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Ocean Surface Topography from Space
TOPEX/Poseidon On-line Tutorial - Part I

Part I.   |   Part II.   |   Part III.

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Data Images

Data Images

  • T/P data images updated monthly beginning September, 1992.
  • There are 5 types of products.
    • Dynamic Ocean Topography
    • Sea Surface Variability
    • Significant Wave Height
    • Wind Speed
    • Percipitable Water Vapor

  • T/P is scheduled to continue collecting data through at least Fall 1998 and Jason-1, the T/P "follow-on" mission, is planned to launch in 2001. Together, these missions will give us at least a decade of data, the minimum amount of data needed to begin to test models of Earth's long-term weather, or climate.
  • The URL for these images is

Ocean & Climate

Ocean and Climate
  • Climatic changes take place over months, years, thousands or even millions of years. Thanks to technological advances, measuring and studying many factors that affect climate is now possible.
  • The T/P satellite makes very precise and accurate measurements of sea surface height.
  • What can such a simple measurement tell us about our Earth? A lot! This is because the oceans are the greatest repository of important "greenhouse" gases such as water vapor and carbon dioxide. Monitoring sea height is a way to measure changes in the levels of these gases over time.
  • Our basic goal is to monitor how the ocean is changing over time.
  • How do we accomplish this?

Satellite Ground Tracks
Satellite Ground Tracks
Satellite Ground Tracks

  • The trace of the satellite on the ground goes over the same spot of ocean once every 10 days.
  • T/P's ground tracks cover over 95% of the ice-free oceans every 10 days.
  • During its first month of operation, T/P collected more ocean data than all the ships had during the previous 100 years!

Measurement System

TOPEX/Poseidon Measurement System
View the TOPEX/Poseidon Measurement System
  • This chart is very complicated so we're just going to focus on how the satellite's measurement is optimized. To do this, we need to know:
    1. where the satellite is in its orbit and
    2. the distance from the satellite to the ocean.

  • Satellite position is known relative to the center of the Earth and so we measure sea height relative to the Earth's center.
  • The position of the T/P satellite is determined using 3 methods.
  • T/P has 2 altimeters that measure the distance from the satellite to the ocean. These altimeters send radar signals straight down to "bounce off" the ocean surface where they are bounced back to the satellite. The time it takes for the radar signal to return to the satellite tells us how far the satellite is from the ocean's surface.
  • To improve the altimeter measurement, we measure the water content of the atmosphere. This is because water in the atmosphere changes the speed at which the altimeter signal travels.
  • T/P makes very precise measurements of sea surface height.
  • Let's discuss the meaning of the term "precise:" You are given two rulers: each a foot long but one only has tick marks to indicate whole inches, and the other has tick marks every 1/16th of an inch... which would provide a more precise measurement of the length of your thumb? Find out the answer.
  • The more precise T/P's measurement is, the smaller the ocean feature we can measure. Later, we'll focus on the relative heights of certain ocean features that scientists want to measure.
  • Right now, T/P's measurement precision for sea surface height is 4.3 cm (1.7 inches). Because the satellite flies at about 1330 km (830 miles) above the Earth's surface, that's comparable to knowing the sea surface height to much less than the thickness of a dime while flying in a jet at 35,000 feet altitude.

Motion in the Ocean

Ocean Motion
Why is there motion in the ocean? Find out the answer.
  • The Sun's energy and force of the wind. Together, the oceans and atmosphere redistribute the Sun's energy from the tropics (where the Sun's energy input is highest) to the poles (where energy input is the lowest).
  • What causes the difference in how much energy is received at the Earth's between the tropics and the poles?Find out the answer

  • One way the Sun drives ocean circulation is by changing the temperature and salinity of water. Near the poles, ocean water sinks because it is cold and salty. The ice formed at the poles doesn't take up salt very well and leaves it behind in the seawater. This makes it heavy, so it sinks.
  • The most obvious way the Sun drives ocean circulation is by wind forcing. Energy is transferred directly from the atmosphere into the oceans.

Wind Speed & Significant Wave Height: January 1995

Wind Speed & Significant Wave Height: January 1995

  • Examples of two types of T/P data are available at
  • The upper image shows wind speed, the lower one shows significant wave height.
  • In this and all other T/P data sets you'll see that color-coding is as follows: purples and blues indicate low values and yellows and reds indicate high values.
  • Based on these images, is there a correlation or match between wind speed and wave height?Find out the answer
  • These data show the conditions during January, 1995. What should these data look like during June, 1995?

Wind Speed & Significant Wave Height: June 1995

Wind Speed & Significant Wave Height: June 1995

  • The wind speed and significant wave height data for June, 1995 show high values near Antarctica. Thus, these images are the "opposite" of the previous example and clearly show the winter conditions in the Southern Hemisphere.
  • Did the tropics change character between January and June, 1995 Find out the answer

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