Locating and delineating sea floor occurrences of petroleum seepage is achieved by apparatus for the detection of the resulting abnormal distribution of electrical potential within the affected sediments. An electrically insulating probe (20) is deployed by a steel cable (18) from a ship (10) for the implantation of electrodes (40,42,44,46,48) within the sediment (14) at depths of between 60 cm and 5 m. Insulated conductors within the probe (20) connect the electrodes (40,42,44,46,48) to a reference electrode by way of an electrometer which facilitates measurement of the difference in electrical potential between any one of the probe electrodes (40,42,44,46,48) and the reference electrode. Digital measurements are conducted to an associated acoustic modem (34) and thence to the ship (10) through the water (12). The system allows rapid assessments of sedimentary electrical conditions over large areas of seafloor by the repeated introduction, utilization, withdrawal, and relocation of the probe (20). Similarly, occurrences of dumped organic refuse, sewage sludge, or other organic matter, may be delineated. IMAGE
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