EVALUATION OF SATELLITE MEASUREMENTS OF FIRE RADIATIVE POWER (FRP) USING AIRBORNE MEASUREMENTS

Abstract

Wildfires and other types of open biomass burning occur seasonally in different vegetated landscapes throughout the world, and are ignited either by natural (e.g., lightning) or anthropogenic (accidental, agricultural, arson, experimental, or prescribed burning) processes. Irrespective of their origin or location, these large fires generate intense heat energy, burning up large amounts of biomass and emitting corresponding amounts of smoke plumes that comprise aerosols and trace gases, which include carbon monoxide (CO), carbon dioxide (CO₂), methane (CH₄), non-methane hydrocarbons, and several other chemical compounds, most of which have adverse effects on human health and environmental processes. Accurate estimates of these emissions are required as model inputs to simulate and forecast smoke plume transport and impacts on air quality, human health, clouds, weather, radiation, and climate. However, accurate estimation of biomass consumption and smoke emissions has eluded the scientific research community for a long time because it depends fundamentally on accurate quantitative determination of fire activity, which is not possible by in situ measurement methods. Recent advancements in the capability of space-borne sensors have enabled routine quantitative measurement of active fire radiative energy (FRE) release rates or power (FRP) from advanced satellite sensors, such as the Moderate-resolution Imaging Spectro-radiometer (MODIS) aboard the Terra and Aqua polar-orbiting satellites [2], [4] and the Spinning Enhanced Visible and Infrared Imager (SEVIRI) aboard the Meteosat-8 geostationary satellite [5]. Presently, FRP is generally derived from radiance measurements at mid-infrared (MIR) wavelengths (typically, in the 3.7 to 4.0 µm wavelength range) [3], [4], [6], [8]. Fig. 1 shows an Aqua-MODIS true-color image acquired over the firestorm that occurred in Southern California, USA, during October 2007, showing the fire locations and smoke plumes, while Fig. 2 shows the fire pixel FRP values (in MW). FRP has been shown to be proportional to the rates of biomass combustion and smoke aerosol emissions, and its effectiveness in estimating these quantities has been demonstrated [1], [6], [7]. The objective of this paper is to quantitatively evaluate the FRP measurements from MODIS using airborne MIR measurements acquired with the Autonomous Modular Sensor (AMS) Wildfire instrument aboard the remotely piloted NASA Ikhana aircraft. This effort will help to reinforce the physical understanding and utilization of satellite FRP measurements to quantitatively characterize the spatio-temporal distribution of biomass burning and to derive smoke particulate and gaseous emissions in different regions of the world. It holds great promise in helping to advance scientific knowledge about the impacts of biomass fires and the associated smoke emissions on land-use changes, air quality, human health and safety, the water cycle, and climate.