After unusual seismic disturbances in the Baltic Sea last week, scientists discovered several leaks in the Nord Street 1 and 2 submarine gas pipelines near Denmark and Sweden, none of the gas pipelines transported gas at the time of the break-up, but still contained compressed methane, which is the main component of natural gas that has been released by forming a broad stream of bubbles on the sea surface.
Since the unexplained release of gas raised a serious question about the impact of the incident on the environment, the experts conducted additional observations from Earth satellites, all equipped with optical and radar tools to describe gas leakage in the Baltic Sea.
Although methane is partially dissolved in water and then emitted as carbon dioxide, it is not toxic, but it is the second most common anthropogenic greenhouse gas in the planet ' s atmosphere, which causes climate change.
Because the compressed gas leaked through a broken pipe and moved rapidly towards the sea surface, the size of the gas bubbles increased as the pressure decreased. By reaching the surface, the largest of them affected the sea surface above the point where the pipeline bursts, and they can be seen on the surface even from space.
Owing to the constant cloud over the area, it was very difficult to obtain images from optical satellites. High-resolution images from the Pléiades Neo and Planet satellites, which are part of the ESA programme, showed a wave of 500 to 700 metres deep on the sea surface.
A few days later, experts noted a significant decrease in the estimated diameter of methane disturbance as gas pipelines were devastated, and the images taken by Copernicus Sentinel-2 and the United States Mission Landsat 8 confirmed this.
One of the fractures occurred south-east of the Danish island of Bornholm, and the images from Sentinel 1 of 24 September did not show any water waves; however, the ICEYE satellite, which flew over the area on the evening of 28 September, received an image that revealed the disturbance of the sea surface over the fracture.
Although optical satellites can provide data on the methane drilling radius above water, they provide little information on how much methane has been released into the atmosphere.