# Patterns of Arctic Tundra Greenness Based on Spatially Downscaled Solar-Induced Fluorescence
## 2 Data and Methods
### Data
#### 2.2.2 SIF Data  
As for the SIF data, the spatially downscaled GOME-2 SIF (denoted as SIF for the study) at 740 nm (spatial resolution: 0.05 degree, approximately 5 km; temporal resolution: monthly; unit: mW/m\({}^{2}\)/sr/nm, where sr is steradian, and nm is nanometer) [(37)], was derived from an original SIF product (version 25), as provided by [PERSON] et al. [(42)]. The original SIF product can be obtained from the Aura Validation Data Center (AVDC), Goddard Space Flight Center (GSFC), and can be downloaded at [[http://avdc.gsfc.nasa.gov/pub/data/satellite/MetOp/GOME_F/](http://avdc.gsfc.nasa.gov/pub/data/satellite/MetOp/GOME_F/)]([http://avdc.gsfc.nasa.gov/pub/data/satellite/MetOp/GOME_F/](http://avdc.gsfc.nasa.gov/pub/data/satellite/MetOp/GOME_F/)). The spatially downscaled SIF can be obtained from [PERSON] and Cescatti [(37)]. The highest latitude of the spatially downscaled SIF just reaches to 75\({}^{\circ}\) N, so no vegetation information higher than 75\({}^{\circ}\) N is included in the study. The spatially downscaled SIF was calculated via a non-linear model based on the concept of light-use efficiency (LUE). The information contained in the original coarse GOME-2 SIF pixels (spatial resolution: 0.5 degree) is spatially disaggregated. At each time step, the remote sensing biophysical variables (MODIS NDVI, land surface temperature, and evapotranspiration) were aggregated to calibrate the downscaling model both independently and locally. Then, the downscaling model was applied to create a new layer with non-aggregated data (spatial resolution: 0.05 degree, approximately 5 km). More details related to spatially downscaled SIF can be found in [PERSON] and Cescatti [(37)].  
We used the annual maximum values of the NDVIs and SIF as the proxies of tundra greenness for the study. In this research, the annual maximum values of the GIMMS NDVI3g, MOD13Q1, and SIF were denoted as NDVImax_g, NDVImax_m, and SIFmax, respectively.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Product Name \({}^{*}\)** & \begin{tabular}{c} **Greenness** \\ **Indicator \({}^{**}\)** \\ \end{tabular} & **Spatial Resolution** & \begin{tabular}{c} **Temporal** \\ **Resolution** \\ \end{tabular} & **Bandwith (nm)** \\ \hline GIMMS NDVI3g & NDVI & 8 km & bi-weekly & \begin{tabular}{c} NIR: 730–1000 \\ R: 550–700 \\ NIR: 841–876 \\ R: 620–670 \\ \end{tabular} \\ \begin{tabular}{c} MOD13Q1 \\ \end{tabular} & NDVI & 250 m & 16-day & \begin{tabular}{c} NIR: 730–1000 \\ R: 550–700 \\ NIR: 841–876 \\ R: 620–670 \\ \end{tabular} \\ Spatially downscaled & SIF & 0.05 degree, & \begin{tabular}{c} 720–758 (spectral \\ resolution: 0.5 nm) \\ \end{tabular} \\ GAME-2 SIF & \
\begin{tabular}{c} **-** \\ **approximately 5 km** \\ \end{tabular} &
\begin{tabular}{c} 720–758 (spectral \\ resolution: 0.5 nm) \\ \end{tabular} \\ \hline \hline \end{tabular} \({}^{*}\) Product name: GIMMS (Global Inventory Modeling and Mapping Studies), GOME (Global Ozone Monitoring Experiment), \({}^{**}\) Greenness indicator: NDVI (Normalized Difference Vegetation Index), SIF (Solar-Induced Fluorescence).  
\end{table}
Table 1: Three satellite-based greenness datasets (2007–2013) for the study.