Fraction of Absorbed Photosynthetically Active Radiation (FPAR) products over Tibetan Plateau

In total solar radiation (TSR), the component essential for photosynthesis is known as photosynthetically active radiation (PAR), which encompasses wavelengths from approximately 400 to 700 nm. The Fraction of Absorbed PAR is a key physiological variable in the study of carbon cycling and is one of the basic variables to describe vegetation ecosystems. The classification results of vegetation types in the Tibetan Plateau region were obtained based on the 30–m resolution Landsat reflectance data. Additionally, for different vegetation types during the growing season, the 98% (NDVI_max) and 2% (NDVI_min) cumulative frequencies of Normalized Difference Vegetation Index (NDVI) were calculated. To overcome the issues of underestimation and overestimation in FPAR estimation, which are based solely on the simple infrared/red ratio (SR) and NDVI, a hybrid model that combines SR and NDVI has been developed for more accurate FPAR estimation. This model was employed to generate average FPAR products for various vegetation types over the Tibetan Plateau between April and September spanning from 1987 to 2022. These FPAR data are instrumental in calculating vegetation carbon sequestration and assessing the status of vegetation ecosystems. The products have been stored in the GeoTIFF format, utilizing the GCS_WGS_1984 spatial reference system (EPSG: 4326).

在总太阳辐射（Total Solar Radiation, TSR）中，为光合作用所必需的组分被称为光合有效辐射（Photosynthetically Active Radiation, PAR），其波长覆盖约400至700纳米。吸收光合有效辐射比例（Fraction of Absorbed PAR, FPAR）是碳循环研究中的关键生理变量，亦是描述植被生态系统的基础变量之一。本数据集基于30米分辨率的Landsat反射率数据，获取了青藏高原区域的植被类型分类结果。此外，针对生长季内的不同植被类型，研究人员计算了归一化差分植被指数（Normalized Difference Vegetation Index, NDVI）的98%累积频率（记为NDVI_max）与2%累积频率（记为NDVI_min）。为解决仅基于简单红外/红光比值（Simple Infrared/Red Ratio, SR）与归一化差分植被指数（NDVI）开展FPAR估算时存在的低估与高估问题，本研究构建了融合SR与NDVI的混合模型，以实现更为精准的FPAR估算。利用该模型，本研究生成了1987年至2022年4月至9月间，青藏高原不同植被类型的平均FPAR产品。此类FPAR数据可用于植被碳固存量计算与植被生态系统状态评估。本数据集产品以GeoTIFF格式存储，采用GCS_WGS_1984空间参考系（EPSG: 4326）。