面向计算区域高分辨率光合与呼吸分量通量的碳同化技术研究

GOSAT, OCO - 2 and TANSAT carbon dioxide（CO2）satellites, which have the observation accuracy better than 1%, bring bright prospects for developing the high-resolution regional carbon assimilation system. The proposed project plans to select an 800 km × 800 km region as the research area that centering on the yucheng ecological experimental station located in Shandong Province. In view of the characteristics of huge dimensions in regional high-resolution carbon assimilation system, we will first develop and improve a new assimilation algorithm (EnKF-4Dvar) integrated with ensemble and variational method advantages. Secondly, based on a variety of ground and satellite CO2 concentration, high resolution regional carbon assimilation system will be built by using EnKF-4Dvar and regional atmospheric model (WRF-VPRM). This carbon assimilation system will be applied to quantitatively estimate high resolution (5km) photosynthetic and respiratory fluxes of surface-atmosphere carbon flux exchange with the boundary field (1°×1°) generated from CT-China developed by the applicant before. Finally, photosynthetic and respiratory fluxes estimated from the “top-down” and “bottom-up” approaches will validate and analysis each other, based on the long period accumulated observations of yucheng ecological experimental station and the surrounding areas, by using scale conversion methods developed from remote sensing and footprint model finished by the surface project of the applicant in 2016.

观测精度优于1%的GOSAT、OCO-2和TANSAT二氧化碳卫星为高分辨率区域碳同化系统的发展提供了契机。本项目拟选取以山东禹城生态试验站为中心的800km×800km的区域为研究区，首先，针对高分辨率区域同化系统巨大维数的特点，研发能够同时具有集合方法与变分方法优势的EnKF-4Dvar同化新算法；其次，基于WRF-VPRM区域大气模式和EnKF-4Dvar同化算法，构建依托地基二氧化碳浓度和卫星二氧化碳柱浓度的高分辨率区域碳同化系统。该同化系统由该项目申请人之前研发的中国碳同化反演系统（CT-China，CAS）提供1×1°的边界场，计算高分辨率（5km）陆-气碳交换的光合和呼吸分量通量。依托禹城生态试验站及其周围区域长期积累的观测数据和项目申请人发展的基于遥感和footprint模型的尺度转换方法，进行自上而下和自下而上估算的光合和呼吸分量通量互为校验分析。

项目首先研发了EnKF集合方法与4Dvar变分方法的混合同化新算法EnKF-4Dvar；基于WRF-GHG V3.6.1模式和WRF-VPRM生态系统碳循环模块，构建依托地基-卫星高分辨率区域碳同化系统TracersTracker。依托禹城生态试验站及其周围区域长期积累的观测数据和基于遥感和footprint模型的尺度转换方法，进行自上而下和自下而上估算的光合和呼吸分量通量互为校验分析。站点观测验证分析结果显示，利用该碳同化系统能够显著改善中尺度陆地生态系统净碳交换量及其分量(GPP 和 Re)估算。进一步将经过卫星XCO2柱浓度数据尺度转换和空间尺度匹配后的卫星观测数据和地基观测CO2浓度数据融合，输入到大气CO2同化反演模型，最小化观测与模拟浓度间的差值，实现了碳通量数据的最优估算。在此基础上，将优化后的碳通量数据集输入到项目研发的TracersTracker。系统，驱动温室气体大气传输模式运行，模拟计算出优化后的CO2浓度数据集，实现大气了CO2浓度/通量的双优化以及生态系统碳循环关键参数（光合和呼吸参数）的优化。项目构建的碳同化系统和研发的相关技术方法对碳中和战略实施背景下的不同尺度碳通量计算和评价具有重要意义。