The PI's request funding to build an inexpensive magnetic drifter that works well for a typical, hypothesis-driven NSF project that studies a specific region. They envision a mode of data collection where investigators release a flotilla of inexpensive surface drifters upstream of an area they wish to study with magnetic field data. The drifters pass over the study site, collecting the desired data. These relatively, small, low power and inexpensive magnetic sensors can be obtained and combined or integrated with the circuitry within the drifter. Because the drifter moves slowly, the magnetometer can be set up to read the geomagnetic field infrequently keeping the data rate low.
Magnetic field data from the oceans have been critical for understanding the origin, evolution and structure of the ocean basins. The marine magnetic stripe anomalies not only document Earth?s magnetic field polarity reversals but also form the basis for the Geomagnetic Polarity Timescale and are used to reconstruct the history of the ocean basins. These anomalies are best resolved by sea surface magnetic measurements. Satellite magnetic measurements, while global in extent, lack the lateral resolution to resolve these magnetic stripe anomalies in detail. While we have a working knowledge of most of the ocean basins there are areas, such as the southern ocean, that have only sparse shiptrack coverage. In a recent global compilation for the World Digital Magnetic Anomaly Map (WDMAM, Purucker, 2007) the available data was so sparse that a model of magnetic anomalies was used to help interpolate data. Shiptime is expensive and global coverage in remote areas is simply not feasible in the near future. The solution we believe is to use the proven technology of ocean drifters and floats used by the physical oceanographic community and mount small, low power, inexpensive magnetometer sensors to these drifters to cover areas of the ocean that are undersampled at present.
Broader Impacts:
The main broader impact emphasized in the proposal seems mainly the advanced training of a post-doc; and potentially involving a summer undergraduate student. Clearly the ability to collect much-needed geomagnetic data at a fraction of the cost of ship time would have broad impacts in the geosciences community. The proposal will support a female postdoctoral fellow. Data obtained will be used by many other researchers and have a broad impact throughout the tectonics community.
The primary objective of this project was to investigate the feasibility of using autonomous sea surface drifter buoys typically used for physical oceanography to collect measurements of Earth's magnetic field instead. Such a capability would go a long way toward enhancing the coverage and density of global marine magnetic field data in areas where ships are unlikely to transit or survey on a regular basis. Marine magnetic field data have been at the center of the plate tectonic revolution in earth sciences for the past 40 years providing insight and constraints on ocean basin evolution, geomagnetic field history, dynamics of earth's interior, and more recently the magnetic signature of ocean circulation. The sea surface is the optimum level at which to collect these data because satellite data lack the spatial resolution at orbital distances. Large areas remain undersampled such as the southern ocean. A magnetic ocean drifter program is an effective way to improve this sampling at a fraction of the cost of ship-based surveying. As part of this experimental program we evaluated two different types of magnetic sensors and then instrumented five surface drifter buoys for a deployment field test in the northeast Pacific Ocean. Those drifters transited over 13,000 nautical miles and relayed their data back to Woods Hole via a satellite communication link for more than a year at sea. The data reside on the magnetic drifter website http://deeptow.whoi.edu/magdrifter.html. Unfortunately, the magnetic field data collected were influenced by the large fields of the drifter battery which makes the interpretation difficult. Nevertheless, magnetic anomaly and regional magnetic fields can be extracted from the data. An improved configuration would envision a sensor on the end of a drogue cable suspended beneath the drifter, although this is risky and not likely to be robust for anything more than a few months at sea. Also, the drifting motion of the surface buoy means that drifter tracks are somewhat unpredictable on an individual basis. A platform such as a wave glider might be more advantageous because it can be directed to move in certain directions over time. The waveglider platform also allows for the magnetic sensor to be shaded from the sun's thermal influence and also for the sensor to be located far enough from the waveglider battery and solar panel to be quiet magnetically.
