Salinity Color Palette & Color Range for a Global view

[Douglas White]

Aloha from Delaware!

Is there a widely accepted academia/industry color palette and a color range for displaying salinity?

I am pulling down global imagery to display on a spherical display and I want to make the data stand out on the globe but I also don't want to make a faux pas & use a color palette that confuses viewers who might be used to viewing salinity in a specific color palette.

I'm exploring various ocean-related color palettes both from the Hycom WMS server as well as external add-on packages for R & MatLab like CMOCEAN (https://matplotlib.org/cmocean/) which has a Haline palette.

TIA! Doug

[Alan Wallcraft]

The NRL GOFS 3.1 plots of all fields at https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/ use a false color palette of 100 values which are coded in colors.f

This isn't a salinity palette, and I would not recommend it for your application, but it does represent values out of range well (mapped to the first and last colors in the palette).  NRL's plots also illustrate that selecting the displayed range is important, and is difficult to do globally where salinity can range from close to zero (e.g. near rivers) to 40 psu (in the Mediterranean Sea).  Alternatives to mapping out of range values onto the palette include skipping these points, or using a distinct  "out of range" color, or defining a non-uniform mapping onto the color bar to cover the full range.

Alan.

[Alexandra Bozec]

To add to Alan’s comment, a commonly used color palette is the Matlab jet color palette (https://www.mathworks.com/help/matlab/ref/jet.html ).

 It is very similar to the HYCOM color palette but without the purple to blue part.

The Haline palette of cmocean is also good choice.

Alex

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[Rodrigo Duran]

matlab's jet is not a good option, especially for salinity or temperature because it creates a false impression of a front. 

It is true that jet is commonly used, probably because it was the default colormap in Matlab for a very long time. Matlab moved away from jet in 2014.

you can read more about the problem with jet here:

https://tos.org/oceanography/article/true-colors-of-oceanography-guidelines-for-effective-and-accurate-colormap

[White, Douglas]

So far I’m liking the occam_pastel-30 with a range of 0-44 for a global scale:

 

https://wms.hycom.org/thredds/wms/datasets/GLBy0.08/expt_93.0/data/hindcasts/2020/hycom_glby_930_2020061512_t000_ts3z.nc?STYLES=&SERVICE=WMS&FORMAT=image%2Fpng&REQUEST=GetMap&HEIGHT=2000&WIDTH=4000&VERSION=1.1.1&BBOX=-180.0%2C-80.0%2C180.0%2C90.0&LAYERS=salinity&PALETTE=occam_pastel-30&SRS=EPSG%3A4326&TRANSPARENT=TRUE&COLORSCALERANGE=0,44

 

Doug

[Dmitry Dukhovskoy]

Hi,

making good salinity plots showing fronts and water masses is not easy. From my experience, you cannot use any existing colormaps in Matlab for creating good plots. I always create my own. There are two options: 1) add as many colors as you can to cover S range of your interest (for example, you are not so interested in the near-shore low S regions) or 2) make exponential transformation of the S field expanding high-value S. 

I couldn't append examples of my S plots to this post, I can email them to you if you like. 

Dmitry

On Tuesday, August 25, 2020 at 11:58:29 AM UTC-4 d...@udel.edu wrote:

[Douglas White]

Yes please - I am looking for example code for plotting in both R and in Python.