David V. Fitterman
20161231
Transient electromagnetic (TEM) sounding data; San Luis Valley, Colorado, 2009
Tabular digital data and portable document format (PDF)
Denver, CO
U.S. Geological Survey
http://dx.doi.org/10.5066/F7D21VQ5
Transient electromagnetic (TEM) soundings were made in the San Luis Valley, Colorado, to map the location of a blue clay unit as well as to investigate the presence of suspected faults. A total of 147 soundings were made near and in Great Sand Dunes National Park and Preserve, an additional 6 soundings were made near Hansen Bluff on the eastern edge of the Alamosa National Wildlife Refuge. The blue clay is a significant hydrologic feature in the area that separates an unconfined surface aquifer from a deeper confined aquifer. Knowledge of its location is important to regional hydrological models. Previous analysis of well logs has shown that the blue clay has a resistivity of 10 ohm-meters or less, which is in contrast to the higher resistivity of sand, gravel, and other clay units found in the area, making it a very good target for TEM soundings. The top of the blue clay was found to have considerable relief suggesting the possibility of deformation of the clay during or after deposition. Because of rift activity deformation is to be expected. Of the TEM profiles made across faults identified by aeromagnetic data, some showed resistivity variations and (or) subsurface elevation relief of resistivity units suggestive of faulting. Such patterns were not associated with all suspected faults. The Hansen Bluff profile showed variations in resistivity and depth to conductor that coincide with a scarp between the highlands to the east and the floodplain of the Rio Grande River to the west.
Data were collected to map the location of clay units and investigate the presence of suspected faults in the San Luis Valley, Colorado.
Transient electromagnetic (TEM) sounding reports and plots are provided in folders (child items), described here, and discussed in more detail in the Data Series by Fitterman (2016).
There is one item for each field season with a name in the format "Transient Electromagnetic (TEM) Sounding Data; San Luis Valley, Colorado, yyyy," where yyyy is the year the data were collected: "Transient Electromagnetic (TEM) Sounding Data; San Luis Valley, Colorado, 2007," "Transient Electromagnetic (TEM) Sounding Data; San Luis Valley, Colorado, 2009," and "Transient Electromagnetic (TEM) Sounding Data; San Luis Valley, Colorado, 2011." The contents of each field season folder are as follows:
A. AVG_DATA - Averaged data files folder
B. EXT_DATA - Extracted data files folder
C. INV_DATA - Inversion output files folder
D. PRV_DATA - Averaged data report folder
E. RAW_DATA - Raw data folder
F. GRSANDyy.TX3 - TEMIXXL database file
E. TEM_plots_yyyy.pdf - TEM resistivity-time and resistivity-depth plots as PDF files
F. TEM_report_yyyy.pdf - Inversion results for all soundings as a portable document format (PDF) file
G. TEM_report_yyyy.txt - Inversion results for all soundings as a text file
GTX FILE FORMAT
The raw data collected in the field are written in Geonics TEM file (GTF) format. Files with the extensions .TEM and .TAV are in GTF format. The GTF files consist of records 256 characters long containing a 50-character header field followed by 25 data fields of 8 characters each. A 4-character, sequential record number follows the last data field. The last 2 characters of the record are a carriage return and a line feed. PROTEM-D and PROTEM (analog) both utlize the TEM format which are divided into fields for header (HDR) and data (OPR) records. These are structured differently and the format is explicitly detailed in the data dictionaries (Table 2-1 to 2-8). The HDR record format with header fields and data fields is described in tables 2–1 and 2–3 for PROTEM-D data and tables 2–5 and 2–7 for PROTEM data. The OPR record with format with header fields and data fields is described in tables 2–2 and 2–4 for PROTEM-D data and tables 2–6 and 2–8 for PROTEM data.
REFERENCES CITED
Grauch, V.J.S., Fitterman, D.V., and Drenth, B.J., 2010, Finding faults using high-resolution aeromagnetic data in Great Sand Dunes National Park and vicinity, San Luis Valley, Colorado, Proceedings of 23rd Symposium on the Application of Geophysics to Engineering and Environmental Problems SAGEEP 2010, Keystone Colorado, Environmental and Engineering Geophysical Society, pp. 428-437.
Valdez, A., 2007, Stop A8 -- Closed basin overflow and origin of Hansen Bluff, in Machette, M. N., Coates, M.-M., and Johnson, M. L., 2007, 2007 Rocky Mountain Section Friends of the Pleistocene Field Trip--Quaternary Geology of the San Luis Basin of Colorado and New Mexico, September 7-9, 2007, in Machette, M.N., Coates, M.-M., and Johnson, M.L., eds., U. S. Geological Survey Open-File Report 2007-1193, pp. 38-39.
20090707
20090718
ground condition
Not planned
-105.784550862
-105.547214551
37.91541792
37.44396808
ISO 19115 Topic Category
geoscientificInformation
USGS Thesaurus
electromagnetic surveying
groundwater
subsurface maps
clay deposits
faulting (geologic)
geophysics
None
fault detection
transient electromagnetic sounding
subsurface mapping
clay
TEM
aquifer
USGS Metadata Identifier
USGS:5841f06ce4b04fc80e518d4f
Geographic Names Information System (GNIS)
Colorado
San Luis Valley
Saguache County
Alamosa County
Great Sand Dunes National Park
Great Sand Dunes National Preserve
Alamosa National Wildlife Refuge
none
There is no guarantee concerning the accuracy of the data. Users should be aware that changes may have occurred since measurement and publication; therefore some parts of this dataset may no longer be applicable. This dataset should not be used to extract precise values but instead be used to examine regional patterns. Users should not use these data for critical applications without a full awareness of their limitations. Any user who modifies the data is obligated to describe the types of modifications they perform. User specifically agrees not to misrepresent the data, nor to imply that changes made were approved or endorsed by the U.S. Geological Survey. Please refer to http://www.usgs.gov/privacy.html for the U.S. Geological Survey disclaimer.
V.J. (Tien) Grauch
U.S. Geological Survey
Mailing and Physical
Denver Federal Center, Bldg 20, MS 964, Box 25046
Denver
CO
80225
United States
303.236.1393
tien@usgs.gov
Andrew Valdez and Fred Brunch (National Park Service) were invaluable in gaining access to Great Sand Dunes National Park and Preserve and the Zapata-Mendano Ranch, familiarizing U.S. Geological Survey (USGS) personnel with the area, and assisting with field operations including the retrieval of stuck vehicles. Ron Garcia (U.S. Fish and Wildlife Service) facilitated access to U.S. Fish and Wildlife Service lands including the Baca National Wildlife Refuge and the Alamosa National Wildlife Refuge. Data collection would not have been possible without the effort of Chad Ailes (USGS), Jay Sampson (USGS), Calvin Johnson (UNAVCO), and Daniel Labson (USGS). Discussions with Tien Grauch (USGS) provided important information about aeromagnetic and drill hole data that helped guide the direction of this work. This work was funded in part by the National Cooperative Geologic Mapping Program and was done in cooperation with the National Park Service.
Environment as of Metadata Creation: Microsoft [Unknown] Version 6.2 (Build 9200) ; Esri ArcGIS 10.3.1 (Build 4959) Service Pack N/A (Build N/A)
No formal attribute accuracy tests were conducted
No formal logical accuracy tests were conducted
Data set is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details.
The accuracy range during location data collection was 4 to 9 meters. No other quantitatve assessments of accuracy were conducted.
Elevation accuracy is +/- 1/2 of the contour interval from the source topographic maps (1:24,000) and dependent on manual interpolation of the point location. No quantitative analyses of accuracy were conducted. The point elevations collected with the survey-grade GPS had sub-meter accuracy.
2009 COLLECTION
In 2009, the field work continued with three goals: (1) to provide detailed subsurface information for monitoring wells that were to be drilled for the National Park Service along the western boundary of the GRSA, (2) to continue mapping of the blue clay inside the GRSA and westward into the Baca National Wildlife Refuge, and (3) to make short profiles across suspected faults identified by aeromagnetic surveys along the eastern edge of the valley (fig. 2) (Grauch and others, 2010). A total of 64 soundings were made, including 10 at the boundary piezometer (BP) sites, 47 across suspected faults, and 17 for clay mapping.
EQUIPMENT
All soundings (BP01 through BP-10 and GSD201 through GSD254) were made using the USGS-CGG PROTEM-D receiver and the battery-powered EM-47 transmitter. A square transmitter loop with a nominal side length of 38.1 m was used. A single-component receiver coil with a moment of 31.4 m^2 was placed at the center of the transmitter loop.
20090701
SOUNDING LOCATION AND ELEVATION
Coordinates of the soundings were determined by Global Positioning System (GPS) measurements for field seasons 2007, 2009, and 2011. Horizontal positions are referenced to the North American Datum of 1927 (NAD27). The GPS unit reported positioning error uncertainties of between 4 to 9 m. Most elevations were obtained by using the GPS coordinates to locate the soundings on 7.5-minute topographic maps and then interpolating between the elevation contours. Accuracy is therefore a fraction of the map contour interval. For a few of the 2011 sites that were located on the western portion of the sand dunes where the validity of the contours on the topographic maps is less reliable, high-resolution GPS measurements were used to determine elevations. The vertical reference for all elevations is the National Geodetic Vertical Datum of 1929 (NGVD 29).
20110801
EQUIPMENT SETTINGS
The equipment settings are for all field seasons (2007, 2009, and 2011). For the EM-47 configuration, the transmitter current was typically 2.5 amperes (A). The receiver coil was a rigid loop about 1 meter in diameter with a moment of 31.4 square meters. The receiver coil was located at the center of the transmitter loop. After adjusting receiver gain to an appropriate level, measurements were made using base-frequency repetition rates of 285 hertz (Hz) and 30 Hz. The base frequency controls the time range over which the transient is recorded. There are 20 logarithmically spaced measurement gates associated with each base frequency. Each measurement represents a stack of several hundred individual transients.
For the EM-57 configuration, the transmitter current was typically 26 A, and the receiver coil located at the center of the transmitter loop had a moment of 200 square meters. The measurement technique was similar to the EM-47 configuration, however, the base-frequency repetition rates were typically 30 Hz and 3 Hz.
20110101
DATA PROCESSING
Processing of the transient electromagnetic (TEM) data included the following steps: (1) downloading, (2) averaging, (3) inversion, (4) extracting results, (5) plotting, and (6) report generation. The data processing is explained in detail in Appendix 1: Description of Transient Electromagnetic (TEM) Data Processing (Fitterman, 2016). http://dx.doi.org/10.5066/YYYY
20111201
CREATION OF SHAPEFILE AND COMMA-DELIMITED FILE (CSV)
The location data were compiled into a data table containing the TEM unique identifier, coordinates, elevation, and year of collection, Sounding_locations_SLV_Colorado_2007_2009_2011.csv. The data table was added to ArcMap, converted to an event layer (right-click, Data, Display XY Data), and exported to a shapefile, Sounding_locations_SLV_Colorado_2007_2009_2011.shp.
20160914
Point
Entity point
153
Universal Transverse Mercator
13
0.9996
-105.0
0.0
500000.0
0.0
coordinate pair
0.6096
0.6096
Meter
D_North_American_1927
Clarke_1866
6378206.4
294.9786982
AVG_DATA - extension .TAV
The files that contain the averaged data have the filename extension .TAV and use the GTF format. The header of the first record indicates the type of instrument the data came from and whether the data have been averaged. If the PROTEM-D digital receiver was used, the header reads "Data from Geonics TEM58 RX. -- AVERAGED"; if the PROTEM analog receiver was used, the header reads "Geonics EMx7 TEM data from PROTEM -- AVERAGED." The data fields of this record are all set to zero. The second record is an HDR record with header fields and data fields as described in tables 2–1 and 2–3 for PROTEM-D data and tables 2–5 and 2–7 for PROTEM data. Next is an OPR record for each frequency average computed by the program DTEMAVG (or NTEMAVG for data recorded with an analog receiver). If different groups of data records were averaged, there will be multiple output records—one for each group. Following the last OPR record is a record whose header field starts with "XXXXX". The numbers in the data fields are meaningless. The OPR record with format with header fields and data fields is described in tables 2–2 and 2–4 for PROTEM-D data and tables 2–6 and 2–8 for PROTEM data.
U.S. Geological Survey
EXT_DATA - extensions .ROT and .ROZ
The text files that contain data and models in a form for plotting have the filename extensions .ROT and .ROZ. These files were compressed into zip files by each type, for example, SLV2007_rot.zip and SLV2007.roz.zip. The .ROT file contains the following information: 1) The sounding name; 2) Tab delimited column headings for the data that follow; 3) Tab delimited time and apparent resistivity data consisting of 6, 9, or 12 columns corresponding to 1, 2, or 3 transmitter repetition frequencies, respectively. Typically, the data are given in order of decreasing repetition frequency corresponding to later time ranges. The contents of the columns are specified in table 2–9 (Fitterman, 2016). When a sounding has fewer than 3 base frequencies (or sweeps), the unnecessary columns are omitted. The masked and m_err data follow immediately after the last sweep. The .ROZ files contain the following information: 1) The sounding name; 2) Tab delimited titles for the data that follow: "Depth (m)" and "Resistivity (ohm-m)"; 3) Tab delimited data for plotting a resistivity-depth plot. The .ROZ files are formatted with 2 columns, Depth (m) and Resistivity (ohm-m) and are sequenced as 1) Depth sequence: 0, z1, z1, z2, z2,..., zn-1, zn-1, zn-1 + max(10, 1.2*zn-1 ) and 2) Resistivity sequence: r1, r1, r2, r2,..., rn-1, rn-1, rn, rn. Depths are given as positive values below the surface. A sounding called ABC101 might have variants ABC101L4 and ABC101L5 to indicate models with four and five layers, respectively. The preferred model will not have the variant model indicator “Ln.” The only restriction on the extra characters in the sounding name is that the total number of characters in the name cannot exceed 8.
U.S. Geological Survey
INV_DATA - extension .INV
The reports generated by the TEM inversion program TEMIXXL have the filename extension .INV. They provide information on the sounding location, the measurement geometry, the model misfit error, the model parameter estimates, the measured resistivity and calculated model response, and usually a resolution matrix.
Misfit error reported by the TEM inversion program (TEMIXXL) is given as percentage RMS misfit for voltage data. The apparent resistivity misfit is approximately two-thirds of this value.
U.S. Geological Survey
PRV_DATA - extension .PRV
A printed summary of the averaging process is written to a file named in the form "aaannn.PRV". The text files that summarize the data averaging process have the filename extension .PRV. The first page of the file consists of a listing of all of the header record (HDR) and data record (OPR) header fields. The first line is a descriptive header indicating with which receiver type the data were collected. If the PROTEM-D digital receiver was used, the header reads "Data from Geonics TEM58 RX"; if the PROTEM analog receiver was used, the header reads "Geonics EMx7 TEM data from PROTEM logger." The second line usually contains HDR header fields. Subsequent lines are OPR header fields associated with the recorded data. Additional HDR header fields will be present if the operator made a change in the header information on the receiver. The output concludes with a record whose header field starts with "XXXXXX" to indicate the end of the data processing.
Following the summary page, a separate page is devoted to data records that were averaged together. There is usually one page for each transmitter repetition frequency used for the sounding. The first line of these pages indicates the program version used to average the data, the averaged-output file name, the record number of the averaged-output file to which this page corresponds, and the GTF-format input file name.
Each data page of the PRV file contains a summary of all of the data recorded by the receiver for a single frequency. For each measurement, there is a data record number (DRN), frequency (FREQ), transmitter current (CUR), receiver gain (GAIN), integrations value (NSTK), transmitter turnoff time (T/O), and a time shift (SHIFT). The time shift is applied during data averaging to adjust for incorrect turnoff time settings during data recording. If no adjustment was made, this value will be zero. This part of the output is followed by a list of the International System (SI) units of the various reported quantities, the transient electromagnetic (TEM) instrument (receiver) used (EM-58 for the PROTEM-D and EM-x7 for the analog PROTEM), the receiver coil moment (RXA), the transmitter loop dimensions (LX and LY), and the location of the receiver coil with respect to the center of the transmitter loop (XR and YR).
The next section of the data page gives the channel number and the voltage induced in the receiver coil divided by the receiver coil moment in units of microvolts per square meter (μV/m^2). The average of these voltages is computed and expressed as receiver units in millivolts (mV). The standard deviation as a percentage of the average data value is also reported.
The last section of the data page presents the voltages after they have been transformed to apparent resistivity. The print out includes the channel number, the receiver channel time, the square root of the time in seconds, the late-stage apparent resistivity, the average of the resistivity values, and the percentage standard deviation of the apparent resistivity.
U.S. Geological Survey
RAW_DATA - extension .TEM
The files of downloaded raw data in Geonics .TEM File (GTF) format are typically given a name of the form "aaannn.TEM," where "aaa" is a three-character identifier associated with the survey or the area and "nnn" is a three-digit number. The sounding "name" would be considered "aaannn". The raw data collected in the field are written in Geonics TEM file (GTF) format. The GTF files consist of records 256 characters long containing a 50-character header field followed by 25 data fields of 8 characters each. A 4-character, sequential record number follows the last data field. The last 2 characters of the record are a carriage return and a line feed. Two types of records are created during PROTEM-D receiver downloading. The record type is indicated by characters 19–21 of the header field: "HDR" for a header record and "OPR" for a data record. A header record is created every time a change is made in certain measurement parameters in the PROTEM-D receiver. For example, changes in the sounding name, transmitter current, transmitter loop size, turnoff time, or receiver moment will produce a new header record. The HDR record format with header fields and data fields is described in tables 2–1 and 2–3 for PROTEM-D data and tables 2–5 and 2–7 for PROTEM data. The OPR record with format with header fields and data fields is described in tables 2–2 and 2–4 for PROTEM-D data and tables 2–6 and 2–8 for PROTEM data.
U.S. Geological Survey
GRSANDyy.TX3
The inversion database (file name extension .TX3) is a proprietary binary file that contains an entry for each transient electromagnetic (TEM) sounding model consisting of equipment parameters, measurement array geometry, the measured data, a layered-earth model, and the calculated response of the model. The measured data corresponds to a particular TEM sounding site. The database, which is created using a commercially available program TEMIXXL from Interpex Limited, can hold a large number of models, usually more than enough for an entire survey. TEMIXXL performs the data inversion to determine the layered-earth, resistivity-depth model that produces to the measured TEM response. Sometimes it is helpful to retain several alternative models for a given dataset. These are stored as separate entrees in the TEMIXXL database. Typically, these alternative models have the original sounding name with up to 3 characters added at the end. For example, a sounding called ABC101 might have variants ABC101L4 and ABC101L5 to indicate models with four and five layers, respectively. The preferred model will not have the variant model indicator “Ln.” Soundings that have a fixed-layer resistivity are given names with an “F” after the sounding name, such as ABC101F or ABC104F5. The former name indicates that a layer resistivity is fixed, while the latter is an alternative model with a fixed resistivity and five layers. The only restriction on the extra characters in the sounding name is that the total number of characters in the name cannot exceed 8.
U.S. Geological Survey
TEM_report_yyyy.pdf
Inversion results for all soundings as a portable document format (PDF) file where yyyy is the year the data were collected.
U.S. Geological Survey
TEM_report_yyyy.txt
Inversion results for all soundings as a text file where yyyy is the year the data were collected.
U.S. Geological Survey
TEM_plots_yyyy.pdf
TEM resistivity-time and resistivity-depth plots as PDF files.
U.S. Geological Survey
TEM data dictionary tables documenting the entity types were provided with this data release, Table2-X.csv, and were published (Appendix tables 2-1 to 2-9) with the Data Series, Transient Electromagnetic Soundings in the San Luis Valley, Colorado, near the Great Sand Dunes National Park and Preserve and the Alamosa National Wildlife Refuge (Field Seasons 2007, 2009, and 2011) (Fitterman, 2016)
Appendix 2: Description of Transient Electromagnetic (TEM) Data Files (Fitterman, 2016 - http://dx.doi.org/10.5066/YYYY
Table 2.1 - https://www.sciencebase.gov/catalog/file/get/57db1f59e4b090824ffc3353?name=Table2_1_PROTEM-D_HDR.csv;
Table 2.2 - https://www.sciencebase.gov/catalog/file/get/57db1f59e4b090824ffc3353?name=Table2_2_PROTEM-D_OPR.csv;
Table 2.3 - https://www.sciencebase.gov/catalog/file/get/57db1f59e4b090824ffc3353?name=Table2_3_PROTEM-D_HDR_gates.csv;
Table 2.4 - https://www.sciencebase.gov/catalog/file/get/57db1f59e4b090824ffc3353?name=Table2_4_PROTEM-D_OPR_gates.csv;
Table 2.5 - https://www.sciencebase.gov/catalog/file/get/57db1f59e4b090824ffc3353?name=Table2_5_PROTEM-analog_HDR.csv;
Table 2.6 - https://www.sciencebase.gov/catalog/file/get/57db1f59e4b090824ffc3353?name=Table2_6_PROTEM-analog_OPR.csv;
Table 2.7 - https://www.sciencebase.gov/catalog/file/get/57db1f59e4b090824ffc3353?name=Table2_7_PROTEM-analog_HDR_gates.csv;
Table 2.8 - https://www.sciencebase.gov/catalog/file/get/57db1f59e4b090824ffc3353?name=Table2_8_PROTEM-analog_OPR_gates.csv;
Table 2.9 - https://www.sciencebase.gov/catalog/file/get/57db1f59e4b090824ffc3353?name=Table2_9_PlottingData_ROTFiles.csv.
U.S. Geological Survey - ScienceBase
U.S. Geological Survey - ScienceBase
Mailing and Physical
Denver Federal Center, Building 810, Mail Stop 302
Denver
CO
80225
United States
1-888-275-8747
sciencebase@usgs.gov
Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty.
Tabular digital data and portable document format (PDF)
http://dx.doi.org/10.5066/F7D21VQ5
None. No fees are applicable for obtaining the data set.
20200929
Michaela R Johnson
U.S. Geological Survey, Southwest Region
Physical Scientist
mailing address
Mail Stop 964, W 6th Ave Kipling St
Denver
CO
80225
United States
303-236-2464
303-236-1229
mrjohns@usgs.gov
FGDC Content Standard for Digital Geospatial Metadata
FGDC-STD-001-1998