IGG-SLR-HYBRID is a series of high-resolution monthly gravity fields computed from satellite laser ranging (SLR) to five satellites, Lageos 1 and 2, Stella, Starlette, and Ajisai. It applies a novel approach in which the temporal changes of the gravity field are represented by the leading empirical orthogonal functions from the GRACE time series; this allows one to reconstruct gravity field changes with unprecedented spatial resolution in the pre-GRACE era.
The time series cover the full period from November 1992 through June 2020. They provide an independent proof of the onset of accelerated mass loss from the Greenland and West Antarctica Ice Sheets in the 90s, which in turn contribute to accelerated sea level rise. They can be also used in studies of the global water cycle and for assessing water resources in the world’s largest hydrological basins.
The SLR technique relies on tracking cannon-ball shaped satellites fitted with retro-reflectors from more than 50 terrestrial observatories. In SLR, one measures the time interval required for a laser pulse to travel to a satellite and return to the transmitting telescope. The range between the satellite and the observing site is approximately equal to one half of the two-way travel time multiplied by the speed of light. Since the orbits of the satellites and thus the measured ranges are affected by the changing Earth’s gravitational field, one can derive mean and time-variable gravity models from SLR. This is less accurate than nowadays possible with the GRACE and GRACE-FO satellites, yet GRACE as only launched 2002 and SLR provides a way of deriving gravity and mass changes in the pre-GRACE era.
Predominantly due to climate change and warming oceans, the Earth’s large ice sheets are not in balance: they lose more ice than is replaced through snowfall. In particular large parts of the West Antarctica Ice Sheet are sitting in an unstable equilibrium on bedrock sloping inwards, this means a small retreat could in theory lead to rapid disintegration. It is thus very important to better quantify the apparent acceleration of mass loss with space-geodetic and -gravimetric measurements and analyses.
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www.apmg.uni-bonn.de | 23.12.2020
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link.springer.com | 23.12.2020