Observed SLA Contours
Sea-surface-height contour lines from satellite rather than forecast — one snapshot a day, about a day behind. Tight lines mean a steeper slope and a stronger current.
Updates daily
More detail
How to see them. Put up any layer from the Observed tab in Data Layers and tap the Altimetry button on the bottom bar, on the iPhone app or the website. The button still says Altimetry, so check which tab your layer came from.
What they show. A warm-core eddy stands up as a dome and a cold-core eddy sits in a bowl. The thick line is the zero level, where the raised side meets the low side. The figures along the lines are whole inches if your depth unit is feet and centimeters if it is meters.
Where they come from. The lines are traced from SLA (DUACS), the sea level measured by radar satellites. The Copernicus Marine Service, the European Union's ocean data service, makes the measurement, and RipIQ traces the lines from it. Every hour of a day shows the same lines.
How they compare with the forecast lines. The Altimetry article covers the lines drawn with a Forecast layer up, which come from HYCOM (U.S. Navy model) and change every three hours. The measured lines are coarser, about 8 nautical miles per cell compared with about 5. The satellite tracks are also smoothed into a map before it reaches us, so you get the big eddies and far fewer lines. Use the measured lines to check that an eddy the forecast shows is really out there, and the forecast lines for finer detail and the days ahead.
Limits. Near the coast the lines often stop short of land. The satellite measurement is least reliable close to land. If the lines disappear, step the date back a day. The button is off again each time you open the app. The lines cover the Gulf of America, the East Coast and Baja.
The numbers
| How often it updates | Once a day |
| How fresh it usually is | About a day behind |
| How detailed it is | About 8 nautical miles per cell |
| Where it covers | Gulf of America, East Coast and Baja. Least reliable close to land |
| Observed or modeled | Observed by satellite |
| What you see on screen | Black lines a fixed step of height apart, 5 cm (about 2 inches). Labeled in whole inches or centimeters. The zero line is drawn thicker. Surface only |
Source: computed by RipIQ from SLA (DUACS) satellite altimetry.