Conditional multivariate functional PCA for the reconstruction of temperature and salinity profiles partially sampled by deep-diving marine mammals
This study addresses the incomplete depth coverage of temperature–salinity profiles collected by deep-diving marine mammals in the Indian Ocean sector of the Southern Ocean, which arises from behavioral differences among individuals. To overcome this limitation, the authors propose a multivariate functional principal component analysis method incorporating geographic covariates. By modeling the mean and covariance structure of complete bivariate profiles, they construct eigenfunction bases and integrate a measurement error model to estimate conditional functional principal scores, enabling high-fidelity reconstruction of truncated profiles across the full depth range. In simulations, the approach improves reconstruction accuracy by 30% for temperature and 33% for salinity in the 20–500 m layer when applied to profiles truncated at 250 m. The method successfully reconstructs approximately 90,000 profiles across a 3-million-square-kilometer region surrounding the French subantarctic islands, marking the first large-scale, accurate recovery of incomplete oceanographic profiles.