The all-weather, global determination of sea surface temperature (SST) has been identified as a requirement needed to support naval operations. The target SST accuracy is +1.0 K with a surface resolution of 10 km. Investigations of the phenomenology and technology of remote passive microwave sensing of the ocean environment over the past decade beginning with the Navy specification of the Remote Ocean-surface Measurement System (ROMS), through the NASA launched Scanning Multichannel Microwave Radiometer (SMMR) flown on both SEASAT and NIMBUS-7, to the planning by NASA of the Large Antenna Multichannel Microwave Radiometer (LAMMR), and development of the Mission Sensor Microwave/Imager (SSM/I) to be flown in 1985 by the Navy/Air Force, have demonstrated that this objective is presently attainable. Preliminary specification and trade-off studies have been conducted to define the frequency, polarization, scan geometry, antenna size, and other essential parameters, as well as the retrieval algorithms and spacecraft interface requirements, of the Low Frequency Microwave Radiometer (LFMR). As presently planned, the LFMR will be a stan6 alone system completely independent of the SSM/I but with a 30 rpm conical scan at 53.1 incidence angle identical to the SSM/I. It will be a dual-polarized, dual-frequency system at 5.2 and 10.4 GHz using a 5.9 meter deployable mesh surface antenna. It is to be flown on the Navy-Remote Ocean Sensing System (N-ROSS) satellite scheduled to be launched in late 1988.