hide
Free keywords:
-
Abstract:
The Orbiting Carbon Observatory-2 (OCO-2), launched in July 2014, is capable of measuring Solar-Induced
chlorophyll Fluorescence (SIF), a functional proxy for terrestrial gross primary productivity (GPP). Although its
primary mission is to measure the column-averaged mixing ratio of CO
2
(Xco
2
) to constrain global carbon
source/sink distribution, one of the OCO-2 spectrometers allows for a robust SIF retrieval solely based on solar
Fraunhofer lines. Here we present a technical overview of the OCO-2 SIF product, aiming to provide the sci-
entific community guidance on best practices for data analysis, interpretation, and application. This overview
consists of the retrieval algorithms, OCO-2 specific bias correction, retrieval uncertainty evaluation, cross-mis-
sion comparison with other existing SIF products, and a global-scale examination of the SIF-GPP relationship.
With the initial three years of data (September 2014 onward), we compared OCO-2 SIF with retrievals from
Greenhouse Gases Observing Satellite (GOSAT) and Global Ozone Monitoring Experiment-2 (GOME-2), and
examined its relationship with FLUXCOM and MODIS GPP datasets. Our results show that OCO-2 SIF, along with
GOSAT products, closely resemble the mean spatial and temporal patterns of FLUXCOM GPP from regions to the
globe. Compared with GOME-2, however, OCO-2 depicts a more realistic spatial contrast between the tropics
and extra-tropics. The linear relationship between OCO-2 SIF and existing modeled GPP products diverges
somewhat across biomes at the global scale, consistent with previous GOSAT or GOME-2 based findings when
modeled GPP products were used, but in contrast to a consistent cross-biome SIF-GPP relationship obtained at
flux tower sites with OCO-2 products. This contrast suggests a critical need to reconcile di fferences in diverse SIF
and GPP products and the relationships among them. Overall, the OCO-2 SIF products are robust and valuable
for monitoring the global terrestrial carbon cycle and for constraining the carbon source/sink strengths of the
Earth system. Finally, insights are offered for future satellite missions optimized for SIF retrievals.
