Floating and Towed Transient Electromagnetic Surveys used to Characterized hydrogeology underlying Rivers and Estuaries: March to December 2018

Surface and water-borne geophysical methods can provide information for the characterization of the subsurface structure of the earth for aquifer investigations. Floating and towed transient electromagnetic (FloaTEM and tTEM) surveys provide resistivity soundings of the subsurface, which can be related to lithology and hydrogeology. In the TEM method, electrical current is cycled through a wire in a transmitter loop (Tx), which in turn produces a static magnetic field. When the current is abruptly terminated, an instantaneous current is induced in the earth, and it moves downward and outward as the induced current decays with time. The decay is controlled by the resistivity of the earth. A receiver (Rx) pulled behind the Tx loop measures the secondary magnetic field as a function of time (dB/dt). Decaying voltage measurements at the receiver are converted to apparent resistivity, which can be inverted to recover the depth-dependent resistivity structure of the earth. FloatTEM surveys were conducted at four locations on the Eel River near Falmouth, Massachusetts,on the Rainbow Reservoir near Windsor, Connecticut, on the Upper Delaware River near Barryville, New York, and on the Tallahatchie River in Shellmound, Mississippi. A tTEM survey was collected adjacent to the Tallahatchie River in Shellmound, Mississippi. The data collected at each site are provided as separate datasets. This data release includes the averaged, culled and inverted TEM data showing resistivity (in ohm-meters) with depth for each of the survey sites.