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Did you regrid your data to a regularly-spaced time axis? Please
show the commands that you tried, and then we can see what's going
on.
Ansley
On 8/20/2015 12:28 AM, Satyam
Srivastava wrote:
Hey Ansley,
Thanks for your kind reply, but I have trued everything which
you guys have suggested even I have tried the script which is
there in Archives but then also I am not getting the solution I
am getting the same error message that is bailing out.
I would add that sometimes an axis is intended to be
regularly spaced but is stored in the netCDF file in such a
way that Ferret detects it as irregular. Ferret reads the
coordinates and looks at the spacing, to the precision of
the coordinate data - that is if they're stored as DOUBLE,
or FLOAT, it looks at the spacing relative to the data
type. However sometimes an axis that seems to be intended
to be regular is in fact not - quite.
It's worth looking at the coordinates themselves to see if
they should be treated as regular, and if so then when
opening the dataset you could tell Ferret to treat the axis
as regularly-spaced. For the dataset containing the
relevant time axis,
I am trying to calculate the FFT for a data set
which has irregular axis
I'm no expert, but I think the FFT algorithm works
only for
evenly-spaced gridded data. If so, what you need is
to map your data
on to an evenly-spaced grid.
Mapping inevitably introduces leaks (aliasing) in the
frequency domain
and if your problem is sensitive to aliasing, you
would have to
carefully choose an appropriate mapping. If, on the
other hand, you
aren't concerned about a bit of aliasing, you can just
use Ferret's
capability of regridding. Look at the Ferret manual
for regridding.
For general information about Fourier transforms of
unevenly-spaced
data, google-search for "FFT uneven grid" without the
quotation marks.
Hope this helps,
Ryo
--
Regards,
Satyam Srivastava,
J.R.F,
Kedareshwar Banerjee Centre of Atmospheric and
Ocean Studies (KBCAOS),