Two satellites which previously worked independently are now co-ordinating their efforts to examine floating sea ice, crucial for understanding how ice cover is changing.
Esa’s CryoSat2 has a radar altimeter which reflects radio waves off the ice surface to calculate the distance from the satellite. Nasa’s IceSat2 uses a laser in the same way. Because the ice is floating, knowing how high the top is above sea level allows the total thickness to be calculated.
However, while the laser beam bounces off snow on top of the ice, the radar goes through snow. Comparing the two readings from a specific point gives the depth of the snow cover. Previously the two satellites passed over a given point several hours apart, so exact comparison was impossible. The different orbits, IceSat2 at 500 km and CryoSat2 at 720 km, mean they could not be lined up. However, scientists realised that a form of synchronisation was possible.
A sequence of fifteen carefully-timed bursts from the IceSat2’s thrusters altered its orbit so that every twentieth IceSat2 orbit now coincides exactly with every nineteenth CryoSat2 orbit. This gives a window when the two share the same view of a two-thousand-mile stretch of polar ice every day or so. The new data will help improve climate models, especially for the Antarctic.
