Quality assessment of GOCE gradients by in-orbit comparison
19/09/2016 | 16:30 | Session 1: Current and future satellite gravity missions
Author(s): Phillip Brieden and Jürgen Müller
Phillip Brieden and Jürgen Müller
ESA’s very successful gravity mission GOCE (Gravity field and steady-state Ocean Circulation Explorer) orbited the Earth for exactly 1700 days (March 2009 to November 2013). During its lifetime approximately 42 months of data had effectively been collected providing the Earth’s gravity field in unprecedented accuracy and spatial resolution.
To ensure high data quality for further use of the data (e.g. gravity field processing), data calibration and validation is carried out in the regular data processing and by external groups applying various methods. In the framework of validation of the GOCE gravitational gradients at IfE Hannover, we work on two strategies for gradient in-orbit comparison. One is the comparison of measured gradients along collinear tracks, the second is the comparison of gradients in satellite track cross-overs.
In this study some of the following fields of application are presented, for which both methods are best suited:
- outlier detection,
- identification of time periods with reduced gradient quality (very useful for the exclusion of less accurate parts of the data before gravity field processing),
- identification of geographical areas were the gradients show an increased noise level,
- assessment of the overall gradients quality.
Also interesting are statistical analyses of the cross-over-point residuals where at high latitudes more intersections occur than data points are available.
Based on both methods, we show the behavior of the gradient quality during the orbit lowering phase in the last year of the mission. Although a significantly stronger gravitational field signal was measured due to the low orbital altitude, the noise level has hardly changed. Only the noise of Vyy increased significantly from about 5 mE in mid-2012 to about 14 mE in mid-2013.