Mitigating Satellite‐Based Fire Sampling Limitations in Deriving Biomass Burning Emission Rates: Application to WRF‐Chem Model Over the Northern sub‐Saharan African Region

Abstract

Largely used in several independent estimates of fire emissions, fire products based on MODIS sensors aboard the Terra and Aqua polar‐orbiting satellites have a number of inherent limitations, including (a) inability to detect fires below clouds, (b) significant decrease of detection sensitivity at the edge of scan where pixel sizes are much larger than at nadir, and (c) gaps between adjacent swaths in tropical regions. To remedy these limitations, an empirical method is developed here and applied to correct fire emission estimates based on MODIS pixel level fire radiative power measurements and emission coefficients from the Fire Energetics and Emissions Research (FEER) biomass burning emission inventory. The analysis was performed for January 2010 over the northern sub‐Saharan African region. Simulations from WRF‐Chem model using original and adjusted emissions are compared with the aerosol optical depth (AOD) products from MODIS and AERONET as well as aerosol vertical profile from CALIOP data. The comparison confirmed an 30–50% improvement in the model simulation performance (in terms of correlation, bias, and spatial pattern of AOD with respect to observations) by the adjusted emissions that not only increases the original emission amount by a factor of two but also results in the spatially continuous estimates of instantaneous fire emissions at daily time scales. Such improvement cannot be achieved by simply scaling the original emission across the study domain. Even with this improvement, a factor of two underestimations still exists in the modeled AOD, which is within the current global fire emissions uncertainty envelope.

Six global biomass burning emission datasets: intercomparison and application in one global aerosol model

“…Each of the two MODIS sensors, from which all of the major BB datasets derive their inputs, can only possibly observe a given fire location twice in 24 h, which leaves excessive sampling gaps in the diurnal cycle of fire activity (Saide et al, 2015). Even for these few times that MODIS makes observations at its nominal spatial resolution of 1 km at nadir, it has the po-tential to miss a significant number of smaller fires (e.g., Hawbaker et al, 2008;Burling et al, 2011;, as well as to miss fires obstructed by clouds, and those located in the gaps between MODIS swaths in the tropics (Hyer and Reid, 2009;Wang et al, 2018). In addition, MODIS fire detection sensitivity is reduced at MODIS off-nadir views, with increasing view zenith angles, especially toward the edge of scan, where its ground pixel size is almost a factor of 10 larger that at nadir (Peterson and Wang, 2013;Roberts et al, 2009;Wang et al, 2018), resulting in dramatic decreases in the total number of detected fire pixels and total FRP (Ichoku et al, 2016b;Wang et al, 2018).…”

In situ measurements of trace gases, PM, and aerosol optical properties during the 2017 NW US wildfire smoke event

“…The Interagency Monitoring of Protected Visual Environments (IMPROVE) program initiated in 1985 implemented long-term monitoring that establishes current visibility conditions and has helped to improve visibility in protected areas. However, record high temperatures, drought, and fire-control practices over the last century have culminated into a situation in which we can anticipate more frequent fires of a larger size and intensity in the western US and Canada (Yue et al, 2015;Westerling et al, 2006). These fires are expected to impact all aspects of air quality in the US -and have other impacts, including on visibility.…”

Characterization and Trends of Fine Particulate Matter (PM2.5) Fire Emissions in the Brazilian Cerrado during 2002–2017

“…It should also be noted that remote sensors have several difficulties in estimating FRP associated to the active fires detected that can potentially impact the final estimate of fire emissions that were obtained from PREP-CHEM-SRC 1.8.3, GFASv1.3, QFEDv2.5r1, and FEERv1.0-G1.2: (i) fires typically are not occurring over the entire area of a pixel, therefore smaller size fires are more difficult to be detected at coarser spatial resolutions, which suggests that a certain proportion of the smallest or less intense fires are not detected by the sensor; (ii) non detection of fires due to cloud cover and thick smoke; and, (iii) the reduced sensitivity of MODIS fire detection at off-nadir viewing angles [33,57,58]. Therefore, future efforts should assess the estimates of fire emissions that were obtained with PREP-CHEM-SRC 1.8.3, GFASv1.3, FEERv1.0-G1.2, QFEDv2.5r1, and GFED4.1s in the Cerrado in order to establish which one presents the best performance.…”