Gross Primary Production - Data Product Factsheet

Gross Primary Production (GPP) is defined as the total amount of carbon fixed by an ecosystem in a given time. GPP maps are provided with a 10 m spatial resolution every 5-days for the period June 2017-December 2023. The period differs site by site depending upon in-situ data availability. The highest temporal resolution of 5-days is achieved in periods with 50% free-cloud conditions in the area of interest. In other cases, when cloud cover exceeds this threshold, the data is excluded, resulting in reduced frequency.

The GPP data products are calculated with a data-driven approach combining Earth Observations with in-situ carbon data. In specific, Sentinel-2 Multispectral data are combined with in situ GPP data derived from ICOS eddy covariance tower systems using XGBoost (Chen and Guestrin, 2016) machine learning algorithm (Spinosa et al., 2024).

The map extent corresponds to the boundaries of the selected long-term observation facilities as provided on the site registry DEIMS-SDR (see https://deims.org/). If the site boundaries cover an area smaller than 1 km² or the site boundaries are not registered in DEIMS-SDR with only point coordinates provided, the map extend is defined by a 1km x 1km bounding box to ensures consistency across all sites and balance computational efficiency with data availability. This extension has also been discussed with users engaged in the co-definition phase of the project.

The methodology integrates data from diverse ecosystems to estimate Gross Primary Production (GPP) using machine learning. Data pre-processing includes selecting sites based on data availability and completeness, extracting environmental data from ICOS, and estimating remote sensing indices from Sentinel 2 data. An XGBoost model is trained and evaluated using MAE, RMAE, and R² to predict time series of GPP. The model is then used for the computation of 5-day GPP maps within the ecosystem boundaries box. Annual error metrics are provided to ensure model accuracy.
Acknowledgement

This work on the AGAME Gross Primary Production data product is funded by the European Space Agency (ESA, contract no. 4000143740/24/I-AG) in the frame of the GEOSS Platform Plus project (Horizon Europe, GA No. GA.Nr. 101039118). The work done is based on the requirements from eLTER contributing in addition to the eLTER Site Information Cluster. In-situ data for model calibration and validation has been derived from the ICOS Carbon Portal.