Investigations on the polar gap problem in ESAs gravity field and steadystate ocean circulation explorer mission (GOCE)

Due to the sun-synchronous GOCE orbit two polar regions with a radius of about 700 km cannot be observed. In this contribution effects of these data gaps are investigated using a regional recovery strategy. It consists essentially of a variant of the time-wise approach, where the geopotential is represented by a system of space-localizing base functions. The ability of the three diagonal tensor components of the gradiometer instrument "to look into" the gaps is investigated. Our investigations show that 1°×1° mean anomalies can be recovered at reduced accuracy. Referred to a simulated gravity field model complete up to degree 360 the rms-values increase with geographical latitude from 3 mGal up to 10–12 mGal. It is not possible to overcome these problems solely by introducing additional GPS data, but if terrestrial or airborne gravity information is available, also datum defects can be successfully fixed. This work on the polar gap problem was done in the framework of the ESA contract on GOCE entitled "From E?tv?s to Milligal".