Abstract's details
Numerical modelling of non-tidal ocean dynamics for the reduction of spatio-temporal aliasing in global grids of sea-level anomalies from radar altimetry
CoAuthors
Event: 2018 Ocean Surface Topography Science Team Meeting
Session: Tides, internal tides and high-frequency processes
Presentation type: Type Oral
Contribution: PDF file
Abstract:
Global grids of sea-level changes derived from altimetry data accumulated over several days are increasingly popular in many applications of both marine research and environmental monitoring. High-frequency variations in sea surface height at periods below twice the averaging period are, however, prone to cause aliasing artefacts in the grids in line with the Nyquist theorem. Such artefacts degrade the quality of the gridded products and potentially result in misleading geophysical interpretations. Since many years, the so-called dynamic atmospheric correction (DAC) based on a global barotropic ocean model is used for this purpose.
In this study, we utilize surface height variations from the ocean general circulation model MPIOM to correct the altimeter data for high-frequency ocean signals. MPIOM is taylored to predict non-tidal perturbations in satellite orbits (AOD1B RL06; Dobslaw et al., 2017). The data extends back to the launch of the GEOSAT mission in 1985 and is routinely updated into present time. Tidal signatures associated with effects of atmospheric tides were carefully removed in order to retain the non-tidal variability only. For our analysis, we have access to 3 hourly global grids of sea surface height anomalies separated into its barotropic and baroclinic components.
Based on data from different satellite missions (Topex, Jason-1, Saral-Altika) for selected years, we will demonstrate that applying model-based corrections to along-track data substantially reduces the high frequency variability of the gridded sea-level anomalies. Whereas modelled density-related sea-level changes turn out to be less effective, we find that removal of barotropic signals caused by time-variable surface wind stresses and atmospheric pressure variations significantly reduces high-frequency variability in global gridded products. The effect of this correction step is in particular visible in areas of strong wind-driven ocean dynamics as the Southern Ocean and the North Atlantic.
Dobslaw, H., Bergmann-Wolf, I., Dill, R., Poropat, L., Thomas, M., Dahle, C., Esselborn, S., König, R., Flechtner, F. (2017). A New High-Resolution Model of Non-Tidal Atmosphere and Ocean Mass Variability for De-Aliasing of Satellite Gravity Observations: AOD1B RL06. Geophysical Journal International, 211(1), 263-269, DOI: doi.org/10.1093/gji/ggx302.
In this study, we utilize surface height variations from the ocean general circulation model MPIOM to correct the altimeter data for high-frequency ocean signals. MPIOM is taylored to predict non-tidal perturbations in satellite orbits (AOD1B RL06; Dobslaw et al., 2017). The data extends back to the launch of the GEOSAT mission in 1985 and is routinely updated into present time. Tidal signatures associated with effects of atmospheric tides were carefully removed in order to retain the non-tidal variability only. For our analysis, we have access to 3 hourly global grids of sea surface height anomalies separated into its barotropic and baroclinic components.
Based on data from different satellite missions (Topex, Jason-1, Saral-Altika) for selected years, we will demonstrate that applying model-based corrections to along-track data substantially reduces the high frequency variability of the gridded sea-level anomalies. Whereas modelled density-related sea-level changes turn out to be less effective, we find that removal of barotropic signals caused by time-variable surface wind stresses and atmospheric pressure variations significantly reduces high-frequency variability in global gridded products. The effect of this correction step is in particular visible in areas of strong wind-driven ocean dynamics as the Southern Ocean and the North Atlantic.
Dobslaw, H., Bergmann-Wolf, I., Dill, R., Poropat, L., Thomas, M., Dahle, C., Esselborn, S., König, R., Flechtner, F. (2017). A New High-Resolution Model of Non-Tidal Atmosphere and Ocean Mass Variability for De-Aliasing of Satellite Gravity Observations: AOD1B RL06. Geophysical Journal International, 211(1), 263-269, DOI: doi.org/10.1093/gji/ggx302.