## 2 Materials and Methods
### Orbiting Carbon Observatory-2 (OCO-2) Sif  
Launched in 2014, the Orbiting Carbon Observatory-2 (OCO-2, NASA) satellite collects SIF observations globally, offering the opportunity to measure photosynthetic activity of vegetation at higher resolution than was possible before and to employ them to address gaps in knowledge about GPP and carbon fluxes in the tropics. OCO-2 based SIF measurements provide superior spatial and spectral resolution, data acquisition techniques, and retrieval precision than previous satellite-based SIF measurements. This allows for improved validation and better determination of SIF-GPP relationships [27; 44; 100]. OCO-2 collects spectral data from 757 to 775 nm (the Oxygen absorption-A band; O\({}_{2}\)A) at approximately 1330 local time (LST) allowing accurate, high resolution retrievals of instantaneous solar-induced fluorescence (SIF) within the Fraunhofer lines at 757 and 771 nm at a spectral resolution of 0.042 nm (FWHM = 0.042 nm) [44]. OCO-2 acquires 24 spectra per second producing eight cross-track spectra each covering about 2 km \(\times\) 1.3 km spatial area, called a footprint, over a narrow swath width with maximum of approximately 10 km. At the Equator, the swath width narrows due to slit rotation and the instrument records spectra of only one ground footprint with all eight independent cross-track spectra [15]. The revisit period is every 16 days. Through 2 July 2015 each revisit time alternated between glint and nadir mode for the instrument, thus the repeat time for a set of nadir measurements is every 32 days. Since 2 July 2015, the instrument alternates modes for every orbit. Nadir mode measurements are recommended for studies such as this one because it follows a similar ground track each revisit time (allowing detection of temporal changes), has a higher spatial resolution, better signal-to-noise ratio and more consistent measurements under varying atmospheric conditions and topography than does glint mode [15; 27; 44; 126; 127]. OCO-2's coverage is global, however, there are gaps between the points and swaths. Continuous spatial coverage is sacrificed for the fine spatial sampling of each OCO-2 footprint. This fine spatial sampling and high resolution SIF measurements provide the opportunity to more accurately address SIF of specific vegetation classes within and across biomes than previous satellite-based platforms used for SIF. Nonetheless, while  
Figure 1: Map of Brazilian biome limits for the study. The six biomes are shown in color on the large map. The inset in the upper right corner is South America with the shaded region representing the extent of Brazil. OCO-2 SIF data have high spectral and spatial resolution, individual footprints are noisy, thus analyses in this study follow previous studies utilizing averaging in space and time [9; 12; 15; 23; 42; 44; 128]. The OCO-2 SIF Lite product (version 8r, \"r\" indicating retrospective dataset) data from September 2014-October 2017 for South America was downloaded and processed. The entire OCO-2 dataset is missing August 2017 due to the sensor not collecting during that period. The data were read in, filtered for nadir mode, and relevant variables, such as IGBP class, VPD, 2m temperature (air temperature, T\({}_{\text{air}}\)), and skin temperature (canopy temperature, T\({}_{\text{can}}\)) were retained for all OCO-2 footprints from the dataset. The source of these environmental variables is the European Centre for Medium-Range Weather Forecasts (ECMWF) and is included in the OCO-2 product. Brazil OCO-2 SIF footprints were co-located with shapefiles of Brazilian biomes from Ministerio do Meio Ambiente (MMA, [[http://mapas.mma.gov.br/i3](http://mapas.mma.gov.br/i3) geo/datadownload.htm]([http://mapas.mma.gov.br/i3](http://mapas.mma.gov.br/i3) geo/datadownload.htm) [102]) and all footprints in Brazil extracted and flagged for biome location.