;+
;PROCEDURE: plastic_check_doy
;PURPOSE: If doy is negative, go back a year.
;
;INPUT
;PARAMETERS:  ratio_doy : doy that we will use for looking up ratios
;             ratio_year: year that we will use for looking up ratios
;
;OUTPUT
;PARAMETERS:  ratio_doy : doy that we will use for looking up ratios
;             ratio_year: year that we will use for looking up ratios
;
;CREATED BY: L. Ellis
;
;LAST MODIFICATION: 09/24/2007
;
;MODIFICATION HISTORY:
;    09/24/2007 Created
;    01/02/2008 Bill Thompson fixed bug.
;-

PRO plastic_check_doy, ratio_year, ratio_doy

IF ratio_doy LT 1 THEN BEGIN
    ratio_year = ratio_year - 1
    SWITCH ratio_year OF 
        2004:
        2008:
        2012:
        2016: BEGIN
            ratio_doy = ratio_doy + 366
            BREAK
        END
        ELSE: ratio_doy = ratio_doy + 365
    ENDSWITCH 
ENDIF 

END