Sea Level arrow Level 1

Reading Sea Surface Height Data

Researchers believe that sea level worldwide is presently rising. Over the last 100 years, global sea level has risen about 15 cm (6 in.) and recently the rate of rise has increased. To study this phenomenon, scientists need to make good measurements of the sea surface height around the world. One tool they use is satellite altimetry, which allows them to look at a snapshot of sea surface height deviation (SSHD) around the world. SSHD is the difference between the height of the sea surface and the expected average height, based on historical data. The scale for SSHD data is measured in meters above and below the average (or mean) value for a given location.

Looking at an SSHD map, one sees immediately that sea level is not the same everywhere. Sea surface continually fluctuates due to natural forces, such as the trade winds, tides, waves, glacier melts, density, and gravity.

Below is an example of a map of sea surface height deviation. Use this map to check your understanding. Then try making your own map using real data.

Map of monthly sea surface height deviation, November 16, 1995

Check your understanding

1. Which location on the map above has a measured sea surface height deviation (SSHD) greater than 0.2 meters above or below average?

 0° latitude and 10° West longitude.
 15° North latitude and 110° West longitude.
 15° South latitude and 110° West longitude.
 40° South latitude and 100° East longitude.

2. According to the map, the monthly SSHD at 40° North and 150° East is approximately:

  0.7 meters.
 -0.6 meters.
  0.3 meters.
  0 meters.