I'm looking to calculate gradients from oceanographic variables (ie. sea
surface temperature, chlorophyll, etc.) for which I have downloaded in ESRI
grid format (.asc).  From some research on gradient analysis, I have found a
few people who have used a Sobel filter to estimate gradients in images (ie.
presumably .tif or similar files).  However, I have tons of data in ESRI
grid format, and all of it is unprojected (ie. lat/lon coordinates).  I'd
appreciate suggestions on this if anyone has ideas.  One of the primary
issues to overcome is that the units of my grids are different (ie.
x=longitude, y=latitude, z=temperature) and my grid files span the entire
south Pacific Ocean.

Thanks,

Tim

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