## 2 Study Area and Data
VIIRS was launched in October 2011 aboard the Suomi National Polar-orbiting Partnership (S-NPP) satellite, a United States mission jointly managed by the National Aeronautics and Space Administration (NASA) and by the National Oceanic and Atmospheric Administration (NOAA) and the data are provided at 12-h intervals. Accuracy assessment is needed to quantify the degree of agreement between mapped products and ground observations. It allows for rigorous evaluation of the quality of thematic maps derived from remotely sensed data. Ideally, accuracy assessment of maps based on remotely sensed data is performed against ground measurements, taken to represent the true status or quantity of the target under analysis. There are limitations to using this ideal approach in the proposed study, due to the very broad extent of the study area (the whole of Cerrado), the limited accessibility of many regions, and the ephemeral nature of the signal, which starts to fade out a few days after the fire occurrence. Currently, this problem is circumvented by using higher spatial resolution satellite imagery as reference data for evaluating the lower resolution derived maps, being a well-established procedure [7; 15; 16; 18; 48; 50; 51; 52]. Accordingly, the higher spatial resolution satellite imagery used in this study as reference data for accuracy assessment came from the Landsat-8 (LS) Operational Land Imager (OLI), which has a spatial resolution (30 m), more than 2-3 orders of magnitude higher than that of the evaluated PROBA-V and MODIS instruments. Thirteen paths/rows from OLI sensor, covering an area corresponding to 17% of the Cerrado (Figure 1), were used to elaborate independent fire reference perimeters. The procedure is based on the International Global Burned Area Satellite Product Validation Protocol [53], which uses a semi-automatic classification approach. The algorithm uses fixed and multitemporal thresholds applied to the Normalized Burn Ratio Long SWIR (NBRL) spectral index, based on OLI bands 6 and 7 (shortwave infrared around 1.6 and 2.1 um). Visual photointerpretation is the ultimate benchmark for any classification and segmentation procedure [54]. Accordingly, the derived scars were then subject to a meticulously, lengthy, and expensive manual and visual quality control, in order to produce the highest quality reference map. The choice of L8 scenes was guided by the spatial and temporal distribution of active fires derived from the VIIRS in 2015 (Figure 2). September was the month with the highest frequency of active fires, followed by October, and they are concentrated in the northern part of the Cerrado, corroborating previous studies [7; 42; 43]. L8 images were then selected according to the period of highest fire activity and lowest cloud cover. We have stratified L8 reference scenes by region according to high, medium, and low fire incidence, to properly assess commission and omission errors. Table 1 shows the path/row and dates (initial and final date) of the L8 images used in this study. Finally, we describe our results through a comprehensive assessment of burned area classification using Landsat fire reference perimeters and comparison with the MCD64A1 collection 5 burned area product [11]. MCD64A1 uses daily reflectance and active fire data from the MODIS sensor aboard