function QS=incident_sw_ratio_plain(a,mu,ga,flag_model,ar,rr)

if flag_model == 1
        QS = (1-mu).*(1-ga) ./ (1-(1-ar.*mu).*a.*rr.*ga);
elseif flag_model == 2
        QS = (1-mu-ga) ./ (1-a.*rr.*ga);
end

end
