First Analysis of GOCE Data after Lowering the Orbit
Bruinsma, Sean¹; Förste, Christoph²; Abrikosov, Oleg²; Marty, Jean-Charles^1
1CNES, FRANCE; ²GFZ, GERMANY

The GOCE mission has been in science operation since November 2009. For the entire nominal and extended mission, the orbit altitude has been kept constant at 255 km thanks to the ion propulsion. More than two years of mission data were collected from November 2009 through July 2012 at that altitude. On the recommendation of HPF as well as ESA's Scientific Advisory Committee, the orbit altitude was decreased by 20 km in three stages, which increases the sensitivity of the gradiometer to the gravity signal. Lowering of the orbit took place in August 2012, November 2012, and February 2013. In between the maneuvers, two 61-day cycles of data are collected at altitudes that are 8.6 and 14 km lower than the nominal altitude, respectively. An analysis of the data quality is given for this new phase of the GOCE mission, or its second mission as ESA calls it, and gravity field models obtained with data before and after August 2012 are compared. The impact of the lower orbit altitudes is visible for degrees above 200 in particular. This is evaluated and quantified by comparing to the release 4 GOCE gravity field model EGM-DIR-4, which is based on more than 2 years of GOCE data.