Utility-Locating Technology Development Using Multisensor Platforms (2014)

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116 D.1 Purpose The purpose of this Standard Operating Procedure (SOP) is to provide general procedures for geophysical data pro- cessing and interpretation of SHRP 2 R01B time domain electromagnetic induction (TDEMI) data sets. This SOP is to be used in conjunction with the SOP for TDEMI digital geophysical mapping (DGM) data collection (see Appendix C). D.2 Scope This SOP applies to the data collected during the DGM activities using TDEMI geophysical detection sensors (SHRP 2 R01B TEM system) integrated with real-time kinematic (RTK) global navigation satellite system (GNSS) equipment. The major elements of this procedure are elec- tronic data transfer, data processing, data analysis and interpretation, data archiving, and data tracking. The objec- tive is to depict resulting information gained from the geophysical investigation via computer-aided design and drafting (CADD) onto the client’s plan sheets, geographic information system (GIS) databases, ASCE 38-02 standard’s Quality Level B (QL-B) information, or other appropriate documents. D.3 Maintenance The Project/Site Geoscientist, in collaboration with the qual- ity control (QC) Geoscientist, is responsible for the mainte- nance of this procedure. Approval authority rests with the Project Manager (PM). Approval authority is the power con- ferred on the PM to commit the geophysical service provider to the procedures, objectives, and data quality standards as set forth in this SOP. D.4 Personnel Requirements and Responsibilities Personnel assigned to perform TEM System DGM data pro- cessing require basic understanding of TDEMI data process- ing concepts and sufficient specific training in Geosoft’s Oasis Montaj software with the geophysics extension, Underground Imaging Technology, LLC (UIT) extension, and UX-process menus. D.5 Data Processing Procedures The data processing, data analysis and interpretation, quality control reprocessing, and quality assurance process steps must flow smoothly, and clear communication must occur. The steps required for this are as follows. D.5.1 Transfer of Field Data and Data Tracking Several files are generated by the geophysical and GNSS sys- tems during a DGM data collection activity. These data are stored on data loggers or field computers. The following file types may be generated for each survey: • Raw geophysical sensor data files (.tem) represent the sig- nal intensity file in non-ASCII binary format. • Preliminary processed geophysical sensor data files (.Data .csv and .AcqParams.csv), generated by EM3D software rep- resent the signal intensity file in ASCII format (one file per data collection set). These files may have positioning infor- mation embedded within them at regular time intervals. • Files with the extension .xyz are generated by merging positioning files with sensor signal intensity files in which each detection sensor data point is tagged with an A P P e n D i x D Standard Operating Procedure for TDEMI Digital Geophysical Mapping Data Processing

117 easting, northing, and time stamp. These files are created with the geophysical data processing software, Geosoft Oasis Montaj. • Survey files are generated by the select positioning instru- ments used on the project site and are generally in comma or tab delimited format, containing headers such as ID, Northing, Easting, Elevation, and Code. • Digital photo files (.jpg) are recorded in the field to repre- sent site characteristics and definable field work operations. They may identify type of terrain, cultural conditions, sur- vey obstacles, elements of the field work, or any other visual depiction relevant to the collection of geophysical data. All DGM data files will be electronically logged, down- loaded from the field computers, and stored on external media (such as flash drives, CD, DVD, PCMCIA card) before the field team’s exit from the project site. If possible, all raw recorded TDEMI DGM files will be transferred to an off-site data stor- age server before the field team’s exit from the project site. The following items will be recorded on the field worksheet (note- book) or electronic spreadsheet for each DGM file collected: • Site ID and location; • Transect ID, grid (unit of production) ID, static test(s), latency test(s), walk away test(s); • Geophysical investigation team identifier; • Date collected; and • DGM data file name(s). D.5.2 TDEMI Initial Data Processing Initial data processing is performed so that data acquisition operational errors, file naming inconsistencies, and/or insuf- ficient data coverage issues can be addressed before a field team’s demobilization. The information gathered here also facilitates a more thorough understanding by the data analyst/ interpreter of the project details. Therefore, the initial data processing should be conducted at the project site if possible. The information gathered during this initial processing phase will be tracked on the TDEMI DGM Initial Data Processing form presented at the end of this appendix. Initial data processing and preliminary QC review consists of the following: • General project information (site ID, date(s) of data collec- tion, coordinate system, geophysical team identifier); • Data file completeness, file naming consistency; • Software used, detection instrument used, positioning instrument used; and • General assessment and comments on TDEMI DGM data quality (coverage, instrument noise, positional accuracy). D.5.3 TDEMI Data Processing Data will be processed and targets will be picked and classified by an experienced TDEMI data processor/analyst. An experi- enced data processor is someone who is familiar with the general operations of data acquisition and the entire geophysical system used to acquire the TDEMI data. The experienced data proces- sor has direct experience in the manipulation of input data with the Geosoft Oasis Montaj program to obtain the desired out- puts. The experienced data processor understands the basic concepts of Geosoft databases, UX-process menu options, visu- alization of electromagnetic induction (EMI) data in map and profile view, and the standard data quality issues associated with TDEMI DGM systems. The typical data processing steps are outlined below. Standard EMI data processing information is tracked in the TDEMI DGM Final Processed Data Sheet and QC Review form that is presented at the end of this appendix. The following is a generalized flow of the TDEMI DGM data evaluation and analysis: • Download data from the acquisition computer to geo- physical service provider server or to personal computer (PC), and review field notes. • Convert data files to x, y, z format for import to geophysical data analysis software. For TEM data sets, the raw *.csv files (converted from *.tem files with EM3D software) are imported into Geosoft Oasis Montage database(s) using the “Import Advanced EM Sensors . . .” option under the UIT menu tab. At this step, offset positions will be applied to sensors that are not located centerline to the positioning rover device (i.e., GNSS antenna). • Convert x, y coordinates to site-specific coordinates as necessary. • Perform latency corrections (as needed) based on instru- ment latency determined from transect lines of the latency chain test. • Review data for completeness, using “graphical window” techniques. This is done by the interpreting geoscientist. • Remove/smooth detection data dropouts, spikes, and physical interference sources. • Level/filter the DGM data using a nonlinear filter. • Grid the sensor reading (z) for each time gate acquired. • Produce an image map of the gridded data. Grids can be stacked to produce a three-dimensional (3-D) representa- tion of decay response. • Post line path and sample location plots on the map. The data analyst/interpreter reviews the map for down-line and cross-line coverage completeness. • Import any and all available assisting graphics (aerial photos, CAD drawings, GIS layers, etc.) to act as reference during interpretation and analysis.

118 • Pick targets at anomaly locations where sensor values are consistently above background levels. Targets are classified based on comparisons to existing records and/or sub- surface utility engineering (SUE) utility delineation. • Produce digital map layers, and their accompanying coor- dinate lists, as the data interpretation deliverable. The geophysical service provider will use Geosoft Oasis Montaj to process, interpret, and review the TDEMI DGM data. The QC Geoscientist will review field data to confirm equipment was tested in accordance with QC plans and oper- ated in accordance with specifications. The processing steps mentioned herein are the minimum steps necessary to effec- tively process the TDEMI data. D.5.4 Standard TDEMI Data Analysis TDEMI DGM data will be postprocessed and analyzed in Geosoft Oasis Montaj software. Standard processing infor- mation will be tracked on the TDEMI DGM Final Processed Data Sheet and QC Review form presented at the end of this appendix. The geophysical service provider will perform the following analysis as appropriate: • Convert easting and northing values to site-specific coordi- nate system, and apply sensor path and offset correction. • Sensor bias, background leveling, and/or standardization adjustment for all TDEMI time gate measurements. • Correct latency. Use the UCELATENCY.GX (for time- based correction) or LAG.GX (for distance-based correc- tion) of Geosoft to perform these latency corrections on the TDEMI DGM data. • Determine the optimum gridding method, search criteria, and contour-level selection with background shading and analysis based on the data collected. D.5.4.1 Sensor Path and Offset Correction Sensor path and offset corrections are required when the number of detection sensors is greater than the number of positioning devices or when the detection sensor is not cen- tered in relation to the positioning device during data acqui- sition. Sensor offset corrections applied within Geosoft Oasis Montaj will be checked as part of the daily QC plan to ensure the offsets do not vary. D.5.4.2 Convert Easting and Northing Raw positioning measurements are often not recorded in the required site-specific coordinate system. This is the case when TEM data is collected with RTK GNSS integration [latitude and longitude information from GGA National Marine Electronics Association (NMEA) sentences]. The site-specific northing and easting values can be attained using the “Coordinates” menu option in Geosoft Oasis Montaj. D.5.4.3 Filtering of Data Each TDEMI channel (TEM time gate measurement) will be leveled independently to remove the effects of instrumental drift. Filtering will also be performed if necessary to remove effects from known surface cultural sources. All TDEMI chan- nels will be viewed by the data analyst in profile view before gridding to ensure proper leveling corrections. D.5.4.4 Latency Correction Latency will be corrected for on the basis of the results of daily latency chain tests and reviews of the opposing direc- tion, adjacent line paths of the production data. If the data analyst notices misshaped anomalies in areas of adjacent but opposing direction traverses, the latency correction will be reviewed and adjusted as required. D.5.4.5 Gridding and Display of Data Monostatic channels of the TEM data will be gridded and displayed using Geosoft Oasis Montaj. Profile data will be reviewed and analyzed to ensure quality and that project per- formance criteria are met. A general rule of thumb for select- ing cell size is 1⁄8 to 1⁄4 nominal line spacing and/or 1⁄2 station sample spacing. Blanking distance is set such that color con- touring does not exceed 1/3 meter from center of sensors’ tra- verse. Grids from the various time gate channels can be stacked to produce a 3-D representation of decay response. Data sample point location plots will also be reviewed to ensure adequate down-line sampling. D.5.5 Target Selection and Characterization The geophysical service provider will use Geosoft Oasis Montaj with the UIT and geophysics extensions to process and analyze target anomalies. Any existing SUE informa- tion and/or field observations may provide the geophysical data analyst with a guide for classifying target anomalies into categories. These categories will be organized such that tar- gets will be placed in defined utility-type classes such as gas, electric, water, unknown. Target selection criteria will be based on contiguous TEM system signals above background response values. Back- ground TDEMI levels will be determined on a site-specific basis and represented through nonspike static tests conducted in the general vicinity of the production zones. Targets may be single points, lines, or polygons. Point targets and line targets

119 will be made at peak signal locations. Polygon targets will cir- cumscribe an area of elevated signal response. In general, the area where the signal response is highest above the surround- ing background values is the point assumed to be directly over the anomaly source. In making the interpretation, the data analyst will also use all pertinent information available (field notes, aerial photos, Quality Level C and D SUE data, docu- mentation on the location of surface features/appurtenances, personal communications with site personnel, other geophys- ical site investigations, etc.). It is important that data analysts making target selection interpretation evaluate all aspects of the TEM DGM data. A thorough analysis should be conducted for each time gate measurement in both map view and profile view. Earliest time gates generally represent the highest level of sensor sensitivity and ambient instrument noise, while anomalous responses within the later time gates generally represent those anomaly sources that are most conductive and/or contain the largest metallic mass within the surrounding area. D.5.6 Quantitative Interpretation and Target Map Development The data analyst will construct colored contoured maps of the gridded TDEMI data to facilitate the target selection pro- cess. Both colored contour maps and profile data will be eval- uated to make appropriate picks of potential targets. The data analyst will select targets within the context of all available geo-referenced data (existing utility drawing, UIT utility line designation, and/or other geophysical systems’ interpreta- tions). All digital maps will be referenced to at least one con- sistent coordinate system. Point, line, and area targets are digitized on a Geosoft Oasis Montaj map and are exported as separate layers for inclusion on the electronic mapping deliverable. Target selections are exported from Geosoft Oasis Montaj in .dxf format and should be of solid-line form (no dashed/dotted lines and no pattern fill; point symbols are to be polygons). Geo-referenced images of the color contoured grid images may also be exported from Geosoft Oasis Montaj in the form of GeoTiffs, including appropriate world files for inclusion into SPADE or other final mapping deliverable. D.5.7 QC Review On completion of the EMI target selections, the QC Geo- scientist will review the interpretation files with the data analyst responsible for making the interpretation. Again, the QC Geo- scientist will conduct the review in the context of all available geo-referenced data. If applicable, the QC Geoscientist will compare the selected target locations with the known locations of seed items. These can be either seed items emplaced by the field team or preexisting seeds (such as manholes, surface valves, metal grating). In either case, the precise center position and diameter of the surface seed item should be recorded during the field effort with the appropriate positioning system. The QC Geoscientist will evaluate the effectiveness of all data processing and corrections performed (latency, leveling, gridding, etc.). If the QC Geoscientist identifies deficiencies in any data sets (pro- duction or QC), the Project/Site Geoscientist will perform a root cause analysis and propose/implement corrective actions. D.5.8 Geophysical Data Archiving All geophysical data will be archived daily following the geo- physical service provider’s project file structure protocol. Files will be copied to alternate digital media. Maintenance of the backup data will be verified by the Project Manager or QC Geoscientist.

120 TDEMI DGM Initial Data Processing Raw/Preprocessed Data Sheet Information Type Site name Project number Project date(s) Name of Project/Site Geoscientist Geophysical instrument used Positioning method used Instrument serial number(s) Acquisition software Coordinate system and unit of measure Raw QC data file names Raw QC data file names Raw Production data file names Raw Production data file names Data coverage comments Data coverage comments Instrument latency comments Positional accuracy comments

121 TDEMI DGM Final Processed Data Sheet and QC Review Information Type Site name Project number Project dates Name of Project/Site Geoscientist Geophysical instrument used Positioning method used Instrument serial numbers Coordinate system and unit of measure Processed data file names Name of Data Analyst Name of QC Geoscientist Data processing software used Latency/lag correction and details Sensor bias, background leveling, and/or standardization adjustment method and details Geophysical noise identification and removal details Other filtering/processing performed and details Anomaly target selection and decision criteria details Geosoft “.map” file for unit of survey Target selection file name(s) Data image file name(s) Other processing comments Date data processing is completed QC review comments