Exploring ECOSTRESS data for wildfires in Mediterranean ecosystems

Abstract

Mediterranean countries have always been affected by wildfires. However, global warming and more frequent hot summers increase the intensity, extension and impact of wildfires and may induce a shift in fire season. Earth Observing (EO) programs such as MODIS, VIRSS, and Sentinel 3 provide valuable information for wildfire detection due to daily overpass and thermal spectral bands, while Sentinel 2 (10-20m/px) and Landsat 8 (30m/px) data can provide more detailed information on small size wildfires and their impact on the ecosystem. In 2018 the ECOsystem Spaceborne Thermal Radiometer Experiment (ECOSTRESS) was deployed on the International Space Station (ISS) in order to provide temperature and evapotraspiration maps of vegetation to be used to detect vegetation water stress at its early stage and provide useful information for decision makers. The instrument has 70 m spatial resolution with 5 thermal spectral bands in the 8-12.5 μm range and an additional band at 1.6 um for geolocation and cloud detection. To minimize the electronic noise the focal plane is cooled by two commercial Thales cryocoolers. Two on board black bodies: one controlled between 16C to 24C and one controlled to 46C are used for calibration. The present study, carried out within the Early Adopter Program, aims to explore how ECOSTRESS data can provide, besides its primary mission, information on active fire that can complement fire characteristics derived by other programs such as Copernicus and Landsat. We examined La Drova wildfire, in Spain that ignited on 6 August 2018 and lasted 4 days. The fire was the result of 11separated fires and went rapidly out of control. 800 fire-fighters and soldiers and 30 helicopters and small aircraft were needed for the suppression while 2500 people were evacuated ECOSTRESS imagery was acquired on 8 August 2018 while the fire was still active. Sentinel 2 and Landsat 8 images acquired during the fire were cloudy. A pre- and post-fire cloud-free Sentinel 2 pair was used for NDVI and burn severity, and these were used for comparison with the ECOSTRESS image. Figure 1 (a) shows the ECOSTRESS image over La Drova fire processed by using band rationing tecnique. We adopted this tecnique to highlight clouds and active fire. Note that the burned area was clearly delineated as the fire is still active; unburned regions within the burn scar were identified with good agreement with vegetated (unburned) areas retrieved using high resolution NDVI (10m/px) derived from Sentinel 2 imagery acquired on 24 August 2018.