Description

New satellite instruments are currently being designed specifically for fire detection, even though to date the detection of active fires from space has never been an integral part of the design of any in-orbit space mission. Rather, the space-based detection of fires during the last two decades has been exploiting measurements obtained for other objectives. The current fire products have proved to be of great benefit and interest, but their usefulness is not fully understood. Part of the confusion about the utility of these measurements stems from the lack of detailed knowledge about the data and its acquisition. The remote sensing research community has spent considerable time and effort trying to rationalize the usefulness of existing satellite imagery for active fire detection. Unfortunately, uncertainties about instrument capabilities pervades much of this research and the true limits of fire detection from space have not been fully evaluated and understood.

To analyze the active fire detection capability of any instrument, the flow of energy from the source to the instrument and the instrument’s response to that energy must be considered. For this reason, an approach has been developed that models the energy emitted from surface fires, allowing for the fact that fire is itself a variable phenomenon. The energy transmission is then modelled along its path through the atmosphere and through the instrument’s optical system. A fundamental concern is in the estimation of the total surface area that emits the energy which defines a single pixel in the image. Unfortunately, most of the fire detection modelling done to date is based on a misconception about the pixel and its actual size. Rather than using the radiometric footprint size, the instantaneous-field-of-view (IFOV) is used to describe the ‘resolution’ of the instrument. In fact, the radiometric footprint is considerably larger than the IFOV and greatly affects the energy modelling used to estimate the fire detection thresholds of a particular instrument. Based on knowledge of the radiometric footprint, the fire detection capability of AVHRR, DMSP-OLS, and MODIS are reviewed.