Evaluating the SEVIRI Fire Thermal Anomaly Detection Algorithm across the Central African Republic Using the MODIS Active Fire Product

Abstract

Satellite-based remote sensing of active fires is the only practical way to consistently and continuously monitor diurnal fluctuations in biomass burning from regional, to continental, to global scales. Failure to understand, quantify, and communicate the performance of an active fire detection algorithm, however, can lead to improper interpretations of the spatiotemporal distribution of biomass burning, and flawed estimates of fuel consumption and trace gas and aerosol emissions. This work evaluates the performance of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) Fire Thermal Anomaly (FTA) detection algorithm using seven months of active fire pixels detected by the Moderate Resolution Imaging Spectroradiometer (MODIS) across the Central African Republic (CAR). Results indicate that the omission rate of the SEVIRI FTA detection algorithm relative to MODIS varies spatially across the CAR, ranging from 25% in the south to 74% in the east. In the absence of confounding artifacts such as sunglint, uncertainties in the background thermal characterization, and cloud cover, the regional variation in SEVIRI's omission rate can be attributed to a coupling between SEVIRI's low spatial resolution detection bias (i.e., the inability to detect fires below a OPEN ACCESSRemote Sens. 2014, 6 1891 certain size and intensity) and a strong geographic gradient in active fire characteristics across the CAR. SEVIRI's commission rate relative to MODIS increases from 9% when evaluated near MODIS nadir to 53% near the MODIS scene edges, indicating that SEVIRI errors of commission at the MODIS scene edges may not be false alarms but rather true fires that MODIS failed to detect as a result of larger pixel sizes at extreme MODIS scan angles. Results from this work are expected to facilitate (i) future improvements to the SEVIRI FTA detection algorithm; (ii) the assimilation of the SEVIRI and MODIS active fire products; and (iii) the potential inclusion of SEVIRI into a network of geostationary sensors designed to achieve global diurnal active fire monitoring.

New fire diurnal cycle characterizations to improve fire radiative energy assessments made from MODIS observations

“…Since the threshold of detectability of a fire is not only dependent on the instrument but also a function of the pixel area, geostationary sensors have a higher minimum FRP detection limit (typically > 40 MW) than MODIS (∼ 8 MW). They therefore do not observe the lowest FRP component of the fire regime Freeborn et al, 2014).…”

“…Wooster et al (2005) and Freeborn et al (2008) previously explored the conversion factors between FRE and DM using small scale experiments, and found that they appeared relatively independent of vegetation type. However, when moving to the satellite-scale there are additional factors influencing this FRE-to-DM relationship, for example the fire regime of an area and the degree to which MODIS misses the lowest FRP fires, and the canopy density of trees that might obscure some of the thermal radiation being emitted by fires burning in the ground fuels (Freeborn et al, 2014). The thermal radiation recorded in satellite products is additionally reduced by cloud cover and erroneous flagging of smoke as clouds during data processing.…”

“…Following previous studies (Freeborn et al, 2009, we used FRP observations derived from data collected by the geostationary SEVIRI instrument at MODIS detection opportunities, rather than actual MODIS observations, to drive the two model approaches and we evaluated the model results against the full SEVIRI time series. We used 3 years of active fire data (2010)(2011)(2012) across Africa and the Mediterranean basin to include a wide range of climates and land cover types, and avoid the use of SEVIRI observations obtained at very far off-nadir angles over South America and northern Europe (Freeborn et al, 2014). Results are intended for application in GFAS within EU's Copernicus Atmosphere Monitoring Service (CAMS, http://atmosphere.copernicus.eu).…”

Standardized Time-Series and Interannual Phenological Deviation: New Techniques for Burned-Area Detection Using Long-Term MODIS-NBR Dataset

“…The images already have atmospheric corrections for gases, thin cirrus clouds and aerosols [55]. The MODIS data is increasingly used to monitor burned areas and active fire over large geographic areas (e.g., [56][57][58][59][60][61][62][63]). The study area is contained in just one MODIS scene (tile h13v10).…”

A Decade Long, Multi-Scale Map Comparison of Fire Regime Parameters Derived from Three Publically Available Satellite-Based Fire Products: A Case Study in the Central African Republic

“…Omission and commission rates are not universal. Rather detection rates have been shown to vary between satellite products, and between validation sites depending on active fire characteristics and burned area patterns, surrounding canopy cover, and atmospheric conditions at the time of the observation [33][34][35][36][37][38][39][40].…”