In this article, the concept of polarization is introduced and the polarization description is detailed as an introduction. Then we describe the present status of planet's polarimetry. The main results from the polarimetric study of the earth's surface features are given. Finally we focused on the polarization characteristics of the earth as an exoplanet. Compared with other probing techniques, the planetary polarimetry becomes more efficient to diagnose the details about the surface features of the exoplanet, and thus the polarimetry of our planet, the earth, is useful to search for the earth-like exoplanet. In this treatise, the earth is treated as a planet resolvable from its father star but its disk is unresolved. The data from polarimeter boarding French satellite PARASOL is used to get the polarimetric results of 5 surface features as well as clouds within the band 662.4nm~677.4nm. The results are expressed in the curves which reflect the variations of linear polarization degrees with the scattering angles and position angles respectively. Under the special case that the scattering angle is set to be 90 degrees, the polarization curves of the earth’s spin is obtained. It is found that the polarization degree is mainly influenced by the ocean as well as the cloud between 18.6% and 49%.And due to the rapid climate change on the earth, the polarization is altered correspondingly and rapidly. This character will help us to distinguish the earth-like exoplanet from other types of exoplanets.
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