Making the GPR grid-free

Testing the grid-free georadar for the first time in Telemark Foto: Christer Tonning

What a grid-free georadar means and how we did it

During the last few weeks, we worked on upgrading our georadar for grid-free use. Grid-free means that we do not need to follow a pre-laid out grid using strings to position our data. Instead, by equipping the georadar with a RTK GPS antenna, basically a highly accurate positioning system, the georadar can be operated by just one person and will thus be much more time-efficient.

The Malå GX 450 georadar we use includes a differential GPS, but it does not provide the centimeter accuracy we need. We therefore use an external GPS antenna mounted on top of the georadar, which is fed a correction signal.

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We use two different computers. The one to the right controlls the georadar, the one to the left helps us to navigate. Foto: Christer Tonning

In order to perform a survey truly grid-free, we also require a navigation tool, telling us which parts of our survey area were already covered by the georadar, and which parts are still missing. To achieve that, we added a second computer to the system, running a separate navigation software. One of the issues in setting this system up was the question of how to connect its individual components with each other. After a bit of trial and error and some exchange with our colleagues at NIKU, we decided for a cable connection between georadar and GPS antenna and for Bluetooth between GPS antenna and navigation computer. The correction signal for the GPS comes through wifi, which is provided by a modem that we carry in a backpack.

To complete our grid-free georadar, we added a so-called PPS device. PPS stands for parts per second and, simplified, aides in making the positioning of the georadar data even more accurate, which is important for the quality of the data.

With the system able to be operated grid-free, we can now begin the next phase of VEMOP – the actual monitoring surveys.






08.12.2020 kl.16:53