Filling-in of near-infrared solar lines by terrestrial fluorescence and other geophysical effects: simulations and space-based observations from SCIAMACHY and GOSAT

Abstract

Global mapping of terrestrial vegetation fluorescence from space has recently been accomplished with high spectral resolution (ν/Δν > 35 000) measurements from the Japanese Greenhouse gases Observing SATellite (GOSAT). These data are of interest because they can potentially provide global information on the functional status of vegetation including light-use efficiency and global primary productivity that can be used for global carbon cycle modeling. Quantifying the impact of fluorescence on the O<sub>2</sub>-A band is important as this band is used for photon pathlength characterization in cloud- and aerosol-contaminated pixels for trace-gas retrievals including CO<sub>2</sub>. Here, we examine whether fluorescence information can be derived from space using potentially lower-cost hyperspectral instrumentation, i.e., more than an order of magnitude less spectral resolution (ν/Δν ~ 1600) than GOSAT, with a relatively simple algorithm. We discuss laboratory measurements of fluorescence near one of the few wide and deep solar Fraunhofer lines in the long-wave tail of the fluorescence emission region, the calcium (Ca) II line at 866 nm that is observable with a spectral resolution of ~0.5 nm. The filling-in of the Ca II line due to additive signals from various atmospheric and terrestrial effects, including fluorescence, is simulated. We then examine filling-in of this line using the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) satellite instrument. In order to interpret the satellite measurements, we developed a general approach to correct for various instrumental artifacts that produce false filling-in of solar lines in satellite measurements. The approach is applied to SCIAMACHY at the 866 nm Ca II line and to GOSAT at 758 and 770 nm on the shoulders of the O<sub>2</sub>-A feature where there are several strong solar Fraunhofer lines that are filled in primarily by vegetation fluorescence. Finally, we compare temporal and spatial variations of SCIAMACHY additive signals with those of GOSAT and the Enhanced Vegetation Index (EVI) from the MODerate-resolution Imaging Spectroradiometer (MODIS). Although the derived additive signals from SCIAMACHY are extremely weak at 866 nm, their spatial and temporal variations are consistent with chlorophyll <i>a</i> fluorescence or another vegetation-related source. We also show that filling-in occurs at 866 nm over some barren areas, possibly originating from luminescent minerals in rock and soil

Spatio-temporal approach to moving window block kriging of satellite data v1.0

“…The GOME-2 spatial footprint (i.e., support) of the observations is 40 km × 80 km (Joiner et al, 2013), and the volume of available data is approximately 2 × 10 5 SIF observations per week. Multiple recent studies have demonstrated the potential use of satellite observations of SIF for understanding the photosynthetic CO 2 uptake at large scales (Joiner et al, 2011(Joiner et al, , 2012(Joiner et al, , 2013Frankenberg et al, 2011Frankenberg et al, , 2012Frankenberg et al, , 2014Guanter et al, 2012;Lee et al, 2013). Satellite SIF measurements can be used with land surface models to understand gross primary production (GPP) response to environmental stress (e.g., Lee et al, 2013) and to improve the representation of GPP.…”

Spaceborne Sun-Induced Vegetation Fluorescence Time Series from 2007 to 2015 Evaluated with Australian Flux Tower Measurements

“…It was shown by Joiner et al [21,33] that the retrieval approaches developed for GOSAT could also be applied to the imaging spectrometers SCIAMACHY and GOME-2. This improves the spatial representativeness because these instruments achieve global coverage within a few days.…”

“…The proposed methods typically require accurate modelling of atmospheric radiative transfer in the absorption bands. A subsequent series of studies showed that filling-in of deep solar Fraunhofer lines can also be used to detect vegetation fluorescence from space [32,33,35,37,43], which in some respects simplifies the retrieval problem. The first maps of global terrestrial fluorescence using filling-in of Fraunhofer lines were achieved with the high-spectral-resolution interferometer aboard GOSAT [32,34,35].…”

“…These include the Greenhouse gases Observing SATellite (GOSAT) [32][33][34][35], the Global Ozone Monitoring Experiment 2 (GOME-2) [21,36], the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) [33,37], and the Orbiting Carbon Observatory 2 (OCO-2) [38]. Future instruments capable of measuring SiF are the TROPOspheric Monitoring Instrument (TROPOMI) [39] and the dedicated FLuorescence EXplorer mission (FLEX) [40].…”

Global and time-resolved monitoring of crop photosynthesis with chlorophyll fluorescence

“…[17][18][19]. The first global maps of SIF were derived using data from the Greenhouse Gases Observing Satellite (GOSAT) (20)(21)(22)(23). Despite the complicated photosynthesis-SIF relationships and the convolution of the signal with canopy structure (16), SIF retrievals showed high correlations with data-driven GPP estimates at global and annual scales (21,22), as well as intriguing patterns of seasonal drought response in Amazonia (24,25).…”