Solar Influence on Fire Radiative Power Retrieved With the Bispectral Method

Fire radiative power (FRP) is a key product to quantify active fires, which indicates fuel consumption and fire emissions. In the case of the bispectral method, it can be calculated from remote sensing data if a midinfrared ( $3.8~\mu \text{m}$ ) and thermal infrared channel ( $\sim 10~\mu \text{m}$ ) are available. While different uncertainty sources have been investigated, the quantitative evaluation of the FRP error as a function of reflected solar radiation is still missing. The ground-reflected solar radiance adds an unknown signal component to the at-sensor radiance during the daytime, which influences the fire detection algorithm as well as the FRP product. FRP errors can reach up to 5%–15% for smoldering fire temperatures of 400–500 K, which is a systematic bias. Errors decrease with increasing temperature and for temperatures higher than 700 K, i.e., flaming fires, the FRP bias is less than 2%. The evaluation is performed for the TET-1 instrument of DLR’s FireBIRD mission using the bispectral method.