Remote sensing of ocean colour from space began in 1978 with the successful launch of NASA's Coastal Zone Color Scanner (CZCS). Despite the fact that CZCS was an experimental mission intended to last only one year, the sensor continued to generate a valuable time-series of data over selected test sites until early 1986. Ten years passed before othere sources of ocean-colour data became available with the launch of MOS, OCTS and POLDER in 1996, and SeaWiFS in 1997. Several new ocean-colour sensors have recently been launched and still more are planned for the near future by various space agencies. There are two types of orbits for Earth observation satellites, polar orbiting and geostationary. Polar-orbiting satellites typically operate at an altitude of around 800 km, with a revisit time of 2-3 days, whereas geostationary satellites operate in time scales of hours, which could theoretically provide data on the diurnal variation in phytoplankton abundance and productivity.