The objective of this study is to investigate the feasibility of extracting intermediate-wavelength magnetic anomalies of wavelengths between 4000 and 400 km from total field data acquired in marine magnetic surveys. The intention is to develop a second data set which may be used in conjunction with the satellite magnetic field to determine anomaly and source distributions. We apply our technique to the recovery of intermediate-wavelength total intensity anomalies over the North Pacific from marine survey data. The technique also provides a record of secular variation during the period 1960 to 1980. In areas of high track density the sea surface data can be used to refine the Magsat data processing techniques and also provide further constraints on source models. In areas of reduced sea surface track density the Magsat field provides higher resolution. The Magsat data set also records vector field data. As will be shown, the filtered sea surface data set provides a higher-resolution field than the Magsat data, due to proximity to lithospheric source bodies. The sea surface data also provide an independent check of the Magsat field, since the two fields should be equivalent after upward continuation of the sea surface field. We notice, however, that for the central Pacific the upward continued sea surface field is approximately 2 times the amplitude of the Magsat field. The spatial correlation of the two anomaly fields is very strong.