Time-series anomaly detection deals with the problem of detecting anomalous
timesteps by learning normality from the sequence of observations. However, the
concept of normality evolves over time, leading to a "new normal problem",
where the distribution of normality can be changed due to the distribution
shifts between training and test data. This paper highlights the prevalence of
the new normal problem in unsupervised time-series anomaly detection studies.
To tackle this issue, we propose a simple yet effective test-time adaptation
strategy based on trend estimation and a self-supervised approach to learning
new normalities during inference. Extensive experiments on real-world
benchmarks demonstrate that incorporating the proposed strategy into the
anomaly detector consistently improves the model's performance compared to the
baselines, leading to robustness to the distribution shifts.

针对非监督时间序列异常检测研究中的 ' 新常态问题 '，本文提出了一种基于趋势估计和自监督方法的简单而有效的测试时间适应策略，通过在推理过程中学习新的常态性，从而提高异常检测器的性能并增强对分布变化的鲁棒性。