Can you carry out GPR measurements on water? 

GPR measurements can be carried out on water, from a boat, drone or from an ice surface, if the water is fresh and not salty (e.g., seawater).  

Prior to the construction of bridges, underwater utilities etc. in lake environments it can be important to have knowledge of the geology of lakes or rivers. This is also true concerning environmental investigations, where the thickness of bottom sediments can be most critical. Sometimes you also need to find dumped objects or just do bathymetry investigation. GPR can aid in all these applications but there are some considerations to make:  


The Ground Penetrating Radar method works well in freshwater environments. However, as water conductivity increases, the penetration depth will decrease. For example, GPR cannot be used to investigate seawater since the conductivity is too high. Polluted freshwater reservoirs will also contain higher levels of dissolved ions, thus increasing conductivity. As an example, freshwater close to over-fertilized farmland could hold elevated levels of nitrogen and phosphorus ions, increasing the conductivity of the water and reducing the usefulness of GPR as an investigation method. 


The GPR wave velocity in water is 0.033 m/ns and is about 1/3 of the velocity in most soils. In order to reach the same reading depth, the instrument therefore needs 3 times as long time to collect one trace. In other words, the time window needs to be set roughly 3 times longer to obtain the same depth reading.    


The low velocity and by that the dielectric constant also affects the footprint of the antenna. The footprint in water is smaller compared to ground, so if the purpose is to find objects this needs to be considered.  

Type of boat 

The boat needs to be made of plastic or wood, so the GPR waves can reach the water and below. It is also good if the boat has a single-hull as a double-hull with even a small amount of water can create severe ringing in the GPR data.   

Measurements from drones 

If you do not have any boat available or if conditions for boats are unsafe (fast running rivers, weak ice) a GPR antenna can be mounted on a drone instead. E.g., GeoDrone80 is a very efficient suitable solution for bathymetrical investigations.  

Trigging and Trace interval 

Since the use of a measuring wheel is more difficult when collecting data across a water volume, time triggering is generally used. The time between traces (trace interval) should be adjusted to the speed of the boat. For example, a 0.1 sec trace interval will give 10 point/sec. So, if the boat has a speed of around 4 knots this equals to around 7 km/h or 2 m/s, giving a trace interval of 20 cm. An even investigation speed will assist in looking at the structure of the radargram as well as hyperbolas. Remember, velocity calibration using hyperbolas is much less accurate, sometimes impossible, when using time triggered data.  


GPR measurements on water need to be positioned by a GNSS. You can use either the internal GNSS device in your GPR antenna or connect an external. Depending on the need for accuracy, use a GNSS with RTK-correction possibilities.  

Measurements on ice 

GPR measurements across ice covered water are much easier to perform and data is normally easier to interpret. Using a vehicle or walking across the ice makes it possible to do normal distance (wheel) triggering of data. Remember to adjust your interpretation using the signal speed of ice if the ice cover is substantial. If the ice cover is not solid but in layers, e.g., ice layer – water/air layer – another ice layer, the signal may get trapped between layers causing ringing phenomena in your data.  

Footprint of the antenna signal is smaller than in soils. Note that the footprint grows with water depth. An approximate value for the footprint can easily be calculated, see help article here


Instrument set-up in a boat and on a drone.  


Example of GPR data, with water surface, sediments, firm bottom, and single objects.  


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