# PerSys - Permafrost Extent and Properties PEX

Permafrost is defined through the thermal state of the ground which makes remote detection a difficult task. In the GlobPermafrost project a numerical permafrost model is used to map circumpolar permafrost extent. The product is based on remotely sensed land surface temperatures from MODIS and ERA reanalysis products from which mean annual ground temperatures can be derived at a spatial resolution of 1 km at continental scales. The calculations are based on a TTOP (temperature at the top of permafrost) model with input parameters derived from GlobSnow and CCI Landcover datasets. A statistical approach allows to estimate the probability of permafrost occurrence within a grid cell so that each grid cell can be classified as continuous, discontinuous and sporadic permafrost. The performance of the method is benchmarked by comparison with in-situ measurements of ground temperatures in boreholes contained in the “Thermal State of Permafrost” database and shows an approximate accuracy of 2.5°C.