Radar is a form of technology that is used all around us, although it generally goes unnoticed. Air traffic control employs radar to track both planes on the ground and in the air, as well as to guide them for smooth landings. Police use radar to detect the speed of passing cars. Radar is used by NASA to create maps of the Earth and other planets, monitor satellites and space debris. The military uses it to guide missiles and to detect the enemy’s. This is just a small sample of the many uses of radar.
Can Radar Penetrate Water?
No, not in any meaningful sense. The microwave frequency range is used by radar, which is very small(mm or cm in wavelength). This wavelength range is used because it is easier to direct the waves with small antennas in narrow beams. Unfortunately, microwaves are almost entirely absorbed by sea water within feet from the source. Underwater radar is thus unusable.
This is how microwave ovens work actually. The microwave radiation interacts with the dipole (separated positive and negative charge) of the water molecule to heat it. Water molecules in the microwave radio frequency field are turned back and forth at the same frequency as the microwaves, giving them energy causing them to vibrate rapidly.
This fact, along others, is why Sonar is the clear choice to use underwater over radar.
Can Ground Penetrating Radar(GPR) Work in Water?
GPR, or Ground Penetrating Radar, is a type of RADAR system. As a result, both of them follow the same basic framework.
Ground-penetrating radar works by sending a tiny pulse of electromagnetic energy into the ground and noting changes and contrasts in the signal when it is reflected back to the receiving antenna.
So yes. ground penetrating radar measurements can be made on fresh water from a boat, drone, or an ice surface if the water isn’t salty.
It may be critical to understand the geology of lakes or rivers before building bridges, underwater utilities, and other lake-related infrastructure. This is also true in environmental inquiries, where the thickness of bottom sediments may be quite important. You might have to look for sunken objects or perform bathymetry investigation on occasion. GPR will help in these applications but some considerations need to be made first.
Conductivity
In freshwater settings, the Ground Penetrating Radar technique works well. However, as water conductivity rises, penetration depth will decrease. GPR, for example, cannot be used to examine seawater since the conductivity is too high. Because polluted freshwater reservoirs have higher levels of dissolved ions, their conductivity will also be greater. Concentrations of nitrogen and phosphorus ions in water may be higher closer to over-fertilized farmland, affecting the conductivity of the water and render GPR unsuitable for study.
Velocity
The water GPR wave velocity is 0.033 m/ns, which is around 1/3 of the soil velocity. In order to acquire the same reading depth, the instrument needs three times as long to record a trace since it does in most soils.
Footprint
The footprint of the antenna is impacted by both the low velocity and dielectric constant. Because the footprint in water is smaller than that on land, it must be taken into account if the goal is to discover things.
Type of boat
The boat must be made of plastic or wood, allowing GPR waves to reach the water and beneath. It’s also preferable if the boat is single-hulled; even a little bit of water can produce significant ringing in the GPR data.
A GPR antenna may be used on a drone instead of a boat if you don’t have one available or the conditions are unsafe (rapid-flowing rivers, weak ice).
Trigging and Trace interval
Since obtaining data over a water volume is more difficult when utilizing a measuring wheel, time triggering is generally utilized. The trace interval should be modified to the boat’s speed. A 0.1 second trace interval, for example, will result in 10 point/second.
Measurements on ice
GPR measurements over ice-covered waters are considerably simpler. Data is frequently easier to interpret when it’s collected across ice. It’s possible to do typical distance (wheel) triggering of data through the use of a vehicle or on foot. If the ice cover is thick, remember to adjust your assessment on the basis of the ice’s signal speed. The signal may get trapped between layers, causing ringing anomalies in your data, if the ice cover is not solid but is instead made up of layers, such as an ice layer – a water/air layer – another ice layer.
Conclusion
While radar has many uses it still has limitations that prevent it to be used in applications such as underwater. GPR is a versatile tool that can be used in a variety of settings, including underwater and on ice. In order to get accurate readings, however, it’s important to understand how conductivity, velocity, and footprint will affect the measurements. Additionally, the type of boat being used for GPR measurements must be considered.
