Present technology allows radiometric monitoring of the earth, ocean, and atmosphere from a geosynchronous platform with good spatial, spectral, and temporal resolution. A new system is proposed that could provide a capability for multispectral remote sensing with a 50-m nadir spatial resolution in the visible bands, 250 m in the 4-μm band, and 1-km in the 11-μm thermal infrared band. The diffraction-limited telescope has a 1 m aperture, a 10-m focal length (with a shorter focal length in the infrared), and linear and area arrays of detectors. The diffraction-limited resolution applies to scences of any brightness, but for a dark, low contrast scene, the good signal-to-noise ratio of the system contributes to the observation capability. The capabilities of the advanced geosynchronous platform system are assessed for quantitative observations of ocean scenes. Instrument and ground system configurations are presented, and projected sensor capabilities are analyzed.