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Time Domain Electromagnetic Surveys Collected to Estimate the Extent of Saltwater Intrusion in Nassau and Queens County, New York, October-November 2017

Metadata Updated: October 26, 2023

During October-November 2017 twelve time domain electromagnetic (TDEM) surveys were collected in Nassau and Queens County. The data were collected to estimate the extent of saltwater intrusion in support of the Long Island Groundwater Sustainability Project in cooperation with the New York State Department of Environmental Conservation. In the TDEM method, an electrical current is run through a wire in a transmitter loop, which in turn produces a magnetic field. The strength of the magnetic field is proportional to the strength of the electrical current. The current is rapidly shut off and due to Faraday’s Law, a secondary current is induced. The strength of the secondary current is proportional to the rate of change (dB/dt) of the magnetic field. These induced currents travel into the subsurface and produce secondary magnetic fields that induce voltages in the central receiver coils. Conductive bodies in the subsurface create higher induced voltages in the receiver coils (Fitterman, 1986). The magnitude and decay of the voltages measured in the receiver coil are used to model a 1D sounding of resistivity with depth. TDEM data were collected using the ABEM WalkTEM acquisition unit. Depending on the size of the site, one of the following transmitter loop geometries were used: 1) 40 by 40 meter square, or 2)100 by 100 meter square. A central induction array was used where two receiver loops were set up within the transmitter loop: 1)A 0.5 by 0.5 meter square, and 2) a 10 by 10 meter square. Due to the quantity of loops in each receiver coil, the effective areas were 35 square meters and 1400 square meters, respectively. Two to three surveys were conducted at each site using various time-gate scripts in the WalkTEM unit and the data were filtered, stacked 10 times, and averaged. This data release includes XML metadata, a site location map, the raw and processed TDEM data, and the inverted soundings showing resistivity (in ohm-m) with depth at the 12 survey sites in Nassau and Queens County. REFERENCES CITED:
Fitterman, D.V., and Stewart, M.T., 1986, Transient electromagnetic sounding for groundwater: Geophysics, v. 51, p. 995–1005.

Access & Use Information

Public: This dataset is intended for public access and use. License: No license information was provided. If this work was prepared by an officer or employee of the United States government as part of that person's official duties it is considered a U.S. Government Work.

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Metadata Created Date June 1, 2023
Metadata Updated Date October 26, 2023

Metadata Source

Harvested from DOI EDI

Additional Metadata

Resource Type Dataset
Metadata Created Date June 1, 2023
Metadata Updated Date October 26, 2023
Publisher U.S. Geological Survey
Identifier USGS:5d3083bfe4b01d82ce84a7d8
Data Last Modified 20200831
Category geospatial
Public Access Level public
Bureau Code 010:12
Metadata Context
Metadata Catalog ID
Schema Version
Catalog Describedby
Harvest Object Id e5cf5294-caf5-45d8-8098-7843f5e5b18f
Harvest Source Id 52bfcc16-6e15-478f-809a-b1bc76f1aeda
Harvest Source Title DOI EDI
Metadata Type geospatial
Old Spatial -73.879669,40.600486,-73.534794,40.720539
Publisher Hierarchy White House > U.S. Department of the Interior > U.S. Geological Survey
Source Datajson Identifier True
Source Hash 038549cee3e28c2e6c2b57e73e47f27663a77e346850385236431734aebf9a0a
Source Schema Version 1.1
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