Global Retrievals of Solar-Induced Chlorophyll Fluorescence with TROPOMI: First Results and Intersensor Comparison to OCO-2

Abstract

In recent years, solarinduced chlorophyll fluorescence (SIF) retrieved from spaceborne spectrometers has been extensively used as a proxy for terrestrial photosynthesis at relatively sparse temporal and spatial scales. The nearinfrared band of the recently launched TROPOspheric Monitoring Instrument (TROPOMI) features the required spectral resolution and signaltonoise ratio to retrieve SIF in a spectral range devoid of atmospheric absorption features. We find that initial TROPOMI spectra meet high expectations for a substantially improved spatiotemporal resolution (up to 7km 3.5km pixels with daily revisit), representing a step change in SIF remote sensing capabilities. However, interpretation requires caution, as the broad range of viewingillumination geometries covered by TROPOMI's 2,600kmwide swath needs to be taken into account. A first intersensor comparison with OCO2 (Orbiting Carbon Observatory2) SIF shows excellent agreement, underscoring the high quality of TROPOMI's SIF retrievals and the notable radiometric performance of the instrument