DOI: 10.5066/p9e5jbaf
title: Floating and Towed Transient Electromagnetic Surveys used to Characterize Hydrogeology underlying Rivers and Estuaries: March - December 2018

description: 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, a primary electrical current is cycled through a wire in a transmitter loop (Tx), which in turn produces a static primary magnetic field. When the current in the TX loop is abruptly terminated, secondary electrical currents are induced in the earth that move downward and outward decaying with time. The decay of the secondary electrical field is controlled by the subsurface resistivity structure of the earth. The decay of the secondary electrical field causes a secondary magnetic field that is measured at a receiver (Rx) loop pulled behind the Tx loop. The Rx loop measures the decay of the secondary magnetic field as a function of time (dB/dt).TEM signals measured 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. (1) Files with *AVERAGED.xyz and *AVERAGED.csv are space- and comma-delimited ASCII files that contain the least processed data where transients were averaged together and most coupled data were removed.Data locations are provided as UTM Zone 15 N projection and datum of WGS-84. (2) Files with *CULLED.xyz and *CULLED.csv are space- and comma- delimited ASCII files containing the processed data where negatively-imapcted transients and coupled data were removed using a combination of automated and manual processing. Data locations are provided as UTM Zone 15 N projection and datum of WGS-84. (3) Files with *INVERTED.xyz and *INVERTED.csv are space- and comma-delimited ASCII files containing the inversion model results. Model locations are provided as UTM Zone 15 N projection and datum of WGS-84. (4) Files with *WATER-DEPTH_DATA.xyz and *WATER-DEPTH_DATA.csv are space- and comman-delimited ASCII files containing the water-depth data as measured from the bottom of the transducer. Water-depth measurement locations are provided as UTM Zone 15 N, WGS-84. (5) Files with *INVERTED_image.png and *INVERTED_image.pdf are the inverted model output as a 2D profile of electrical resistivity distribution in the subsurface.(5) Files with *INVERTED_image.png and *INVERTED_image.pdf are the inverted model output as a 2D profile of electrical resistivity distribution in the subsurface. (6) File: *AEM2018_EM_Mag_Rad_rawData_L8072002.csv is comma-delimited ASCII file that contain the least processed data. Data locations are provided as latitude/longitude, and Albers Conus projection and datum of NAD-83. (7) File: *AEM2018_ProcessedData_L8072002.csv is comma- delimited ASCII file containing the processed data . Data locations are provided as latitude/longitude, and Albers Conus projection and datum of NAD-83. (8) File: *AEM2018_ResistivityModels_L8072002.csv is comma-delimited ASCII files containing the inversion model results. Model locations are provided asas latitude/longitude, and Albers Conus projection and datum of NAD-83. (9) File: *AEM_LINE120_INVERTED_image.png and *AEM_LINE120_INVERTED_image.pdf are the inverted model output as a 2D profile of electrical resistivity distribution in the subsurface.