Survey of Transverse Range Fire Scars in 10 Years of UAVSAR Polarimetry

Abstract

The Geospatial Multi-Agency Coordination (GeoMAC) has been collecting and storing data on wildland fire perimeters since August 2000 (Walters et al., 2011), although the continuing collection since 2020 has been transferred to the National Interagency Fire Center (NIFC). The GeoMAC repository retains the perimeter information of interest for this work. According to the United States Forest Service (https://www.fs.fed.us/ nwacfire/home/terminology.html), the fire perimeter is defined to be the entire outer edge or boundary of a fire. But fire boundaries are fractal in nature, so approximations are made for convenience. According to https://www.nwcg.gov/course/ffm/mapping/51-burn-area-and-perimeter, "Because fires often burned in unusual shapes such as fingers, the perimeter of a fire can be approximated by assembling a combination of known shapes and lines."In addition, fires may be more or less severe, depending on fuel density, wind speed, topography, weather, and other factors (e.g., Countryman, 1964;Harris et al., 2017). It is expected that some fires in the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) polarimetry (herein PolSAR) record will show nearly complete elimination of brushy or leafy biomass within a fire perimeter, while others will be less complete, perhaps even showing distinct patches of destruction among clusters of intact trees and brush.Polarimetry is performed using the L-band (23.84 cm) UAVSAR system, mounted under a NASA Gulfstream III aircraft. The PolSAR product artificially colors the image with blue for VV, red for HH, and green for the HV return. In a typical image, these three polarized returns, respectively, indicate (blue) rough surface scatterers, (red) double-bounce scatterers such as buildings or tree trunks, and (green) volume scatters,

Assessment of Pre‐ and Post‐Fire Fuel Availability for Wildfire Management Based on L‐Band Polarimetric SAR

“…Fuel moisture content studies generally utilize readily available satellite C-band data along with in situ measurements (Bourgeau-Chavez, et al, 2008;Saatchi et al, 2007) with recent studies containing optical imagery comparisons as well (Rao et al, 2020;Wang et al, 2019). Parker et al (2021) explores an archive of high spatial resolution L-band products, but only visually analyzes the fire scars in the Angeles National Forest over the past decade. Post-fire, C-band SAR has been used to monitor vegetation recovery (Zhou et al, 2019), and has been compared with Normalized Difference Vegetation Index (NDVI) to assess regeneration time (Tariq et al, 2021).…”

“…Parker et al. (2021) explores an archive of high spatial resolution L‐band products, but only visually analyzes the fire scars in the Angeles National Forest over the past decade. Post‐fire, C‐band SAR has been used to monitor vegetation recovery (Zhou et al., 2019), and has been compared with Normalized Difference Vegetation Index (NDVI) to assess regeneration time (Tariq et al., 2021).…”