
Hello All

I am currently looking at spatial data - Chorophyll A concentration in sea
water over a wide geographic area. These data are used to determine the
location of ocean fronts and hence where tuna are located. A front is
identified by a steep gradient in the change in chloroA concentration. I
have been looking at these data qualitatively using persp, contour, and
image but would like to determine a metric for the rate of change in
concentration between evenly spaced cells - essentially determine the
maximum gradient of the surface at each point. It would be preferable to use
a smoothing function first (such as what contour is providing) but not
essential - the surfaces are quite complex. Does anyone have any suggestions
that use existing functions?

Thank you in advance.

Adam 

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Adam Langley
Senior Fisheries Scientist 
Oceanic Fisheries Programme
Secretariat of the Pacific Community
BP D5, 98848 Noumea Cedex, New Caledonia 
Tel:	+687 262 000 (Ext. 192)
Fax:	+687 263 818




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