[ferret_users] defining common time axis for 2 datasets with different origin/end

[DELCLAUX Francois <delclaux@xxxxxxxxxxxxxxxxxxx>]

Hi Ferret users,

I would like to compare (bias and correlation maps) 2 monthly 
precipitation datasets.

The first one, D1, starts on 1rst january 1901 and ends on 1rst december 
2006, so 106 years and 1272 months: L varies from 1 to 1272
 01-JAN-1901 /    1:    60.
 31-JAN-1901 /    2:    10.
 03-MAR-1901 /    3:    31.
....
 01-OCT-2006 / 1270:    88.
 01-NOV-2006 / 1271:     9.
 01-DEC-2006 / 1272:    16.


The second one, D2, starts at 16 jan 1951 and ends at 16 december 2007, 
so 57 years and 684 values: L varies from 1 to 684
 16-JAN-1951 /   1:   21.4
 15-FEB-1951 /   2:    3.3
 18-MAR-1951 /   3:    7.0
...
 16-OCT-2007 / 682:   42.4
 16-NOV-2007 / 683:    2.3
 16-DEC-2007 / 684:    0.0

In order to compare D1 and D2 over the same period, I defined a common 
time axis/grid over 1951-2006 period such as :
define axis/t="1-jan-1951":"31-dec-2006":30.436875/units=day axd ; 
define grid/t=axd gtd
and regrid the two datasets on this axis.

let p1 = pm[d=D1, gt=gtd]
let p2 = pm[d=D2, gt=gtd]

But when I list these new variables on one point new datasets, I have 
the following output:
                     P1     P2
01-JAN-1951 /   1:    4.0   ....
31-JAN-1951 /   2:   36.5   12.3
02-MAR-1951 /   3:   33.2    5.1
...
31-OCT-2006 / 671:   11.2   11.3
01-DEC-2006 / 672:   16.8    9.1
31-DEC-2006 / 673:   ....    8.7

Consequently, it's impossible to compare these 2 regridded datasets.
Then, how can I define the correct time axis (i.e. identical L values)  
wich will give consistent regrided datasets ?

Thanks in advance.

--
Francois DELCLAUX
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UMR HydroSciences Montpellier
Universite Montpellier II - Place Eugene Bataillon
Case courrier MSE
34095  Montpellier Cedex 5      FRANCE
http://www.hydrosciences.fr/
mailto: delclaux@xxxxxxxxxxxxxxxxxxx
Tel : (33) (0)4 67 14 90 11      Fax : (33) (0)4 67 14 47 74
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