FIRE-MAPS: SAR-derived tree canopy cover

This dataset provides per-pixel percent tree canopy cover (TCC) derived from polarimetric radar backscatter and airborne lidar. TCC is defined as the proportional, vertically projected area of vegetation (including leaves, stems, branches, etc.) of woody plants above a given height (Sexton et al. 2013) and is measured here as the horizontal percentage of the ground surface covered by tree crowns within 30x30-meter pixels. The study site is a 71,000-hectare patch of Fish Lake National Forest (38.537, -112.023), a mixed temperate forest in Utah that includes Quaking aspen (Populus tremuloides), Douglas fir (Pseudotsuga menziesii), Engelmann spruce (Picea engelmannii), and Subalpine fir (Abies lasiocarpa). A prescribed burn was applied to this area on October 10, 2023, by the National Park Service with the goal of managing fuels and increasing the growth of aspen trees. Data for this analysis were collected during the NASA FireSense project. Airborne lidar observations acquired in June 2024 provided two patches of data; this analysis primarily used the patch closest to the UAVSAR midrange, covering an 8-square-kilometer area that includes the 2023 burn scar. These lidar data were used to generate a reference canopy height model (CHM) at 0.3-m spatial resolution with a root mean square deviation (RMSD) of < 8 cm. A 5-meter minimum height associated with tree canopies was determined by applying a range of height thresholds (Montesano et al. 2023) and validated against high-resolution optical images. A 30-m resolution reference map was created by computing the number of lidar canopy pixels within each 30x30-m area. Synthetic Aperture Radar analyses utilized UAVSAR post-fire observations collected between 2023 and 2025, specifically using the June 26, 2024 acquisition (Granule ID: fishla_01601_24031_000_240626_L090_CX_01). The analysis focused on backscatter values at HH, HV, and VV polarizations. To derive TCC from the radar data, a binary map (tree / no tree) was first produced for each UAVSAR 6-m pixel using the criteria: 10 * log10(hv / (hh + vv)) > -9 and hv [db] > -25. For each 30x30-m pixel on the reference map, the number of UAVSAR pixels classified as "tree" was computed. Results showed good correspondence with the reference lidar estimates, yielding an R² of 0.42 and a significant linear correlation (P < 0.05). UAVSAR imagery was acquired as part of NASA’s FireSense campaign, courtesy of NASA/JPL-Caltech (www.uavsar.jpl.nasa.gov), and can be accessed through the Alaska Satellite Facility (ASF).