# Improving Spatial-Temporal Data Fusion by Choosing Optimal Input Image Pairs
## Study Area and Data
### Satellite Data and Preprocessing
#### 2.2.1 MODIS Data Products  
MODIS sensors are on Terra (EOS A.M.) and Aqua (EOS P.M.) satellites. Both Terra and Aqua have a sun-synchronous and near polar orbit. Aqua crosses the equator daily at around 1:30 P.M. in ascending mode and Terra crosses the equator at about 10:30 A.M. in descending mode. Table 1 lists the MODIS data products (downloaded from [32]) from both Terra and Aqua used in this study. MODIS surface reflectance and BRDF data products [26; 27] for the entirety of 2015 were downloaded and used, as well as the most recent annual land cover product (MCD12Q1) [33]. MODIS tile h10v04 covers study site 1 and tile h10v05 covers site 2. MODIS sensors (both Terra and Aqua) have a large fields of view (FOV, \(\pm\)55 degrees), but Landsat sensors have a smaller FOV (\(\pm\)7.5 degrees) and observe close to the nadir view. To improve the consistency of surface reflectance between MODIS and Landsat, MODIS products were used to generate three kinds of daily NBAR test datasets, including Terra NBAR, Aqua NBAR and the Terra and Aqua combined NBAR data product (Table 2). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**MODIS Products**} & **Spatial Resolution (m)** & **Temporal Resolution** & **Description** \\ \hline \multirow{2}{*}{**MOD09 GQ**} & \multirow{2}{*}{250} & \multirow{2}{*}{Daily} & Directional reflectance product acquired by Terra \\  & & & (red and NIR bands only) \\ \hline \multirow{2}{*}{**MOD09 GA**} & \multirow{2}{*}{500} & \multirow{2}{*}{Daily} & Directional reflectance product acquired by Terra \\  & & & (for all land bands) \\ \hline \multirow{2}{*}{**MYD09 GQ**} & \multirow{2}{*}{250} & \multirow{2}{*}{Daily} & Directional reflectance product acquired by Aqua \\  & & & (red and NIR bands only) \\ \hline \multirow{2}{*}{**MYD09 GA**} & \multirow{2}{*}{500} & \multirow{2}{*}{Daily} & Directional reflectance product acquired by Aqua \\  & & & (for all land bands) \\ \hline \multirow{2}{*}{**MCD43A1**} & \multirow{2}{*}{500} & \multirow{2}{*}{16-day} & Terra and Aqua combined BRDF/Albedo Model \\  & & & Parameters product \\ \hline \multirow{2}{*}{**MCD43A4**} & \multirow{2}{*}{500} & \multirow{2}{*}{Daily} & Terra and Aqua combined NBAR product \\ \hline \multirow{2}{*}{**MCD43A2**} & \multirow{2}{*}{500} & \multirow{2}{*}{Daily} & Quality information product for the corresponding \\  & & & MCD43A4 product \\ \hline \multirow{2}{*}{**MCD12Q1**} & \multirow{2}{*}{500} & \multirow{2}{*}{Annual} & Land cover \\ \hline \hline \end{tabular}
\end{table} 
Table 1: List of the MODIS products used in the study. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Product Name**} & \multirow{2}{*}{**Data Source**} & \multirow{2}{*}{**Resolution**} & \multirow{2}{*}{**Coverage**} & **Solar Zenith Angle** \\ \hline \multirow{4}{*}{**Terra NBAR**} & In-house BRDF correction using MCD43A1, MOD09 GQ, MOD09 GA, MCD12Q1 & & Clear pixels from Terra & At Terra \\  & & & and NIR bands & overpass time & overpass time \\  & & & MOD09 GA, MCD12Q1 & & \\ \hline \multirow{4}{*}{**Aqua NBAR**} & In-house BRDF correction using MCD43A1, MYD09 GQ, MYD09 GA, MCD12Q1 & & Clear pixels from Aqua & At Aqua \\  & & & and NIR bands & overpass time & overpass time \\ \hline \multirow{2}{*}{**Terra/Aqua**} & Standard Collection 6 MODIS NBAR products combined (MCD43A2 and MCD43A1) & & Clear pixels from 16-day & Mean solar \\  & & & period (at least two clear & zenith angle \\ \hline \hline \end{tabular}
\end{table} 
Table 2: List of MODIS NBAR data products used in the study. MODIS daily 250 m directional surface reflectance from Terra (MOD09 GQ) and Aqua (MYD09 GQ) were corrected to nadir BRDF-adjusted reflectance (NBAR) using the BRDF parameters (MCD43A1) and angular information from surface reflectance products (MOD09 GA and MYD09 GA) [34]. These two datasets of MODIS daily NBAR will be referred to as Terra NBAR and Aqua NBAR. MODIS Collection 6 daily NBAR products (MCD43A4) at 500 m spatial resolution from 2001 forward have been available since 2016.