products retrieved from the TanSat data were compared with other remote sensing datasets, including OCO-2 SIF, MODIS NDVI, EVI and GPP.The overall consistency between TanSat and OCO-2 SIF products(R^2= 0.86) and the consistency of the spatial patterns and temporal variations between the TanSat SIF and MODIS vegetation indices and GPP enhance our confidence in the potential and feasibility of TanSat data for SIF retrieval.TanSat, therefore, provides a new opportunity for global sampling of SIF at fine spatial resolution(2 km × 2 km), thus improving photosynthesis observations from space.
文摘植被物候是监测陆地生态系统和全球气候变化的重要生物指标。基于经典遥感植被指数的陆表物候监测在不同植被类型的精确分析方面存在较大挑战,日光诱导叶绿素荧光(SIF)可以直接反映植被实际光合作用的动态变化,能够更精确地刻画出植被的年际变异。本研究基于2001~2020年GOSIF数据集,通过D-L拟合函数和动态阈值法提取东北地区植被物候参数,结合一元线性回归分析、稳定性和持续性分析,在多时空尺度下分析2001~2020年东北地区植被物候的时空演变特征,并探讨植被物候对气候变化的响应机制。结果表明:(1)植被生长季开始(Start of Season,SOS)、结束(EndofSeason,EOS)、生长季长度(LengthofSeason,LOS)和生长峰值(Position of Peak,POP)整体上分别呈现出提前、推迟、延长和提前趋势;(2)草丛SOS提前、EOS推迟趋势较为显著,针叶林EOS提前趋势显著;SOS提前、EOS推迟导致LOS延长,除针叶林外,所有植被类型LOS均呈现出延长趋势;除草丛和草原外,其余植被类型POP均呈提前趋势;(3)20年来植被SOS、EOS、LOS和POP变化较为稳定,变异系数均小于0.1;(4)大部分区域植被SOS、EOS、LOS和POP的H值介于0.35~0.5之间,说明其变化趋势与过去相反,将呈现微弱延迟、提前、缩短和延长的趋势;(5)整体上气温和降水对植被物候的影响机制相反,即气温升高(降水增加)导致SOS和POP提前(推迟)、EOS推迟(提前)以及LOS延长(缩短);相对湿度与植被物候参数均呈负相关关系。本研究结果有助于理解植被进行光合作用的时空格局变化及对气候变化的响应机制,也为东北地区生态环境的评估和管理提供参考。
