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20041004: Possible bug in "ocean s-coordinate"

>From: Rich Signell <address@hidden>
>Organization: USGS
>Keywords: 200410041742.i94HgRUE000566 IDV ocean-s bug

Hi Rich-
>
>IDV-developer-folk,
>
>I think there is a problem with the implementation of the
>"ocean s-coordinate" in IDV 1.1.    I should have caught this
>sooner, but...

Oh, sure, now you tell us. ;-)

>In the attached CF 1.0 Compliant file containing s-coordinate
>model results for the Adriatic Sea, when I make a vertical slice
>using IDV across the deepest part of the Adriatic Sea, the top of the 
>section
>appears to be about 150 m below the sea surface, when in fact
>it should be about 10 m below the sea surface.
>
>In the CF Convention,
>
>
>        Ocean s-coordinate
>
>standard_name = "ocean_s_coordinate"
>
>/Definition:/
>
>z(n,k,j,i) = eta(n,j,i)*(1+s(k)) + depth_c*s(k) +
>             (depth(j,i)-depth_c)*C(k)
>
>  C(k) = (1-b)*sinh(a*s(k))/sinh(a) + 
>         b*[tanh(a*(s(k)+0.5))/(2*tanh(0.5*a)) - 0.5]
>
>where z(n,k,j,i) is height, positive upwards, relative to ocean datum 
>(e.g. mean sea level) at gridpoint (n,k,j,i), eta(n,j,i) is the height 
>of the ocean surface, positive upwards, relative to ocean datum at 
>gridpoint (n,j,i), s(k) is the dimensionless coordinate at vertical 
>gridpoint (k), and depth(j,i) is the distance from ocean datum to sea 
>floor (positive value) at horizontal gridpoint (j,i). The constants a, 
>b, and depth_c control the stretching.
>
>The format for the formula_terms attribute is
>
>formula_terms = "s: var1 eta: var2 depth: var3 a: var4 b: var5 depth_c: 
>var6"
>
>
>The parameters in this file are:
>
>depth_c=3
>a=3
>b=0.8
>
>and if we pick (approximating the deepest part of the adriatic):
>eta=0, depth=1200,
>
>we should get:
>C(k)      z(i)
>-0.979 -1174.9
>-0.937 -1124.8
>-0.895 -1073.6
>-0.850 -1019.4
>-0.801 -960.7
>-0.747 -896.0
>-0.687 -824.5
>-0.622 -746.3
>-0.552 -662.5
>-0.479 -575.2
>-0.406 -487.4
>-0.335 -402.4
>-0.269 -323.3
>-0.210 -252.2
>-0.158 -190.5
>-0.115 -138.3
>-0.079 -95.3
>-0.050 -60.2
>-0.027 -32.1
>-0.008  -9.5
>
>
>So the top of the vertical section in the deepest part of the basin should
>be more like 9.5 m (instead of 150 m)

Good detective work.  You get the prize for finding the bug of the
day.  The code in ucar.unidata.geoloc.vertical.OceanS.java was doing:

  C(k) = (1-b)*sinh(a*s(k))/sinh(a) + 
         b*[tanh(a*(s(k)+0.5))/(2*tanh(0.5*a))] - 0.5

Just a little matter of getting the parentheses in the right places.
I've put out a new idv.jar at:

ftp://ftp.unidata.ucar.edu/pub/idv/untested/idv.jar

Replace your version with this one (making a backup copy first of course).

The fix will be in the next release.  Also, your bundle pointed out
another bug that just got introduced in a recent change so you're
actually getting a 2-fer-1!

Thanks for finding this.

Don
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>Date:    Mon, 04 Oct 2004 16:14:50 EDT
>From:    Rich Signell <address@hidden>
>Subject: Re: 20041004: Possible bug in "ocean s-coordinate"
>
>Fantastic!  
>
>They like to say you get what you pay for, but I've never seen a piece 
>of *commercial* software where you get bugs fixed in a couple of *hours*!!!!
>
>Thanks,