# The DLR FireBIRD Small Satellite Mission: Evaluation of Infrared Data for Wildfire Assessment
## 3 Results and Discussion
It is important to note that these results are obtained by considering each individual data point contained within the complete set of overpasses, instead of averaging the overpass mean values. To assess the influence of the time lag between FireBIRD and the respective reference satellite, the concluding analysis is performed twice: Once considering only the FireBIRD overpasses with a time lag to the reference overpass of less than 45 min, yielding a subset of five overpasses. In a second step, the analysis is also conducted for the complete dataset, covering all 14 overpasses. This second run also takes data into account which shows a significant temporal difference between FireBIRD and the respective reference satellite. The result is thus less expressive. The results are separated by reference sensor. For each category, the upper row shows the results regarding MODIS, the lower one refers to VIIRS. All values are given in fractions (the result obtained with FireBIRD divided by the reference result). The fire grid cells of the FireBIRD data which correspond to the reference is given in the first line, named true positives (TP). FireBIRD shows a spatial correspondence of 83% and 84% compared to MODIS and VIIRS, respectively, in case the MWIR method is used, and the analysis is performed on the dataset with similar acquisition time. When the complete dataset is analyzed, which shows time lags of up to 12 h, these numbers decrease to 75% and 54% regarding MODIS and VIIRS, respectively. The MWIR/LWIR method yields slightly fewer corresponding results for both datasets regarding MODIS. For VIIRS, the results show an identical correspondence for both methods regarding the subset, and a slight superiority of the MWIR method regarding the complete dataset. The false negatives (FN), given in the next line of the table, indicate how much actual fires were missed, according to the reference. The MWIR method shows rates of 17% and  
Figure 3: FireBIRD active fire data (derived using the MWIR method) and reference data for a fire event in northern Portugal, August 2016. (**a**) shows active fires derived from four FireBIRD/HSRS overpasses (11–14 August 2016), pigmented by FRP. (**b**) shows MODIS active fire data of the Aqua/Terra overpasses in closest temporal vicinity to the respective FireBIRD overpasses. (**c**) shows VIIRS active fire data of the Suomi-NPP overpasses in closest temporal vicinity to the respective FireBIRD overpasses. Background: Stamen/OpenStreetMap shaded terrain map, shown in gray scale. 16% for the subset with a time lag of below 45 min, and 25% and 46% for the complete dataset. These values are complementary to the true positive values. The false positives (FP) indicate fire locations detected by FireBIRD, which are not included in the reference data. A ratio of 1.0 refers to a perfect match between both data sources, meaning that no false positives occur. Accordingly, a ratio of 1.5 indicates an overestimation of 50%. Regarding the subset, HSRS shows an overestimation according to MODIS of 124%, while the comparison with VIIRS shows 78% additional area (referring to the number of affected grid cells). When using the full dataset, HSRS detects an additional area of 192% and 117% when compared to the area detected by MODIS and VIIRS, respectively. This does not inherently mean that the additional FireBIRD detections are false, however. In fact, this number rather reflects the increased detection capabilities facilitated by the higher spatial resolution and radiometric sensitivity of the HSRS sensor. Therefore, the term additional positives would be more appropriate. Such a situation is clearly observable in Figure 7, when comparing the results by HSRS and MODIS. Since it cannot be stated whether the false positives and false negatives are caused by shortcomings either in the FireBIRD data or in the reference data, only true positives, referring to fire locations detected by both FireBIRD and the reference, are considered for the radiometric analysis.