The Visible Infrared Imager Radiometer Suite (VIIRS) sensor on the NPOESS Preparatory Project (NPP) and Joint Polar Satellite System (JPSS) satellites has capabilities for active fire detection and characterization for a broad range of fires, and observing and environmental conditions. This capability represents a potential for the continuation of the data record from MODIS (Moderate Resolution Imaging Sprectroradiometer) on the NASA Earth Observing System (EOS) Terra and Aqua satellites. To establish a consistent data record useful for the long-term monitoring and analysis of fire dynamics, however, includes the detailed comparison of the fire mapping capabilities of MODIS and VIIRS. While NPP and Aqua have similar orbital characteristics and compatible sampling of the diurnal cycle of fire activity, sensor differences, including pixel sizes, along-scan aggregation and swath width result in inherent differences in the expected fire observations. These differences can be analyzed in two fundamental ways. First, theoretical simulations produce estimates of detection capabilities and their variations with view angle along the scanline. Second, actual fire observations from higher spatial resolution sensors, such as the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Landsat-5 Thematic Mapper (TM) and Landsat-7 Enhanced Thematic Mapper (ETM+) can be used to determine differences in detected fire counts from MODIS and VIIRS. These analyses form an integral part of the NPP VIIRS active fire product development and validation activities by the JPSS program and the NASA NPP Science Team. This presentation includes details of the methodology and results from analysis for several representative observing scenarios.