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Workshop at the Conference on Computer Vision and |
Pattern Recognition to benchmark automated computer vision |
capabilities for localizing and scoring the degree of damage |
to buildings after natural disasters [3]. In this challenge, |
participants had to train their model offline and upload |
their predictions for evaluation and display on the public |
leaderboard based on a single unlabeled test dataset, which |
they could download. While this challenge provided a great |
opportunity for AI researchers to weigh in on damage |
assessment tasks, it assumed no constraints on the level of |
computational resources available to participants for model |
training and did not strictly prevent the potential hand-labeling |
and use of the test datasets in the training phase. The winning |
solutions used large ensembles of models, and although they |
perform well on the test set, they were not optimized for |
inference runtime and require a prohibitively large amount |
of compute resources to be run on large amounts of satellite |
imagery on demand during disaster events. For example, the |
first-place winner proposed an ensemble of four different |
models, requiring 24 inference passes for each input. |
In this study, we propose a single model which predicts |
both building edges and damage levels and that can be run |
efficiently on large amounts of input imagery. The proposed |
multitask model includes a building segmentation module |
and a damage classification module. We use a similar model |
architecture proposed by previous studies on building damage |
assessment [4], [5]; however, we use a simpler encoder and do |
not include attention layers. We evaluate the performance of |
our model extensively for several different splits of the dataset |
to assess its robustness to unseen disaster scenarios. From an |
operational perspective, the model’s runtime is of paramount |
importance. Thus, we benchmark the inference speed of our |
model against the winning solutions in the xView2 competition |
and the existing models deployed by our stakeholder. We show |
that our model works three times faster than the fastest xView2 |
challenge winning solution and over 50 times faster than the |
slowest first place solution. The baseline solution available to |
our stakeholder consists of two separate models for building |
segmentation and damage classification [6]. We were able to |
show that our proposed approach works 20% faster than the |
baseline model available to the stakeholder and also conducts |
the task in an end-to-end and more automated way, which can |
improve their field operations and deployment. |
Finally, we develop a web-based visualizer that can display |
the before and after imagery along with the model’s building |
damage predictions on a custom map. This is an important |
step in deploying a model for real-world use cases. Even |
a perfect building damage assessment model will not be |
practically useful if there is not a mechanism for running |
that model on new imagery and communicating the results |
to decision-makers that are responding to live events. A web- |
based visualizer allows anyone to see both the imagery and |
predictions without GIS software for any type of disaster. |
II. R ELATED WORK |
Convolutional neural networks (CNN) have been used |
for change detection tasks in satellite imagery for disaster |
response and other domains including but not limited to |
changes in infrastructures. [7] proposed using pre-trained |
CNN features extracted through different convolutional layers |
and concatenation of feature maps for pre- and post-event |
images. The authors used pixel-wise Euclidean distance |
to compute change maps and thresholding methods to |
conduct classification. [8] leverages hurricane Harvey data, in |
particular, to train CNNs to classify images as damaged and |
undamaged. While they report very high accuracy numbers, |
they did not focus on detecting building edges and used a |
binary damage scale at the image-frame level. A Siamese |
CNN approach was proposed in [9] to extract features directly |
from the images, pixel by pixel. To reduce the influence of |
imbalance between changed and unchanged pixels, the authors |
used weighted contrastive loss. The unique property of the |
extracted features was that the feature vectors associated with |
changed pixel pairs were far away from each other in the |
feature space, whereas the ones of unchanged pixel pairs |
were close. Fully convolutional Siamese networks for changedetection were introduced in [4] and were proposed by other |
studies as well [10], [11]. |
In [4], convolutional Siamese networks are trained end-to- |
end from scratch using only the available change detection |
datasets. The authors proposed fully convolutional encoder- |
decoder networks that use the skip connection concept. |
[12] presented an improved UNet++ model with dense skip |
connections to learn multiscale and different semantic levels |
of visual feature representations. Attention layers have been |
proposed for general change detection networks [13] as well |
as building damage assessment tasks as presented in [5]. Also, |
[14] proposes an attention-based two-stream high-resolution |
network to unify the building localization and classification |
tasks into an end-to-end model via replacing the residual |
blocks in HRNet [15] with attention-based residual blocks |
to improve the model’s performance. RescueNet, an end- |
to-end model that handles both segmentation and damage |
classification tasks was proposed in [16]. It was trained using |
a localization aware loss function, that consists of a binary |
cross-entropy loss and dice loss for building segmentation and |
a foreground-only selective categorical cross-entropy loss for |
damage classification. [6] explored the applicability of CNN- |
based models under scenarios similar to operational emergency |
conditions with unseen data and the existence of time |
constraints. [17] proposed a dual-task Siamese transformer |
model to capture non-local features. Their model adopts |
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