Comparison between the recent U.S. composite magnetic anomaly map and Magsat anomaly data

The present investigation is concerned with a comparison of Magsat data with a Composite Magnetic Anomaly Map (CMAM) of the conterminous U.S. reported by Zietz (1982). The investigation was initiated to test the validity of the satellite measurements, and to provide insights into error or problems in either data set. It is found that upward continuation of the digital CMAM data is not in qualitative agreement with the Magsat map. However, if a least squares fit polynomial surface is taken out prior to upward continuation, there is improved quantitative agreement between a residual CMAM and Magsat. Causes for the remaining differences between the residual, upward continued CMAM and the Magsat map are also considered.