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Remote Sens. 2017, 9(8), 764; doi:10.3390/rs9080764

A Simple Normalized Difference Approach to Burnt Area Mapping Using Multi-Polarisation C-Band SAR

1
CSIR Meraka Institute, Pretoria 0001, South Africa
2
Department of Geography & Environmental Studies, Stellenbosch University, Stellenbosch 7600, South Africa
*
Author to whom correspondence should be addressed.
Academic Editors: Quazi K. Hassan, George P. Petropoulos, Ioannis Gitas and Prasad S. Thenkabail
Received: 12 June 2017 / Revised: 7 July 2017 / Accepted: 19 July 2017 / Published: 31 July 2017
(This article belongs to the Special Issue Remote Sensing of Wildfire)
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Abstract

In fire-prone ecosystems, periodic fires are vital for ecosystem functioning. Fire managers seek to promote the optimal fire regime by managing fire season and frequency requiring detailed information on the extent and date of previous burns. This paper investigates a Normalised Difference α-Angle (NDαI) approach to burn-scar mapping using C-band data. Polarimetric decompositions are used to derive α-angles from pre-burn and post-burn scenes and NDαI is calculated to identify decreases in vegetation between the scenes. The technique was tested in an area affected by a wildfire in January 2016 in the Western Cape, South Africa. The quad-pol H-A-α decomposition was applied to RADARSAT-2 data and the dual-pol H-α decomposition was applied to Sentinel-1A data. The NDαI results were compared to a burn scar extracted from Sentinel-2A data. High overall accuracies of 97.4% (Kappa = 0.72) and 94.8% (Kappa = 0.57) were obtained for RADARSAT-2 and Sentinel-1A, respectively. However, large omission errors were found and correlated strongly with areas of high local incidence angle for both datasets. The combined use of data from different orbits will likely reduce these errors. Furthermore, commission errors were observed, most notably on Sentinel-1A results. These errors may be due to the inability of the dual-pol H-α decomposition to effectively distinguish between scattering mechanisms. Despite these errors, the results revealed that burnt areas could be extracted and were in good agreement with the results from Sentinel-2A. Therefore, the approach can be considered in areas where persistent cloud cover or smoke prevents the extraction of burnt area information using conventional multispectral approaches. View Full-Text
Keywords: burnt area; synthetic aperture radar (SAR); polarimetric decomposition; Sentinel-1; RADARSAT-2 burnt area; synthetic aperture radar (SAR); polarimetric decomposition; Sentinel-1; RADARSAT-2
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Engelbrecht, J.; Theron, A.; Vhengani, L.; Kemp, J. A Simple Normalized Difference Approach to Burnt Area Mapping Using Multi-Polarisation C-Band SAR. Remote Sens. 2017, 9, 764.

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