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Sentinel-1 observation frequency significantly increases burnt area detectability in tropical SE Asia

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journal contribution
posted on 19.05.2020, 11:33 by Joao MB Carreiras, Shaun Quegan, Kevin Tansey, Susan Page
Frequent cloud cover in the tropics significantly affects the observation of the surface by satellites. This has enormous implications for current approaches that estimate greenhouse gas (GHG) emissions from fires or map fire scars. These mainly employ data acquired in the visible to middle infrared bands to map fire scars or thermal data to estimate fire radiative power and consequently derive emissions. The analysis here instead explores the use of microwave data from the operational Sentinel-1A (S-1A) in dual-polarisation mode (VV and VH) acquired over Central Kalimantan during the 2015 fire season. Burnt areas were mapped in three consecutive periods between August and October 2015 using the random forests machine learning algorithm. In each mapping period, the omission and commission errors of the unburnt class were always below 3%, while the omission and commission errors of the burnt class were below 20% and 5% respectively. Summing the detections from the three periods gave a total burnt area of ~1.6 million ha, but this dropped to ~1.2 million ha if using only a pair of pre- and post-fire season S-1A images. Hence the ability of Sentinel-1 to make frequent observations significantly increases fire scar detection. Comparison with burnt area estimates from the Moderate Resolution Imaging Spectroradiometer (MODIS) burnt area product at 5 km scale showed poor agreement, with consistently much lower estimates produced by the MODIS data-on average 14%–51% of those obtained in this study. The method presented in this study offers a way to reduce the substantial errors likely to occur in optical-based estimates of GHG emissions from fires in tropical areas affected by substantial cloud cover.

Funding

The re-projected monthly GeoTIFF version of the MODIS MCD64A1 burnt area product was made available by the University of Maryland. The daily MODIS MCD14ML active fire product was produced by the University of Maryland and provided by NASA FIRMS operated by NASA/GSFC/ESDIS with funding provided by NASA/HQ. The daily Terra MODIS MOD06_L2 fractional cloud cover product was downloaded from NASA's Level-1 and Atmosphere Archive & Distribution System (LAADS) Distributed Active Archive Center (DAAC). We acknowledge and thank ESA CCI Fire for providing access to a burnt area map of Kalimantan. JMBC and SQ were supported by the Natural Environment Research Council (Agreement PR140015 between NERC and the National Centre for Earth Observation).

History

Citation

Joao M B Carreiras et al 2020 Environ. Res. Lett. 15 054008

Version

VoR (Version of Record)

Published in

Environmental Research Letters

Volume

15

Issue

5

Pagination

054008

Publisher

IOP Publishing

eissn

1748-9326

Acceptance date

18/02/2020

Copyright date

2020

Available date

18/02/2020

Publisher version

https://iopscience.iop.org/article/10.1088/1748-9326/ab7765/meta

Spatial coverage

Tropical SE Asia

Temporal coverage: start date

01/08/2015

Temporal coverage: end date

31/10/2015

Language

en