A field survey of late‐summer depths to frozen ground within 1.5 m of ground surface was performed in July and August of 1994, in support of the Cryospheric System programme of the Earth Observing System. This project's stratified sampling technique was devised to be a simple and efficient means to sample a very large number of sites over two areas of interest, within a relatively short period. The successful completion of the 1994 field season resulted in the compilation of a large and representative dataset of depths to frozen ground near Mayo, Yukon Territory. The survey suggests that most late‐summer depths to frozen ground cluster within a narrow depth range in the main study area, while a much smaller proportion of this study area's dataset extends deeper to the 1.5 m depth limit of this study. Furthermore, the results of the survey suggest that considerable differences can exist between closely spaced study areas with regard to predominant depths to frozen ground, as well as relations between surface variables and depths to frozen ground. This implies that computer‐based models designed to map active layer thicknesses through correlation with landcover and topographic imagery must be supported by field measurements made in all areas being mapped. The extrapolation of correlations measured between active layer conditions and surface variables from one study area to an unsurveyed study area cannot be assumed to be valid. The mapping of active layer thickness over large regions (e.g. central Yukon) will therefore require a considerable field effort if reliable correlative mapping products are to be generated.
- active layer