Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

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D iscussion P aper
| D iscussion P aper |
D iscussion P aper
| D iscussion P aper |
Ocean is unphysical, and subtract it from each along-track row; this approach is similar to those applied in previous studies (Boersma et al., 2007).
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