| Summary: | Prior to development of the Circumpolar Active Layer Monitoring (CALM) programme, little attention was paid to formal spatial sampling designs for measuring active‐layer thickness (ALT). This omission made the accuracy of many data‐sets questionable, in part because spatial periodicities caused by landscape features such as ice‐wedge polygons and thaw lakes can significantly influence the depth of thaw. Early in the development of CALM's protocols, ALT was sampled in the continuous permafrost zone in northern Alaska and simulated by computer, to determine how ALT could be measured accurately. The simulated and field data‐sets were analysed by comparing the means, variances and frequency distributions obtained using four spatial sampling designs (random, systematic, systematic random and systematic stratified unaligned). By a small margin, systematic stratified unaligned sampling provided the most accurate results. Systematic designs can, however, provide adequate estimates of the statistical moments of ALT with significant savings in cost, time and ease of implementation. Based on these results, the CALM programme recommended use of 10 x 10, 100 x 100 or 1000 x 1000 m grids, with sampling intervals of 1, 10 and 100 m, respectively. Most probed CALM sites now employ this strategy, except in terrain with unusual landscape elements or other special constraints. Copyright © 2016 John Wiley & Sons, Ltd.
|
|---|