An oil company is searching for potential future oil reserves in Poole Harbour.
The seismic testing at Wytch Farm has the backing of Dorset council, but it has angered some environmental campaigners.
Wytch Farm is the largest on-shore oil field in western Europe, producing twenty thousand barrels a day.
Oil reserves are estimated at 40 million barrels, but now they're searching for more.
The seismic survey of the subsurface has been approved by Dorset council, which says its planning policies support exploration for oil and gas, and that this project meets the criteria for permitted development.
In the neighbouring BCP Council, Green Party politicians are not impressed.
Cllr Simon Bull of BCP Council says: "We are in a situation where the climate crisis is affecting people across the world already. We should be looking at how we can reduce our oil use rather than looking for more ways of finding oil."
Oil exploration in this area provoked protests as recently as March this year, when an oil rig was sited in Poole Bay for more than two months.
There was also test drilling in the early 1990s, and in 1997 a temporary drilling platform was build on the Purbeck coast.
So far, not enough oil has been discovered to make it worthwhile expanding Wytch Farm. This has pleased campaigners who say that increasing output would also increase the risk of a leak, which happened at Wytch Farm ten years ago.
In a statement the oil company Perenco said that its geological survey is a "safe, low impact, highly regulated and widely used activity in the gas and oil industry" and it has no "negative impact on wildlife or the environment."
- Watch Richard Slee's report below