get xarray dataset file handle to LSM files

def xd(self):
        """get xarray dataset file handle to LSM files"""
        if self._xd is None:
            path_to_lsm_files = path.join(self.lsm_input_folder_path,
                                          self.lsm_search_card)
            self._xd = super(NWMtoGSSHA, self).xd
            self._xd.lsm.coords_projected = True
        return self._xd