From what I can find online, the province of Drenthe had commisioned a study of hydrologocial effects in the nearby Drentse Aa (a National Park).

Low altitude survey flight over the Dutch coastal dunes using the SkyTEM system to map fresh ground water deposits, with the helicopter flying at a height of about 75 meters. The huge 30-meter probe is attached to a 40-meter long cable system, meaning that the probe is about 35 meters above the ground and only about 15-20 meters above the higher trees.

Near head-on view of a SkyTEM survey flight to map deep fresh ground water deposits. This photo clearly shows the details of the complicated 40-meter long cabling system that holds the huge 30-meter probe. The entire setup is very impressive, and is making the helicopter look very small.

Doing a survey flight over the Dutch coastal dunes for mapping deep fresh ground water deposits to a depth of 150 meters. The helicopter is flying many parallel tracks 50-200 meters apart over the area, at a height of 75-100 meters. A huge probe with a diameter of 30 meters is attached to a 40-meter long cable system below the helicopter, see here.

Survey flight by SkyTEM over the Dutch coastal dunes, mapping deep fresh ground water deposits to a depth of 150 meters. The helicopter is flying parallel tracks 50-200 meters apart, at a height of 75-100 meters. The huge probe (30 meters in diameter) is attached to a 40-meter long cable system.

Pictured just lifting off.

Helicopter was dropping rock flour above the region for a few weeks.