IRS-P4 (OCEANSAT) is the first satellite primarily built for Ocean applications, weighing 1050 kg placed in a Polar Sun Synchronous orbit of 720 km, launched by PSLV-C2 from SHAR Centre, Sriharikota on May 26, 1999.

This satellite carries Ocean Colour Monitor (OCM) and a Multi - frequency Scanning Microwave Radiometer (MSMR) for oceanographic studies. IRS-P4 thus vastly augment the IRS satellite system of ISRO comprising four satellites, IRS-1B, IRS-1C, IRS-P3 and IRS-1D and extend remote sensing applications to several newer areas.

Mission completed on August 8, 2010 after serving for 11 years and 2 months.