Seasonal soil active layer measurements from a Circumpolar Active Layer monitoring (CALM) grid, R55a Bely island, West Siberia 2009-2020

The Circumpolar Active Layer Monitoring (CALM) program represents the only coordinated program providing collection, standardization, open access, and dissemination of active-layer data world-wide. Widespread, systematic changes in the thickness of the active layer could have profound effects on the flux of greenhouse gases, on the human infrastructure in cold regions, and on landscape and hydrologic processes. It is therefore critical that observational and analytical procedures continue over decadal periods to assess trends and detect cumulative, long-term changes. This dataset contains active-layer observations conducted by the CALM program since the 1990s, supported by a series of National Science Foundation (NSF) awards. CALM program is an integral part of the Global Terrestrial Network for Permafrost.
CALM 2020 data are significantly reduced due to pandemic-related travel restrictions. Available 2020 data are limited in terms of extent, and observations were not as controlled as previous years in terms of measurement timing or method, and therefore should be treated with caution.

环极活动层监测（Circumpolar Active Layer Monitoring, CALM）计划是全球范围内唯一一套可开展活动层数据采集、标准化处理、开放获取与传播的协同性项目。活动层厚度出现广泛且系统性的变化，可能会对温室气体通量、寒区人类基础设施以及景观与水文过程造成深远影响。因此，长期开展观测与分析工作以评估变化趋势、检测累积性长期变化至关重要。本数据集收录了自20世纪90年代以来由CALM计划实施的活动层观测数据，相关工作得到了美国国家科学基金会（National Science Foundation, NSF）多项资助项目的支持。CALM计划是全球多年冻土陆地网络（Global Terrestrial Network for Permafrost）的核心组成部分。
受疫情相关旅行限制影响，2020年的CALM数据量大幅缩减。2020年可获取的数据在覆盖范围上存在局限，且观测在测量时序与方法上均未如往年那般严格受控，因此使用该年度数据时需谨慎对待。