Typical and not-so-typical applications of IceMap GPR systems

Summary: IceMap GPR systems have been used for more than 20 years to map ice thickness in northern areas, but in that time, innovative customers have found other interesting applications for the technology.

The Sensors & Software IceMap system uses ground penetrating radar (GPR) technology to measure and map the ice thickness across frozen lakes and rivers used as winter roads in northern areas of Canada and the USA.

IceMap was originally introduced in 2011 after several winters of working closely with the Northwest Territories (Canada) Department of Transportation. Over the last 20 years, GPR technology has completely changed the procedure for safely building, monitoring and closing ice roads. This includes providing high-density, accurate ice thickness measurements to improve ice weight capacity calculations and by helping to extend the ice road season as long as safely possible.

A typical application for IceMap is for monitoring the ice for an ice “bridge”. An ice bridge, as the name suggests, is a short ice road across a river. Permanent bridges in remote areas are usually not practical to construct, but ice bridges provide shortcuts that can save significant time and transportation costs during the winter months.

One such ice bridge is the one that crosses the Peace River near La Crête, Alberta (Figure 1a) . During the warmer months, this is a ferry crossing, but every winter, a 700-meter (0.5 mile) ice bridge is constructed to save time for vehicles travelling through the area. The nearest permanent bridge across the Peace River is 75 km away in Fort Vermillion (Figure 1b), but 100 km (60 miles) by road.

Figure 1a

The 700-meter-wide ice bridge across the Peace River near La Crête, Alberta saves driving 100 km (60 miles) to the nearest permanent bridge.

Figure 1b

The La Crête ice bridge, built across the Peace River in northern Alberta every winter, saves driving 100 km (60 miles) to the nearest road bridge in Fort Vermillion.

The time lapse videos in Figures 1c and 1d show the ice thickening from early January to late February, going from about 40 cm to over 170 cm in thickness. The thicker the ice, the higher the weight capacity to support heavier trucks.

While IceMap was designed for this specific application of measuring ice thickness on ice roads and bridges, over the years we have had customers use IceMap for other applications we had never even thought of when we originally developed it. Some of those applications are outlined below.

Detecting Grounded Ice

“Grounded ice” means that the ice has frozen to the bottom of the water body. For ice roads grounded ice is a good thing for two reasons: 1) the ice does not have to be engineered to a certain thickness like floating ice must be, as it is supported from underneath and, 2) in terms of safety, if the ice is grounded, there is no danger of vehicles going through the ice into deep water.

Fortunately, because of the favorable physics, IceMap can usually detect areas of grounded ice easily. This is because the reflectivity of the bottom of ice when it is floating on water is much higher (K_ice of 3, K_water = 80, R = 0.68) than when the ice is frozen to the sediments or rock on the bottom of the water body (K_ice of 3, K_rock = 5, R = 0.13). This difference in reflectivity makes areas of grounded ice stand out in the GPR data (Figure 2a). With the GPS integrated into the IceMap system; after adding point interpretations using the EKKO_Project software, the positions of grounded ice can be plotted on Google Earth (Figure 2b).

Figure 2a

IceMap data image showing low amplitude reflections caused by “grounded” ice, where the ice has frozen to the bottom of the water body, so it is no longer floating on water.

Figure 2b

Google Earth image showing the path of the IceMap survey (green line) and the locations of grounded ice (red dots).

Analyzing Ice Quality

Weight capacity measurements on ice are based on “pure” ice. If ice has “contaminants” embedded within it, such as air bubbles, water bubbles, organic matter, an internal unfrozen layer (Figure 3a), it is no longer pure and that can affect the weight capacity of the ice.

Figure 3a

Ice with contaminants such as air bubbles, water bubbles, organic matter, slush layers reduce the weight capacity of the ice. IceMap can be used to detect objects embedded within the ice, even when the ice is completely snow-covered.

When Manitoba Infrastructure analyze their IceMap data, they specifically look for internal reflectors associated with materials that reduce the ice quality. Pure ice is a homogeneous material, which means that there is no contrast in materials to cause GPR reflections (Figure 3b right). However, if internal objects or layers are present in the ice, GPR will often detect those (Figure 3b left).

In the example below, Manitoba Infrastructure, with an abundance of caution, re-routed the ice road to avoid the ice that had internal contaminants, that could compromise safety on the ice.

Figure 3b

IceMap data image (left) shows many internal reflections, interpreted as air bubbles trapped in the ice, which could reduce the weight capacity of the ice. As a result, the ice road was re-routed along a path where there were no internal reflectors within the ice (right).

For the full story, see: https://www.sensoft.ca/blog/evaluating-ice-road-quality-icemap/

Water Reservoir Volume Calculations

An IceMap customer in Iceland used the system to measure snow thickness over a large catchment area to improve the calculations of the volume of water expected to runoff into the local reservoir (Top photo and Figure 4):

IceMap was used to provide continuous snow data from the catchments, improving the conventional “point” measurements and adding to the knowledge of snowpack extent and winter snow accumulation. In total, 65 cross-sections were surveyed on land to assess snow thickness and spatial distribution in catchment areas. IceMap enables acquisition of much higher spatial resolution water content data resulting in more informed decisions regarding operation of the hydroelectric system.

Figure 4

IceMap is a great tool for measuring the thickness of snowpack helping to estimate water volumes for hydroelectric power generation.

For the full story, see: https://www.sensoft.ca/wp-content/uploads/2016/01/2015-07-Subsurface-Views.pdf/

Ice thickness in Environmentally Sensitive Areas

Wetlands such as swamps, bogs and muskeg (Figure 5a) are environmentally sensitive areas, so work is often performed in the winter when the area is frozen, plants are dormant, and animals are hibernating.

Figure 5a

Northern wetlands are environmentally sensitive areas where construction projects are often delayed until winter.

A customer used IceMap to measure the ice thickness to determine the maximum weight of a construction vehicle that the ice could support without breaking and damaging the wetland.

Similar but more extreme than the application above about ice quality being affected by embedded materials, ice in a wetland is full of organic matter, that makes accurately measuring the ice thickness more difficult due to scattering and attenuation of the GPR signal. However, it is often possible to see the bottom of ice reflector (Figure 5b).

Figure 5b

Although the presence of organic matter embedded in the ice limits the penetration depth of IceMap signals, the bottom of ice boundary is often a strong reflector.

Detecting water pockets in ice frozen to the bottom

This application is kind of the opposite of the application above of using IceMap to find grounded ice. In this case, a customer, Agnico Eagle Mining, needed to find liquid water for drilling exploration holes (Figure 6a). The problem was the exploration project was being conducted in the dead of winter with an ambient temperature of -40⁰C (-40⁰F) so all the local water bodies were frozen all the way to the bottom.

Figure 6a

Agnico Eagle Mining using an early IceMap system (left) to find pockets of liquid water under the ice in conditions that were so cold, most of the ice in the area had frozen right to the bottom of the lake. Water is critical for their exploration projects.

Fortunately, the IceMap operators understood the physics of GPR and IceMap GPR in particular. The reflectivity of the bottom of ice when it is floating on water is much higher (K_ice of 3, K_water = 80, R = 0.68) than when the ice is frozen to the sediments or rock on the bottom of the water body (K_ice of 3, K_rock = 5, R = 0.13). This difference in reflectivity makes areas of water under the ice stand out in the GPR data (Figure 6b).

Figure 6b

For most of this 110-meter-long cross-section, the ice is frozen to the bottom, indicated by a weak boundary reflection. The patches where this reflection is much stronger are locations where there is still water present under the ice, and it has not frozen to the bottom. These are the locations that were drilled for water to use in the exploration drilling activities.

We love to see the ingenuity of our customers when using our GPR products. If you have any other examples of using IceMap or any other GPR system for applications it was not exactly designed for but is effective for, contact us.

For more information about IceMap, see the IceMap product page.

Ice Bridge data courtesy of Mackenzie County, Alberta
Grounded ice data image courtesy of Lithogen Inc.
Analyzing ice quality data courtesy of Manitoba Infrastructure
IceMap system photo and snowpack story courtesy of Landsvirkjun, Iceland
Detecting water under ice data and photos courtesy of Agnico Eagle Mines Ltd, Canada