The design and specifications of the Sentinel-3 MWR have been based on those of the Envisat MWR.

The instrument will measure brightness temperature at 23.8 GHz and 36.5 GHz covering a bandwidth of 200 MHz in each channel. The lower frequency channel is mostly sensitive to atmospheric water vapour and the higher frequency channel to cloud liquid water.

Conceptually, it is a balanced Dicke radiometer for brightness temperatures below the Dicke load temperature. Balancing is achieved by means of a noise injection circuit. For brightness temperatures higher than the Dicke load temperature, a conventional Dicke mode is used.

The radiometer employs a single offset reflector of 60 cm diameter and two separate feeds for the two channels. Calibration is achieved through a dedicated horn antenna pointing at the cold sky and the highly stable and precisely monitored internal Dicke load.

Figure 1: MWR Instrument (Credit: ESA)

Figure 2: MWR Instrument (Credit: ESA)