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Focus Area on Fire Product Validation

Gareth Roberts, Southampton University, UK
Louis Giglio, University of Maryland, USA

 

Burned Area, Active Fire, and Fire Radiative Power Definition

Fire Disturbance includes Burned Area (BA) as the primary variable, and two supplementary variables: Active Fire (AF) and Fire Radiative Power (FRP), as stated by the Global Terrestrial Observing System (GTOS) in Csiszar et al. (2009). Burned Area is defined as the area affected by wildfires. Active Fire is the location of burning at the time of the observation. Fire Radiative Power is the rate of emitted radiative energy by the fire at the time of the observation.

Units:
  Burned Area is expressed in units of area such as km2.
  Active Fire is often a spatially explicit digital raster map indicating of presence or absence of fire, and can
also be provided as spatial coordinate pairs.
  Fire Radiative Power is expressed in units of power, such as Watts (W).


Highest Validation Stage Currently Reached for Satellite-derived Fire Products

Validation stage 3 (LPV validation stage hierarchy) - The highest LPV validation stage reached for satellite-derived burned area products. Most burned area products are made publicly available along with a Stage-2 or Stage-3 validation.

Validation stage 3 (LPV validation stage hierarchy) - The highest LPV validation stage reached for satellite-derived active fire detection products. The main challenge to validate fire products is the generation of reference data due to the ephemerality of the phenomenon to be mapped and the current revisit times of moderate-high spatial resolution observing systems. Reference data samples are consequently scarce and often not coincident with product estimates.

Validation stage 3 (LPV validation stage hierarchy) - The highest LPV validation stage reached for satellite-derived fire radiative power (FRP) products. As with active fire detection products, a major challenge in validating FRP products is the generation of reference data due to the ephemerality of the phenomenon. FRP validation has the added complication of demanding “fire-friendly” sensors that have the high dynamic range needed to sense actively burning fires without saturating.  Reference data samples are consequently even more scarce and rely heavily on ground-based instrumentation.


Validation Good Practices

The standard procedure to generated reference data for Burned Area includes the use of pairs of Landsat-class imagery, as described in CEOS LPV good practices guidelines (Boschetti et al. 2009). Cross-tabulation analysis is the most common validation approach, although other regional or patch-level analyses are of interest (Boschetti et al. 2004; Padilla et al. 2014a; Roy and Boschetti 2009; Boschetti et al. 2019; Stroppiana et al. 2021). Validation results showed that most BA products have high to moderate commission and omission errors and tend to highly underestimate BA.

Active Fires have been validated with simultaneous observations with higher spatial resolution. This was the case for MODIS (Csiszar et al. 2006; Morisette et al. 2005), on board the Terra satellite that also carries a moderate resolution sensor (ASTER). More recently, Active Fires have been validated with Landsat imagery (Schroeder et al. 2008; Tansey et al. 2008; Hantson et al. 2013; Hall et al. 2019).

Validation work is limited for fire radiative power since it requires coincident unsaturated radiance measurements (Csiszar et al. 2009). Coincident measurements currently are not routinely available, even opportunistic experiments used BIRD FRP estimates (Zhukov et al. 2006) and airborne thermal imaging systems (Schroeder et al. 2014).

The Fire focus area of CEOS LPV is currently developing a good practices protocol for the validation of satellite-derived active fire and burned area products. The current draft version on burned area validation will be complemented by sampling schemes of reference data and an active fire validation component.


Active Fire and Burned Area Reference Data Sets

  • Globcarbon project, from the European Space Agency: Reference data derived from 72 Landsat image pairs from year 2000.
  • Burned Area Reference Database (BARD), from the European Space Agency Fire Climate Change Initiative (CCI): An extensive compilation of global and regional burned area reference datasets generated primarily from Landsat-8 and Sentinel-2 imagery.
  • MODIS Burned Area: Reference data derived from 558 Landsat images distributed across the globe using a stratified sampling approach.

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