## 5 Conclusions  
This paper demonstrates the potential for S2 and S1 data to detect and monitor fire outbreaks in forest ecosystems at finer temporal and spatial resolution than was previously possible. Burnt areas totalizing an area of 36,000 ha were detected in the north of the Republic of Congo thanks to the  
Figure 11: Regrowth of Marantaceae in an area affected by fire (photo taken on 29 May 2016).  
combined used of S1 and S2 time series. At its peak in early 2016, the fire was spreading at a rate of 1600 ha per day. Indications of the forthcoming event were in evidence in late December, both from the high detection of active fires in the region and the low SPI rainfall values.  
The fifteen S2 images analyzed from December 2015 to May 2016 represent the first time series of S2 data released over the study area and show a great potential for tropical forest monitoring applications. The burnt area maps derived from each S2 image are adding a precise spatial extent to the point location of the MODIS active fire product and provide a better documentation of the fire propagation in the Marantaceae forests. The two burnt areas maps derived from S1 bi-monthly composites provides a gap filling capacity (in case of cloud cover) and brings confidence to the S2 results, with over 60% concurrence between the two data sets.  
The arrival of the S1 and S2 satellites, soon supported by the Sentinel 3 SLSTR sensor with bands optimized for fire monitoring, can provide forest managers and national agencies with a rapid and accurate assessment of fire events. From the methodology proposed here, some points have to be addressed to move from a case study to an operational monitoring tool. The combination of the radar and optical information is robust in terms of burnt area detections but the respective S1 and S2 methodologies should evolve into algorithms that are independent from locally tuned thresholds.  
A review of climatic data and vegetation susceptibility to fire could also be employed to highlight anomalies which may lead to fire outbreaks and provide managers with an early warning of the possibility of such events. Of concern to all parties, forest managers, national agencies, etc., is the long-term perspective for these ecosystems which have been subjected to this exceptional fire event. Is this just a one-off event that in fact helps to maintain these open forests, or is this a precursor to more frequent revisits of fire events which may induce a change in the landscape of Central African forests and their future uses?  
The authors would like to thank [PERSON] from Interholco AG for his comments about the fire outbreak in the Ngombe logging concession. The authors would also like to thank the team from Interholco AG working in the Ngombe logging concession for the making a field visit possible.  
All authors contributed to the design of the experiment. The analyses with Sentinel 2 data were mainly conducted by [PERSON], the analyses with Sentinel 1 and climatic data by [PERSON], and the analysis of the MODIS active fires product as well as the processing of the Very High Resolution image by [PERSON] The Methodology and Results Sections of the manuscript were mainly written by [PERSON], [PERSON] and [PERSON]. The rest of the authors mainly contributed to the Discussion and Conclusion Sections.  
The authors declare no conflict of interest.