Continuous Resistivity profiling in shallow marine and fresh water environments

In this paper, we describe an instrument system for performing continuous resistivity profiling in shallow freshwater and marine environments. Using a streamer cable containing 9 electrodes, the system continuously samples the dipole-dipole resistivity at n-spacings 1 through 6. The system can be installed aboard a variety of small inboard or outboard powered vessels in a few hours. Hand-held or marine GPS units provide location information that is recorded by a laptop computer. With this system, up to 40 line-km/day of dipole-dipole data have been collected. The resistivity data are merged with the GPS positions as a post-processing step. The final step in the post-processing is the inversion of overlapping segments of each profile using a 2-D smooth model. The inversions provide high resolution images of the geoelectric cross-section. The depth of investigation ranges from 20-30 m, with a 10 m dipole spacing. Over the last 4-years, we have performed surveys on the Ohio River, near Louisville, KY, on tidal estuaries and bays along the Atlantic coast in Delaware, Maryland, Virginia, and North Carolina, and in Tampa Bay, Florida. Data from these surveys will be used to illustrate the final deliverable from a survey.