Ground Surface Temperature (GST) is defined as the near-surface temperature of the ground (bedrock or surficial deposits), measured in the uppermost centimeters of the ground. GST is not a direct proof of permafrost existence but a proxy for estimating potential permafrost presence or absence in the subsurface and can be used for calibrating and validating numerical models. GST has to be distinguished from the Bottom Temperature of Snow cover (BTS), which is the temperature measured at the snow/ground interface in late winter. The APD does not collect raw GST data but the Mean Annual Ground Surface Temperature (MAGST) of a certain depth.

GM are punctual evidence of potential presence or absence of permafrost derived from geophysical methods. Electrical Resistivity/Impedance Tomography (ERT/EIT), Ground Penetrating Radar (GPR) or Seismic Refraction (SR) are suitable methods for the indirect detection of permafrost.

Temperature measured in boreholes (BH) is the most reliable evidence of permafrost presence or absence. BH data provides min/max/mean subsurface temperature at differing depth, maximum active layer thickness (ALT) and (if available) the depth of zero annual amplitude (ZAA). The APD does not collects raw borehole data but yearly synthesis data.

Other indirect permafrost evidence (OIE) such as patterned ground (features produced by the repeated annual freezing and thawing of the active layer in permafrost soils) or thermokarst depressions.

The presence of massive ice-lenses in periglacial areas can be a direct proof of permafrost occurrence. Such evidence from trenches or construction sites in high-mountain areas can provide useful information. Massive ice can also be observed in rockfall scars and can represents evidence of permafrost.

The Alpine Permafrost Data (APD) is an on-line service for collecting and sharing permafrost data, or permafrost evidence, in the European Alps. The permafrost evidence is a direct or indirect proof of the presence or absence of permafrost in a specific location obtained by field measures or observations. The Alpine Permafrsot Database (APD) collects Rock Glacier Inventories and the following Permafrost evidence: - Boreholes Temperature (BH) - Ground Surface Temperature (GST) - Surface Movement in periglacial areas (SM) - Results of Geophysical Prospecting - Perennial-ice in rock-fall scars, trenches or construction sites - Other indirect permafrost evidence