Ein Ölunfall auf der Bohrinsel   Satellitenüberwachung     Like its predecessor ERS-1 (launched in July 1991 by Ariane 4, the ERS-2 satellite (launched on 21 April 1995 also by Ariane 4) monitors the ground day and night under all weather conditions thanks to its powerful sharp-eyed, cloud-piercing radars. ERS-2 also carries an instrument to help monitor the ozone layer. Schiffsüberwachung     The biggest contributor to oil pollution in the world's oceans is operational discharges from tankers. That is oil dumped during cleaning operations. The amount of oil introduced in the sea by such operations is equivalent to one full tanker disaster every week.