High-Resolution Global Contiguous SIF of OCO-2

Abstract

The Orbiting Carbon Observatory-2 (OCO-2) collects solar-induced chlorophyll fluorescence (SIF) at high spatial resolution along orbits ((Formula presented.) oco2_orbit ), but its discontinuous spatial coverage precludes its full potential for understanding the mechanistic SIF-photosynthesis relationship. This study developed a spatially contiguous global OCO-2 SIF product at 0.05° and 16-day resolutions ((Formula presented.) oco2_005 ) using machine learning constrained by physiological understandings. This was achieved by stratifying biomes and times for training and predictions, which accounts for varying plant physiological properties in space and time. (Formula presented.) oco2_005 accurately preserved the spatiotemporal variations of (Formula presented.) oco2_orbit across the globe. Validation of (Formula presented.) oco2_005 with Chlorophyll Fluorescence Imaging Spectrometer airborne measurements revealed striking consistency (R 2  = 0.72; regression slope = 0.96). Further, without time and biome stratification, (1) (Formula presented.) oco2_005 of croplands, deciduous temperate, and needleleaf forests would be underestimated during the peak season, (2) (Formula presented.) oco2_005 of needleleaf forests would be overestimated during autumn, and (3) the capability of (Formula presented.) oco2_005 to detect drought would be diminished.