A new approach to the determination of a mean sea surface model using multi-satellite altimeter data
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Models for the mean sea surface (MSS) are created by combining and interpolating on a specified spatial grid inhomogenous data sets from different satellites with different ground track coverage. There are various approaches in which the sea surface height (SSH) data from different satellites can be combined to create an accurate reference surface. The orbit errors (especially from the early missions) need to be reduced, and systematic biases between different satellites can be decreased by re-processing them using the improved models and geophysical corrections. In this research, a new method for the data adjustment (or error reduction), which attempts to compensate for both long-wavelength orbit errors and systematic biases, simultaneously and efficiently. The approach is based on using an accurate sea surface profile as a reference surface for the integration process. The new data adjustment technique is based on along-track SSH gradients computed for each satellite, which are integrated along-track with initial values obtained by dual crossover computation with respect to an accurate set of sea surface heights. The accurate Jason-1 SSH data were used to determine the reference surface, and a total of 5 different satellites (Geosat ERM, ERS-2, T/P, Envisat and ERS-1 geodetic mission) data were adjusted to the Jason-1 SSH data. After editing, the new homogeneous SSH datasets were averaged into mean SSH profiles. Then, they were gridded into a 5-minute resolution mean sea surface over the global ocean within ±60º latitudes, as defined by the Jason-1 mean profile, using a 2-D spline interpolation in tension with Green’s function approach. The new gridded mean sea surface, named CSRMSS14 was validated by three comparisons. First, it was compared with two accurate altimeter data sets: 7-year Jason-1 and 8-year Envisat mean profiles. Second, two recent MSS models, DNSC08 and DTU10, were compared to investigate the accuracy of CSRMSS14. Third, a somewhat independent test is obtained by comparing a 2-year Jason-2 mean profile with the three MSS models (CSRMSS14, DTU10 and DNSC08), since Jason-2 data were not used in their construction. These three validations demonstrated that CSRMSS14 mean sea surface model obtained with this new approach is comparable in accuracy to DNSC08 and DTU10.