pro sxig12_ngdc2cat, time0, time1
 
ngdctop='http://sxi2.ngdc.noaa.gov/archive/fits/'

if n_elements(time0) eq 0 then time0='1-sep-2001'
if n_elements(time1) eq 0 then time1='1-jan-2002'

dgrid=timegrid(time0,time1,/day,out='ecs',/date)
months=strmid(dgrid,6,2)                          ; monthly cat cadence
umonths=uniq(months) 

dailyurls=concat_dir(ngdctop,dgrid)

for i=0,n_elements(umonths)-1 do begin            ; for each month
   ss=where(months eq months(umonths(i)),dcnt)    ; days(urls) / month
   for d=0,dcnt-1 do begin                        ; for each day