## 2 Data  
### MODIS Sensing Geometry and Active Fire Data  
MODIS observes actively burning fires in a sun-synchronous orbit, with a repeat cycle of 16 days ([PERSON], 2017). MODIS crosses the equator at approximately 01:30 (Aqua, descending orbit), 10:30 (Terra, descending orbit), 13:30 (Aqua, ascending orbit), and 22:30 (Terra, ascending orbit) local time (Terra, descending orbit) local time (Terra, descending orbit), which provides near-global coverage four times a day. Over a 110\({}^{\circ}\) field of view, a MODIS swath consists of ten scan lines and each line has 1354 pixels with a swath width of 2340 km (Terra, descending orbit). As scan angle varies from nadir to the scan edge, the nominal pixel size increases from \(\sim\)1 km to \(\sim\)2.01 km and \(\sim\)4.83 km in the along-track and along-scan directions, respectively ([PERSON], 2017). Accordingly, the pixel area increases by a factor of \(\sim\)9.6 (Figure 1), and adjacent scans overlap by up to 50%, which is called the \"bow-tie\" effect (Terra, descending orbit). As a result, the \"bow-tie\" effect results in the repeat detection of the same fires by adjacent scans (Terra, 2017; Terra, descending orbit). MODIS provides a full coverage of the globe every 2 days due to daily swath gaps across equatorial regions between 30\({}^{\circ}\)S and 30\({}^{\circ}\)N (Terra, 2017), which results in missing observations of fires within the swath gaps (Figure 2). MODIS sensing geometry information (i.e., geolocation and angles) is stored in the swath-level geolocation products (abbreviated MOD03 for Terra and MYD03 for Aqua).  
The collection 6 (C6) MODIS 1 km Level-2 active fire products (abbreviated MOD14 for Terra and MYD14 for Aqua) are generated in MODIS sensing geometry (or a swath-level product). The products provide for each fire pixel the observing time, coordinates, detection confidence (0%-100%), FRP (units: MW per pixel), view zenith angle (VZA), brightness temperatures at the 4 and 11-\(\upmu\)m bands, and average brightness temperature of ambient background pixels at these two bands (Terra, 2017), as described in Equation (1). FRP in the C6 products is estimated using radiances of the fire pixel and its ambient non-fire pixels at the 4-\(\upmu\)m band (Terra, 2017). This study obtained the C6 Aqua MODIS geolocation product (MYD03) and Level-2 active fire product (MYD14) from the NASA's Level-1 and Atmosphere Archive and Distribution System (LAADS) ([[https://ladsweb.modaps.eosdis.nasa.gov/](https://ladsweb.modaps.eosdis.nasa.gov/)]([https://ladsweb.modaps.eosdis.nasa.gov/](https://ladsweb.modaps.eosdis.nasa.gov/))) for the year 2017. The MYD14 product for the 2003-2018 period was also obtained for the correction of historical MODIS FRP. MYD03 was used to locate and extract the swath gaps. For the sake of brevity, hereafter Aqua MODIS is referred to as MODIS.  
\[FRP=\Big{(}\frac{A\sigma}{\alpha}\Big{)}\Big{(}L_{f,MIR}-L_{b,MIR}\Big{)} \tag{1}\]  
where \(FRP\) is fire radiative power (units: MW); \(A\) is pixel area (units: km\({}^{2}\)); \(\sigma\) is the Stefan-Boltzmann constant (\(\sigma=5.67\times 10^{-8}\) Wm\({}^{-2}\) K\({}^{-4}\)); \(\alpha\) is a sensor-specific constant; \(L_{f,MIR}\) and \(L_{b,MIR}\) are radiances of the fire pixel and its ambient background non-fire pixels at the 4-\(\upmu\)m band.  
Figure 1: Variation of the area of a Moderate Resolution Imaging Spectroradiometer (MODIS) (blue line) and VIIRS I-band (red line) pixel along the scan angle from nadir to the scan edge.