Mapping ocean properties in regions of complex topography

Two algorithms are presented for mapping ocean properties in regions of complex topography. These algorithms greatly reduce the distortion introduced into mapped fields by interpolation methods that use isotropic correlation functions in regions of non-uniform geomorphology. They were developed for inclusion in a new high-resolution seasonal atlas of temperature, salinity, oxygen, nitrate, phosphate and silicate covering the major seas around Australia, New Zealand, Papua New Guinea and Indonesia (100–180°E, 50°S–10°N). Our schemes adjust the weighting of data-points to allow for bottom topography (topographic adjusted relief, TAR) and land barriers (barrier adjusted relief, BAR). The inclusion of these schemes in the mapping process allows the bathymetry to influence the mapped fields in a natural way, reduces leakage of structure between deep and shallow regions and produces far more realistic coastal gradients (it reduces the tendency to smear properties uniformly). In this study, the schemes are applied to a locally weighted least-squares filter, which involves projecting the data onto quadratic spatial functions. However, the approach should be applicable to other popular mapping techniques such as optimal interpolation. Examples are presented that demonstrate the improvements gained in mapping ocean properties in regions of complicated topography.