642 



Ihe epoch 1995 World Magnetic Model (WMM), which was 

 designed to meet DoD needs until the year 2000. Project 

 MAGNET flights (500 hours per year) and the DoD Geomag- 

 netic Library are funded through FY 95. However, the Navy 

 plans to terminate its entire geomagnetic project by FY 96. 



MEDEA is particularly concerned tliat magnetics data may be 

 especially vulnerable to loss, and we feel it is essential that these 

 data be protected. T!ie collected geophysical data have many 

 scientific purposes. Rapid release of the data to tlie academic 

 community would solve the problem of continued viability. 

 Experience shows that any database that is not regularly used is 

 almost certain to disappear in short order. Unused data have a 

 short shelf life because of the difficulties of adequately 

 documenting and storing data for future use. 



e. Scientific Utility 



.'\ceess to dense, marine magnetic surveys would be extremely 

 valuable to the geophysical community m several important 

 scientific applications. 



i) Improvements in the Accuracy of Plate Tectonic 



Reconstruction 

 The data-dense magnetic surveys can be used to place more 

 accurate constrai nts on the age of tile seafloor. Combined with 

 the recently available satellite radar bathymetrv' (Geosat and 

 ERS-I) measurements, magnetic survey data will make it 

 possible to increase the precision of calculated plate 

 reconstruction rotation parameters including finite rotations 

 associated with the long-term evolution of the Pacific and 

 Atlantic. These rotation parameters are the foundation of most 

 plate tectonic studies. 



II j Analysis of the Jurassic and Cretaceous Quiet Zones 

 The ongin of Ihe magnetic quiet zones, which encompass large 

 areas of the ocean Hoor, is still unknow n. Analysis of dense 

 magnetic surveys would be very helpful for evaluating various 

 proposed models. One idea that could be tested, with 

 fundamental implications for geomagnetism, is that the Jurassic 

 and Cretaceous Quiet Zones have different origins. The 

 Cretaceous Quiet Zones may represent a period of time when 

 ihe field intensity was strong but the polarity was not reversing. 



while the Jurassic Quiet Zones may represent a period of time 

 when the field was reversing very rapidly but the intensity was 

 low. High-resolution magnetic surveys could test this idea. 



Hi) Origin of Intermediate Wavelength Crustal Anomalies 

 One of the most poorly understood aspects of the crustal 

 magnetic field data is intermediate wavelength anomalies of 

 roughly 500-3,000 wavelengths in size. Anomalies at these 

 wavelengths have been identified in satellite magnetic fields, 

 but their source within the crust (and even their existence) has 

 been difficult to establish and is a matter of debate. There is 

 currently a mismatch in the amplitude of these anomalies by 

 about a factor of two, when sea surface observations are 

 extrapolated for comparison with satellite observations (e.g., 

 NASA MAGSAT). It has been suggested that these differences 

 are caused by satellite altitude errors combining to attenuate the 

 magnitude of an average vector of component data, but they are 

 more probably due to assumptions about interpolation implicit 

 in the upward continuation process. The resolution of this 

 question is important not only in determining the size of 

 intermediate wavelength magnetic anomalies, but also in 

 deciding what can be resolved from magnetic satellite data 

 Current sea surface data sets suffer from inadequate secular 

 variation corrections because of their irregular temporal and 

 spatial distributions, complicating comparisons between surface 

 and satellite observations. The good temporal and spatial 

 resolution of the Navy data could allow resolution of the source 

 of these ambiguities. 



ii ■) Geomagnetism and Earth 's Core 

 The magnetics data collected by the Navy were collected over 

 several decades while the seculardong-term. indefinite duration) 

 variation in Earth's field changed significantly and a series of 

 International Geomagnetic Reference Fields (IGRF) were 

 developed to allow the study of anomalous variations in the 

 field. The detailed, well-navigated, well-calibrated surveys 

 copducted in three dimensions (x, y, t) should provide a data- 

 base currently unequaled for understanding the details in the 

 evolution of the main geomagnetic field. This information will, 

 in turn, constrain estimates of the flow in the fluid core 

 and interactions between the core and the mantle at the core- 

 mantle boundary. 



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