The Spafleximp Project: Spanish Flex-S3 Mission Calibration and Validation Plan Implementation

The European Space Agency's FLuorescence EXplorer-Sentinel 3 (ESA FLEX-S3) mission, scheduled for launch in 2026, aims to remotely detect vegetation fluorescence at 300x300-meter pixel resolution. The ESA requires a national Calibration and Validation (Cal/Val) plan for FLEX-S3 products that addresses the selection of test sites, measurement protocols, and uncertainty budgets. Despite Spain's significant Cal/Val test sites, it lacks a permanent instrumented site in international networks. The SpaFLEXImp initiative aims to implement a FLEX Cal/Val plan, standardizing protocols, and establishing a coordinated network of sites. Led by the National Institute of Aerospace Technology (INTA), the project involves the University of Valencia and the Doñana Biological Station-CSIC. With a long experience in in situ, airborne, and spaceborne measurements, the teams will conduct specific Cal/Val campaigns in 3 sites, making Spain a European and international reference for terrestrial Cal/Val activities.