The AVHRR component of a long-term global active fire data record

The increased thermal signal in the 3.7 µm channel, together with radiometric measurements in the longwave and shortwave channels, enable the detection of thermal anomalies from AVHRR for a wide range of environmental and observing conditions. The AVHRR has been used worldwide for operational fire monitoring and for research purposes since at least the early 1990s. The long data record of AVHRR makes it an essential part of a long-term, multisensor record of fire activity. Fire Disturbance is an Essential Climate Variable (ECV) defined by the Global Climate Observing System (GCOS). Within the Fire Disturbance ECV, active fire occurrence is one of the supplementary variables. General requirements for long-term satellite-based data records for ECVs are articulated in the GCOS Climate Monitoring Principles for satellite measurements, which specify requirements both for observing systems and for product generation and distribution. In this paper we provide an overview of the history of fire monitoring from AVHRR, and the potential and limitations for establishing a long-term data record in the context of the GCOS Climate Monitoring Principles. Major sensor-related challenges include the relatively low saturation level of the 3.7 µm channel, the orbital drift of the early NOAA satellites and pixel geolocation inaccuracies. Additionally, fire detection requires full resolution observations and therefore the globally and systematically available Global Area Coverage (GAC) data are inadequate for global active fire monitoring. The need for the compilation and reprocessing of full resolution measurements from on-board Local Area Coverage (LAC) data and direct-readout High Resolution Picture Transmission (HRPT) receiving stations is articulated by the Fire Mapping and Monitoring Implementation Team of the Global Observation of Forest and Landcover Dynamics (GOFC-GOLD) program, in collaboration with the Committee on Earth Observation Satellites. As fire detection capabilities strongly depend on the observing system, establishing a continuity is also needed among AVHRR and other major observing systems, such as the (Advanced) Along-Track Scanning Radiometer ((A)ATSR), the Moderate Resolution Imaging Spectroradiometer (MODIS), and the upcoming Visible Infrared Imager Radiometer Suite (VIIRS) and Sea and Land Surface Temperature Radiometer (SLSTR). Such continuity can be established by improved understanding of detection capabilities through product validation and simulations and by using geostationary fire observations as a reference to account for differences in satellite overpass times and the consequent different sampling of the diurnal cycle of fire activity from polar orbiters.