X-ray imaging spectroscopy of Supernova remnants (SNRs) enables us to estimate the
abundances and spatial distribution of heavy elements synthesized by the progenitors.
This information provides us with many insights into the evolution process and explosion
mechanism of the progenitors.  Recent studies have revealed that the formation process,
ionization state, and X-ray emission process of SNRs are more complex than that expected
by the conventional picture.  For example, recent studies point out the importance of
charge exchange (CX) and resonance scattering (RS) in SNRs.  Since signs of the RS or CX
are expected to be found in intensity ratios of multiplet lines (e.g., OVII He alpha), which
cannot be resolved with widely-used detectors such as CCDs, it is difficult to obtain
the observational evidence for CX or RS. These processes apparently reduce or enhance
intensities of some lines, ignoring its contribution can sometimes lead to, for example,
biases in elemental abundance measurements. On the other hand, if we can quantify the
effects of these processes, we can obtain several important information such as
micro-turbulence velocities and 3D structure of SNRs.

We perform a high-resolution X-ray spectroscopy of N49, J0453.6-6829 and 1E 0102-72.9
with the RGS onboard XMM-Newton. RGS spectra of N49, J0453.6-6829 show a high resonance
to forbidden ratio of O VII Heα lines, which cannot be explained by the emission from a
thin thermal plasma. From information on the surrounding gas and other X-ray emission
line ratios, we found that the cause of this anomalous line ratios are likely due to CX
and RS. Based on our results and previous studies, we summarize the physical conditions
in which CX and/or RS efficiently take place. Using high statistical RGS data of 1E
0102-72.9, we present a method to constrain the 3D structure of SNRs by measuring their
line-of-sight length through the effects of RS. These results are useful for future high
resolution X-ray spectroscopy with XRISM.