## 3 Results
### Assessment of the Correct Time of Disturbance  
The evaluation of the correct time of CCDC-detection of disturbance occurrence from the ensemble VI approach showed larger uncertainties in days for events of savanna clearing than for events caused by fire. This fact was indicated in Figure 8 by the lower data dispersion around the zero-day line recorded for fire disturbance detection (Figure 8b) when compared to clearing detection (Figure 8a). Disturbance by fire comprised more abrupt events than savanna clearing, which usually includes gradual processes of degradation before the complete removal of vegetation cover. The degradation process produces uncertainties in establishing the exact date of vegetation suppression. On the other hand, clearing events are more detectable than disturbance by fire because of the predominant period of their occurrence in the beginning and middle of the dry season. The great availability of cloud-free images in this period favors the detection of three consecutive observations of clearing change by the CCDC algorithm, which does not occur for fire. Using single VIs in the data analysis, results were approximately similar to those observed with the ensemble approach.  
The availability of clear observations in the images of the study area was variable over space and time. The greatest difficulties of tracking over time such disturbance events were noted during the rainy season, when the frequency of satellite observations decreased due to cloud cover and related shadows. For instance, the average number of Landsat clear observations per pixel reached its maximum value in the dry season between July and August (Figure 9). Therefore, the assessment of the correct time of disturbance occurrence detected by the CCDC was biased to some extent by the dry season period. Moreover, disturbances that occurred in areas with a low number of clear observations can be detected with greater delay when compared to the real date of its occurrence.  
Figure 7: CCDC performance of each vegetation index (VI) and ensemble VIs to correctly detect disturbance over areas affected by fire (\(n=147\) samples) and savanna clearing (\(n=147\) samples).  
From the set of reference samples detected as disturbance by CCDC, 74% of them matched \(\pm\)5 days of the occurrence of fire. Considering the most favorable period of imagery (dry season), when the combination of sensors can generate up to four monthly observations (Figure 9), this difference in days is likely non-statistically significant. It is lower than the 8-day spaced interval of data acquisition in the dry season. For clearing, 70% of the reference samples matched \(\pm\)30 days of the occurrence of the events. As mentioned before for savanna clearing, early detection by the CCDC was generally associated with processes of vegetation degradation preceding the complete removal of vegetation.  
Figure 8: Time accuracy of CCDC-detection over (**a**) cleared- and (**b**) burned-savanna areas. Negative values indicate early detection compared to the reference, while positive values indicate late detection. Values close to zero represent timely detection. In both figures, samples with a large number of days were omitted for better graphical representation.