Utility-Locating Technology Development Using Multisensor Platforms (2014)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

106 A p p e n d i x B B.1 purpose The purpose of this Standard Operating Procedure (SOP) is to provide general procedures for geophysical data processing and interpretation of TerraVision II multichannel ground- penetrating radar (GPR) during and after field activities. This SOP is to be used in conjunction with the SOP for GPR digital geophysical mapping (DGM) subsurface geophysical investigation data collection (see Appendix A). B.2 Scope This procedure applies to the data collected during DGM sur- veys using the TerraVision II multichannel GPR geophysical detection sensor integrated with real-time kinematic (RTK) global navigation satellite system (GNSS) and/or robotic total station (RTS) equipment. The major elements of this proce- dure are electronic data transfer, data processing, data analysis and interpretation, data archiving, and data tracking. The objective 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. B.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. B.4 equipment The following is a list of equipment and software that will be necessary to complete GPR data processing and interpreta- tion tasks: • Computer with sufficient hard drive space and RAM (it is recommended that free hard drive space be at least twice the size of the largest merged file and total RAM amounts of 8 GB or greater); • Appropriate means to receive and transfer large quantities of digital data (network connection, external hard drive, USB flash drive); • GPR processing/filtering software (e.g., Geophysical Sur- vey System Inc.’s RADAN); and • Positioning processing software sufficient to merge recorded positioning information with geophysical sensor data result- ing in a geo-referenced GPR data set 44 Underground Imaging Technologies, LLC (UIT) Data Processing Engine (DPE), and 44 Geosoft Oasis Montaj; and • Interpretation software 44 UIT Semi-Automated Process and Detect (SPADE). B.5 personnel Requirements and Responsibilities Personnel assigned to perform GPR DGM data processing must be proficient in the use of GPR processing and interpre- tation software, or they should be under supervision of other proficient personnel at the time of processing and interpreta- tion of any results to be included in a DGM deliverable. Before the initiation of GPR GDM data processing and interpretation, a project briefing will be held for all person- nel responsible for GPR GDM data processing and quality control of data. Survey data collection scheme, project Standard Operating Procedure for Multichannel GPR Digital Geophysical Mapping Data Processing

107 requirements and goals, field documentation review, data naming conventions, and data organization will be explained in detail. The briefing will include an overall discussion of the survey approach and how the data collection, field documen- tation, and processing and interpretation tasks integrate into the overall QC and project management program. The brief- ing will also include review of the internal QC procedures listed in this SOP. The Project Manager will be responsible for providing this briefing and any follow-up training deemed necessary. B.6 data processing procedures The data processing, data interpretation, quality control repro- cessing, and quality assurance process steps must flow smoothly, and clear communication must occur. The steps required for this are as follows. B.6.1 Transfer of Field Data and Data Tracking Several files are generated by the geophysical and GNSS sys- tems during DGM data collection. These data are stored on various data loggers or field computers. The following file types may be generated for each survey: • Raw GPR files generated by both single-channel and multi- channel GPR sensors. • Raw RTS data containing position track data of the prism affixed to the GPR cart. These files may be generated using provided project site control information or in a local coordinate system. For TerraVision II data collected with Data Acquisition Shell (DAS) data acquisition software, the National Marine Electronics Association [NMEA_pos(_1)] files are the raw RTS positioning logs. • Raw GNSS data containing position track data of the GPS rover affixed to the GPR cart. These files are generated with a real-world coordinate system (usually latitude/longitude or UTM). For TerraVision II data collected with DAS data acquisition software the NMEA_raw(_1) files are the raw DGPS positioning logs. • Encoder Capture Module (ECM) time marker files (.tmf). The ECM is a device that outputs the number of GPR data scans acquired in each transect with the TerraVision II GPR array. The scan count data are stored in a time marker file. The ECM increases the positional accuracy of the GPR data collected (especially in curved transects). • 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 represent site characteristics and definable field work operations. They may identify type of terrain, cultural conditions, survey obstacles, elements of the field work, or any other visual depiction relevant to the collection of geophysical data. The above files are to be placed into appropriate folders on the geophysical service providers file storage system drive(s) by the end of the next business day following the return of the field investigation team. B.6.2 In-Field Data Processing In-field data processing is performed so that data acquisition errors, file naming inconsistencies, and/or insufficient data cov- erage issues can be addressed before a field investigation team’s demobilization from the project site. The information gathered here also facilitates a more thorough understanding by the data analyst/interpreter of the project details. Therefore, the in-field data processing should be performed while at the project site or immediately following data collection if possible. It is the responsibility of the Project/Site Geoscientist to keep track of the information gathered during this in-field data processing phase, including performance of the processing. Preliminary data processing may also be performed by office staff while the field investigation team remains in the field, in consultation with the Project Manager and/or QC Geoscientist. In-field data processing and preliminary QC review con- sists of a review of the following: • Ensuring general project information is recorded 44 Site ID, date(s) of data collection, coordinate system; and 44 Acquisition software used, detection instrument settings used, positioning instrument and settings used; • File naming consistency; • Production of data coverage maps indicating those areas over which data were collected; • General preliminary assessment of GPR DGM data quality, including depth of penetration and instrument noise; and • Proper instrument function and positioning accuracy through examination of data sets for foil tape position. B.6.3 GPR Data Processing Data will be processed and geophysical targets will be picked and classified by an experienced data analyst or project geo- scientist. An experienced data analyst is one who is proficient

108 in data analysis from extensive training and supervision under other geoscientists. Data analysis includes positioning, processing, and interpreting the GPR data. The typical data processing steps are outlined below. It is the responsibility of the assigned data analyst to track the progress and settings applied during GPR data processing. B.6.3.1 Multichannel GPR Data Processing 1. Download GPR .dzt files, DAS positioning files, and sur- vey files from the appropriate electronic media to personal computer (PC); and review field notes, sketches, and photographs. 2. Locate multichannel GPR positioning files in the DAS ses- sions collected during data acquisition with DAS software in the field. These files—either NMEA_raw(_1) files (DGPS) or NMEA_pos(_1) files (RTS)—are imported into the posi- tion processing software along with the multichannel GPR .dzt files generated. Before position processing, the settings in DPE must be set. The settings include the input and out- put coordinate systems and the TerraVision II time delay. Once the correct settings are in place and the geophysical sensor and positioning files are imported into DPE, .map files for each multichannel GPR transect are created by DPE and output into the DZT folder. 3. Bundle .map files with their associated .dzt multichannel GPR files for viewing in SPADE. Create an .xml file using DPE for import into SPADE. 4. Import multichannel GPR .dzt files into SPADE using the .xml file. Import client-defined project site boundaries, aerials, and/or CAD, drawing into SPADE to determine appropriate data coverage and to check the positions and orientations of the GPR transects. 5. Process multichannel GPR .dzt files in Geophysical Survey Systems, Inc.’s (GSSI) RADAN data processing software, using various filters to clean up and enhance the raw data for better viewing during data interpretation. Filtering in RADAN does the following to improve the quality of the GPR data: • Correct time; • Remove flat-lying ringing system noise; • Remove high-frequency noise (i.e., snow); • Remove ringing multiples; • Remove diffraction (compress hyperbolas) and correct dipping layers; • Increase visibility of low-amplitude features; • Detect subtle features; and • Generate clearer data displays for reports. 6. Import multichannel GPR .dzt files (now filtered) back into SPADE with supporting files for interpretation. Before inter- pretation and to improve the efficiency of the workflow, individual multichannel GPR files are bundled together into merged files for ease of use in data handing and inter- pretation. The steps for merging files are as follows: a. Using the .xml file created in DPE, import individual multichannel GPR .dzt files into SPADE. b. Section off groups of GPR files into areas of contiguous coverage. Keep files of the same orientation together; do not merge perpendicular files. c. Remove significant overlap between files that are to be merged by creating regions (.dzt) and new region .map files. Keep track of the regions to be merged. d. Create merge files by selecting files and region files cre- ated from removing overlap, and stitch them together. This creates a merged .dzt file with the positioning embedded within the file, and therefore it does not have an associated .map file. e. Import all merge files into SPADE and take a screenshot. Create a “Merge Map” in Microsoft PowerPoint, Paint, or any other graphics program using the screenshot. Label each merge file on the screenshot as you labeled the file during merging. This “Merge Map” helps other data analysts and the QC Geoscientist quickly access merge files during interpretation and QC review of the results. Save as a PDF or PPT and put the document in the same folder as the merge files. 7. Import multichannel GPR merged .dzt files into SPADE with supporting files for interpretation. Supporting files include utility information CAD files, survey data, and project site aerials. Targets are picked during interpretation based on the scope of the project. The targets interpreted from the data are exported as points, lines, and polygons (.csv and .dxf files) for later results mapping. During inter- pretation, targets are classified based on existing records and/or field utility delineation from other methods, such as radio frequency pipe and cable locators. B.7 Target Selection Data will be interpreted and targets will be picked and clas- sified by an experienced data analyst using SPADE software. All GPR data are imported via an .xml file or by loading merged files. TerraVision II multichannel GPR data typi- cally represent 100% coverage of accessible areas and are interpreted from a combination of vertical cross-section profiles and horizontal plan-view time slices. The following procedure describes targets interpreted from GPR data in SPADE: • A point target is a feature that is not extensive enough to be considered a contiguous, subsurface horizontal structure or large enough to be designated as an area of interest.

109 Generally, these features would be on the order of approxi- mately 1 square foot or less in extent. The shape of features determined to be point targets ranges from round to sub- round. Point targets must be well pronounced within the data set to warrant inclusion in the interpreted results. • A GPR linear feature is designated as such if the response is contiguous for a predetermined length and well defined by a linear morphology. The origins of these targets are unknown other than that they express a distinct linear expression in the data. • A GPR utility feature exhibits geophysical characteristics consistent with a utility signature such as a similarly sized and depth-consistent hyperbola, in addition to correspond- ing to a known mapped utility at the site. • A GPR planar feature is designated as such if the response constitutes a defined contiguous area over a horizontal or sloping plane within the subsurface, as visible in a plan-view horizontal “slice” of constant approximate depth. These fea- tures are of a greater areal extent than point targets. • A GPR area of interest is defined as an area of unknown origin where a sufficiently distinct geophysical response is seen in plan view and/or cross section that differentiates it from the background geophysical signature. Data analysts will also use all pertinent information avail- able [field documentation, aerial and site photos, Quality Level C and D subsurface utility engineering (SUE) data, documentation on the location survey of surface features and utility appurtenances, personal communications with site personnel, other geophysical site investigations] to aid the interpretation effort and to discriminate between tar- gets seen in both plan view and cross-sectional GPR data. When possible, this additional information can be used to attribute utility type to individual targets and otherwise assist in identifying the origins of certain geophysical targets. B.8 Quality Control Review On completion of the GPR target selections, the QC Geosci- entist will review the interpretation files with the data analyst responsible for making the interpretation. The QC Geoscien- tist 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 seed items can either be emplaced by the field team or may be preexisting seeds (such as manholes, surface valves, metal grating). In either case, the precise center posi- tion and diameter of the surface seed item should be recorded during the field effort with the appropriate positioning sys- tem. 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 (production or QC), the Project/Site Geo- physicist will perform a root cause analysis and propose/ implement corrective actions, including reprocessing of posi- tioning data, and refiltering the GPR data. B.9 Geophysical data Archiving All geophysical data including pick and feature files will be archived daily following the geophysical service provider’s project file structure protocol. Files will be copied to alternate digital media. It is the data analyst’s responsibility to ensure all geophysical data are placed in the appropriate folders. Data filing is to be verified by the Project Manager.