Studying landscape-level wildfire behavior with repeat-pass airborne thermal infrared imaging

Keywords: wildfire, thermal infrared, remote sensing, Mediterranean-type vegetation
Abstract Type: Paper Abstract

Abstract

Repetitive airborne thermal infrared (ATIR) imaging conducted in a coordinated manner enables wildfire behavior to be studied at finer spatial and temporal scales than with satellite or conventional ATIR imaging missions. We estimate rate of spread (ROS) and intensity of free-burning wildfires at landscape scales for the Detwiler and Thomas fires in Southern California which burned as crown fires in Mediterranean-type shrublands and woodlands. The USDA Forest Service FireMapper 2.0 imaging system captuerd images with 10 m spatial resolution approximately every 5 to 10 minutes and with a high degree of overlap over the active fire head, along flight lines oriented perpendicular to the predominant fire spread direction. Images were orthorectified and registered within an error of < 1 pixel. Active fire fronts and fire spread vectors were generated semi-automatically from sequential orthoimages. ROS was calculated for each spread vector. Fire intensity was generated for each temperature calibrated image and fire radiative energy density is estimated from the time sequence of fire intensity images. We assessed statistical relationships between ROS and directional slope (slope angle in the direction of fire spread) and prefire fuel metrics generated from aerial orthoimages. We found that the strongest control on ROS is directional slope for these wildfires that burned relatively homogeneous fuels on complex terrain, while wind speed was also important. Descriptive analyses of fire spread behavior were achieved through geovisualizations of image-derived fire fronts and spread vectors overlaid on 3-D surfaces. Fire radiative energy density maps portray spatial distributions energy input to ecosystems.