Description: Estimation of ocean circulation is investigated via assimilation of satellite measurements of the dynamic ocean topography (DOT) into the global finite-element ocean model (FEOM). The DOT was obtained by means of a geodetic approach from carefully cross-calibrated multi-mission altimeter data and GRACE gravity fields. The spectral consistency was achieved by consistently filtering both, the sea surface and the geoid. The filter length is determined by the spatial resolution of the gravity field and corresponds to approximately 241 km half width for the GRACE-based gravity field model ITG-Grace03s. The assimilation of the geodetic DOT was performed by employing a local singular evolutive interpolated Kalman (SEIK) filter in combination with the method of weighting of observations. It is shown that this approach leads to a successful assimilation technique that reduced the RMS difference between the model and the data from 16 cm to 5 cm during one year of assimilation. The ocean model returns an optimized mean dynamic ocean topography. The effects of assimilation on transport estimates across several hydrographic World Ocean Circulation Experiment (WOCE) sections show improvements compared to the FEOM run without data assimilation. As a result of the assimilation, DOT estimates are available in the polar or coastal regions where the geodetic estimates from satellite data alone are not adequate. Furthermore, more realistic features of the ocean can be seen in these areas compared to those obtained using the filtered data fields.

Description: The dataset contains the results of airborne gravimetry realized by the GEOHALO flight mission over Italy in 2012. The intention was to show whether and how an efficient airborne gravity field determination is feasible in wide areas when using a fast jet aircraft like HALO at higher altitudes. Here, unlike in airborne gravimetry for exploration purposes, the aim is not primarily to reach the highest spatial resolution by flying as low and slowly as possible. A challenge for HALO would be to map areas (e.g., Antarctica) where only insufficient or no terrestrial gravity data are available to achieve a resolution which is better than that of satellite-only gravity field models. This is beneficial for the generation of global gravity field models which require a uniform, high spatial resolution for the gravity data over the entire Earth. The raw gravimetry recordings were recorded by the GFZ air-marine gravimeter Chekan-AM. Kinematic vertical accelerations were calculated from Doppler observations which were derived by GNSS carrier phase measurements (1 Hz). To remove the high-frequency noise, a low-pass filter with a cut-off wavelength of 200 s (corresponding to a half-wavelength resolution of approximately 12 km) was applied to both the Chekan-AM measurements and GNSS kinematic accelerations. To investigate how future airborne gravity campaigns using jet aircraft could be optimized, a dedicated flight track was repeated two times which shows that the equipment worked well also at higher altitude and speed. For the accuracy analysis 17 crossover points could be used. This analysis yielded a RMS of the gravity differences of 1.4 mGal which, according to the law of error propagation, implies an accuracy of a single measurement to be 1 mGal. The dataset is provided in as ASCII text (Lu-et-al_2017-001_Tracks_GEOHALO.txt) and is described in the README. For a detailed description of the set-up and analysis of the data, please see Biao et al. (2017, http://doi.org/10.1002/2017JB014425).