Validation of solar-induced chlorophyll fluorescence products derived from OCO-2/3 observations using tower-based in situ measurements

Spaceborne solar-induced chlorophyll fluorescence (SIF) products have emerged over the past decade. However, limited by the spatial-temporal mismatch between satellite-based and ground measurements or the absence of sufficient in situ SIF observations, no direct validation results of satellite-derived SIF products have been provided to date. The Orbiting Carbon Observatoty-2/3 (OCO-2/3) platforms allow us to validate SIF products using in situ SIF observations benefiting from comparable spatial resolution (1.3 km x 2.25 km and 1.6 km x 2.2 km, respectively) to ground measurements. In addition, the automated in situ SIF measurement technique facilitates accuracy validation of spaceborne SIF dataset. In this communication, we describe a direct validation of OCO-2/3 SIF products using tower-based SIF measurements acquired at six sites across China. There were 1-7 and 1-18 successful observations overpassing six in situ sites for OCO-2 and OCO-3, respectively. An overall consistent temporal variation pattern was observed between the OCO-2/3 SIF products and tower-based SIF measurements. The validation accuracies of OCO-2 and OCO-3 SIF products were 0.26 and 0.33 mW m(-2) sr(-1) nm(-1), respectively. To best use satellite-based SIF products in a wide range of applications, we suggest that further accuracy validation using more in situ SIF observations is required, which in turn requires increased availability of public in situ SIF observations.