Magnetic fields are omnipresent in the Milky Way and play a crucial role in many physical processes in the interstellar medium (ISM). In order to study the interplay between the magnetic fields and the interstellar matter, the diffuse polarised synchrotron emission is one of the best tracer. Being present almost everywhere in the Galaxy, it is a powerful tracer of the magnetised turbulent non-thermal medium over a broad range of spatial scales. However to interpret the structures in such polarised emission data, we need robust analysing techniques. Stokes parameters Q and U are not invariant under arbitrary translations and rotations and choice of the local coordinate frame. Also, polarisation data are usually interpreted in terms of the amplitude or the angle of the polarisation vector separately, which leads to an incomplete analysis of the magnetic field power spectrum in the ISM.

In this presentation, I will talk about new wavelet methods that can be applied on polarisation data in order to interpret the spatial fluctuations of the Galactic magnetic field. Wavelet based formalisms allowed us recently to develop a multi-scale analysis of the gradient of linear polarisation. This technique gives us access to a unique view of the Galactic magnetic field fluctuations at different angular scales. I will also talk about the possibility of producing rotation measure (RM) maps using wavelet algorithms on multifrequency data.