Temperatures

In addition to snow depth, air and ground temperatures are the most important data to be monitored. Due to the heterogeneity of the ground conditions often encountered in mountainous environments, it is recommended to measure air temperatures and ground temperatures at location with different elevations and slope aspects. Wide-ranging active layer thicknesses and ground surface temperatures help in outlining permafrost conditions. Changes in temperature gradients below the depth of the zero annual amplitude further provide valuable information about past climatic conditions and the geothermal phase the permafrost is in, i.e. long-term cooling, warming or steady state (Fig. 14). Generally, changes in the temperature gradients below the depth of zero annual amplitude are good indicators for past long-term temperature conditions. However, effects due to the mountainous topography as indicated above must be included in the interpretation of the borehole temperature data.

Temperature Gradient Soil
Figure 14. Effect of long-term surface temperature changes on the geothermal gradient. Warming periods result in temperatures below the depth of zero annual amplitude (ZAA) that are warmer than the deep temperature gradient would imply (red) and vice versa for long cooling periods (blue).

Ground temperatures at depth are to be measured within boreholes using thermistor strings. Close thermistor spacing at shallow depth is important to determine active layer thicknesses accurately. Temperatures should further be recorded at three to four locations below the permafrost base to obtain the local geothermal gradient, which is to be used in the geothermal model. Close thermistor spacing is also recommended at the permafrost base where thermal irregularities due to groundwater or air flow may occur (Vonder Muhll et al., 2003; Vonder Muhll et al., 1998). More information on installing thermistor strings can be found in Vonder Muhll et al. (2004).

Spatial distributions of the bottom temperature of the snow cover (BTS) allow further information about the permafrost distribution (Haeberli, 1973). Miniature temperature loggers (Hoelzle et al., 1999) are ideal for such temperature measurements and should be buried at 5cm depth. Interpretations of the ground temperatures are easier if the snow depth distribution is known for the site.

Infrared thermography is a useful tool when controlling insulation efficiency in buildings or the efficiency of active/passive cooling systems. Infrared cameras are widely available to date and any thermal anomalies can be visualised in real time.

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