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High-frequency sea level altimeter data for the validation of GRACE ocean-dealiasing products | ALT4VAL

Three maps of the root mean square of the sea level are shown with global coverage (66°S to 66°N). The range of values is between 2 and 10 cm, with the overall signal showing the highest values. The high-frequency signal occurs primarily in the Antarctic Circumpolar Current and the western boundary currents (Kuroshio and Gulf Stream). The low-frequency signal is particularly pronounced in the tropics, but is also significant in the western boundary currents.
Root mean square of the sea level calculated from daily radar altimetry of the Envisat mission for the period 01/2003 to 12/2008. Top left: Total signal, top right: high frequencies (< 30 days) and bottom left: low frequencies (> 30 days). Instead of the commonly used dynamic atmospheric correction (DAC), a combination of AOD-1B RL05 with inverse barometric height was employed. (Data ADS and AOD-1B RL05, Figure S. Esselborn, GFZ)

Data from satellite altimeters are often used to validate ocean circulation models. In order to eliminate the alias effects in the GRACE measurements, high-frequency mass variations in the ocean are modeled at GFZ with the 'Ocean Model for Circulation and Tides' (OMCT) and made available as a so-called Atmosphere and Ocean De-Aliasing Level-1B Product (AOD-1B). The versions RL05 and RL06 of this product were validated with Jason-2 and Envisat altimeter data from the ADS system of the GFZ.

For this purpose, the altimeter data were corrected along the satellite tracks as standard. However, instead of the usual dynamic atmospheric correction (DAC), a combination of an inverse barometric correction and 6-hourly oceanic mass variations from different versions of the OMCT model (RL04, RL05, RL06) was subtracted. The corrected altimeter data were finally interpolated to daily 1°x1° grids. To filter out signals with periods longer than 30 days from the data, a Butterworth filter was applied.

The analysis of the Envisat and Jason-2 data shows an improvement of the oceanic mass variations in the high frequency range from RL04 to RL05 for most ocean areas, especially in subpolar regions, while the changes from RL05 to RL06 are less pronounced and regionally more limited.

Project partners:

  • TU München

Project duration:

  • 2012-2015

Budget:

  • Househalt

Project related publications:

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