The GRACE principle
The GRACE principle
The idea behind the GRACE principle is quite simple: GRACE is used to ‘weigh’ ice sheets and continents to see how their mass decrease or increases from month to month. To do this, the two satellites fly one behind the other at an average distance of only around 220 kilometres, recording the masses of ice sheets and continents solely based on their gravitational effect. The stronger the gravitational force, the more the leading satellite is attracted by the mass as it flies over it. This causes the first satellite to accelerate and move away from the one behind. The weaker this force is, the less the leading satellite is accelerated. The first satellite then gets closer to the satellite behind it again. Their relative distance variations and speed will be constantly and precisely measured using lasers, achieving an accuracy of 200 to 300 picometres – roughly the size of an atom.
