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.

​

What makes GPR such a good tool to investigate archaeological sites?

Before geophysical methods arrived on the scene, archeologists had enjoyed centuries of success using excavation and shovel test grids to narrow down the most likely areas in which to dig. This time-tested site surveying method involves laying out a grid and excavating a unit, typically 50 centimeters by 50 centimeters. Archaeologists sift through the material to determine whether artifacts are present, and if so, from which layers. They then move on to the next unit, which may be 10 to 20 meters away.

However, this method has one major problem – if 20 percent of shovel tests contain artifacts using 10-meter spacing, there is a great likelihood that researchers can jump right over a discrete feature. It takes time and effort to excavate shovel tests on the scale necessary to accurately narrow down artifact locations. This process is labor and time intensive – and it results in a high potential to miss something.

Take the example of early sites from the 1600s, which may not contain a lot of cultural material – just a few bits of pottery, pipe stems, or nails. It is very likely that you may not recover cultural material from a shovel test even if you are right in the middle of the site.

In recent decades it has become clear that GPR and other geophysical technologies could really help with surveying sensitive archeological sites remotely and non-destructively. Targeting what to excavate saves time, money and protects fragile artifacts. GPR can also aid investigations comparing the site’s natural soils with archeological components.
GPR and other geophysical technologies are not generally used as “first phase” methods; rather, they are used when other information is needed to help refine the site, usually after an initial shovel test finds artifacts that point toward something interesting. They may also be used after plowing an agricultural field turns up artifacts, or if researchers have a detailed historical map that suggests a house or farm used to be at a site.

Such methods can pinpoint the best places to excavate and indicate which areas should be avoided. This is especially useful for large multi-acre areas, where GPR can be used to build a high-resolution map of what the site might have looked at when it was occupied. Surveying a few acres in high resolution could help locate all the roads in a farm complex, as well as all the paths, activity areas (blacksmith shop, yards), and even individual buildings.
On a smaller scale – say a researcher finds a house and a well – the GPR can be used to produce a more localized survey across discrete features to get a better idea of their size and depth, and to determine if the walls are intact and if the cellar hole is filled with rubble or clean material.

What are the geophysical methods archaeologists use in the field?

Archaeologists use several geophysical methods, including GPR, electrical resistivity imaging (ERI), magnetometry, and electromagnetic induction (EM or EMI).

GPR works by sending a tiny pulse of energy into a material via an antenna. An integrated computer records the strength and time required for the return of any reflected signals. Subsurface variations create reflections that are picked up by the system and stored on digital media. GPR is considered the most accurate, highest resolution geophysical technology. It works best in dry sandy soils with little salt content; the technique is not useful on the coasts where there is a high salt content, for example salt marsh. Dense clay-based soils are difficult to penetrate with GPR, it cannot see through metal and is also incapable of identifying bone.

ERI is used for mapping the depth of soils and rock. It involves placing stakes in the ground and measuring electrical resistance. Technicians must set up a row of about 24-48 sensors (metal stakes) along the ground typically in a straight line; information is only collected along that one line. This tool works well in clay soil, but takes longer and costs more to get the required data coverage than GPR. One can collect 80 or more profiles of similar length with GPR in the same time it takes to collect 2-4 profiles using ERI.

Magnetometers are passive sensors that measure the strength and sometimes the direction of a magnetic field. By detecting irregularities in the earth’s magnetic field, a magnetometer can indicate the location of items made of ferrous material. Archaeologists use them to measure human activity that increases magnetism. For example, old fire pits have higher magnetic readings, as do bricks, storage pits, and even old trenches. Magnetometers do a good job of finding ferrous objects, but do not provided accurate depth information like GPR.

Electromagnetic induction (EM or EMI) devices measure the change in mutual impedance between a pair of coils on or above the earth’s surface. Most EM instruments are comprised of two or more sets of coils, electrically connected and separated by a fixed distance. EM devices can simultaneously examine soil conditions and locate objects found beneath the surface of the earth spatially, but do not provide good depth information.

It is important to emphasize that these methods are often complementary, because each is better at measuring different things. For example, magnetometers are often paired with ER surveys. But here’s the vital point: Only GPR can provide true depth information that can be calibrated. Unlike other available geophysical methods, a GPR survey can indicate where an anomaly or archaeological feature is in high resolution spatially, enabling archaeologists to say how deep it is below the surface. That’s a huge advantage.

How to use GPR for surveying?

Before even starting to scan, it is absolutely critical to obtain as much information as possible about the site. GPR surveyors should seek out any historical maps and make sure they have access to the results of walkover surveys showing concentrations of archaeological features and artifact density. GPR surveyors should also have an idea of what researchers expect the GPR to show them so they can get a sense of what they should be looking for.

As part of this information gathering, researchers should pay close attention to what the landscape looks like. Is it at the side of a mountain where it may be difficult to access? Is it clear of vegetation or densely vegetated? GPR equipment needs to be pushed in a straight line and the antenna sits on the ground, so if a site is overly vegetated it must be cleared before conducting a GPR survey. Essentially, anything one would not want to go over with a lawn mower would also be difficult for GPR equipment.

Other factors surveyors should know is the time period being investigated, results from the initial archaeological investigation, and the density of archaeological features to be mapped. A pre-contact Native American site may contain mainly debris from making stone tools or food remains, so there may not be much to image. A historical 17th century farm complex might contain at least one building or a cellar hole, or perhaps a large underground feature that can help orient the site, like a barn, well, privy or farm lane.

What type of planning can GPR surveyors do to guarantee an efficient survey?

GPR surveys are a great tool to fill in gaps between shovel tests to ensure a complete picture of a site. Surveying budgets are always tight, so the key is to collect as much data as possible within the time and budget allocated.

Context is everything, so the right surveying parameters will always be based on the type of site and the findings of the initial archaeological investigation. Collection parameters will vary by the type of site and the density of features. Ideally, one should carefully consider line spacing parameters and direction of lines based on the specific site features.

GPR surveys should always be collected on grids. Surveyors should place a larger grid over a feature so they can determine what is happening near the feature or is associated with it. A recommended practice is to bracket the area with space buffers to collect more information. This can be difficult, since projects are often restricted spatially by property boundaries. Development projects affected by the National Preservation Act’s Cultural Resource Management (CRM) requirements are generally restricted to the area of potential effect; surveyors do not usually have permission to survey beyond the project boundaries. For academic projects, one should keep surveying to collect as much data as possible in the allotted time. A GPR survey provides a digital archive of the recording process; even if the site is damaged or destroyed, the digital archive will remain.

The GPR surveyor conducts the survey and tells researchers where there are anomalies. In an ideal world, the GPR surveyor would later get feedback about the anomalies, with information on what was eventually found. This would enable surveyors to go back in and re-examine the data, providing a better sense of what particular data findings mean.

House sites and cemeteries are common geophysical survey locations. What are special considerations about using GPR at these site types?

Early American house sites are very feature rich, with numerous underground targets. Researchers are typically looking for former extensions of a house that have since been demolished, as well as kitchen wings, foundation walls, and even gardens and pathways. As noted earlier, it is important to conduct background research before surveying, including deed research and use of the Historic American Buildings Survey (HABS) and Historic American Engineering Record (HAER) collections.

Geophysical surveys can help with investigation of cemeteries – both formal ones with standing stones and informal cemeteries, with unmarked graves or single burials. GPR can be used to image internment, but, Hollywood portrayals to the contrary, it is incapable of identifying bones. Use of GPR is also hampered by the fact that there may be variable states of preservation across a particular landscape, depending on soil types and topographical features. One part of a cemetery from 1750 could be remarkably preserved, whereas a grave from a different part of the cemetery might be completely decayed.

Another factor is that older coffins were wood or brick, which are difficult to image with GPR. The technique targets hyperbolic reflectors (an upside down U); in the absence of those reflectors GPR surveyors rely on vertical disturbances in the soil profile that come from digging, which shows up fairly well in GPR data.

The accompanying graphic shows two-dimensional GPR data taken from a cemetery site. The data represents six burials, approximately 10 nanoseconds in depth.

Whats the added value in processing software?

Regular GPR profiles are interesting, useful, and powerful for people who can read them – but they are also limited. It is difficult to see the shape of a feature by just seeing a cross section. GPR data does not show up on the screen labeled – surveyors must interpret what the features are. This is where post-processing software can play a role.

Similar to software used to process camera images, post-processing allows researchers to downplay some features and highlight others. Noise is inherent in digital GPR data, and the post-processing software enables users to reduce or remove noise to accentuate what they are looking for. The accompanying figure shows a three-dimensional GPR data image that identifies nine anomalies that could represent burials. The data was processed with RADAN post-processing software.
​
One excellent software-based technique is called time-slicing, in which all the individual lines of data collected are stitched together using the assigned coordinates into a three-dimensional cube of the survey area. Horizontal slices (also called time slices) can isolate specific depths to show the soil layers and review lateral relationships and actual feature shapes. Time slices help researchers really see the shape of a feature, like a circular well or building foundation, or a long linear pipeline. The slices add an immense amount of interpretative data and are often the best way to illustrate findings to the general public.

To use the tool to its best advantage, GPR surveyors should collect the right information before beginning a GPR survey, carefully plan data collection parameters to get the highest resolution data at the highest percent coverage for each specific site, and use software based post-processing tools, especially time-slicing.

Figure 1. A three-frequency transmitter waveform. 

Figure 2. First 33 points of Figure 1.

Figure 3. The base period of the bit-stream for the GEM-2 is set to 1/30th of a second for areas having a 60-Hz power. The TX switches at 192 kHz and, therefore, the bit-stream contains 6,400 steps within the period. Through a Fourier transform of the transmitter current waveform above, we obtain a power spectrum of the primary field, which shows each transmitted frequency. 

Figure 4. With multiple frequencies, one can determine layered conductivity structure of the earth, conceptually shown below. This is called "frequency sounding" method.

Canadian rivers are known for its gold findings. Once again we received fantastic pictures of a happy gold seeker. With his Black Hawk metal detector he was looking for natural gold streams on the riverside in British Columbia/ Canada. The result you can see here - wonderful gold flakes. The OKM Black Hawk is available with different search coils for the detection of natural gold and buried metal objects.

To order please click here

​New research out from the journal Current Biology discovered that different movement patterns of elephants (walking stomping, charging) create unique ultra low frequency seismic waves.

​Paired with earlier evidence that elephants are able to detect low energy seismic waves, scientist hypothesize that these self created seismic waves might be used communicate with other elephants up to 6.4 kilometers away!

Listening for elephant vibrations would certainly be one of the more unique use-cases for our Geode Seismograph, but it is totally possible given this research. It only goes to show that there are still many undiscovered use cases for seismographs like our Geode!

Aquapulse was the tool used for this amazing find!

The crew of a boat known as “Capitana” recently discovered over 350 gold coins! The Capitana is part of the 1715 Fleet-Queen’s Jewels, LLC historic shipwreck salvage operation. The famous 1715 fleet sank in the year 1715, with millions of dollars in lost treasures. The vast amount of coins just recovered were found on exactly the 300th Anniversary of the 1715 Fleet!

According to Brent Brisben, the co-founder of of the 1715 Fleet-Queen’s Jewels, LLC, there were 9 rare coins also found, known as “Royals”. Those coins are valued at $300,000 a piece!! Brisben also mentioned, in a recent press release, that the coins were meant for the King of Spain and these make up 30% of all the known Royals out there! Brisben said that all the artifacts were discovered in shallow waters, about 6 feet deep, off the coast of Vero Beach, Florida. The treasure hunter that made the amazing find was William Bartlett, near a location where Co-Captain, Jonah Martinez chose.

You can order your aquapulse here

Our scientific echosounders for fisheries and aquatic habitat assessment include everything you need to explore aquatic ecosystems using hydroacoustics. Our proven single and split beam sonar echosounder system are versatile, optimized for flexibility, reliability and ease of operation and include the data acquisition, real-time analysis, data visualization and post-processing software you need to get results.

DT-X Extreme Autonomous Portable Scientific Echosounder – This versatile echosounder is ideal for mobile surveys, or as a fully autonomous system for ASV/AUV surveys, surface buoys and other unmanned or fixed location monitoring applications for aquatic ecosystem research and management.

DT-X SUB Autonomous Submersible Echosounder – Our autonomous, fully submersible echosounder, for marine envoriments, optimized for ocean observatories and long-term AUV or ASV missions.

DT-X AMS Automated Monitoring Systems – Designed for fixed location, long-term or permanent deployments to monitor passage, migration and entrainment of fish and marine life or debris.

MX Aquatic Habitat Echosounder – A low cost, turn-key solution for rapid assessment and mapping of aquatic vegetation, substrate and bathymetry.

​

​What is EM Locator Technology?

Electromagnetic (EM) Locator technology relies upon the detection of an alternating magnetic field. This magnetic field is created by the flow of current through a conductor, whether a wire, cable, pipe, or other conductive material. Often, additional ‘tracer wires’ are run in parallel to non-conductive pipes such as gas lines expressively for the purpose of facilitation such detection. AC power utilities, as long as current is flowing in the form of power usage, usually radiate a very detectable magnetic field as a side-effect of normal operation. It is also possible to intentionally induce a ‘tracer’ current (by inductive clamp or direct attachment) onto otherwise passive conductors in order to create a detectable field that can be followed.

LineTrac technology is a multi-sensor fashion technology that combines the power and advantage of GPR with the specific target-identifying capabilities of EM location. Linetrac operates in both “Power” (50 or 60 HZ Utility Power) and in arbitrary “Frequency Mode” up to 50KHz, using a customer-supplied transmitter.

We provide two models of EM locator technology. The LineTrac system for our UtilityScan series and the LineTrac XT for our StructureScan Mini XT system.​

Seismic refraction maps contrasts in seismic velocity – the speed at which seismic energy travels through soil and rock. This parameter typically correlates well with rock hardness and density, which in turn tend to correlate with changes in lithology, degree of fracturing, water content, and weathering.

There are two basic approaches to seismic refraction data analysis: layer-cake and tomographic inversion. The former is the more traditional approach, although tomography has become more popular as faster computers have made it much more feasible than in the past.

Especially in the near-surface, it is not always the case that seismic velocities are divided into high-contrast, discrete layers. Nor is it the case that velocities are constant horizontally. Conventional layer-cake inversion techniques, such as the delay-time method, assume both, and require the geophysicist to provide layer assignments before the data inversion can be completed.

Tomography is less constrained in this sense; it does not “think” in terms of layers, and it better accommodates horizontal velocity variations. If discrete layering is not apparent in the raw data, the tomographic approach is generally more appropriate. As such, Geometrics’ SeisImager Refraction Analysis software offers both options.

Common applications:

1. Estimating rippability prior to excavation
2. Mapping depth to bedrock/bedrock topography
3. Mapping depth to ground water
4. Calculation of elastic moduli/assessment of rock quality
5. Mapping thickness of landslides
6. Identification and mapping of faults

Considerations:
The depth of penetration in a seismic refraction survey is approximately 1/5th of the length of the geophone spread, including offset shots. So if you need to see 10m deep, you will need room to lay out a (minimum) 50m seismic spread, as measured from offset shot to offset shot.

For most engineering refraction work, the best possible source is a 14 or 16lb sledgehammer. A downhole seisgun is not a good refraction source in general, except in cases where the surface is too soft to use a hammer effectively. An accelerated weight drop can be a good source, but is not portable and requires vehicle access to the shot points. Small explosives, such as Kinepak, are ideal when portability is required and the depth of interest is greater than what can be reached with a hammer.

Benefits/Limitations
Seismic refraction requires that velocities increase with depth. A lower velocity layer beneath a higher velocity layer will not be detected by seismic refraction, and will lead to errors in depth calculations. Fortunately, this is a fairly uncommon occurrence in the shallow subsurface.

The seismic source employed must match the desired depth of penetration. For hammer and plate work, the maximum depth you can expect to explore to is about 15-20m; however, this can vary significantly depending on geology, surface conditions, cultural noise, and the person swinging the hammer. Refraction is a relatively broad-brush technique – it looks at gross velocity differences, and you should not expect to be able to map more than 3-4 individual velocity layers.

Cultural noise can be a problem – it is more difficult to conduct a seismic survey in an urban environment than in a rural one. Surveying along busy roadways should be avoided when possible. Shooting at night is sometimes necessary in order to achieve acceptable signal-to-noise ratio in busy areas.
​
​

The final product of a refraction survey is a velocity model, such as the layer-cake inversion shown on the left, or a tomographic inversion as shown below