Radiative Transfer Modelling for the characterisation of natural burnt surfaces

Philip Lewis, Mat Disney, Jose Gómez-dans, Martin John Wooster, Bernard Pinty, david roy
2022 figshare.com  
Fire is arguably the most important and widespread agent of ecosystem disturbance worldwide. It affects the Carbon cycle, is a control on ecosystem structure, and can potentially impact humans both directly and indirectly. There is a long history of using Earth Observation (EO) data in monitoring wildfires that has led to the development of operational products measuring fire occurrence. These tend to use thermal and/or optical observations to denote an area as being affected by fire if, for
more » ... tance, the thermal signature is high or the reflectance in near infrared (NIR) or middle infrared (MIR) follows the patterns expected of fire impacts. In recent years, more refined information from time series of thermal observations has allowed the calculation of Fire Radiative Energy that can be related to Carbon release due to fire. Various researchers have attempted to characterise fire ̳severity' from optical data — usually focusing on a change in a normalised ̳burn ratio' (NBR) from satellite measurements in the NIR and MIR. Such measures have been criticised because: (i) they have no direct physical meaning (they require local calibration for interpretation); (ii) they do not make full use of available spectral information; and (iii) they can be far from optimally related to fire impacts. An additional consideration is that high temporal resolution observations help in monitoring several types of wildfire. But this tends to imply the use of moderate spatial resolution data. This in turn generally implies that the observations will be taken under varying viewing and/or illumination geometries. While it is well known that satellite reflectance varies as a function of such geometries ( ̳BRDF effects') and there are several quite straightforward methods for taking these into account, studies involving NBR tend to ignore such effects. Further, if moderate or coarse spatial resolution optical data are to be used to monitor fires, the sum of pixels identified as ̳fire affected' will over-report the area affected if [...]
doi:10.6084/m9.figshare.19657785.v1 fatcat:sghgq4exljbt7nlza37ghg34su