Permafrost

increased emissivity; (2) the negative spectral gradient ( ∆T ∆ f < 0 ) was due to the volume
scatter darkening.
The decision tree was set up based on the sample analysis and statistics. The key
classification filters were the Scatter Index (SI) and the 37V GHz brightness temperature with
vertical polarization. The SI was used to distinguish the stronger scatter and the weak one. And
the 37V was used to distinguish the cold scatter and the warm one due to the highly correlation
between 37V and the surface temperature. In order to improve the accuracy of classification,
the other filters were introduced to identify the desert, the precipitation or the cloud which has
the similar negative spectral gradient as the frozen soil.
The soil temperature data at 4cm depth from GEWEX/Game-Tibet CEOP 2002
representing the ground truth were used to validate the decision tree. The result shows that the
total accuracy of the classification can be more than 90%.
192
Frozen
YES
37V30
NO
SI>=5
YES Desert
165+0.49*85V