We analyze the MODIS and VIIRS active-fire Fire Radiative Power (FRP) products and suggest an approximation for the FRP detection limit as a linear function of a pixel area and develop analytical observation operators for both pixel-level and gridded FRP products. We have shown that the collection-6.1 of MODIS has the FRP detection limit at 3.7 MW in case of a nadir retrieval at a clear-sky night. For a daytime sideview, it reaches as high as 40 MW. For VIIRS, the smallest fire reliably detected at night is 0.5 MW. Application of the developed operators for the cross-mapping the MODIS and VIIRS datasets at the pixel/granule level confirmed their consistency. Applying the grid-level operators alongside satellite overpass and weather data, we generated global maps of fire detection probabilities, revealing regional variations. As a global average, probability of detection of powerful fires is 78 % for MODIS (88 % for VIIRS). Variations between regions are large: in some equatorial areas this probability is less than 30 % for MODIS (40% for VIIRS).