RES2DINV format continuous resistivity profiling data collected in Greenwich Bay, Rhode Island, May 14 and 15, 2009, on U.S. Geological Survey Field Activity 2009-021-FA
As part of a larger investigation to understand groundwater-surface water interactions in Greenwich Bay, Rhode Island, a geophysical survey was conducted from a small research boat on 14-15 May 2009. The specific research objective was to gain an improved understanding of the role of direct groundwater discharge in delivery of excess nitrogen to the bay, which may have contributed to the development of low-oxygen conditions in waters of the bay and associated fish kills. Data collected in this survey included digital navigation information, continuous resistivity profiling (CRP) data, and point salinity measurements. The CRP method is a survey and data processing approach that is sensitive to differences in electrical properties of surface water and underlying porewater in sediments that have contrasting salinities. During the survey, Greenwich Bay salinity was approximately 27 ppm, so surface water would be expected to have low electrical resistivity (high conductivity), and any areas of active groundwater discharge from less salty aquifer sources would yield relatively higher resistivity values. This survey is identified as field activity 09021 (also referenced as 2009-021-FA) by the U.S. Geological Survey, Woods Hole, Massachusetts, and additional information is available from: https://cmgds.marine.usgs.gov/fan_info.php?fan=2009-021-FA.
Cross, VeeAnn A., 2018, RES2DINV format continuous resistivity profiling data collected in Greenwich Bay, Rhode Island, May 14 and 15, 2009, on U.S. Geological Survey Field Activity 2009-021-FA: data release DOI:10.5066/F7DR2TSX, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.
Bratton, John F., and Cross, VeeAnn A., 2018, Continuous Resistivity Profiling Data and Associated Data from Greenwich Bay, Rhode Island collected in 2009, U.S. Geological Survey Field Activity 2009-021-FA: data release DOI:10.5066/F7DR2TSX, U.S. Geological Survey, Reston, VA.
Suggested citation: Bratton, J.F., and Cross, V.A., 2018, Continuous resistivity profiling data and associated data from Greenwich Bay, Rhode Island collected in 2009, U.S. Geological Survey Field Activity 2009-021-FA: U.S. Geological Survey data release, https://doi.org/10.5066/F7DR2TSX.
The purpose of this dataset is to provide the linearized continuous resistivity profile data from Greenwich Bay, Rhode Island in the RES2DINV format. These data were collected by the AGI SuperSting system and recorded in the AGI format. RES2DINV is another format for resistivity data that is used by numerous universities and researchers.
The continuous resistivity profile (CRP) system used on this cruise was an AGI SuperSting marine system described at the website: www.agiusa.com/marinesystem.shtml. Two streamer systems were used during this field activity - a 50-m streamer and a 100-m streamer. The 50-m streamer has an 11 electrode array with electrodes spaced 5 meters apart. The 100-m streamer has an 11 electrode array with electrodes spaced 10 meters apart. In both cases the source electrodes are graphite, while the receiver electrodes are stainless steel. A dipole-dipole configuration was used for the data collection in which two fixed current electrodes are assigned with the measurement of voltage potential between electrode pairs in the remaining electrodes. The maximum depth below the water surface the streamer can reach is approximately 1/4 the streamer length. So for the 50-m streamer, maximum depth is about 12.5 meters while the 100-m streamer maximum depth is about 25 meters. Each line of data acquisition records several files. The two files necessary for processing are the *.stg and the *.gps file. The STG file contains the resistivity data, while the GPS file contains the navigation information. The navigation system used in concert with the CRP system is a Lowrance LMS-480M with an LGC-2000 GPS antenna and a 200 kHz fathometer transducer. The antenna and fathometer transducer were mounted on the starboard side of the boat. The streamer tow point was on the port side aft. The layback offset between the navigation antenna and the first electrode was 16.5 meters. This layback offset was not accounted for during data acquistion, so was entered during processing of the data. The approximately 2.5 m lateral offset between the streamer tow point and the navigation antenna is not accounted for. The Lowrance transducer also contains a temperature sensor that records temperature in degrees Celsius. For depth measurements, Lowrance indicates the speed of sound used by the system is 4800 feet/second, but depths are recorded in meters. Both the temperature and depth information are recorded in the logged GPS file. The CRP system images the subsurface electrical properties of an estuarine, riverine or lacustrine environment. Resistivity differences can be attributed to subsurface geology (conductive vs less conductive layers) and hydrogeologic conditions with fresh water exhibiting high resistivity and saline conditions showing low resistivity.
The linearized STG and DEP files generated by AGI's Marine Log Manager software AGI SSAdmin MLM v 1.3.4 were converted to a format suitable for the RES2DINV processing software. The STG and DEP files are available from this data release. The conversion was accomplished by a Visual Basic 6 program written at the USGS office in Woods Hole (AGI2res2d.exe - no version number). The DEP file used has a water resistivity value of 0.296 ohm-m.
Person who carried out this activity:
VeeAnn A. Cross
U.S. Geological Survey
Woods Hole Coastal and Marine Science Center
Woods Hole, MA
(508) 548-8700 x2251 (voice)
(508) 457-2310 (FAX)
Data sources used in this process:
Data sources produced in this process:
Date: 08-Sep-2020 (process 2 of 2)
Added keywords section with USGS persistent identifier as theme keyword.
Person who carried out this activity:
How accurate are the geographic locations?
The navigation system used was a Lowrance 480M with an LGC-2000 Global Positioning System (GPS) antenna. The antenna was located 1.5 meters forward of the resistivity streamer tow point and directly above the fathometr transducer. The GPS is assumed to be accurate to within 10 meters.
How accurate are the heights or depths?
All bathymetry values were acquired by the 200 kHz Lowrance fathometer. The fathometr was mounted on the starboard side of the University of Rhode Island pontoon boat, cirectly below the GPS antenna. The Lowrance manufacturer indicates the speed of sound used by the system to calculate depth is 4800 feet/second. The depth values are not corrected for the approximately 0.2 m transducer draft. All depth values are assumed to be accurate to within 1 meter.
How consistent are the relationships among the observations, including topology?
Each file was looked at individually, but the files as a collection were handled in the same manner. All files on May 14, 2009 were collected with a 50-m resistivity streamer. The command file (*.cmd) used for data acquisition has a 1 meter electrode spacing. To adjust to the actual 5 meter spacing between electrodes of the 50-m streamer, a scaling factor of 5 was applied during data acquistion. All files on May 15, 2009 were collected with a 100-m resistivity streamer. The command file (*.cmd) used for data acquistion has a 1 meter electrode spacing. A scaling factor of 2 was erroneously applied during data acquistion. Since this data of data acquisition used the 100-m streamer, the scaling factor of 10 should have been used, but wasn't. This problem was resolved during the processing of the data by supplying a scaling factor of 5.
What's the catalog number I need to order this data set?The 2009-021-FA_res2dinv.zip file contains the RES2DINV formatted resistivty data - as individual files in the folder 2009-021-FA_res2dinv. Additionally, the zip file contains FGDC CSDGM metadata in the following formats: XML, HTML, and text.
Neither the U.S. government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.