def get_albedo_data(self, interval='season'):
        """
        calculate albedo as ratio of upward and downwelling fluxes
        first the monthly mean fluxes are used to calculate the albedo,

        This routine uses the definitions of the routines how to
        read upward and downward fluxes
        """

        if self.start_time is None:
            raise ValueError('Start time needs to be specified')
        if self.stop_time is None:
            raise ValueError('Stop time needs to be specified')

        #~ tmpdict = copy.deepcopy(kwargs)
        #~ print self.dic_vars

        routine_up = self.dic_vars['surface_upward_flux']
        routine_down = self.dic_vars['sis']

        #sw_down = self.get_surface_shortwave_radiation_down(interval=interval, **kwargs)
        cmd = 'sw_down = self.' + routine_down
        exec(cmd)

        #sw_up = self.get_surface_shortwave_radiation_up(interval=interval, **kwargs)
        cmd = 'sw_up = self.' + routine_up
        exec(cmd)

        # climatological mean
        alb = sw_up[0].div(sw_down[0])
        alb.label = self.experiment + ' albedo'
        alb.unit = '-'

        # original data
        alb_org = sw_up[1][2].div(sw_down[1][2])
        alb_org.label = self.experiment + ' albedo'
        alb_org.unit = '-'

        retval = (alb_org.time, alb_org.fldmean(), alb_org)

        return alb, retval