<div dir="ltr"><div><div>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.<br><br></div><div>As I recall, a Cressman scheme uses a distance weighting method while a Barnes method uses an exponential distance weighting method.<br></div><div>---<br><br>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.<br><br>Attached is the f77 code called by the NCL function.<br>---<br></div><div> I am also attaching a Cressman code from NCEP on a FYI basis. <br>---<br>If you prefer to develop your own code, you could write it is NCL. <br></div><div>---<br></div><div><br><br></div></div><br><br></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Nov 9, 2016 at 1:18 PM, Brennan Bean <span dir="ltr"><<a href="mailto:brennan.bean.20@gmail.com" target="_blank">brennan.bean.20@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div class="m_-8829148215144859066gmail_signature"><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><span style="font-size:12.8px">Hello,</span><div style="font-size:12.8px">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 <span style="color:rgb(51,51,51);font-family:verdana,sans-serif;font-size:13.3333px">an </span><span style="color:rgb(51,51,51);font-size:13.3333px"><font face="arial, helvetica, sans-serif">"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? </font></span></div><div style="font-size:12.8px"><span style="color:rgb(51,51,51);font-size:13.3333px"><font face="arial, helvetica, sans-serif"><br></font></span></div><div style="font-size:12.8px"><span style="color:rgb(51,51,51);font-size:13.3333px"><font face="arial, helvetica, sans-serif">Thank you, </font></span><span class="HOEnZb"><font color="#888888"><br clear="all"><div><div class="m_-8829148215144859066gmail-m_-2941474322496098836gmail_signature"><div dir="ltr"><div dir="ltr"><div dir="ltr">Brennan Bean</div></div></div></div></div></font></span></div><div><br></div></div></div></div></div></div></div>
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