Abstract
This study establishes a new technique for peatland fire detection in tropical environments using Landsat-8 and Sentinel-2. The Tropical Peatland Combustion Algorithm (ToPeCAl) without longwave thermal infrared (TIR) (henceforth known as ToPeCAl-2) was tested on Landsat-8 Operational Land Imager (OLI) data and then applied to Sentinel-2 Multi Spectral Instrument (MSI) data. The research is aimed at establishing peatland fire information at higher spatial resolution and more frequent observation than from Landsat-8 data over Indonesia’s peatlands. ToPeCAl-2 applied to Sentinel-2 was assessed by comparing fires detected from the original ToPeCAl applied to Landsat-8 OLI/Thermal Infrared Sensor (TIRS) verified through comparison with ground truth data. An adjustment of ToPeCAl-2 was applied to minimise false positive errors by implementing pre-process masking for water and permanent bright objects and filtering ToPeCAl-2’s resultant detected fires by implementing contextual testing and cloud masking. Both ToPeCAl-2 with contextual test and ToPeCAl with cloud mask applied to Sentinel-2 provided high detection of unambiguous fire pixels (>95%) at 20 m spatial resolution. Smouldering pixels were less likely to be detected by ToPeCAl-2. The detected smouldering pixels from ToPeCAl-2 applied to Sentinel-2 with contextual testing and with cloud masking were only 35% and 56% correct, respectively; this needs further investigation and validation. These results demonstrate that even in the absence of TIR data, an adjusted ToPeCAl algorithm (ToPeCAl-2) can be applied to detect peatland fires at 20 m resolution with high accuracy especially for flaming. Overall, the implementation of ToPeCAl applied to cost-free and available Landsat-8 and Sentinel-2 data enables regular peatland fire monitoring in tropical environments at higher spatial resolution than other satellite-derived fire products.
Highlights
Tropical peatland is a significant source of global carbon [1,2]
Reflected solar energy in shortwave infrared (SWIR) may interfere with the detection of flaming at daytime, while the background temperature may affect the detection of cool fire in Longwave Infrared (LWIR) [55]
We found that NDWI can map water bodies well in clear atmospheric conditions, but for some images with many fires and smoky conditions, near infrared (NIR) does not perform well due to smoke aerosol scattering; MNDWI with SWIR wavelengths which are able to be better detected through smoke was used to map the water bodies
Summary
The state of tropical peatland is mainly disturbed by conversion of peatland forest to other uses, especially for plantations. Peatland drainage [3] and peatland fires [4] have contributed to accelerating atmospheric carbon increases. 2 of 37 fuels and consequential climate change [5,6]. Smouldering peatland fires burn organic soil and thick (e.g., decaying leaves, tree branches and trunks), which release more carbon and smoke with greater consequential climate change [5,6]. Smouldering peatland fires burn organic soil and thick fuels Drought, unmanaged drainage, and land use change decaying leaves, tree branches and trunks), which release more carbon and smoke with greater from particulate natural peatland habitatthan to agricultural/plantation areas have led to high flammability concentration flaming fires [7,8]. Drought, unmanaged drainage, and landconditions use of degraded peatlands [9–16]
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