This paper addresses radar time series acquired with two polarization channels, one copolar and the other contrapolar. We show that the Eigenvalue decomposition of the coherence-covariance matrix of the complex Jones vectors contains the same information as the Stokes vector that would have been obtained by integrating all measurements into a single Stokes intensity measurement. We use two main parameters of this equivalent Stokes vector: its degree of polarization and its principal orientation. We then proposed two polarimetric decompositions: the "Equivalent-Stokes" representation, totally independent of the total intensity, and the "Polarimetric with main orientation" representation. We test these decompositions on the (HH,HV) Tandem-X, and (VV,VH) Sentinel-one time series of the same area.