The GPR (Ground Penetrating Radar) conference in Hong Kong year 2016 marked the 30th anniversary of the initial meeting in Tifton, Georgia, USA on 1986. The conference has been being a bi-annual event and has been hosted by sixteen cities from four continents. Throughout these 30 years, researchers and practitioners witnessed the analog paper printout to digital era that enables very efficient collection, processing and 3D imaging of large amount of data required in GPR imaging in infrastructure. GPR has systematically progressed forward from “Locating and Testing” to “Imaging and Diagnosis” with the Holy Grail of ’Seeing the unseen’ becoming a reality. This paper reviews the latest development of the GPR’s primary infrastructure applications, namely buildings, pavements, bridges, tunnel liners, geotechnical and buried utilities. We review both the ability to assess structure as built character and the ability to indicate the state of deterioration. Finally, we outline the path to a more rigorous development in terms of standardization, accreditation, and procurement policy.

A review of Ground Penetrating Radar application in civil engineering: A 30-year journey from Locating and Testing to Imaging and Diagnosis

Noninvasive 3D ground-penetrating radar (GPR) imaging with submeter resolution in all directions delineates the internal architecture and processes of the shallow subsurface. Full-resolution imaging requires unaliased recording of reflections and diffractions coupled with 3D migration processing. The GPR practitioner can easily determine necessary acquisition trace spacing on a frequency-wavenumber (f-k) plot of a representative 2D GPR test profile. Quarter-wavelength spatial sampling is a minimum requirement for full-resolution GPR recording. An intensely fractured limestone quarry serves as a test site for a 100-MHz 3D GPR survey with 0.1 m × 0.2 m trace spacing. This example clearly defines the geometry of fractures in four different orientations, including vertical dips to a depth of 20 m. Decimation to commonly used half-wavelength spatial sampling or only 2D migration processing makes most fractures invisible. The extra data-acquisition effort results in image volumes with submeter resolution, both ...

Full-resolution 3D GPR imaging

A system and method of mapping underground utilities and other subsurface objects involves one or more of acquiring utility location data using a number of different detectors and sensors, processing the multiple detector/sensor output data to produce mapping data, storing the mapping data in a database, and providing access to and use of the stored mapping data by subscribing users on a usage fee basis.

Utility mapping and data distribution system and method

A method and apparatus, including software, for the development and operational use of precise utility location and utility asset management information. Field-usable data sets may be produced that meet standards of accuracy and usability that are sufficient for use by field operations personnel participating in damage prevention activities associated with ground penetrating projects (e.g., excavating, trenching, boring, driving, and tunneling) or other asset applications. Some embodiments relate to integrating utility asset data including coordinate location, and geographical information data using a consistently available and accurate coordinates reference for collecting the data and for aligning the geographical information data. Some embodiments relate to managing projects with equipment that provides real time images and the updating of the data as required with this desired accuracy.

Precision gps driven utility asset management and utility damage prevention system and method

Locating and/or marking equipment, such as a locate transmitter or locate receiver, a marking device, or a combined locate and marking device, may be communicatively coupled to and/or equipped with a mobile/portable device (e.g., a mobile phone, personal digital assistant or other portable computing device) that provides processing, electronic storage, electronic display, user interface, communication facilities and/or other functionality (e.g., GPS-enabled functionality) for the equipment. A mobile/portable device may be mechanically and/or electronically coupled to the equipment, and may be programmed so as to log and generate electronic records of various information germane to a locate and/or marking operation (e.g., locate information, marking information, and/or landmark information). Such records may be formatted in various manners, processed and/or analyzed on the mobile/portable device, and/or transmitted to another device (e.g., a remote computer/server) for storage, processing and/or analysis. The mobile/portable device also may provide redundant, shared and/or backup functionality for the equipment to enhance robustness.

Locating equipment communicatively coupled to or equipped with a mobile/portable device

An apparatus and method for combining a survey measurement dataset and a position dataset into a single dataset containing both measurement and position data is disclosed. The survey measurement data may be obtained from a ground penetrating radar, an inductometer, a magnetometer, or an optical camera. Positioning information is collected and merged with the survey information so that the position of the survey tool is known at each data point. Also provided are channel-equalization filters, spiking deconvolution filters, and frame filters that can be used in conjunction with the positioning information to enhance the quality of the images obtained from the data collected by the survey tool.

Method for merging position information with measurements and filtering to obtain high-quality images that are positioned accurately with respect to global coordinates

Position measurements by a tracking system associated with a survey tool are corrected for tilt. The tracking station typically incorporates some offset from the surface across which a survey is conducted, and the offset will be subject to angular displacement as the tool tilts with respect to its normal orientation. The tracking system records the 3D position of the survey tool, with angular offset errors. In the disclosed examples, an inertia! measurement unit (IMU), a dual axis inclinometer or a combination of two single axis inclinometers measures the amount of angular offset. The angular offset data is used to correct the position data, e.g. to reduce or eliminate errors caused by the angular offset, e.g. from vertical. If the tool provides measurement data, e.g. GPR readings, processing of the measurement data from the survey tool uses the corrected position data, e.g. to produce images of sub-surface features or objects.

Method for correcting a 3D location measured by a tracking system assuming a vertical offset

We describe a system for displaying buried utilities to operator to an excavator (Fig. 1). The display is based on 3D images of the subsurface obtained from advance locating methods (1). As the excavator (2) moves, the display changes so that it remains centered on the region near the bucket (10) where the buried pipes are in danger of being broken.

Virtual camera on the bucket of an excavator displaying 3D images of buried pipes

Ground-penetrating imaging radar ("GPiR") combines standard GPR with accurate positioning and advanced signal processing to create three-dimensional (3D) images of the shallow subsurface. These images can reveal soil conditions and buried infrastructure typically down to depths of about 2-3m with high resolution. A commercial GPiR called the CART Imaging System, which was designed for mapping urban infrastructure, has been developed. The CART system uses a radar array consisting of 17 antennas (9 transmitters and 8 receivers) that cover a 2m swath on the ground and can collect data while moving at speeds up to about 1 km/h. A laser theodolite tracks the position of the array during operation. The system collects enough data in a single pass to form a 3D image beneath its track; side-by-side passes are stitched together to create a seamless image of the subsurface. GPiR was first tested on a large scale in a project that mapped an area of approximately 12,000m2 in the south Bronx in four nights. Positions of surface features were also surveyed with the theodolite to provide a local reference grid. Final images were visualized with large-scale maps and electronic movies that scroll through the 3D data volume and show the enormous complexity of the subsurface in large cities.

Efficient large-scale underground utility mapping in New York City using a multichannel ground-penetrating imaging radar system

Ground-penetrating imaging radar (GPiR) combines standard GPR with accurate positioning and advanced signal processing to create three-dimensional (3D) images of the shallow subsurface. These images can reveal soil conditions and buried infrastructure typically down to depths of about 2-3m with high resolution. A commercial GPiR called the CART Imaging System, which was designed for mapping urban infrastructure, has been developed. The CART system uses a radar array consisting of 17 antennas (9 transmitters and 8 receivers) that cover a 2m swath on the ground and can collect data while moving at speeds up to about 1km/h. A laser theodolite tracks the position of the array during operation. The system collects enough data in a single pass to form a 3D image beneath its track; side-by-side passes are stitched together to create a seamless image of the subsurface. GPiR was first tested on a large scale in a project that mapped an area of approximately 12,000m 2 in the south Bronx in four nights. Positions of surface features were also surveyed with the theodolite to provide a local reference grid. Final images were visualized with large-scale maps and electronic movies that scroll through the 3D data volume and show the enormous complexity of the subsurface in large cities.

Ralf Birken

Papers

Method for merging position information with measurements and filtering to obtain high-quality images that are positioned accurately with respect to global coordinates

Method for correcting a 3D location measured by a tracking system assuming a vertical offset

Virtual camera on the bucket of an excavator displaying 3D images of buried pipes

Efficient large-scale underground utility mapping in New York City using a multichannel ground-penetrating imaging radar system

Efficient large-scale underground utility mapping in New York City using a multi-channel ground-penetrating imaging radar system