FlameFinder: Illuminating Obscured Fire through Smoke with Attentive
  Deep Metric Learning
Hossein Rajoli Sahand Khoshdel Fatemeh Afghah Xiaolong Ma
FlameFinder is a deep metric learning (DML) framework designed to accurately
detect flames, even when obscured by smoke, using thermal images from
firefighter drones during wildfire monitoring. Traditional RGB cameras struggle
in such conditions, but thermal cameras can capture smoke-obscured flame
features. However, they lack absolute thermal reference points, leading to
false positives.To address this issue, FlameFinder utilizes paired thermal-RGB
images for training. By learning latent flame features from smoke-free samples,
the model becomes less biased towards relative thermal gradients. In testing,
it identifies flames in smoky patches by analyzing their equivalent
thermal-domain distribution. This method improves performance using both
supervised and distance-based clustering metrics.The framework incorporates a
flame segmentation method and a DML-aided detection framework. This includes
utilizing center loss (CL), triplet center loss (TCL), and triplet cosine
center loss (TCCL) to identify optimal cluster representatives for
classification. However, the dominance of center loss over the other losses
leads to the model missing features sensitive to them. To address this
limitation, an attention mechanism is proposed. This mechanism allows for
non-uniform feature contribution, amplifying the critical role of cosine and
triplet loss in the DML framework. Additionally, it improves interpretability,
class discrimination, and decreases intra-class variance. As a result, the
proposed model surpasses the baseline by 4.4% in the FLAME2 dataset and 7% in
the FLAME3 dataset for unobscured flame detection accuracy. Moreover, it
demonstrates enhanced class separation in obscured scenarios compared to VGG19,
ResNet18, and three backbone models tailored for flame detection.