By Gary Thomas
In 2010, Earth-observing satellite CryoSat was launched to measure the thickness of sea ice in the Arctic region, but data from the satellite have also been used for other studies. Now, high-resolution measuring of the topography of the ocean surface has been added to the repertoire of ice mission. The main purpose of the polar-orbiting satellite is to evaluate polar sea ice’s thickness and monitor variations in the ice sheets that cover Antarctica and Greenland.
The radar altimeter of CryoSat not only detects tiny changes in the height of the ice but is also capable of measuring the sea level. The topography of the ocean floor imitates the dips and rises of the ocean surface because of the gravitational force. Areas of greater mass, including underwater mountains, have a stronger gravitational attraction, pulling more water and creating a small rise in ocean-surface height. Therefore, devices that measure the height of sea surface incidentally record the ocean surface in earlier uncharted areas.
There have been a number of recent global gravity missions, including ESA’s GOCE satellite, that provide exact measurements of the gravitational pull at the spatial degrees of hundreds of kilometres. However, the satellite’s radar altimeter can perceive the gravity area at the ocean surface in order that the characteristics of seafloor are revealed at scales of 5–10 km.
Recent studies conducted at the Scripps Institution of Oceanography in San Diego indentified that CryoSat’s range precision is almost 1.4 times better compared to the US's Geosat or ESA's ERS-1. They estimated that the improved range precision joined with three or more years of mapping of ocean will lead to global seafloor topography, bathymetry that is 2 to 4 times more precise than the currently available measurements.
The 369-day repeat cycle of CryoSat provides a compact mapping of the global ocean floor at a track spacing of more than 4 km. Up to four years of data from the satellite can be averaged to decrease the noise due to tides and currents and record the permanent topography concerning marine gravity in a better way.