Quantitative differences in detection of fire pixels using Aqua/MODIS and NPP-Suomi/VIIRS satellites

Since 2002, the AQUA (MODIS) satellite has been used as a “reference” by the Brazilian National Institute of Space Research to analyze spatial and temporal trends over fire pixel detection in all South America. Since this satellite will stop providing data in the near future, in order to continue the trend analyzes it will be necessary an integration and adjustment between AQUA fire pixels data with the data from the next reference satellite: the Suomi NPP (VIIRS). Therefore, this study has as objective to analyze the differences in fire pixels detection from AQUA and S-NPP satellites at country, state and municipal level. During the 10 years period assessed, the S-NPP detected, on average, 5.13 times more fire pixels than the AQUA on the South America continent. Venezuela was the country with the highest S-NPP/AQUA ratio (6.81) and Chile the lowest (3.87). When analyzing the fire pixels only in the Brazilian states, Acre presented the lowest S-NPP/AQUA ratio (3,72), while in Sergipe the highest (10,07). In the Pará’s municipalities, the lowest S-NPP/AQUA ratio was in Quatipuru (2.84), while the highest in Ananindeua (11.25). Despite the differences in the ratio, the number of fire pixels detected by the AQUA and S-NPP presented, almost in all cases, a significant correlation. Only the smallest municipalities in Pará had no significant correlation, probably due to low data and/or detection location errors. The changes in the S-NPP/AQUA ratio occurred probably due to factors such as sampling characteristics (pixel enlargement away from nadir), geographic area analyzed, timing of satellite overpasses, predominant type of vegetation, and others. Therefore, there isn’t one unique formula to adjust AQUA data to S-NPP, variations will persist at different locations.