External Assessment of GOCE Gravity Model Accuracy
Abstract
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, and the two latest ESA gravity field model releases, EGM-DIR-R4 and EGM-TIM-R4, have been constructed with that set. On the recommendation of ESA's Scientific Advisory Committee, ESA decided to decrease the altitude by 20 km in three stages, thereby increasing the sensitivity of the gradiometer to the gravity signal. Lowering of the orbit took place from August 2012 through February 2013. In between the maneuvers, two 61-day cycles of data are collected at altitudes that are 8.6 and 15 km lower than the nominal altitude, respectively, followed by a 70-day cycle 20 km lower. In May 2013, after a quick internal evaluation, ESA performed a fourth and final orbit lowering of 10 km (i.e. altitude of 225 km), and a 143-day repeat cycle with 56 days sub-cycles started on 29 May. The formal errors of the GOCE gravity field models computed using the direct numerical approach (EGM-DIR-R4) or the time wise method (EGM-TIM-R4) do not agree by a factor of about 3, the former model having the smaller cumulated geoid error at 100 km scale of 1.3 cm. It is crucial to determine what the true error is for many applications, as well as for ESA to establish if the mission is or is not within specifications (or will be after ingestion of all lower altitude data), i.e. an error of 1-to-2 cm at 100 km resolution. We have experimented with a novel approach to determine the accuracy based on altimetry data. According to results of this method, the accuracy of both GOCE gravity field models is significantly better than the EGM-TIM-R4 formal error.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.G51A0863B
- Keywords:
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- 1214 GEODESY AND GRAVITY Geopotential theory and determination