Altimetry satellites basically determine the distance from the satellite to a target surface by measuring the satellite-to-surface round-trip time of a radar pulse. However, this is not the only measurement made in the process, and a lot of other information can be extracted from altimetry.
The magnitude and shape of the echoes (or waveforms) also contain information about the characteristics of the surface which caused the reflection. The best results are obtained over the ocean, which is spatially homogeneous, and has a surface which conforms with known statistics. Surfaces which are not homogeneous, which contain discontinuities or significant slopes, such as some ice, rivers or land surfaces, make accurate interpretation more difficult.
Products that use Satellite Altimitry: ECCO V4, GECCO
Argo is an international collaboration that collects high-quality temperature and salinity profiles from the upper 2000m of the ice-free global ocean and currents from intermediate depths. The data come from battery-powered autonomous floats that spend most of their life drifting at depth where they are stabilised by being neutrally buoyant at the "parking depth" pressure by having a density equal to the ambient pressure and a compressibility that is less than that of sea water. At present there are several models of profiling float used in Argo. All work in a similar fashion but differ somewhat in their design characteristics. At typically 10-day intervals, the floats pump fluid into an external bladder and rise to the surface over about 6 hours while measuring temperature and salinity.
Satellites or GPS determine the position of the floats when they surface, and the floats transmit their data to the satellites. The bladder then deflates and the float returns to its original density and sinks to drift until the cycle is repeated. Floats are designed to make about 150 such cycles.
Products that use ARGO : ECCO V4, GECCO
GRACE is a collaboration of the US and German space agencies (NASA and DLR). GRACE ground segment operations are currently co-funded by the GFZ German Research Centre for Geosciences and the European Space Agency (ESA). NASA, ESA, GFZ and DLR are supporting the continuation of the measurements of mass redistribution in the Earth system. The key partners in the design, construction and launch of the mission have been the Jet Propulsion Laboratory, the University of Texas Center for Space Research, GFZ German Research Centre for Geosciences, as well as Astrium GmBH, Space Systems Loral (SS/L), Onera and Eurockot GmBH.
Products that use GRACE : ECCO V4, GECCO