Temporal Variations of the Gravity Field from Lageos 1 and Lageos 2 Observations

Precise orbit computations, based on a numerical approach, have been carried out for the Lageos 1 and Lageos 2 satellites to derive temporal variations of the Earth’s gravity field. Eleven years (1984–1994) and two years (1993–1994) of laser data have been analysed respectively for Lageos 1 and Lageos 2. The secular rates of J₂, J₃ and J₄ have been estimated, with the following solution: $${\dot J_2} = - 3.0 \pm 0.5 \times {10^{- 11}},{\dot J_3} = - 1.7 \pm 0.1 \times {10^{ - 11}}and{\text{ }}{\dot J_4} = - 0.8 \pm 1.5 \times {10^{- 11}}$$ The seasonal variation of J₂ has also been computed over the eleven years period. As reported earlier, the annual component of J₂ is essentially due to air mass redistribution in the atmosphere. Over the years 1993–1994, the annual ocean mass contribution has been estimated using sea surface height data of the Topex-Poseidon altimeter satellite. It is shown that the ocean effect is quite small, only a few % of the atmospheric effect at the annual frequency.