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.

98 A p p e n d i x A A.1 purpose The purpose of this Standard Operating Procedure (SOP) is to provide general procedures for geophysical data collection during subsurface utility field investigations using SHRP 2 R01B multichannel ground-penetrating radar (GPR) digital geophysical mapping (DGM) prototype system, also known as the TerraVision II system. This SOP is to be used in con- junction with the SOP for multichannel GPR DGM data pro- cessing (see Appendix B). A.2 Scope This SOP applies to the collection of geophysical and associ- ated spatial location coordinate data. A differential global navigation satellite system (GNSS) and/or robotic total sta- tion (RTS) will be coupled with the geophysical instrument(s) to record the x and y coordinates for the collected geophysical data points. The objective of the geophysical survey is to detect subsurface metallic objects that are utilities and/or other client-defined targets of interest to ASCE 38-02 stan- dard’s Quality Level B (QL-B) information. The purpose of the DGM surveys is to provide information that may be used to support the determination of the exact location of the utilities and targets of interest. A.3 Maintenance The Project/Site Geoscientist, in collaboration with the QC Geoscientist, is responsible for the maintenance of this SOP. Approval authority rests with the Project Manager (PM). Approval authority is the power conferred on the PM to commit the geophysical service provider to the proce- dures, objectives, and data quality standards as set forth in this SOP. A.4 equipment The following is a list of equipment that will be necessary to complete a multichannel GPR DGM survey with the geo- physical instrumentation for the project: • TerraVision II antenna banks and control unit; • Instrumentation platform (cart, wheels, GNSS mast, tow vehicle); • Appropriate signal and power cables for all instruments; • Real-time kinematic (RTK) GNSS rover/receiver, GNSS base station (if applicable), data logger, antennas; • RTS instrument, prism, data collector, tripod(s), survey pole(s); and • Sufficient batteries for daily operation of all instrumen- tation. The following additional equipment and forms will be assembled by the Site Geoscientist(s): • Task-specific field data logbook, QC tests form, survey report form; • Pin flags, spray paint, traffic cones, tape measures, miscellaneous; • Digital camera, USB thumb drive; and • Personal protective equipment (as required by current health and safety plan). A.5 personnel Requirements and Responsibilities All personnel assigned to the geophysical investigation team must demonstrate the ability to perform assigned tasks associated with the subsurface geophysical investi- gation, using equipment and associated software at the Standard Operating Procedure for Multichannel GPR Digital Geophysical Mapping Data Collection

99 designated project location. This equipment and software include • RTK GNSS; • RTS; • TerraVision II multichannel GPR array a. Pair of antenna array banks (L & R); b. All necessary cables; c. Control unit; d. Field acquisition computer; e. Encoder capture module (ECM); f. 12 V deep-cycle battery; and g. Deployment cart apparatus, including frame, antenna bank tub, positioning system mast, wheels, tongue, hitch, and distance measuring instrument (DMI); • Data Acquisition Shell (DAS) data acquisition software; and • TerraVision II control software. Before the initiation of geophysical survey data collection, a project briefing will be held for all personnel responsible for geophysical surveying, the downloading of data, and quality control of data. Survey methodology, data requirements, field note protocol, data naming conventions, and raw data orga- nization will be explained in detail. The briefing will include an overall discussion of the survey approach and how the data collection and field documentation tasks integrate into the overall QC and project management program. The brief- ing will also include a review of the internal QC procedures listed in this SOP. The Field Lead will be responsible for providing this briefing and any follow-up training deemed necessary. A.6 preparatory Activities A.6.1 Survey Layout and Methods Before conducting the subsurface geophysical investigation, the geophysical investigation team must have accurate knowl- edge of the precise location(s) of the survey area boundary. Although it is the client’s ultimate responsibility to provide the exact survey area boundaries for any given project, the geophysical service provider (PM and/or Project/Site Geo- scientist) shall attempt to gather sufficient geo-referenced site information through reasonably ascertainable means before mobilization to the project site. The survey area boundary information shall include geo-referenced points, lines, and/or polygons that are all referenced to a specific and consistent coordinate system. If possible, an electronic geo-referenced base map should be created and loaded into the data acquisi- tion and processing software for assurance purposes. This base map should include the project coordinate system and correct distance units. On arrival at the project site and before performing DGM data collection activities, the geophysical service provider and/or a land surveyor shall check the points shown on the base map with RTK GNSS and/or RTS equip- ment (if work area is referenced to a real-world coordinate system), to ensure location accuracy. The field investigation team shall then determine the most appropriate means for the survey area boundary to be identified and recognized by the DGM operator during data acquisition. Either the DGM operator will have a heads-up computer display showing his/ her location in relation to the survey boundary, or the survey boundaries shall be delineated by markings (flags, paint, traf- fic cones, etc.) or permanent reference points in the field (buildings, street boundaries, fence lines, etc.). Once the project areas that will undergo DGM have been identified and sufficiently delineated, the geophysical investi- gation team must determine an optimal data acquisition design. Data shall be collected by traversing along equally spaced parallel paths, unless site conditions and/or the proj- ect plan call for an alternate data collection scheme. If possi- ble, data should be collected perpendicular to the orientation of suspected utility orientations. If data collection perpen- dicular to utility orientation cannot be achieved or is not practical, data may be collected in a direction parallel to a suspected utility location with a portion of data (≥5%) col- lected as tie lines or repeat data, where data is collected per- pendicular to the main data acquisition orientation. Any changes to the field plan must be made by the PM (if present) or Field Lead (if PM is not present). A.6.2 Data Collection Parameters Final data collection parameters will be determined on the basis of project requirements, site conditions, and the adap- tive detection/positioning capabilities of the geophysical instrumentation system. If possible, an evaluation of a site- specific sample of DGM data will be evaluated by the field team before the commencement of data acquisition to better define optimal parameters. These parameters include • Lane spacing—determined by detection footprint of the geophysical system and project requirements. • Comprehensive coverage—complete inclusive coverage offers greatest detection capability. • Data collection speed (≤5 mph)—data are recorded on dis- tance intervals (either six or 12 scans per foot); exceeding 5 mph may overwhelm the input bandwidth of the control unit’s storage system and result in dropped scans. • General settings—requirements for acquisition software.

100 A.6.2.1 Lane Spacing During data collection, TerraVision II parallel transects should be collected with a minimum of two-channel (antenna) overlap to ensure full coverage of the project site over all accessible areas. Keeping track of transect coverage may be achieved by painting dashed marks on the surface during data collection. More than a two-channel overlap is permit- ted and expected to occur at most project sites. Surface obstructions and confined areas may cause more overlap. Data collection should be weighted toward more overlap rather than less because the latter may produce gaps between adjacent transects. A.6.2.2 Coverage Unless otherwise specified by the client and agreed to by the Project Manager, 100% coverage in all accessible areas within the survey area boundary of the project site is required when collecting GPR data using the TerraVision II. Obstructions within the project site that prevent the collection of data must be documented with photographs and/or a sketch if photo- graphs are not permitted on the project site. Any changes to the field plan must be made by the PM (if present) or Field Lead (if PM is not present). A.6.2.3 Speed Data collection speeds for the TerraVision II GPR array are 3 mph to 5 mph. Maintaining a consistent and constant speed produces better results. Due to the limitations of the instru- ment, data collection speeds over 5 mph will produce poor and incomplete data sets. A.6.2.4 General Settings General settings for the TerraVision II should be set at the beginning of each data collection day and should be checked for retention after every system restart and shutdown. There are settings for both DAS and the TerraVision II control software. The general settings for DAS are as follows: • General 44 Set directory for files collected. 44 Enter session and channel prefixes here or use the default naming conventions of SS and CH. • Connections 44 Enable Differential Global Positioning System (DGPS), RTS, or both depending on the positioning instruments to be used. 44 Enable Encoder Capture Module (ECM), which is defaulted and must be set at 768 ticks per foot. • Carts 44 Select land-based platform type. 44 Check positioning equipment offsets. The general settings for TerraVision acquisition software are as follows: • Setup 44 Project file name format, 44 Project site name, 44 Operator, 44 Date and time, 44 Notes on the current project, 44 Soil type, 44 Depth, and 44 Initializing of GPR antennas. • Configuration 44 Scans per unit, 44 Survey wheel, 44 External device, 44 Soil type, 44 Dielectric, and 44 Depth. A checklist for these settings is provided at the end of this appendix. A.7 Geophysical data Collection procedures A.7.1 Daily Data Collection The following set of general procedures should be followed for each field day: 1. Hold tailgate safety and daily project objectives meeting; tailgate safety forms will be filled out and signed by all field investigation team members. 2. Set up equipment. 3. Set DAS and TerraVision II control software parameters. 4. Initialize GPR antennas over a representative area. 5. Perform QC checks and checklist as described in Sec- tion A.8 of this SOP. 6. Send field team to production area. 7. Activate the geophysical and RTK GNSS/RTS equipment and check that both units are collecting valid data. 8. Proceed with the DGM activities. One member of the team will be responsible for main- taining the field documentation record. Note, this does not necessarily mean that person is responsible for creating each document; individual documents may be produced by any member of the field investigation team. Field documen tation

101 includes, at a minimum, the checklists and forms included with this SOP and other relevant SOPs. These documents are delivered to the Field Lead at the end of each production day. Each page of the field documentation will be dated, sequentially numbered, and identified by the project name/ number; all entries will be signed by the Field Lead. At a minimum, the following information should be recorded as field documentation: • Unit area for data set identification; • Time survey started; • Time survey completed; • Names of geophysical investigation team members; • Equipment and software settings; • Weather conditions; and • File names for the digitally recorded data. At the end of the day, • All data are downloaded onto transferable media. • All equipment is returned to storage, and the batteries are placed on charge. • The completed survey areas are recorded in the tracking log. • The DGPS/RTS positional track maps and logbook pages are accessible for periodic verification by the QC Geoscientist. A.7.2 Full Coverage (Grid) Geophysical Survey One hundred percent of accessible areas within the project site will be geophysically surveyed with the TerraVision II, integrated with RTK GNSS/RTS. If a DGPS/RTS signal is not achievable or of good quality (low number of visible satellites, too many obstructions, etc.), then data will be collected in straight transects using an established local coordinate system and by marking the endpoints on the ground for subsequent surveying. Data collected in straight transects and in a local coordinate system will be posi- tioned on the basis of measurements from existing struc- tures and/or referenced to GNSS static points collected outside the production area where DGPS signal is achiev- able and of good quality. Data collected using local coordi- nates will be translated to project coordinates during data processing. To ensure that 100% of accessible areas are covered dur- ing geophysical data collection, those in charge of the data acquisition must employ measures to keep track of cover- age. A few methods include (i) establishing markers in the field to delineate data collection lanes using flags, ropes, painted lines, or cones; (ii) using the heads-up data track display on the data acquisition computer; and (iii) using swath light-bar guidance systems. Employing one or more of these methods allows for comprehensive data coverage and maximum productivity by eliminating data gaps and overlaps. A.7.3 Equipment Initialization When transitioning to areas that have significantly different soil conditions during data collection at the project site, the TerraVision II should be reinitialized. Reinitialization should be conducted in an area believed to be free from subsurface metallic objects and where the subsurface conditions are characteristic of the transition. For example, soil conditions could be expected to differ when moving from a paved area to an unpaved area. By doing so, the data will generally be better gained to the particular soil near the point of initial- ization. The location of the initialization will be recorded in the field documentation and digitally, by collecting a short 5-foot to 10-foot swath of data and logging the positioning information. A.7.4 Inaccessible Areas Physical features such as rock outcrops, boulders, trees, build- ings, structures, utilities, stationary vehicles, and water may result in inaccessible areas. All inaccessible areas will be photo- graphed, with the position and the orientation of the photo- graph documented, sketched on the team’s grid sheet, and/or noted on a project site aerial. Reasonable attempts are to be made to have parked vehicles and other potentially moveable obstacles moved. If possible, the boundaries of physical fea- tures that obstruct data collection will be geo-referenced using RTK GNSS/RTS for later reference during data process- ing and mapping. A.7.5 Deviation from Lane Orientation and Spacing Deviation from geophysical survey lane spacing and orienta- tion will be determined and documented in the field. The Project/Site Geoscientist will be responsible for determining whether an area is considered inaccessible due to site condi- tions. All inaccessible areas will be photographed and/or sketched in the field documentation and denoted as to their source. Examples of typical obstructions include manmade immovable structures; unsafe terrain/conditions; and cul- tural objects such as cars, power lines, signs, and fences. Rea- sonable attempts are to be made to have parked vehicles and other potentially moveable obstacles moved. The Field Lead will designate one member of the field investigation team to document deviation from standard lane setup due to terrain, slope, or other conditions that make the area impassable. The

102 following steps are recommended for performing lane devia- tion documentation: • Deviations will be tied to an individual data set. If devia- tion is necessary, a sketch and/or photograph of the data set boundary will be denoted with the cause of the devia- tion. Data gaps caused by deviations from line path and not obstacles should be filled in with a subsequent data collection set if possible. • Obstacles may cause inaccessibility and result in additional sources of lane orientation and/or spacing deviations that should be documented. Remove obstacles from the inves- tigation area if possible. A.7.6 Daily Data Management Several files are generated by the geophysical and positioning systems for the acquired data at each investigation area of a project site. These data are stored on the data logger(s), field computer, and RTK GNSS receiver during data acquisition activities. At the end of daily field activities, the data collected by the field investigation team will be uploaded to a desig- nated data management computer or included in the project binder, as appropriate. The following file types are generated for each survey: • Geophysical data files (.dzt and .ind) and RTK GNSS/RTS positioning coordinates; • Data acquisition software session folders containing indi- vidual GPR file positioning and timestamp information; • Digital photo files (.jpg); and • TerraVision II field sheet and checklist (see end of this appendix). A.8 Quality Control (QC) and Quality Assurance (QA) This section outlines the quality control function through discussion of generalized field procedures and testing to document the execution and completion of a subsurface tar- get detection project using GPR digital geophysical map- ping. The Project/Site Geoscientist, in collaboration with the QC Geoscientist, is responsible for the maintenance of this procedure. A.8.1 Response, Detectability, and Interpretability Utilities and other targets of interest are detectable and inter- pretable based on differences in the electrical properties of the targets and the electrical properties of the surrounding soil. The responses received vary based on the site conditions and the target properties. Target properties that determine the magnitude and value of responses include, but are not limited to, depth of burial, size, orientation, and material properties. A.8.2 Equipment Functionality and QC Tests The geophysical service provider will perform QC tests tai- lored to the project’s specifications to ensure both instrument functionality and consistency of measurements from the TerraVision II GPR multichannel array. On a daily basis, all QC tests will be documented by the Project/Site Geoscientist. The suite of tests is instrument specific and may include some or all of the items in Table A.1. A.8.2.1 Bank Testing ApplicAbility TerraVision II procedure Before mobilization to the project site, the TerraVision II GPR antenna banks that are to be used on site need to be tested, and settings need to be adjusted to ensure quality data are collected. During bank testing, the Project/Site Geoscientist needs to perform the following tasks and adjust the associated settings if necessary: • Time Zero Calibration—the top reflector of each channel should be aligned. • Missing Channel Check—ensure all 14 channels are active. • Channel Alignment Check—ensure that data collected over a test object line up properly without any offsets or other inconsistencies in the location of the test object’s data signature. All of the above calibrations and checks can be completed with the collection of one or more data files. Place a strip of foil tape on the ground within the testing area. Collect one or more GPR transects perpendicular to the orientation of the Table A.1. QC Tests Test # Test Description Frequency 1 Bank testing By data set 2 Equipment warm-up Daily 3 RTK GNSS/RTS streaming check Daily 4 Initialization check Daily 5 Foil tape By data set

103 foil tape. The foil tape is used for the Channel Alignment Check and does not affect the other checks and calibrations. All of the above checks and calibrations have to be assessed with processing and interpretation software. It is the re- s ponsibility of the Project/Site Geoscientist to process and review the collected GPR transects and determine if the TerraVision II GPR antenna banks are ready for transport to the project site. Frequency Once before mobilization or DGM data collection activities A.8.2.2 Equipment Warm-Up ApplicAbility TerraVision II procedure The multichannel array is particularly sensitive to cold weather conditions. This instrument requires several minutes to accli- mate to ambient weather conditions (temperature, humidity, etc.) and stabilize before data collection can take place. Equip- ment is to be turned on and left to rest for 5–10 minutes before collection of DGM data. Frequency Daily A.8.2.3 DGPS/RTS Streaming Check ApplicAbility TerraVision II procedure Before collecting data at the project site, the positioning sensor needs to be configured for data streaming. The project Loca- tion Surveyor is responsible for using the Trimble GPS Con- figurator software to apply the correct settings for streaming National Marine Electronics Association (NMEA) GGA posi- tioning data from the RTK GNSS. The Location Surveyor or the Project/Site Geoscientist is responsible for confirming that during TerraVision II data collection the proper NMEA out- put is being received. This can be checked by setting up the GPR array with the positioning sensor and collecting a test strip of data. Within the DAS data acquisition software, if the positioning sensors are counting up during collection, then streaming positioning data are being collected. Alternatively, a terminal software program such as HyperTerminal that can monitor serial data inputs can be used to check that data are streaming correctly. Frequency Daily and throughout the entirety of DGM activities A.8.2.4 Initialization Check ApplicAbility TerraVision II procedure After the configuration of all general settings (as discussed in Section A.6.2.4), initialize the GPR antennas. Collect a test tran- sect to record the location of the initialization and to review the gain that was applied during initialization. To review the gain applied, download the test transect file to the acquisition com- puter and review the data with GPR processing software. If the gain applied is not acceptable (high enough, too high, cloudy data, etc.), the TerraVision II array may be over buried metal or saturated ion-rich soils. In this case, change the initialization location and collect another test file. Continue until a gain set- ting is obtained that provides for an evenly gained data file. Frequency Daily and whenever subsurface soil conditions are reasonably expected to change (e.g., when moving from pavement to grassy area) A.8.2.5 Foil Tape ApplicAbility TerraVision II procedure Foil tape will be laid at multiple points within the project site to ensure there are no latency errors within the multichannel GPR data set collected. Foil tape should be laid on the ground perpendicular to the direction in which a majority of the multichannel GPR data transects will be collected. During data collection activity at the project site, GPR transects will be collected over the foil tape, and its position within the GPR will be checked daily during data processing. Foil tape end- points shall also be geo-referenced by the Location Surveyor. On grassy areas, a metal chain should be laid, using the same parameters as foil tape. Frequency Daily within each production area

104 TERRAVISION™ II FIELD SHEET AND CHECKLIST

105