function get_zr_rain,dbz,a,b,max_dbz=max_dbz
;
; *** First, calculate a nominal maximum rain rate using
; *** max_dbz dB as maximum reasonable reflectivity
;
    if(NOT KEYWORD_SET(max_dbz)) then max_dbz = 55

    x_max = 0.1D*(max_dbz - 10*alog10(a))/b
    rr_max = 10^(x_max)
    if(dbz ge max_dbz) then begin
        rr = rr_max
        return,rr
    endif
;
; *** Now calculate the rain rate from the pass dBZ value
;
    x1 = 0.1D*(dbz - 10*alog10(a))/b
    rr = 10^(x1)

    return,rr
    end