## Materials and Methods
### Burnt Areas Detection  
Burnt area mapping is carried out using S1 and S2 datasets independently and all pixels detected as burnt will be combined into a map composite. Independent burnt area maps will be generated from the images acquired respectively by the sensors on S1 and S2 during the period of the 1 November 2015 to the 30 April 2016 for S1 and the 3 December 2015 to the 21 May 2016 for S2. The maps will then be combined at a 20-m resolution. Three different scenarios are foreseen when generating the map composite: (i) a pixel is detected as burnt in either S1 or S2 maps; (ii) both S1 and S2 detected a pixel as burnt; and (iii) neither S1 nor S2 detect a pixel as burnt. The different results are presented and discussed but the final goal is to combine S2-based and S1-based maps to take advantage of the sensors complementarity. The S1 and S2 images are processed using the Google Earth Engine cloud environmental analysis platform. A field visit to one of the sites was carried out in May 2016, noting the damage to trees and the regrowth of the burned herbaceous vegetation. Sentinel 2  
The S2-A satellite was successfully launched on the 23 June 2015, as part of the European Copernicus program (European Commission funding, ESA implementation) and the first images were delivered four days later [42]. S2 satellites carry an innovative wide-swath, high-resolution Multi Spectral Instrument with 13 spectral bands spanning from the visible and the near infrared to the short wave infrared. The spatial resolution varies from 10 m to 60 m depending on the spectral band. The swath is 290 km. The temporal resolution of the S2-A satellite is 10 days. A revisit period of five-days at the equator will be ensured when the S2-B twin satellite becomes operational [43]. Over the study area, a time series of fifteen Level 1C (Top of Atmosphere reflectance) S2 images is available from the 3 December 2015 to the 21 May 2016. These show the progression of the firesin the area (Figure 2). A gap in the 10-day temporal acquisition occurred during two weeks (from the 21 February to 2 March 2016) due to an anomaly in the ground segment production chain. This anomaly affects the radiometric quality of the S2 L1C products. The Level 1C S2 images are contaminated with cloud and aerosols which need to be masked out before further processing. No robust cloud masking for S2 was available at the time of processing. Together with the Level 1C product, ESA provides a quality band (QA60) masking cloud and cirrus. However, a visual check revealed that this quality band does not give sufficiently reliable results for the study area. A cloud mask therefore is based on band 1 (sensitive to aerosols), the blue band 2 (sensitive to atmospheric contaminations), the near infrared band 8A and the short-wave infrared band 11. Thresholds are defined on the combination of these bands to eliminate clouds and cloud shadows from the S2 images. The detection of burnt areas is based on the difference of two vegetation indices computed on the 10-days time series of S2 cloud-free images and a pre-fire baseline value. The first step of the burnt area detection is a baseline cloud free mosaic which is built taking the median value of the first four images (3 and 23 December 2015, 1 and 12 January 2016). In the second step, the acquisitions from the 12 January 2016 to the 21 May 2016 are compared to the baseline mosaic to determine the precise timing and location of the fire events. Burnt areas are identified according to the difference in the value of two vegetation indices between each date and the base mosaic. Both the Normalized Difference Water Index (NDWI; also known as the Normalized Difference Moisture Index, NDMI) [44; 45] and the Normalized Difference Vegetation Index (NDVI) [46] are used to detect burnt areas on the S2 images. The NDWI is calculated according to the formula of Gao [44] and adapted to S2, using the NIR band 8 (842 nm) and the SWIR band 11 (1610 nm). The use of the band 11 constrains the spatial resolution of the product to 20 meters.