GOCE, Satellite Gravimetry and Antarctic Mass Transports

Abstract

In 2009 the European Space Agency satellite mission GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) was launched. Its objectives are the precise and detailed determination of the Earth's gravity field and geoid. Its core instrument, a three axis gravitational gradiometer, measures the gravity gradient components V xx , V yy , V zz and V xz (second-order derivatives of the gravity potential V) with high precision and V xy , V yz with low precision, all in the instrument reference frame. The long wavelength gravity field is recovered from the orbit, measured by GPS (Global Positioning System). Characteristic elements of the mission are precise star tracking, a Sun-synchronous and very low (260 km) orbit, angular control by magnetic torquing and an extremely stiff and thermally stable instrument environment. GOCE is complementary to GRACE (Gravity Recovery and Climate Experiment), another satellite gravity mission, launched in 2002. While GRACE is designed to measure temporal gravity variations, albeit with limited spatial resolution, GOCE is aiming at maximum spatial resolution, at the expense of accuracy at large spatial scales. Thus, GOCE will not provide temporal variations but is tailored to the recovery of the fine scales of the stationary field. GRACE is very successful in delivering time series of large-scale mass changes of the Antarctic ice sheet, among other things. Currently, emphasis of respective GRACE analyses is on regional refinement and on changes of temporal trends. One of the challenges is the separation of ice mass changes from glacial isostatic adjustment. Already from a few months of GOCE data, detailed gravity gradients can be recovered. They are presented here for the area of Antarctica. As one application, GOCE gravity gradients are an important addition to the sparse gravity data of Antarctica. They will help studies of the crustal and lithospheric field. A second area of application is ocean circulation. The geoid surface from the gravity field model GOCO01S allows us now to generate rather detailed maps of the mean dynamic ocean topography and of geostrophic flow velocities in the region of the Antarctic Circumpolar Current.

Short‐term transport variability of the Antarctic Circumpolar Current from satellite gravity observations

“…While the barotropic flow component is obtained from GRACE, sea surface height anomalies from the satellite altimetry mission TOPEX/Poseidon and its successors can provide information on a large part of the baroclinic variability [ Gille et al , 2001]. Improved retracking algorithms suitable to obtain highly accurate sea level anomalies also near the coasts (see, e.g., for recent technological developments, Gommenginger et al [2011]), in connection with an independently obtained high‐resolution geoid from GOCE [ Rummel et al , 2011] serving as a reference surface for calculating absolute surface geostrophic velocities, calls for a reassessment of previous studies that attempted to monitor the variability of the Antarctic Circumpolar Current from space.…”

GOCO06s – a satellite-only global gravity field model

“…To increase the spatial resolution, tailored to the requirements of geodetic, geophysical and oceanographic applications, the Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission (Battrick, 1999;Floberghagen et al, 2011) was realized and launched in 2009. In addition to SST-hl, a gradiometer served for the first time as a core instrument to measure the second derivatives of the Earth's gravitational potential in gradiometer reference frame (Rummel and Colombo, 1985;Rummel et al, 2002;Rummel et al, 2011b;Johannessen et al, 2003). Due to the design of the instrument (Stummer et al, 2012;Siemes et al, 2012Siemes et al, , 2019, only four out of the six derivatives of the Marussi tensor could be measured with high precision (V XX , V XZ , V Y Y and V ZZ ).…”

GOCE's view below the ice of Antarctica: Satellite gravimetry confirms improvements in Bedmap2 bedrock knowledge

“…ESA's GOCE satellite mission has determined the Earth's static gravity field during a ~4 year data collection period (from 2009 to 2013) using a dedicated gravity gradiometer for the measurement of second derivatives of the gravitational potential at ~260 km altitude [Rummel et al, 2011;van der Meijde et al, 2013]. As a second major measurement system, GPS-based satellite-to-satellite tracking was deployed aboard the GOCE satellite for orbit determination, augmenting the gradiometer observations in the long wavelengths.…”

“…Significant advancements in high-resolution mapping of Earth's static gravity field from space have now been made with European Space Agency (ESA)'s Gravity field and Ocean Circulation Explorer (GOCE) satellite [Drinkwater et al, 2003;Rummel et al, 2011]. During its 4 year mission phase, GOCE has delivered high-precision gravity gradient and orbit trajectory data that have been used as input for the computation of a series of new global gravity models with up to ~80 km spatial resolution [Pail et al, 2011].…”