Like its predecessor ERS-1 (launched in July 1991 by an Ariane 4 and successfully operational in-orbit at an altitude of some 780 km), the ERS-2 satellite launched on 21.04.95 by an Ariane 4, is monitoring the Earth day and night under all weather conditions thanks to its powerful sharp-eyed, cloud-piercing radars. ERS-2 carries on board an instrument to help monitor the ozone layer around the Earth.