[ncl-talk] process underlying obj_anal_ic_Wrap()

[Dennis Shea]

This code was derived from a fortran code originally written 25+ years ago.
The original code was a 'classic' iterative correction approach where
observation differences from a user provided 1st guess field were used to
modify the original 1st guess grid.

As I recall, a Cressman scheme uses a distance weighting method while a
Barnes method uses an exponential distance weighting method.
---

The NCL function does *not* use a  1st guess field. It is *direct*
interpolation of the observations to grid points. It assumes that the raw
observations are reasonably dense and reasonably well distributed. An
exponential (Barnes-like) weighting is used. The 'iterative' part of the
function name is because the 1st estimate of the field (very large radius)
is subsequently modified by reducing the search radii. After the each field
(grid) estimate, some arbitrary smoothing between the (n-1)-th and n-th
field is performed.

Attached is the f77 code called by the NCL function.
---
 I am also attaching a Cressman code from NCEP on a FYI basis.
---
If you prefer to develop your own code, you could write it is NCL.
---





On Wed, Nov 9, 2016 at 1:18 PM, Brennan Bean <brennan.bean.20 at gmail.com>
wrote:

> Hello,
> In an effort to understand a colleague's NCL code, I had a question
> regarding the obj_anal_ic_Wrap() function. The documentation describes this
> function as an "iterative improvement type objective analysis" but does
> not specify the way this iterative process is carried out. I wanted to know
> if this is done by a Cressman or Barnes correction scheme, or if it was
> carried out by something more sophisticated than either of these methods?
>
> Thank you,
> Brennan Bean
>
>
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