Improved SIFTER v2 algorithm for long-term GOME-2A satellite retrievals of fluorescence with a correction for instrument degradation

Abstract

Abstract. Solar-induced fluorescence (SIF) data from satellites are increasingly used as a proxy for photosynthetic activity by vegetation and as a constraint on gross primary production. Here we report on improvements in the algorithm to retrieve mid-morning (09:30 LT) SIF estimates on the global scale from the GOME-2 sensor on the MetOp-A satellite (GOME-2A) for the period 2007–2019. Our new SIFTER (Sun-Induced Fluorescence of Terrestrial Ecosystems Retrieval) v2 algorithm improves over a previous version by using a narrower spectral window that avoids strong oxygen absorption and being less sensitive to water vapour absorption, by constructing stable reference spectra from a 6-year period (2007–2012) of atmospheric spectra over the Sahara and by applying a latitude-dependent zero-level adjustment that accounts for biases in the data product. We generated stable, good-quality SIF retrievals between January 2007 and June 2013, when GOME-2A degradation in the near infrared was still limited. After the narrowing of the GOME-2A swath in July 2013, we characterised the throughput degradation of the level-1 data in order to derive reflectance corrections and apply these for the SIF retrievals between July 2013 and December 2018. SIFTER v2 data compare well with the independent NASA v2.8 data product. Especially in the evergreen tropics, SIFTER v2 no longer shows the underestimates against other satellite products that were seen in SIFTER v1. The new data product includes uncertainty estimates for individual observations and is best used for mostly clear-sky scenes and when spectral residuals remain below a certain spectral autocorrelation threshold. Our results support the use of SIFTER v2 data being used as an independent constraint on photosynthetic activity on regional to global scales.

Intermediate Aerosol Loading Enhances Photosynthetic Activity of Croplands

“…Socioeconomic factors, such as industrialization and farming activities, could alter both pollution and agricultural productivity across the study region, which might confound the spatial relationship between SIF and AOD. In addition, the current algorithm employed for GOME‐2 SIF retrieval cannot completely eliminate the impacts of aerosol on the transmission of SIF through the atmosphere (van Schaik et al., 2020). Moreover, the overpass time of GOME‐2 is drifting toward the early morning, when plants are less stressed and inclined solar angles increase the diffuse radiation fraction.…”

“…Solar‐induced chlorophyll fluorescence (SIF), which has been suggested to be a direct proxy of ecosystem photosynthesis, especially for heavily managed agricultural ecosystems, was used to approximate ecosystem photosynthetic activity of the croplands (Guanter et al., 2014; Miao et al., 2018, 2020; Sun et al., 2017). We used the new long‐term GOME‐2A SIF data set with SIFTER v2 algorithm, which corrected the instrument degradation of GOME‐2A satellite (Kooreman et al., ; van Schaik et al., 2020). SIF retrievals at daily scale were prescreened to exclude data with cloud fraction ≥ 0.4 (van Schaik et al., 2020).…”

“…We used the new long‐term GOME‐2A SIF data set with SIFTER v2 algorithm, which corrected the instrument degradation of GOME‐2A satellite (Kooreman et al., ; van Schaik et al., 2020). SIF retrievals at daily scale were prescreened to exclude data with cloud fraction ≥ 0.4 (van Schaik et al., 2020). Satellite‐retrieved data sets of daily diffuse PAR (difPAR), air temperature (T air ), and RH, and yearly land cover were also collected for the NCP area (Method ).…”

Sun-induced fluorescence and near-infrared reflectance of vegetation track the seasonal dynamics of gross primary production over Africa

“…In determining African net ecosystem exchange (NEE), GPP was more important than total ecosystem respiration (TER) (Ciais et al, 2011;Ardö, 2015). It dominates the interannual variability in the terrestrial ecosystem carbon uptake, and as a consequence of fertilization, it is likely to continue its substantial increase and play an important role in carbon-climate coupling (Vermote et al, 1997;Friedlingstein et al, 2019). Therefore, quantification of the spatiotemporal variations in GPP is important to assess biogeochemical cycling in the terrestrial biosphere, ecosystem functioning, carbon budgets, and food production in the context of global climate change.…”

The TROPOSIF global sun-induced fluorescence dataset from the Sentinel-5P TROPOMI mission

“…Since then, a number of global SIF datasets have been produced from spaceborne spectrometers originally intended for atmospheric research, such as GOME-2 (e.g. Joiner et al, 2013;Köhler et al, 2014;van Schaik et al, 2020), SCIAMACHY (Köhler et al, 2014;Khosravi et al, 2015;Joiner et al, 2016), OCO-2 (e.g. Frankenberg et al, 2014;Sun et al, 2018), and TanSat (e.g.…”