Surface topography varies on several scales of time and space. Satellite altimetry is capable of measuring these variations globally and almost instantaneously with centimetre accuracy, allowing scientists to:

• map deformations of the sea’s surface in relation to global ocean circulation,
• map the major marine currents, such as the Gulf Stream and the Kuroshio, much as atmospheric pressure is measured by meteorologists,
• monitor ocean changes (eddies, for example), tides and seasonal and climate events like El Niño,
• estimate the topology of the ocean floor, little known, but of crucial importance.

The principal mission for altimetry today, however, is to to provide accurate and continuous measurements of mean sea level. Since the launch of Topex-Poseidon in 1992, observations have revealed a mean increase in sea level of approximately 3 mm/year (with variations of ± 20 mm/year in some regions). This increase is an incontrovertible indicator of global warming.

Although altimeters were originally designed to measure the height of the oceans, they are capable of observing water levels over land surfaces, in particular over any stretch of water wide enough to be detected. This capability has opened up new possibilities for continental hydrology studies. Altimetry satellites make it possible to monitor seasonal variations in the levels of lakes and major rivers. Such applications are particularly important in regions where in situ observations are rare because they are difficult to access, such as the Amazon Basin.

Advance knowledge of mean wave heights and surface wind speeds helps navigators choose the best and safest routes. These data are processed and made available almost in real time by Météo France.

Marine navigation charts established with Jason aid the ships of both the French Navy and US Navy.

Oceans play a decisive role in the evolution of climate, acting as both a regulating and disturbing influence. The oceans store considerable amounts of heat near the equator, which they gradually transfer toward the poles via ocean currents.

Jason-1 is an element of the Mercator operational oceanography project launched in 1997, for which a public interest grouping was formed in 2002, under a partnership between CNES, CNRS/INSU, Ifremer, IRD, Météo-France and SHOM. Mercator supports real-time monitoring of the oceans with weekly sea-state bulletins. One of its application is long-range forecasting —2 weeks.

Over 50% of the world's population lives near a coast. These zones are vulnerable, particularly when faced with rising ocean levels which can result in repeated flooding, acceleration of cliff erosion, and many other undesirable effects besides. Mitigating risks and careful planning of coastal development are therefore of prime importance, particularly in the atolls of the Pacific, or in Bangladesh, which are barely above current sea levels.

Data from Jason-1 enable studies of short- and medium-term effects of ocean currents and tides in these regions, and serve as a valuable decision-support tool for policymakers.

Knowledge of currents at depths of hundreds or even thousands of metres is essential for the offshore petroleum industry. Oil exploration now takes place farther and farther from the shoreline, in increasingly deep waters, sometimes subjecting companies to potentially enormous losses due to submarine eddies.

Jason data help to size drilling rigs and manage pumping operations more efficiently. They also go into planning for certain operational or maintenance activities that can only be carried out in calm conditions.