Charting of Outer Continental Shelf Surface Currents by Aerial Tracking of Tracers

As part of a physical oceanographic study of the New England OCS sponsored by the U.S. Bureau of Land Management, techniques have been developed for acquisition of synoptic surface currents data over large areas. Dye-emitting Lagrangian tracers, equipped with radio location beacons, are seeded in patterns and tracked by aircraft for several days. The aircraft-deployed tracers consist of 132 cm-long cylinders, containing a fluorescent dye mixture, which are weighted to float vertically. Four color coded arms joined to the cylinder near its top provide for unique visual identification, and frequency-audio coded VHF radio location beacons are mounted in the top of selected tracers. Tracer tracking is accomplished with a Cessna Skymaster aircraft with VHF homing equipment, vertically mounted Hasselblad cameras, a radiometer, and an advanced Loran C unit. The photographic tracer data is subsequently digitized in the lab and computer-processed into tabular and graphical displays. In a typical study, between 60 and 180 tracers are deployed in several patterns dispersed over an area of approximately 25,000 km². A cargo aircraft such as a Beechcraft G-18 is used for tracer deployment, and relocation of tracers takes place with the Sky-master for several days thereafter. Results to date have yielded interesting data on regional circulation, diffusion, and circulation within a warm-core eddy.