Prospects for chlorophyll fluorescence remote sensing from the Orbiting Carbon Observatory-2

Abstract

The Orbiting Carbon Observatory-2 (OCO-2), scheduled to launch in July 2014, is a NASA mission designed to measure atmospheric CO 2 . Its main purpose is to allow inversions of net flux estimates of CO 2 on regional to continental scales using the total column CO 2 retrieved using high-resolution spectra in the 0.76, 1.6, and 2.0 μm ranges. Recently, it was shown that solar-induced chlorophyll fluorescence (SIF), a proxy for gross primary production (GPP, carbon uptake through photosynthesis), can be accurately retrieved from space using high spectral resolution radiances in the 750 nm range from the Japanese GOSAT and European GOME-2 instruments. Here, we use real OCO-2 thermal vacuum test data as well as a full repeat cycle (16 days) of simulated OCO-2 spectra under realistic conditions to evaluate the potential of OCO-2 for retrievals of chlorophyll fluorescence and also its dependence on clouds and aerosols. We find that the single-measurement precision is 0.3-0.5 Wm (15-25% of typical peak values), better than current measurements from space but still difficult to interpret on a single-sounding basis. The most significant advancement will come from smaller ground-pixel sizes and increased measurement frequency, with a 100-fold increase compared to GOSAT (and about 8 times higher than GOME-2). This will largely decrease the need for coarse spatial and temporal averaging in data analysis and pave the way to accurate local studies. We also find that the lack of full global mapping from the OCO-2 only incurs small representativeness errors on regional averages. Eventually, the combination of net ecosystem exchange (NEE) derived from CO 2 source/sink inversions and SIF as proxy for GPP from the same satellite will provide a more process-based understanding of the global carbon cycle.

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

“…This finding indicates that SIF data can help us improve our current models of the global carbon cycle, which we have shown to substantially underestimate GPP in some large agricultural regions such as the US CB and the Indo-Gangetic Plain. The launch of the Orbiting Carbon Observatory-2 and the Sentinel 5-Precursor satellite missions in 2014 or 2015 will enormously improve the observational potential for SIF, up to a 100-fold increase in spatiotemporal resolution (42,43). This will especially benefit measurements over the typically fragmented agricultural areas, which suggests that SIF-based estimates of crop photosynthesis will soon become a unique data set for both an unbiased monitoring of agricultural productivity and the benchmarking of carbon cycle models.…”

Reconstructed Solar‐Induced Fluorescence: A Machine Learning Vegetation Product Based on MODIS Surface Reflectance to Reproduce GOME‐2 Solar‐Induced Fluorescence

“…Dry to wet transitional regions are correctly characterized, such as in Portugal‐Spain, North Africa, the Sahel, the east‐west gradient in the continental United States, and in India. Deserts are also correctly characterized with the lowest RSIF values, whereas the original SIF data tend to be noisy over deserts and more erratic due to the inherent noise in the small‐amplitude SIF data (Frankenberg et al, 2014; Joiner et al, 2011; Köhler et al, 2014). …”

“…Recently, a new retrieval of red SIF from GOME‐2 instrument was developed (Joiner et al, 2016), which is noisy but could yield important additional information on LUE. New fluorescence observations at higher spatial and temporal resolution and with higher signal‐to‐noise ratio, such as from OCO‐2 (Frankenberg et al, 2014; Li et al, 2017; Schimel et al, 2015), Florescence Explorer (FLEX) (Kraft et al, 2012), TROPOspheric Monitoring Instrument (TROPOMI) (Guanter et al, 2015), or Geostationary Carbon Cycle Observatory (GeoCARB) (O'Brien et al, 2016), might help better retrieve changes in LUE, maybe in combination with this RSIF product. In addition, SIF observations at other spectral frequencies and at higher temporal resolution (diurnal) might yield critical information regarding variations in SIF yield and LUE.…”

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.…”