In cemeteries across the United States, there are “the forgotten” burials of unmarked and lost graves. Geophysical techniques, such as Ground Penetrating Radar (GPR), are needed to nondestructively locate these burials in cemeteries and in other locations. Here, we discuss the common causes for lost graves and present three keys to survey success.
Common Causes for Lost GravesThere are many causes for lost, unmarked graves, but two of the most important are cemetery age and population growth.
Historical cemeteries can go back hundreds of years. Over time, missing, fallen, or poorly placed headstones can complicate the assumed physical location of grave sites. The original documentation may be unavailable or rendered unreadable, further leading to confusion. For these and other reasons it is common for cemetery maintenance managers, or other stakeholders, to enlist GPR service providers to generate up-to-date burial maps or clear areas for new burials.
Modern population growth has led to increased infrastructure and city sprawl. As local and state regulations have evolved over time there are documented cases where contractors were given permission to build over known or forgotten burial grounds. In these situations, it is possible that civil and political pressure may lead to a GPR investigation to determine the existence of a cemetery, presence or absence of burials, whether the graves have been disturbed, and factors related to relocation recommendations. In other cases, cemeteries were relocated due to urban expansion but some of the graves could have been overlooked.
Due to the sensitivity of these sites, the GPR service provider’s challenge is to quickly explore the subsurface without disturbing the burials. Every cemetery is different, and local environmental and soil conditions can complicate the investigation. Below, we outline three steps to get started in mapping cemeteries.
How to Get Started: Three Keys to Success
With this application, it is just as important to understand the appropriate type of GPR equipment, as well as potential limitations, as it is to know about what you’re going to encounter onsite. As with all technical subjects, mastery of cemetery investigations with GPR requires practice and dedication. Armed with GSSI GPR and an understanding of burial characteristics, you can help locate and protect human burials.
We’re here to help – we’re educators and want to provide you with the tools to be successful. To learn more, here are some recommended readings:
RADAN® is GSSI’s post-processing software for ground penetrating radar (GPR). Short for Radar Data Analyzer, RADAN was first developed by GSSI in 1984 and released in 1987 to post-process GPR data. This software allows users to select the processing functions that best suits their needs. RADAN is Windows™ based, which provides a familiar and easy-to-use environment for all levels of user experience. In 1994, RADAN changed from a disk operating system (DOS) to Windows.
RADAN 7 Software Options
There are three types of software packages for RADAN 7. RADAN 7 Main is the primary platform for all GPR applications. Users have the ability to customize their RADAN 7 software with additional modules:
3D: The 3D Module allows the user to view and build 3D visualizations. This module helps interpret and annotate complex subsurface structures and is often used to create report graphics.
RoadScan™: The RoadScan Module is used to analyze pavement, base, and sub-base layers in roadways.
BridgeScan™: The BridgeScan Module allows users to process bridge deck GPR data and account for skew angles. Features included aids users to map bridge deck deterioration and export data in multiple file formats, such as .kml and excel.
GSSI also offers two versions of RADAN that are application specific for the concrete inspection and utility locating markets. These packages are separate from RADAN 7 Main and cannot be upgraded.
RADAN 7 for StructureScan™ Mini is designed to process, view and document 2D and 3D data collected with the StructureScan Mini series systems.
RADAN 7 for UtilityScan® is designed to process, view and document 2D and 3D data collected with our UtilityScan product line.
How to Activate RADAN 7
When users purchase RADAN 7, they are provided a unique digital product key and serial number that is needed to install the software on their computer. RADAN 7 will automatically activate purchased modules when the activation codes are input. If one does not input the activation codes, the software will go into Demo Mode for 30 days or 33 uses, whichever comes first. After which, the software defaults to a RADAN Reader version.
When importing your GPR data into RADAN, you will see different files depending on the systems you collected the data on. Below we’ll list out the types of file names and differences between them.
Setting up a Source Directory
Lastly, users should know how to generate and set up a source directory in RADAN before beginning any processing. The source directory tells the RADAN program where to look for the data for processing.
When opening the software, click on the global settings option, which will open a pane on the right side of the screen. Upon double clicking on the word source directory, a file browser will open allowing users to browse the location containing the data for processing. Once this source directory is set to the correct location, clicking “Home > Open” will open that source directory right away.
Note: If “Autosave files” is set to Yes when setting up the source directory, RADAN will automatically save files in the source directory in a folder called “PROC,” short for processed files. Alternatively, “Autosave files” can be set to No, which gives users the ability to rename files as they’re being created.
Geologic and environmental investigations are integral in determining the geology of any work site. Ground Penetrating Radar (GPR) used as Non-Destructive Testing for subsurface exploration remains one of the safest, quickest, and highest resolution survey options available. Researchers and professionals have been using GPR for geophysical investigation for nearly a century and the applications are seemingly endless. From depth to bedrock, ground water exploration, ice and snow investigation, geomorphology, bathymetry, stratigraphy and sedimentation, structural investigation (along with geohazards), and prospecting, we offer a wide range of antenna frequencies with never before seen depth penetration and data quality.
Ground penetrating radar (GPR) offers an accurate, non-destructive solution to mapping the subsurface of the earth. With GSSI GPR antennas, it is simple to locate features of interest and subsurface layers in real time, up to 100 feet or more.
We offer many different analog and digital antennas, giving you the freedom to choose the right combination of depth penetration and resolution. High frequency antennas provide higher resolution, but typically offer limited penetration. Lower frequency antennas collect deeper data, but they do not image small targets or closely-spaced soil boundaries. Whatever your survey requires, we’ve got you covered.
Welcome to another blog about Ground Penetrating Radar. This post is from GSSI Academy and provides GPR theory basics and key concepts of ground penetrating radar. In this post, we discuss how to determine different material types when conducting underground utility locating surveys.
GPR Theory: Determining Material Types
One of the most critical tasks in using Ground Penetrating Radar, or GPR, technology is that of determining materials types for materials in the ground. Given that GPR technology works by transmitting and receiving a high frequency electromagnetic wave through the ground, distinguishing between different materials – typically air, water, and metal – is possible by analyzing the degree of difference in the dielectric constant of the material. Dielectric constant measures how easily radar waves move through a material; for more in-depth information about it, check out this blog post.
Air, Water, or Metal?
For underground utility locating, the three main material types encountered are metal, air, and water. Determining material type is possible by analyzing dielectric change, or the change in how easily radar waves penetrate the ground as compared with the material in the ground. The larger the dielectric change, the stronger the reflection and the brighter the image produced on the GPR control unit. Greater change produces brighter targets on screen, and smaller changes produce dimmer targets. The color of the target onscreen indicates whether the dielectric change is positive or negative.
Metal has an infinite dielectric constant – GPR cannot pass through metal because it’s a perfect reflector for GPR energy – and so it will be shown onscreen as the brightest possible positive dielectric change.
Whereas an air-filled PVC pipe, through which the radar energy moves easily, will demonstrate a negative change, since the dielectric constant of air is less than that of ground materials. The data image below shows a water-filled PVC pipe that clearly identifies the top and bottom of the pipe.
The same is true when identifying underground voids. Below is an example of a well-defined void underneath a reinforced concrete slab with an asphalt overlay.
Finally, in the case of a water-filled PVC target, the screen will show a positive change like that of metal because water has a higher dielectric constant than any ground materials. Determining water targets compared to metal, however, is possible because while water has a high dielectric constant, it is not impermeable to GPR and thus will show up as a dimmer positive target on the screen of a GPR unit.
In this new blog we present a new chapter from GSSI Academy. It is a basic introduction to some of the key concepts of ground penetrating radar. To begin, we discuss the importance of the dielectric constant and methods to determine the right dielectric. Just as Ground Penetrating Radar is also known as GPR, Georadar, and ground probing radar, the term dielectric constant can also be known as velocity and medium type, depending on specific GPR manufacturers.
GPR Theory: Understanding the Dielectric Constant:
GPR works by transmitting and receiving a high frequency electromagnetic wave through the ground, whether it’s soil, concrete, gravel, or other material. Radar waves travel at different velocities depending on what material it’s traveling through; anything ‘different’ that it interacts with will produce a reflection, to be received by the GPR device. Upon receiving the reflection, a GPR device will take note of the amount of time it takes for the signal to return and the strength of that reflection. The system will take these two pieces of information and convert them into a depth reading; in order to do so, they must be programmed with what’s known as the dielectric constant. This constant describes the speed at which electromagnetic waves move through a particular material.
The Importance of the Dielectric Constant:
The dielectric constant is critically important to getting accurate depth readings with GPR systems. Dielectric constants, also known as relative dielectric permittivity, are measured on a scale of 1 to 81, where 1 is the dielectric constant for air (through which radar waves travel most quickly) and 81 the constant for water (through which radar waves travel most slowly). Metallic objects exist outside the scale, since radar waves cannot penetrate them at all; they are described as having an infinite dielectric constant.
In order to convert the variable that is produced by a radar reading – time – into the desired product of the reading – depth – GPR systems must be accurately programmed with the correct dielectric constant for the ground material in question. This enables GPR systems to produce meaningful depth readings, instead of timed reflection readings; these time reflection readings are transformed in an equation with the proper dielectric constant. As a result, depth readings from GPR systems are only as accurate as the dielectric constant with which they are programmed for each particular ground material. There are three key methods for determining an accurate dielectric constant, each with their own benefits and drawbacks.
Methods of Determining the Dielectric Constant:
One way of determining the dielectric constant is by utilizing a published reference, available from GSSI in manuals and products documentation, as well as online. Using a published reference is the quickest and easiest way to obtain a dielectric constant because it doesn’t require field analysis if ground material type is known. It’s not the most accurate, though, because published references are averages and not site specific.
A more accurate way to determine the constant can be with utilizing a method known as migration, or hyperbola fitting. Hyperbola fitting relies on data gathered from pipe-like targets in the ground; individual GPR units are capable of calculating dielectric constants for different soils simply by fitting a hyperbola tool to hyperbola data gathered in real-time from one of these pipe-like targets. This is the most consistent way to determine the dielectric constant in the field.
The final method for determining the dielectric constant is through what’s known as ground truth. In this case, a GPR unit is positioned over something for which the actual depth is known; by programming the unit with this known depth (known from a prior dig or a chart), the unit can calculate the dielectric constant and effectively gauge depths for other objects in the field.
Newly released software for the StructureScan Mini XT system.
Visit https://lnkd.in/eTd7Xa4 to download the latest version.
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It is not uncommon for concrete contractors to request the location of rebar, conduits, post-tension cables, electrical, or plumbing in order to aid in remediation risks. Additionally, savvy contractors have been using GPR technology to determine concrete slab thickness. This provides the concrete contractor with several benefits including: the proper assignment of concrete cutting and coring tools, and the ability to better quote the work required. Trained and certified GPR operators understand the benefits and limitations of the technology and how to determine the best course of action in challenging survey conditions. Yet, even the most knowledgeable operators will wonder if there’s a tip or trick that they can deploy in the field to collect better data. Here we explore the difference between suspended slab and slab-on-grade surveys, and infield processing techniques which operators can use to get the best out of their slab-on-grade data.
The detectability of the slab bottom depends on the underlying material and amount of steel within the slab. It is easier to see when a contrasting material such as water, air or metal is under the slab because they will have a stronger dielectric contrast. In Figure 1, the data is representative of an elevated concrete slab. Note the several hyperbolic reflections on the screen, this is indicative of a double rebar mat. Towards the bottom of the data image, there is a strong dielectric contrast at the concrete-to-air boundary and therefore products a clear indicator of the bottom of the slab.
In slab-on-grade situations, the bottom may be very weak or invisible if the slab rests on sand or another concrete structure (supporting beam, for instance) with similar dielectric properties. This can be challenging due to the low dielectric contrast for the concrete-to-sand boundary and intersecting hyperbolic tails from objects embedded in the slab. The former results in weak or non-existent reflections and the latter tends to mask the reflection from the bottom of the concrete interface. Figure 2 illustrates a reinforced concrete roadway with a strong reflective boundary towards the center of the roadway. This is an example of a void. The concrete-to-grade boundary is less reflective as the air-filled void.
2-D versus 3-D Data Collection: In most cases, GPR manufacturers recommend using 2D scanning for real-time locating and simple imaging services, and to use 3D data collection for complex survey sites. However, slab-on-grade surveys are an exception to this rule. It is recommended to conduct 2D scanning in these situations because the layer interface is a planer target which is more easily viewed from the side.
Depth Setting: Conducting a preliminary scan of the area will help the operator determine the appropriate GPR system settings. A common mishap is that the system is set to a depth that is less than the overall concrete depth. This inherently causes data loss at the deeper levels. Remember to always set the depth range 2-3 inches deeper than the expected slab thickness to ensure that the full slab thickness is captured.
Gain: Display Gain and System Gain can be used to brighten a weak back reflection. However, these settings should be used with caution. Display Gain and System Gain settings often influence the rest of the data. Some systems apply a correction factor to gain based on assumed material dielectric.
Migration: Migration eliminates hyperbolas by collapsing them into dots representing the actual targets. This can be helpful to make target identification more intuitive and makes the data easier to interpret. This is especially true for slab-on-grade because the tails of hyperbolic targets can sometimes intersect and hide the concrete-to-sand boundary reflection. By collapsing the hyperbolas into dots, the bottom of the slab can become more recognizable.
Cross Polarization: When detecting linear metal targets (pipes, rebar, etc.), antenna orientation relative to the target becomes important. Antenna dipoles (transmitter and receiver) are most sensitive to the metal targets that are parallel to them. In other words, if an operator is scanning across the slab with the GPR system in its normal orientation, it is sensitive to targets that are running perpendicular to the direction the operator is moving (parallel to the antenna dipoles).
Some systems can be modified to turn the antenna 90 degrees. This method is known as “cross-polarizing”. If the operator scans over a metal target that is again perpendicular to their direction of travel, the GPR system is not as sensitive to it. This “weakens” the amplitude of the metallic objects and may result in a stronger concrete bottom reflection.
In summary, GPR interpretation and survey efficiency is a skill that requires training, field experience, time, and practice. These tips are intended to help operators troubleshoot a very specific type of survey scenario. An operator may employ all of them, some of them, or only one of them in an attempt to conduct a successful survey. In some extreme cases none of the solutions may work, and only a trained operator will know what tools to use and when.
The world’s leading manufacturer of ground penetrating radar (GPR) equipment, introduces the new 200 MHz (200 HS) antenna, the first of the next-generation high-performance GS Series, designed for applications that require deeper depth penetration. The new 200 HS antenna serves as the foundation for the GS Series, which is ideal for geophysical, geotechnical, or environmental applications that require high reliability under challenging survey conditions.
The newly designed 200 HS antenna is paired with the HS Module and wirelessly connects to a Panasonic Toughpad G1 or SIR 4000 control unit. The wireless HS Module incorporates system electronics, an internal GPS, and connectivity ports in an IP-65 rated housing. The 200 HS uses GSSI’s patented HyperStacking technology, which improves signal to noise performance and increases the antenna depth penetration, nearly double the conventional GPR antenna designs, under all soil conditions. The 200 HS is FCC, RSS-220, and CE certified.
The GS Series features a modular design that allows the user to select which controller best suits their needs; the rugged SIR 4000, combined with our new WiFi Module, or the Panasonic G1. Both controller options provide different advantages to the customer. The SIR 4000 builds on the same user interface and menu options that customers are familiar with to accommodate the 200 HS. The Panasonic G1 features a GIS map mode that will display GPR data collected on the left side of the screen and a location map on the right side of the screen.
Designed alongside the 200 HS are several survey accessories to enhance the ease of use in data collection. The antenna comes with a tow handle with various grip options. Optional accessories include a GPS mount and a four-piece wheel kit that will decrease the wear of the antenna on prepared surfaces such as grass and asphalt.
Source: Palawan News (www.palawan-news.com)
The Department of Environment and Natural Resources (DENR) is set to charge the management of a beach hostel in El Nido after the discovery of its “illegally installed” polymerizing vinyl chloride (PVC) pipeline within the easement zone over the weekend.
A statement sent to Palawan News Tuesday by the DENR MIMAROPA Region said the PVC pipeline was excavated from the beachfront of Outpost Beach Hostel in Barangay Corong-Corong through the use of the ground penetrating radar (GPR) by a survey team of the regional and central offices of the Mines and Geosciences Bureau (MGB).
“The pipeline measuring six inches in diameter and six meters in length was uncovered in front of Outpost Beach Hostel in Corong-Corong. It was also found discharging black and foul-smelling liquid directly into Bacuit Bay, one of the province’s ecotourism sites undergoing massive rehabilitation,” the statement said.
The DENR MIMAROPA said to confirm the source of the wastewater, the Environmental Management Bureau (EMB) used a green tracer solution into Outpost Beach Hostel’s last chamber to which the excavated pipe was connected.
The DENR regional and central offices survey team is seen in this photo using the ground penetrating radar (GPR) to detect the presence of the illegally installed sewerage pipe in front of the Outpost Beach Hostel in Corong-Corong, El Nido. (Photo courtesy of the Mines and Geosciences Bureau)
“After almost 20 minutes, the green solution drained into the said pipe, indicating that the said establishment was the one discharging wastewater from the tank. The EMB shall be conducting further investigation to determine if there are other sources of wastewater discharge aside from the hostel,” it pointed out.
Paul Sepulveda, one of the co-owners of Outpost Beach Hostel, reportedly admitted that they owned the pipe.
Nevertheless, the statement said DENR MIMAROPA regional executive director Henry Adornado ordered the immediate removal of the sewage line as it violates the provisions of Presidential Decree 1067 or the Water Code of the Philippines, which prohibits structures within the easement zones without permission from the government.
Meanwhile, the excavation site was filled with sand using the backhoe sent by the local government of El Nido. The end of the cut pipe was left open for sampling and analysis by the EMB.
“We have to remind everyone that we are preparing Bacuit Bay as Water Quality Management Area so we shall be conducting regular water sampling and analysis not only to Outpost Beach Hostel but also to other establishments to ensure they do not discharge untreated wastewater into Bacuit Bay,” EMB Regional Director Michael Drake Matias said.
Besides regular effluent sampling, the DENR and the MGB have been conducting a GPR survey of the coastal areas of El Nido since March 18 to detect buried waste pipelines. They are calling business establishments to take Outpost Beach Hostel as an example to avoid interruption in their business operations.
“You cannot hide them (pipes) forever. We will eventually uncover them so we advise you to remove your illegal sewage lines and comply with the laws for your own good,” MGB MIMAROPA regional director Roland De Jesus was also quoted in the statement.
The DENR, EMB, and MGB in MIMAROPA vowed to impose the maximum penalty to any establishments found continuously breaking environmental rules and regulations; and employ unified action to ensure environmental protection remains as a top priority.
GSSI, the world’s leading manufacturer of ground penetrating radar (GPR) equipment, announces the release of a major software update for the StructureScan™ Mini XT – the newest generation of GSSI’s popular all-in-one concrete inspection GPR system. The update expands StructureScan™ Mini XT capabilities with an increased depth range, improved Focus Mode, and a new Auto Drill feature.
The update increases StructureScan™ Mini XT’s depth range by 20% to up to 24 inches for greater visibility in survey situations involving thick structural concrete and slab on grade. Additionally, algorithm improvements enhance the StructureScan™ Mini XT’s gain at greater depths.
The improved Focus Mode uses input from the StructureScan™ Mini XT’s 2.7 GHz high-resolution antenna to resolve closely spaced and bundled targets within concrete, offering precise visualization where traditional GPR hyperbolas would condense data into a singular dot. Users can sweep between raw GPR data and the easy-to-read focused view. The new Auto Drill feature searches for potential obstructions to a planned core location. The innovative software tool uses a specialized algorithm to identify possible obstacles to drilling operations by analyzing a user-selected position and size (1/2’ to 6”) on a 3D grid.