Saturated color scale

Lively Data : April 16, 2004

Merged (Topex/Poseidon+ERS-1) sea level anomaly global map for October 14, 1992 (Ssalto/Duacs delayed time Maps of Sea Level Anomalies). Up, the map plotted with the automatic color scale: outside very localized points, most heights are between -20 and +20 cm. Middle, same map plotted with (-15,15,1) defined in "fill option" ("output options" section): areas where heights exceed +/-15 cm are blank; bottom, the map plotted by defining (-90)(-15,15,1)(170) in "fill option": height between -15 and -90 cm are in the same purple, those between 15 and 170 cm in the same red.

Altimetric measurements have often very high extreme values, mostly in strong turbulence areas -- typically in the majors currents like Gulf Stream or Kuroshio. A plot of a global map without specification can lead to a nearly uniformly colored map, since typical sea level variations are hidden by the amplitude of the color scale needed to have the extreme values.
The Live Access Server allow to impose color scale minima and maxima, depending on what we wish to see. For major current variations +/-30 cm (or even +/-50 cm) are needed; for El Niño, +/-20 to 25 cm are OK. For the rest of the ocean +/-15 cm are more than enough most of the time. To fix those extrema, we saw (Scaling the ocean - July 7, 2003) that you have to click on "output options", then typing in "fill option": (min, max, interval). But this lead to blank areas, where values exceed the defined extrema. To avoid this, you can type (absolute min)(min, max, interval)(absolute max), where absolute min and max are the map extreme values (or very high ones). Color scale is then saturated.