HASNet: A Foreground Association-Driven Siamese Network With Hard Sample Optimization for Remote Sensing Image Change Detection

Remote sensing change detection (RS-CD) relies on the model’s ability to learn features of marked change objects, known as foreground targets. Beyond foreground targets, the background targets are more valuable samples for change detection, such as unlabeled ones, semantically ambiguous ones, pseudo-changes, and non-interesting changes, referred to as hard case samples (HCSs) in this article. There are two additional challenges to learning HCSs: 1) the loss function focusing on the foreground targets with rich labels and ignoring the HCSs in the background, called the imbalance problem and 2) it is difficult for a model to learn the change information of HCSs directly, which is called HCSs missingness. This article proposed a foreground association-driven Siamese network with hard sample optimization (HASNet). To deal with the imbalance problem, we propose an equilibrium optimization loss (EO-loss) function to regulate the optimization focus of the foreground and background, determine the HCSs through the distribution of the loss values, and introduce dynamic weights in the loss term to gradually shift the optimization focus of the loss from the foreground to the background hard cases as the training progresses. To address the HCSs missingness, we propose the scene-foreground association module by using potential remote sensing spatial scene information to model the association between the target of interest in the foreground and the related context to obtain scene embedding to reinforce the feature of hard cases. Experiments on four public datasets with 11 baselines show that HASNet outperforms current state-of-the-art CD methods, particularly in detecting HCSs. The source code is available at https://github.com/GeoX-Lab/HASNet.